Photocatalytic Water Splitting: Quantitative Approaches toward Photocatalyst by Design
View Author Information
King Abdullah University of Science and Technology (KAUST), KAUST Catalysis Center (KCC) and Physical Sciences and Engineering Division (PSE), 4700 KAUST, Thuwal 23955-6900, Saudi Arabia
*E-mail: [email protected]
Copyright © 2017 American Chemical Society
ACS AuthorChoicewith CC-BY-NC-NDlicense
Abstract
A widely used term, “photocatalysis”, generally addresses photocatalytic (energetically downhill) and photosynthetic (energetically uphill) reactions and refers to the use of photonic energy as a driving force for chemical transformations, i.e., electron reorganization to form/break chemical bonds. Although there are many such important reactions, this contribution focuses on the fundamental aspects of photocatalytic water splitting into hydrogen and oxygen by using light from the solar spectrum, which is one of the most investigated photosynthetic reactions. Photocatalytic water splitting using solar energy is considered to be artificial photosynthesis that produces a solar fuel because the reaction mimics nature’s photosynthesis not only in its redox reaction type but also in its thermodynamics (water splitting: 1.23 eV vs glucose formation: 1.24 eV). To achieve efficient photocatalytic water splitting, all of the parameters, though involved at different time scales and spatial resolutions, should be optimized because the overall efficiency is obtained as the multiplication of all these fundamental efficiencies. The purpose of this Review is to provide the guidelines of a concept, “photocatalysis by design”, which is the opposite of “black box screening”; this concept refers to making quantitative descriptions of the associated physical and chemical properties to determine which events/parameters have the most impact on improving the overall photocatalytic performance, in contrast to arbitrarily ranking different photocatalyst materials. First, the properties that can be quantitatively measured or calculated are identified. Second, the quantities of these identified properties are determined by performing adequate measurements and/or calculations. Third, the obtained values of these properties are integrated into equations so that the kinetic/energetic bottlenecks of specific properties/processes can be determined, and the properties can then be altered to further improve the process. Accumulation of knowledge ranging in fields from solid-state physics to electrochemistry and the use of a multidisciplinary approach to conduct measurements and modeling in a quantitative manner are required to fully understand and improve the efficiency of photocatalysis.
Introduction
ARTICLE SECTIONS
General Strategy for Improved Photosynthetic Reactions
A photocatalyst is a substance that absorbs photons and generates excited states, which then cause photophysical and photochemical processes as they return to their original ground states. (1) Photocatalyst materials can consist of additional catalytic components, often called cocatalysts, that catalyze electrochemical redox reactions. (2) Such an electrocatalyst is often essential to the photocatalyst (photon absorber) because its surface is not typically designed to catalyze redox reactions unless the reaction is an outer-sphere electrochemical reversible reaction. The time scale of electrocatalysis during the photocatalytic process is sufficiently longer than the time scales of photophysical or photochemical processes; (3) in many photocatalytic reactions, the photocatalysis can thus be considered to be electrocatalysis where electrocatalyst components induce the redox reactions driven by the potential shifts caused by the photocatalyst (photon absorber). Photocatalysis eventually builds an electromotive force (emf), a difference in chemical potentials or Fermi levels, to enable electrocatalysis. (1) This emf transient charging at electrocatalytic sites is indeed required for water-splitting photocatalysts because both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) require multiple electron transfer reactions at the active species and thus a relatively slow process compared to prior photophysical processes.
One may consider the difference between a photocatalyst (photon absorber and electrocatalyst) and a device that consists of a photovoltaic and an electrolyzer (PV + E). Making hydrogen by PV + E technology is still more expensive than using natural gas reforming. (4, 5) A large number of elementary events are common; however, the photocatalyst may induce charge separation utilizing an electrocatalyst–semiconductor interface and a solid–liquid junction directly, (1) potentially skipping the p–n junctions in solid–solid structures. This is the major driving force of cost reduction in photocatalytic system compared to PV + E system. Photocatalytic materials also do not require the wiring of a PV (but instead require the collection of produced gases). On the other hand, in a PV + E configuration, separating the functions of photovoltaic current generation (PV) and electrocatalysis (E) is easily optimizable for these two separate components, and PV + E systems are therefore expected to produce higher efficiencies than photocatalyst systems. (6) To combine these systems, PV material can be immersed into aqueous solution, (7-9) which allows the material to avoid a detrimental temperature increase (because of the water) and the resultant efficiency loss. There is a significant chance, however, that the PV material corrodes because the water itself is corrosive and even worse at extreme pH values; additionally, fewer photons are expected to be absorbed when the PV is in water because, besides photon loss due to reflection by the water, the absorption coefficient of water is nonzero especially beyond 600 nm. (10) Lewis recently reviewed the future possibilities for solar energy conversion technology in industry and academia. (5) Practical use of either of these systems requires future efforts: PV + E prices must be decreased by engineering or some technical advancement that produces a reasonable device and system, and the photocatalytic efficiency of photocatalysts must be improved without forgetting a final, scaled-up reactor design. Recently, immobilization of photocatalyst powder in sheets for use in overall water splitting was demonstrated, (11) but the overall efficiency of this catalyst remains low, predominantly because of inefficient charge separation by the photocatalyst materials. Collective efforts are needed to address these complex issues in clearly desired solar energy conversion technology.
As recently emphasized by Osterloh, (12) photosynthetic reactions (ΔG > 0) require detailed photon management and charge separation, in contrast to photocatalytic reactions (ΔG < 0), whose performance is most sensitive to surface area. Basing the selection of materials for photon absorption (photocatalyst) solely on their bandgap and electrocatalyst, often called the cocatalyst, is not enough to result in high photocatalytic efficiency. We will review that defect density, carrier concentrations, and interfaces (metal, semiconductor, electrolyte, etc.) strongly influence efficiency, even when the same materials are used. This fact is widely known, yet there is no consensus as to how to evaluate these properties and consequences. In addition to the use of disparate reporting protocols, (13-23) this discrepancy is the reason why every research article reports different efficiencies even when the same composition of photocatalyst is used. For instance, there are multiple methods to prepare photocatalyst materials, (24) but they result in different photocatalytic performances because unquantifiable or difficult-to-measure properties vary. (25) Photocatalysis research is becoming largely arbitrary because of an infinite number of variables, for example, different precursors, synthesis protocols, annealing, pre/post-treatment, and addition of small quantities of dopants/impurities/additives (often unconsciously); it is very difficult to reproducibly make photocatalysts. In a specific operation, one may want to concretely determine how overall efficiency is improved by a particular “quantity”. (25) There are excellent review articles concerning photocatalyst and photoelectrochemical reactions: many focus on various materials and techniques of characterization. (26-45) This Review is specifically targeted to developing a guideline as to what fundamental key parameters improve photocatalytic efficiencies, regardless of the photocatalyst material. It is time to integrate advanced modeling into the design of photocatalyst materials. Without these efforts, photocatalytic research remains abstract, unestablished, and unquantifiable.
Consolidation of Chemical Potentials and Fermi Levels
The basic concept of photocatalysis relies on the same protocol as all types of catalysis research: a description of chemical potentials of electrons, or Fermi levels. A strong connection between solid-state chemistry and physical chemistry, or photophysics and electrocatalysis, is the accurate description of chemical potentials of electrons in various substances (metals, semiconductors, redox ions in the solution, etc.) at thermodynamic equilibrium or under steady-state illumination. The concepts of the chemical potentials of electrons in metals to semiconductor is well described in an excellent book by Sato. (46) Each elementary step/event in “catalysis” including photocatalysis, in terms of thermodynamics and kinetics, becomes quantitatively describable if we have tools to appraise the chemical potentials of electrons, especially reactive ones, in molecules, nanoparticles, and solids (catalyst materials) and in both reactants and products during (photo)catalysis. Work functions of metals, Nernstian redox potentials of molecules/ions, and Fermi levels or flatband potentials of semiconductors are useful statistical measures of energy equilibrium and flow, although overlapping reactive energy states in solids and interfaces makes determining the value of these potentials difficult. Recent advances in solid-state physics and chemistry establishes reasonable theories that can measure (estimate) or calculate such energy levels and their densities of state. This estimate, consisting of a large number of quantifiable parameters, (25) can ideally be used to predict overall photocatalytic efficiency, even without experiments. It is thus possible to determine which parameter is most influential in improving overall efficiency. This strategy is one step forward to “photocatalysis by design”—the design of systems to reach a target by altering specific parameters rather than randomly screening materials.
Successful photocatalysis requires that charged-up electrocatalysts are maintained at the potentials where steady-state redox reactions occur. A scheme can be derived, on a scale of the chemical potential of electrons (and holes), that visualizes the ideal energy transfer (and loss) that occurs during sequential photocatalytic processes. Figure 1 describes an example of the use of a single semiconductor powder as a photocatalyst that is decorated with HER and OER electrocatalysts on the surface, in an attempt to achieve overall water splitting. The process is initiated with photon absorption, as depicted in the middle of Figure 1. Upon light absorption, an excited hole and electron are generated in the valence band and conduction band, respectively, on the femtosecond time scale. (47) After rapid relaxation to the edges of their respective bands in femto- to picoseconds, an exciton (electron–hole pair) is separated into free carriers and the semiconductor-catalyst interface guides the electron and hole to the HER and OER catalysts, respectively, generally in nano- to microseconds. (47) Substantial losses of potentials are expected at the interface (“interfacial loss”) and may originate from entropic contributions of electrons (48-50) and interfacial potential barriers that are generated by inadequate alignment. Successful electron/hole transfer to the electrocatalyst shifts the potentials either negatively or positively at transient time on the millisecond to second time scales, and then maintain steady-state potentials that are allowed to drive steady-state electrochemical redox reactions to produce H2 and O2. (47) The solution properties may influence the overall performance by limiting the mass transfer of the reactant ions. How can we draw this type of scheme for every photocatalyst? What properties are involved that determine such potentials at each event? Can we identify the bottleneck that limits the overall efficiency? In the next section, the selected key parameters as well as photocatalysis events that occur at different time scales are identified.
Figure 1
Figure 1. Schematic image of the photocatalytic water splitting process. The gear with the number indicates the order of the photocatalytic process to be successful for overall water splitting. For a detailed description, please refer to the text.
List of Properties Involved in Photocatalytic Water Splitting
The primary effort of this Review focuses on discussing the fundamental parameters that are involved in photocatalytic water splitting and their quantitative measurement using powdered semiconductor material (the concept can be applied to other photocatalysis as well). Photocatalysis for water splitting indeed involves a complex series of photophysical and electrocatalytic processes. (25) The processes involved in photocatalytic reactions are divided into the following six components:
| 1. | Photon absorption | ||||
| 2. | Exciton separation | ||||
| 3. | Carrier diffusion | ||||
| 4. | Carrier transport | ||||
| 5. | Catalytic efficiency | ||||
| 6. | Mass transfer of reactants and products | ||||
Events 3 and 4 can occur simultaneously and coherently, but are separated here for convenience. Figure 2 shows this six-gear concept, which represents the photocatalytic water-splitting process sequentially occurring at different time scales. (25) Photon absorption initiates nonequilibrium photophysical and photochemical processes. The photon absorption generates an exciton, that is, excitation of an electron in the valence band (VB) or the highest occupied molecular orbital (HOMO) to the conduction band (CB) or the lowest unoccupied molecular orbital (LUMO). (47) The probability to occupy such states are predominantly determined by the electronic structure (local displacement of atoms) of the semiconductor. This femtosecond process is followed by relaxation of the electron and the hole to the bottom of the CB and the top of the VB, respectively, on a similar time scale. (47) Next, the exciton (electron–hole pair) is generally separated after overcoming the exciton binding energy determined by the electronic structure; this structure should guide the excited electron and hole (polaron) to move independently, being influenced by their effective masses. The combination of carrier diffusion and transport effectively utilizes the introduced interfaces (i.e., potential differences) and successful charge transfer typically in microseconds to the electrocatalysts decorated on the surface needs to occur. Because the kinetics of electrocatalysis are unfortunately sluggish compared to the prior events, such electrocatalytically active species will be charged either negatively or positively and drive electrocatalytic redox reactions on a time scale typically longer than microseconds. (47) The key is that most of the semiconductor and electrocatalytic properties and measures of efficiency at each stage are listed separately and are quantitatively measurable by using various characterization and kinetics measurements. Once a material is synthesized, these properties and efficiencies are quantified so that the bottleneck of the process is identified, leading to improved overall efficiency. A previous report describes the associated equations and measurement protocols in more detail. (25) This contribution aims to emphasize the most influential key components in determining overall photocatalytic efficiency.
Figure 2
Figure 2. Parameters associated with photocatalysis. Overall water splitting is only successful for high efficiencies of all six gears depicted in the scheme. The different time scales of the reactions are also displayed.
Quantification of Key Properties Relevant to Photocatalytic Water Splitting
ARTICLE SECTIONS
Generation Rate
When solar energy conversion is the primary concern, analysis of the solar spectrum provides useful information regarding theoretical maximum efficiency. The solar-to-hydrogen (STH) conversion efficiency is defined by the H2-energy generated divided by the entire solar irradiance. Using the NREL standard spectrum of AM 1.5G, (51) integration of UV photons accounts for a maximum of 3.3% STH efficiency. Including light from the UV to the visible (to 600 nm) results in a maximum theoretical STH efficiency of 17.8%, while up to 800 nm results in >35% (using a single semiconductor). Analysis of the solar spectrum reveals that development of a visible-light-responsive photocatalyst material is essential to achieving substantial solar energy conversion. (52) A representative scheme for various visible light responsive materials is shown in Figure 3, which is taken from the review paper by Sivula and van de Krol. (45) The bandgap of the materials is minimum thermodynamic requirement for high-efficiency photocatalysis; however, the shape of conduction and valence bands are unique to each electronic structure, and densities of state typically become very weak at band edges (bands are not rectangular as depicted in Figure 3).
Figure 3
Figure 3. Bandgap structure of oxide and oxynitride semiconductors for photoelectrochemical applications. Contribution of metal cation and oxygen anion states to the conduction and valence bands. The bandgap energy (red for n-type, black for p-type) is shown with respect to the reversible hydrogen electrode and the water redox energy levels (assuming Nernstian behavior four the band-edge energies with respect to electrolyte pH). Reprinted with permission from ref 45. Copyright 2016 Macmillan Publishers Limited.
It is obvious that if no photons are absorbed, no photocatalysis occurs. The initial step of photocatalysis is unambiguously the absorption of a photon and exciton generation by the photon absorber. Once the photocatalyst material is chosen for investigation, it is crucial to identify its electronic structure (displacements of the atoms or a crystal structure), which in turn determines the densities of the relevant energy states. Commonly, photon flux of incident light, I0, commonly lead to the following relationships:
(1)where A% is absorptance, the ratio of the absorbed to incident electric field, and T, Rs, S, Rd are lights that are transmitted, specularly reflected, forward-scattered, and backscattered, respectively. (53) Most importantly, the absorption coefficient, α(λ), an indicator of how far photons of a particular wavelength can penetrate before it is absorbed by the material, can be measured or calculated as a function of wavelength. (25, 27) It also determines important absorption properties such as the bandgap, band positions (flatband potentials), and the direct/indirect nature of light absorption. The absorption spectra indicate the consequences of bandgap excitation, d–d transitions, phonon absorptions, and excitations associated with defect states. (53) To practically measure absorption coefficients, the single crystal thin-film configuration of semiconductors provides a more precise description because contribution of scattering is minimized and the film thickness is well-defined. (54) From transmittance, T, and reflectance, R, (55) values, we obtain α for the film thickness, d, when Re–αd ≪1: (56)
(2)The number of electron–hole pairs that are generated per photon striking the semiconductor as a function of depth, x, and wavelength, λ, is described using the generation rate, G, per geometric area. After considering Rayleigh and Mie scattering by the powder, which depend on the size of the particle, (57) and reflection and transmission by the medium with distinct refractive indices, (58) the Beer–Lambert law approximation leads to (59, 60)
(3)where I0 is photon flux of irradiated light per geometric area. From this equation, it is thus obviously essential to obtain photon flux densities by irradiance measurements. Other intrinsic parameters can then also be quantified: for example, the refractive index, n; the extinction coefficient, κ(λ); and the dielectric constant, εr, which can be divided into contributions from the electronic density, ε∞, and from the motion of ions in the material, εvib; εr = ε∞+ εvib. (61) Methods to obtain these properties can be found in the literature. (25)
(1)where A% is absorptance, the ratio of the absorbed to incident electric field, and T, Rs, S, Rd are lights that are transmitted, specularly reflected, forward-scattered, and backscattered, respectively. (53) Most importantly, the absorption coefficient, α(λ), an indicator of how far photons of a particular wavelength can penetrate before it is absorbed by the material, can be measured or calculated as a function of wavelength. (25, 27) It also determines important absorption properties such as the bandgap, band positions (flatband potentials), and the direct/indirect nature of light absorption. The absorption spectra indicate the consequences of bandgap excitation, d–d transitions, phonon absorptions, and excitations associated with defect states. (53) To practically measure absorption coefficients, the single crystal thin-film configuration of semiconductors provides a more precise description because contribution of scattering is minimized and the film thickness is well-defined. (54) From transmittance, T, and reflectance, R, (55) values, we obtain α for the film thickness, d, when Re–αd ≪1: (56)(2)The number of electron–hole pairs that are generated per photon striking the semiconductor as a function of depth, x, and wavelength, λ, is described using the generation rate, G, per geometric area. After considering Rayleigh and Mie scattering by the powder, which depend on the size of the particle, (57) and reflection and transmission by the medium with distinct refractive indices, (58) the Beer–Lambert law approximation leads to (59, 60)(3)where I0 is photon flux of irradiated light per geometric area. From this equation, it is thus obviously essential to obtain photon flux densities by irradiance measurements. Other intrinsic parameters can then also be quantified: for example, the refractive index, n; the extinction coefficient, κ(λ); and the dielectric constant, εr, which can be divided into contributions from the electronic density, ε∞, and from the motion of ions in the material, εvib; εr = ε∞+ εvib. (61) Methods to obtain these properties can be found in the literature. (25)Once the absorption coefficient is obtained, we obtain the absorption depth, which is a useful measure how far light can penetrate into a material before being absorbed; the absorption depth can be determined by simply taking the inverse of the absorption coefficient α. (25) The absorption depth, together with scattering and reflection, is critical to deciding how thick a photocatalyst film or suspension should be or how many semiconductor particles are required to be able to report a useful photocatalytic efficiency. To be able to compare photocatalytic performances from different laboratories, the maximum photon absorption should be achieved by a photoreactor that is used to obtain an “optimal rate” that is not perturbed by the amount of photocatalyst used. (20) Absorption coefficients of typical direct bandgap semiconductors fall into the range of 1 × 104 – 1 × 106 cm–1, equivalent to absorption depths of 1000–10 nm. A typical indirect bandgap semiconductor, Si, possesses a typically low absorption coefficient of 1 × 103 – 1 × 105 cm–1, corresponding to absorption depths of up to a few micrometers for visible light (400–800 nm). (62) We emphasize that the density of state (DOS) is the primary criterion to select a semiconductor for photocatalysis. Essentially, the Franck–Condon principle (63, 64) suggests that the displacement of atom positions does not change upon photon absorption and that accurate determination of a local crystal structure (Brillouin zone) with an appropriate consideration of spin–orbit coupling predominantly determines these optoelectronic properties. Recent advances in density functional theory (DFT) calculations give quite accurate and reliable estimates of the electronic structures and resultant DOS of semiconductors with a given crystal structure. (61) When new photovoltaic and photocatalytic materials are developed, it is recommended that the accurate crystal structure (e.g., via Rietveld refinement), which dictates the electronic structure and resultant optoelectronic properties, be determined.
As mentioned, single-crystal thin films are preferred in measurements of optoelectronic properties because of minimized contribution of scattering and diffuse reflection. It is also noted that the Kubelka–Munk function, (65) used in diffuse reflectance spectroscopy equipped with an integrating sphere, is a useful tool for measuring the absorption properties of powder samples. However, use of this function often leads to an exaggerated interpretation of the absorption intensity, especially when close to bandgap. One must consider that near band edges, absorption coefficients can be exceptionally low, which is not obvious from the spectra plotted using a Kubelka–Munk function. The absorption spectra and the Kubelka–Munk function also contain quantitative information, where a value of zero is especially meaningful. When impurities are present in the system, nonzero absorption data reflects not only that the spectrum does not purely represent the desired compound or material but also the extent of dopant or metallic character; therefore, do not forget to plot zero in absorption spectra or Kubelka–Munk function. The impurity energy levels beyond the bandgap energy also empirically follow the Ulbach rule, (66) which can be additionally considered to quantify the absorption properties of the semiconductors.
Exciton Binding Energy
After successful photon absorption and the resultant exciton generation, electron–hole pairs (67) are to be separated to generate excited electrons and holes (free carriers), or otherwise to recombine easily. The next criterion for selection of a photocatalyst is the exciton binding energy, which represents the energy required to ionize an exciton from its lowest energy state. (68) For a Mott–Wannier-type exciton, the 1s state energy, E1, of an exciton described by the Bohr theory is the exciton binding energy, Rex, and it can be described as
(4)where εr is a relative permittivity or dielectric constant, m* is the reduced effective mass of the electron (n)–hole (p) system (
), e is the elemental charge, and h is Planck’s constant. (61) A database containing these parameters for a large number of typical semiconductors is already available. (69) The benchmark energy value is that of thermal energy (25 meV at room temperature), (61) and the efficient separation of excitons requires that the binding energy be lower than this value. For Mott–Wannier excitons, the typical binding energy is less than 10 meV, and the exciton radius is ∼10 nm. For Frenkel excitons, such as carbon nitride, these values can be greater than 1 eV and ∼1 nm. (70) Such a high exciton binding energy necessitates charge separation at the molecular level, similar to the case of bulk heterojunctions of organic semiconductors. The key properties that affect the values of the exciton binding energy are the effective masses and dielectric constant. The effective masses of the electron and hole are determined by the curvature of the electronic structure in the conduction and valence bands, respectively. The electronic dielectric constant is also predominantly determined by the electronic structure of a given material. High dielectric materials, such as perovskite structures, are typically excellent photocatalysts. Currently, DFT calculation can estimate exciton binding energies and effective masses as well as different crystal orientations at high accuracy; typically, high distortion creates an anisotropic electronic field upon exciton generation, and this field assists charge separation. (36)
(4)where εr is a relative permittivity or dielectric constant, m* is the reduced effective mass of the electron (n)–hole (p) system (), e is the elemental charge, and h is Planck’s constant. (61) A database containing these parameters for a large number of typical semiconductors is already available. (69) The benchmark energy value is that of thermal energy (25 meV at room temperature), (61) and the efficient separation of excitons requires that the binding energy be lower than this value. For Mott–Wannier excitons, the typical binding energy is less than 10 meV, and the exciton radius is ∼10 nm. For Frenkel excitons, such as carbon nitride, these values can be greater than 1 eV and ∼1 nm. (70) Such a high exciton binding energy necessitates charge separation at the molecular level, similar to the case of bulk heterojunctions of organic semiconductors. The key properties that affect the values of the exciton binding energy are the effective masses and dielectric constant. The effective masses of the electron and hole are determined by the curvature of the electronic structure in the conduction and valence bands, respectively. The electronic dielectric constant is also predominantly determined by the electronic structure of a given material. High dielectric materials, such as perovskite structures, are typically excellent photocatalysts. Currently, DFT calculation can estimate exciton binding energies and effective masses as well as different crystal orientations at high accuracy; typically, high distortion creates an anisotropic electronic field upon exciton generation, and this field assists charge separation. (36)Carrier Lifetime
For successful photocatalysis, the generated free carriers are transferred to redox-active sites on the catalyst surfaces (or to the back contact, in the case of photoelectrochemistry). The next useful parameter is the minority carrier lifetime, τ, which is another intrinsic indicator of whether a semiconductor material can be an effective photocatalyst. Generally, the recombination can occur through the following mechanisms; “surface” recombination, “bulk” Shockley–Read–Hall (defects) (srh), (71, 72) the band-to-band radiative (bbr), and the band-to-band Auger (bba), (73) and more; the lifetime of which are reciprocally correlated:
(5)Once the carrier lifetime is obtained, recombination rate can be estimated, depending on the recombination models. Essentially, the generation rate will be canceled out by the recombination rate to leave the effective carrier rates for electrocatalysis. (25) The carrier lifetime also gives the minority carrier diffusion length, L, representing the average distance that the excess minority carrier travels from where it was generated to where it is annihilated.
(6)where Dc is the diffusion coefficient of the carriers, which will be described more in details in the following section. The comparison of this value with the particle size of the photocatalyst or the film thickness of the photoelectrode is critical in designing the photon absorber. (74)
(5)Once the carrier lifetime is obtained, recombination rate can be estimated, depending on the recombination models. Essentially, the generation rate will be canceled out by the recombination rate to leave the effective carrier rates for electrocatalysis. (25) The carrier lifetime also gives the minority carrier diffusion length, L, representing the average distance that the excess minority carrier travels from where it was generated to where it is annihilated.(6)where Dc is the diffusion coefficient of the carriers, which will be described more in details in the following section. The comparison of this value with the particle size of the photocatalyst or the film thickness of the photoelectrode is critical in designing the photon absorber. (74)An empirical expression between carrier lifetime and dopant concentration was reported by Law et al. for indirect bandgap Si (Figure 4), but it describes very interesting trend as a function of dopant concentration. (75) Two types of srh and bba recombinations are integrated into this model:
(7)where τ0 is the low-concentration lifetime, ND is the doping carrier concentration, Nref is the roll-off concentration, and CA is the Auger coefficient. From this analysis, it is obvious that the carrier lifetime increases as the doping level decreases, i.e., the more intrinsic semiconductor generally has longer carrier lifetimes. This parameter is primarily associated with bulk recombination that originates from the srh process and impurity concentrations (and therefore, strictly speaking, the descriptor is not the carrier concentration alone). The GaAs semiconductor shows a similar trend. (76) Relatedly, the surface treatment (etching or shell formation) of single-crystal surfaces substantially improves the minority carrier lifetime, as measured by time-resolved photoluminescence, or the photoconductivity lifetime, as measured by terahertz photoconductivity. Examples of this behavior include that of well-investigated photovoltaic semiconductors such as CdTe, (77, 78) InP, (79) and GaAs. (80)
(7)where τ0 is the low-concentration lifetime, ND is the doping carrier concentration, Nref is the roll-off concentration, and CA is the Auger coefficient. From this analysis, it is obvious that the carrier lifetime increases as the doping level decreases, i.e., the more intrinsic semiconductor generally has longer carrier lifetimes. This parameter is primarily associated with bulk recombination that originates from the srh process and impurity concentrations (and therefore, strictly speaking, the descriptor is not the carrier concentration alone). The GaAs semiconductor shows a similar trend. (76) Relatedly, the surface treatment (etching or shell formation) of single-crystal surfaces substantially improves the minority carrier lifetime, as measured by time-resolved photoluminescence, or the photoconductivity lifetime, as measured by terahertz photoconductivity. Examples of this behavior include that of well-investigated photovoltaic semiconductors such as CdTe, (77, 78) InP, (79) and GaAs. (80)Figure 4
Figure 4. (A) Hole and (B) electron lifetimes in heavily doped n-type and p-type silicon, respectively. Reprinted with permission from ref 75. Copyright 1991 Institute of Electrical and Electronics Engineers.
In the case of powder samples or nanostructured architectures, whose surface contributions are large relative to that of the bulk, the surface states largely influence the minority carrier lifetime. The carrier concentration is obviously an important factor in photocatalysis, but what is the relevant quantity in the semiconductor powders? When a highly defective material with a carrier concentration of 1018 cm–3 is used, a typical 10 nm cube of photocatalyst contains only one carrier per photocatalyst particle in the bulk. If fewer dopant materials with a carrier concentration of 1016 cm–3 can be synthesized, a 50 nm cube of photocatalyst contains one carrier per particle, and a 100 nm cube photocatalyst contains 10 carriers. Since the contribution from the bulk is so low, contributions from the surface are easily observed. (42) The surfaces and interfaces are, by definition, defects, often possessing nonstoichiometric and/or dangling bonds that are electronically active. The potential of the surface states is a difficult-to-measure quantity: surface dipoles associated with functional groups, adsorbate, and redox ions in electrochemical double layer all affect. The consequence is, however, known that they create intermittent states within bandgap or HER-OER redox potentials. (81) Therefore, the surface not only acts as a charge separation interface but also as a recombination site of excited carriers such as impurities and abrupt terminations. What is the concentration of such surface sites? In the case of an oxide material, the maximum concentration should be comparable to the surface hydroxyl site density, which typically reaches ∼4 nm–2, depending on the identity of the oxide, its treatment, and characteristics of the exposed facets. (82) On a fully hydroxylated surface, there are ∼60 000 surface sites on a 50 nm cube-shaped particle, giving a surface site to bulk carrier ratio >100. From this number, it is clear that management of surface states is critical to controlling the photocatalytic activity of powder materials. (83) If surface sites are insulated or deactivated to the point at which their concentration is 100 times less than that of complete exposure, the surface and bulk atoms of the same system become comparable. This idea is visualized in Figure 5, and it is consistent with the common observation that having “high crystallinity” and a minimal number of defects enhances photocatalytic efficiency, in contrast to a simple increase in surface area. (84) In summary, the minority carrier lifetime is prolonged with a more intrinsic semiconductor (fewer dopants) in the bulk, and surface modification at the interface is crucial for photocatalysts, which is further interacted with the following parameters.
Figure 5
Figure 5. Rough estimation of the ratios of the numbers between the active surface sites (assuming ∼4 nm–2 hydroxylated surface as maximum) (82) to the bulk carrier. The cubic particle of 100 nm diameter is used as an example.
Carrier Diffusion and Transport
The important parameters to consider when selecting photocatalyst materials are, at this point, predominantly the electronic structure, which determines the absorption coefficient, and the charge carrier concentration, which influences carrier lifetime and diffusion length. The next event that occurs during the photocatalytic process is excited carrier transport. Charge separation is a primary concern for the photosynthetic reaction, and solid liquid interface should be effectively utilized. (12) The generated free charge carriers must travel through the bulk of semiconductor to the surface redox sites. (85) Such phenomena can be described in terms of electron flow, i.e., current. There are two driving forces for electron (n) and hole (p) movement: diffusion driven by concentration gradient and drift driven by potential gradient: (67)
(8)
(9)
(10)where e is the elementary charge, D is the diffusion coefficient, ∇p and ∇n are the gradients of electrons or holes, μ is the mobility of the charge carrier, p denotes hole concentration, n denotes electron concentration, and E is electric field. The diffusion contribution is associated with the diffusion coefficient and mobility of intrinsic semiconductors: (61)
(11)where kB is the Boltzmann constant. The mobility in a specific direction can be further described by
(12)where τc is the collision time of the charge carrier and m* is the effective mass. The criterion for good mobility under ambient condition is considered to be m* < 0.5me (e for electron). (61) As mentioned previously, the electronic structure predominantly determines the effective masses and thus the mobility and diffusion coefficient. Practically, the resistivity, charge carrier concentration, and resultant mobility of the semiconductors can be measured by using the van der Pauw technique and Hall measurements, (86, 87) although this method is better when using a high-quality semiconductor slab. If there is no potential gradient, free carriers are transferred via diffusion, which is a very inefficient form of carrier transport. The minority carrier diffusion length can be as short as a few nm, but only when the carrier lifetime is on the order of picoseconds.
(8)(9)(10)where e is the elementary charge, D is the diffusion coefficient, ∇p and ∇n are the gradients of electrons or holes, μ is the mobility of the charge carrier, p denotes hole concentration, n denotes electron concentration, and E is electric field. The diffusion contribution is associated with the diffusion coefficient and mobility of intrinsic semiconductors: (61)(11)where kB is the Boltzmann constant. The mobility in a specific direction can be further described by(12)where τc is the collision time of the charge carrier and m* is the effective mass. The criterion for good mobility under ambient condition is considered to be m* < 0.5me (e for electron). (61) As mentioned previously, the electronic structure predominantly determines the effective masses and thus the mobility and diffusion coefficient. Practically, the resistivity, charge carrier concentration, and resultant mobility of the semiconductors can be measured by using the van der Pauw technique and Hall measurements, (86, 87) although this method is better when using a high-quality semiconductor slab. If there is no potential gradient, free carriers are transferred via diffusion, which is a very inefficient form of carrier transport. The minority carrier diffusion length can be as short as a few nm, but only when the carrier lifetime is on the order of picoseconds.Therefore, movement of free charge carriers must be adequately guided by potential gradients, generating drift current. Such gradients can be made by effective utilization of metal–semiconductor, semiconductor–electrolyte, and semiconductor–semiconductor interfaces including surface modifications. (85) The decoration of the surfaces of semiconductors causes several effects: the reduction of surface recombination, the introduction of potential gradient, and modification with catalytic components.
At the metal–semiconductor interface, the key parameters that control the energy level are the work function of the metal and the Fermi level of the semiconductor, (46) which may result in a Schottky barrier or ohmic contact, depending on their relative positions and the carrier concentrations. For details, please refer to, e.g., the work of Tung. (88) In the literature, (89, 90) barrier heights at the semiconductor–metal interface were correlated with the electronegativity of the metal and nature of a semiconductor, either ionic (Si, Ge, etc.) or covalent (oxides, like TiO2, SrTiO3, etc.). Figure 6 shows representative interesting trends of barrier heights, ϕBn0, for various metals and semiconductors. An index, “S”, the slope of Figure 6A, gives sensitivity of electronegativity of metal, XM, to the barrier heights. Relatively small S for ionic semiconductors shows that barrier heights are insensitive to electronegativity (or workfunction) of metals, whereas large S for covalent semiconductors indicate they are more sensitive to the difference between Fermi level of semiconductor and metal workfunction. Ohmic contacts have been reported for various combinations of semiconductor and metals and metal alloys. (89) Such smooth contacts may improve efficiency by bridging excited electrons to electrocatalysts. Practically, Ti is commonly used as a contact layer for p-Si, (91) and Ti and Ta are used for some covalent materials, such as SrTiO3 (92) and LaTiO2N. (93) For an unique case, the Cu2O photocathode achieved high photocathodic current when there is successive deposition of ZnO:Al and TiO2 before Pt catalyst deposition. (94) Powder semiconductor seem to be more challenging to achieve this type of decoration in nanoscale, so the establishing technique that allow to develop the smooth contact may lead to high efficiency.
Figure 6
Figure 6. (A) Barrier height versus electronegativity of metals deposited on Si, GaSe, and SiO2. (B) Index of interface behavior S as a function of the electronegativity difference of the semiconductors. Reprinted with permission from ref 89. Copyright 2006 John Wiley & Sons, Inc.
At the semiconductor–electrolyte interface, (95, 96) the Fermi level of the semiconductor and the reduction potential of the solution play a crucial role in determining potential gradient. A successful application of the solid–electrolyte interfaces is the dye-sensitized solar cell, where TiO2 collects excited electrons to its conduction band from the dyes anchored to its surface. (97) A key to avoid charge recombination is a band bending of TiO2, guiding the injected electrons to its back contact. (74) Similarly, the photocatalyst surface will experience the band bending when immersed in water. Solving the Poisson equation for x-direction (eq 13) leads to description of band bending, and this space charge layer should be utilized to achieve effective charge separation. (67)
(13)where Φx is the potential as a function of x, ND is the majority carrier density, ε0 is the static permittivity in vacuum, εr is the static relative permittivity or dielectric constant of the semiconductor. The key parameters in determining the space charge layer are the carrier concentration and the dielectric constant of the semiconductor. The electrolyte is strongly influenced by the surface state and potential-determining ions at the surface. (98) In water, the isoelectric point of the semiconductor provides a useful indication of whether the surface is negatively or positively charged. (99) Semiconductor–semiconductor interfaces can form p–n junctions, but the details regarding this process are described elsewhere. (67)
(13)where Φx is the potential as a function of x, ND is the majority carrier density, ε0 is the static permittivity in vacuum, εr is the static relative permittivity or dielectric constant of the semiconductor. The key parameters in determining the space charge layer are the carrier concentration and the dielectric constant of the semiconductor. The electrolyte is strongly influenced by the surface state and potential-determining ions at the surface. (98) In water, the isoelectric point of the semiconductor provides a useful indication of whether the surface is negatively or positively charged. (99) Semiconductor–semiconductor interfaces can form p–n junctions, but the details regarding this process are described elsewhere. (67)The consequence of potential gradients at interfaces account for the photovoltage: the origin of emf of the electrocatalysts, determining primary efficiency of the photocatalytic system. It is emphasized that the bandgap is not equivalent with the photovoltage; substantial potential losses are expected at surfaces and other interfaces. The Si bandgap of 1.1 eV typically gives an open-circuit voltage or photovoltage gain of only 0.7 eV (∼40% loss) in photovoltaic system. (100) Therefore, reporting the bandgap is not likely to be sufficient in further understanding photocatalytic processes and material properties. At the same time, band alignment of various materials is a good start for discussion; however, the Fermi level equilibration between two materials (p–n or n–n junctions with type I and II alignments, etc.) does not result in smooth interface, which is strongly influenced by lattice match, impurities, degree of atom diffusion in mutual phases at interface (related to annealing). At this moment, there seems only empirical choices to achieve least-barrier interface for most cases, but in the case of simplified bulk semiconductor, there is a theory to predict the electronic structure, which certainly helps the guideline for material design. (101-106)
Simplified two-dimensional numerical modeling, a widely known calculation in solar cell community, is able to describe potential gradients inside the semiconductor using classical semiconductor device equations. (39, 107) These simulations can provide reasonable estimates of quantum efficiency and STH efficiency as a function of wavelength. The quantification of several parameters, i.e., absorption coefficient, band positions, dielectric constant, carrier concentrations, effective masses, mobility, and lifetime, has been discussed thus far. The beauty of this modeling is that the sensitivity of the fundamental parameters can be investigated and the properties that are most influential in determining the overall photocatalytic efficiencies can be identified, i.e., modeling brings us one step closer to “photocatalysis by design”. The overpotentials that are required for HER and OER on the surface are input variables (future work is required to make them outputs of the modeling) in this approach, (107) and the diffusion-drift current equation can be solved using generation and recombination rates when the system is under steady-state illumination. In this way, the influence of the metal dispersion on the photocatalytic performance can also be evaluated. (99) For many of the equations that are involved in the estimation of photovoltaic currents, the readers are referred to previous studies. (25, 107)
A scheme in Figure 7 shows how the potential gradient close to HER electrocatalyst on an n-type semiconductor under steady-state illumination may look in the bulk of the semiconductor when carrier concentrations, carrier lifetimes and carrier mobilities are varied. (107) The semiconductor surface was decorated with HER catalyst particle that collects excited electrons, assuming ohmic contact at the interface. The photocatalyst surface was designed to oxidize water, where Schottky contact with electrolyte was assumed. On the photocatalyst surface (left side of Figure 7A), it was assumed that potential gradient exists between HER catalyst and semiconductor bare surface to achieve overall water splitting (1.53 eV). In Figure 7B, excited electrons should flow from right (semiconductor bulk) to left (surface) and downward, following the slope generated at the semiconductor-electrolyte interface. At high carrier concentrations, a substantial energy barrier (peak), related to the so-called pinch-off effect, (88) was observed close to the surface, even if ohmic contact was assumed. On the other hand, lower carrier concentrations result in gradual slopes that guide the excited electron to the left side of the HER catalyst. This observation coincides with finding resultant larger AQE and STH efficiencies at lower carrier concentrations. This type of modeling certainly helps determining the properties that should be targeted to improve overall performance; for example, the carrier lifetime should be greater than hundreds of picoseconds, among other properties.
Figure 7
Figure 7. (A) Geometric model schemes using n-type semiconductor with HER catalyst decoration with the boundary conditions and the assumptions used for the simulations. (B) Potential gradients under the HER catalyst (red dotted line in A) at different donor concentrations, carrier mobility, and carrier lifetime. The x-direction represents the depth from surface (left) into the bulk (right) of the semiconductor. An ohmic junction was assumed for the HER catalyst in contact with the semiconductor, whereas a Schottky contact was assumed to calculate the electrolyte interface. The potential difference between HER site and OER site is assumed to be 1.53 eV. Reprinted with permission from ref 107. Copyright 2016 Royal Society of Chemistry.
Similar simulations suggest that using defective materials, such as dispersions (in particle size and density) of metal nanoparticles, on semiconductor absorbers does not significantly influence efficiency, although a metal catalyst is essential in achieving effective charge separation. (107) This result suggests that even though photocatalytic efficiency remains the same, the turnover frequency (TOF; e.g., rate per surface metal site) varies with different electrocatalyst dispersions. (23) This variation is because, in this case, charge separation efficiency determines overall efficiency, and electrocatalysts only consume carriers as they arrive. The potential, determined as a consequence of charge separation, is different for each particle, and the current (rate) per particle is also thus different; that is, photocatalysts are electrocatalysts, so the rate (current) is based on the potential. (23) A smaller particle, or greater surface area, does not necessarily result in the best overall STH efficiency, and moreover, a high TOF does not always lead to high photocatalytic efficiency of the entire system. On the contrary, it is expected that high exciton binding energy materials may only require high dispersion of catalyst to create more number/density of interfaces. As a result, the modeling provides guidance whether photocatalyst properties should be altered or the identity or dispersion of the electrocatalyst should be improved, which is another step forward to “photocatalysis by design”.
As seen above, a quantitative description of such optoelectronic properties can be used to estimate theoretical photocatalytic efficiency in ideal semiconductor situations. It gives, at minimum, a good estimate whether the improvement of a semiconductor (including its interface) or an electrocatalyst should be investigated and even which specific parameters should be altered, such as minority carrier concentrations or the catalyst dispersion on the surface. (23) It also may allow researchers to consider the potential loss associated at the interfaces. There are measurement techniques that can be used to estimate the potential drop at the (oxy)hydroxide layer on semiconductor surfaces. (108-112) It is already effective to simply isolate bare photocatalyst surface from the water electrolyte, for example, by using some oxide (e.g., SiO2, Al2O3, or TiO2), thus avoiding the surface state and the photocorrosion that is prevalent in some semiconductor compounds. (91, 94, 113-115) However, precisely describing the potential at the interface is still under development. For example, the classic model fails to describe realistic porous ion-permeable electrocatalysts (i.e., oxyhydroxide cocatalysts for water oxidation). Classical semiconductor equations are applicable to bulk materials (the smallest particle size in the COMSOL model used above was 100 nm). (107) The smaller particles have a higher specific surface area, a shorter travel distance to the surface for their charge carriers, a lower degree of band bending, and, possibly, a wider band gap because of quantum size effects. (83) Substantial efforts on efficient interfacial development have been made, especially in photoelectrochemistry applications, and one may refer to a recent excellent review by Li and co-workers on this topic. (116) Nevertheless, diffusion and drift remain fundamental principles that describe carrier transport from the bulk to the surface. Simple simulations, as described above, already predict a substantial loss in the potential gradient at the surface. Successfully incorporating anisotropy in electronic structures of crystals by a simple manner (simpler than conventional fabrication of a p–n junction) is the way to make photocatalysts more efficient and cheaper. (83) Other directions may include preventing electrolyte junctions from inducing surface recombination as well as improving the majority carrier pathway, for example, by using a metal–insulator–semiconductor-type junction or a carefully embedded buried-junction active-site that is electronically isolated from environmental effects. (117, 118) Paradoxically, an approach to insulating a semiconductor from solution is by actually minimizing the beneficial possible utilization of band bending at solid–liquid interfaces. Unlike photoelectrochemical measurement, photocatalysis using a powder photon absorber cannot apply external electric field: that is, the electrons and holes must find their own way to lead to electrocatalysts. A breakthrough to boost the photoconversion efficiency resides in unique establishment of the interface bridging photon absorber and electrocatalyst.
Electrocatalytic Activity
The climax of the water-splitting reaction finishes with the successful consumption of the photogenerated charge carriers by electrochemical redox reactions. The mismatch between the time scales of charge transfer and electrocatalysis causes accumulation of electrons/holes at their respective redox-active species at the surface, resulting in potential shifts (transient charge up) on metal or metal (oxy)hydroxide particles or, in some cases, the photocatalyst surface itself, as a catalyst component. Measurements of such potential shifts were reported for metal particles by using probe molecules under illumination. (119-123) and for metal (hydr)oxides using electrochemical techniques. (109-112) At given potentials, the catalysts should electrocatalyze HER and OER, respectively; the performances of these reactions can be separately measured by using electrochemical techniques that can determine the exact values of applied potentials. (1) Electrocatalysis is another unique interface event: (124) The reaction proceeds on the catalyst surface atoms together with electrolyte within a double-layer region where at least three-water-equivalent ions/molecules are involved in covalent and noncovalent nature. This requires consideration of not only inner Helmholtz layer but outer Helmholtz layer to describe, e.g., transition states, which means that counter “supporting ions” play significant role in electrocatalytic kinetics. (125) It is tremendously difficult, if not possible, to precisely describe the chemical potentials at double-layer region, (126) but various efforts are ongoing as electrocatalysis is indeed a core technology to convert renewable energy resources to useful chemical forms. (5)
Electrocatalytic water splitting itself is a field of study in which many efforts are currently ongoing. Electrocatalytic activity can be ranked using the quantitative values of the exchange current of a given catalyst, i0, and the transfer coefficient, α, which are described by the Tafel equation when the reverse reaction is neglected; (1) however, the terms of these extracted values are still ambiguous due to the lack of a method that can precisely determine active surface areas. Total product formation rate can be described as follows:
(14)where n is the number of electrons involved in the reaction, F is the Faraday constant, Ecat and E0 are the Fermi level of the catalyst and the redox potential in solution, respectively, R is the universal gas constant, and T is the absolute temperature. The overpotential is defined as the difference between Ecat and E0, an additional voltage required relative to the thermodynamic potential to drive the respective redox reaction. Microkinetic Tafel analysis for water redox chemistries has been reviewed elsewhere. (127) Key aspects of the fundamental study of HERs and OERs include finding descriptors of electrocatalytic activity. Based on Sabatier’s principle, metal–hydrogen bond strengths characterize the HER exchange current density. (127, 128) Generally, the OER catalyst is also characterized by using the metal–oxygen bond strength as a descriptor, because a linear relationship exists among metal–oxygen, metal–hydroxide, and metal–oxyhydroxide bond strengths, all of which may be involved in the rate-determining steps. (129-131) When acidic conditions are chosen, the development of a non-noble metal electrodes with acid tolerance is required. The recent development of metal phosphide materials is of significant interest because they contain only abundant transition metals, such as Ni, Fe, and Co. (132-134) For OERs, mixed oxyhydroxides, (135) such as nickel–iron, (136, 137) perovskites, (138) and spinels (139) have also been reported as low overpotential electrocatalysts in alkaline conditions that do not use noble metals. One must remember that for industrial applications, catalyst durability is often more important than catalytic performance. (9) “Self-healing” capability, that is, the dissolution–redeposit process of the electrocatalyst during electro- and photocatalysis is a compelling method to achieve long-term durability. (140-144) Additionally, the temperature of the solution in a practical photoreactor may be substantially higher than room temperature because the photoreactor may absorb infrared irradiation; this factor should be considered in experiments regarding activation energy. Ironically, high activation energies lead to a highly sensitive current increase with temperature changes, resulting in excellent performance under certain relevant water-splitting conditions (e.g., 10 mA cm–2 at mild pH for Ni vs NiFe OER catalysts) (144) or enthalpy–entropy compensations (e.g., in the case of HER at mild pH for Pt, Ni, NiCu, etc.). (145)
(14)where n is the number of electrons involved in the reaction, F is the Faraday constant, Ecat and E0 are the Fermi level of the catalyst and the redox potential in solution, respectively, R is the universal gas constant, and T is the absolute temperature. The overpotential is defined as the difference between Ecat and E0, an additional voltage required relative to the thermodynamic potential to drive the respective redox reaction. Microkinetic Tafel analysis for water redox chemistries has been reviewed elsewhere. (127) Key aspects of the fundamental study of HERs and OERs include finding descriptors of electrocatalytic activity. Based on Sabatier’s principle, metal–hydrogen bond strengths characterize the HER exchange current density. (127, 128) Generally, the OER catalyst is also characterized by using the metal–oxygen bond strength as a descriptor, because a linear relationship exists among metal–oxygen, metal–hydroxide, and metal–oxyhydroxide bond strengths, all of which may be involved in the rate-determining steps. (129-131) When acidic conditions are chosen, the development of a non-noble metal electrodes with acid tolerance is required. The recent development of metal phosphide materials is of significant interest because they contain only abundant transition metals, such as Ni, Fe, and Co. (132-134) For OERs, mixed oxyhydroxides, (135) such as nickel–iron, (136, 137) perovskites, (138) and spinels (139) have also been reported as low overpotential electrocatalysts in alkaline conditions that do not use noble metals. One must remember that for industrial applications, catalyst durability is often more important than catalytic performance. (9) “Self-healing” capability, that is, the dissolution–redeposit process of the electrocatalyst during electro- and photocatalysis is a compelling method to achieve long-term durability. (140-144) Additionally, the temperature of the solution in a practical photoreactor may be substantially higher than room temperature because the photoreactor may absorb infrared irradiation; this factor should be considered in experiments regarding activation energy. Ironically, high activation energies lead to a highly sensitive current increase with temperature changes, resulting in excellent performance under certain relevant water-splitting conditions (e.g., 10 mA cm–2 at mild pH for Ni vs NiFe OER catalysts) (144) or enthalpy–entropy compensations (e.g., in the case of HER at mild pH for Pt, Ni, NiCu, etc.). (145)One of the unique features of photocatalysis is that the photon absorber materials are not stable under extreme pH conditions (acidic or alkaline), which is the regime in which commercial electrolyzers are operated. (146) Interestingly, pure water without any supporting electrolyte can be used in overall water splitting with a powder semiconductor photocatalyst (147, 148) because of the very short distance between the HER (cathode) and the OER (anode), which should occur on the same surface with minimum solution resistance. Electrochemistry is a powerful tool to quantitatively evaluate reactions under near-neutral (or mild) pH conditions. (146) The impact of pH on these reactions will be discussed in greater detail later. In short, one must first identify the “reactants” of respective redox reactions: pH change will cause “reactant switching” at a given current level, which is associated with the diffusion contribution. (149) In general, hydronium ions (protons) are more easily reduced than water molecules, (149) and hydroxyl ions are more readily oxidized than water molecules. (146) One critical note is that the “water-splitting” reaction rather paradoxically does not prefer water molecules to be its reactant. (146, 149) This preference results from the fact that water molecules contain very strong O–H bonds (as is also obvious from the fact that H2O is one of the most thermodynamically stable compounds). To facilitate the water molecule dissociation, anisotropic sites on the surface are effective for heterolytic dissociation of water molecules. (150) For example, in alkaline conditions, Markovic and co-workers reported that islands of nickel or cobalt species on noble metal surfaces (such as Pt) further enhance both HERs and OERs. (151)
Knowledge obtained by electrocatalytic studies should be successfully transferred to the photocatalytic studies. In any case, electrocatalysis should catch up with current flow from the electrons and holes that are generated in the semiconductor underneath. It is obvious that small potential shifts should trigger the corresponding current flow, and excellent electrocatalysts are thus preferred as efficient photocatalysis. (52) An excellent example is rough CoOx modification on n-Si photoanode, where almost full utilization of the generated photovoltage was achieved for OER by CoOx under illumination. (152) If there is difference in “ranking” electrocatalyst materials during photocatalysis and pure electrocatalysis, it arises from different degrees of potential shifts at the catalyst/semiconductor interfaces, causing the electrocatalysts to not experience the same potentials due to, e.g., different degree of Schottky contact and barrier height, as discussed above, Figure 6. (52) On the contrary approach, if the kinetics of electrocatalysts for HER and OER require substantial overpotentials (e.g., overvoltage of ∼2.0 V), the required bandgap to maximize theoretical STH efficiency essentially becomes larger; the best scenario as large as ∼2.4 eV, thus never reaching 10% STH benchmarking efficiency. (153) Excellent activity of electrocatalysts that are optically transparent is desired.
To achieve efficient overall water splitting in a membrane-less configuration, as Gerischer stated in his early work, (85) the suppression of the back reactions of H2 and O2 to form H2O must be suppressed. Noble metals, in particular, are generally excellent HER catalysts but also typically catalyze the back reaction either thermally or electrocatalytically (oxygen reduction reaction). (154, 155) Successful suppression with nanometer-scale decorations on such electrocatalyst surfaces ([email protected] structure) have been reported and use chromium, (156, 157) molybdenum, (158) titanium, (159) and lanthanoids, (160) in the form of (oxyhydr)oxide as shells. The amorphous structure of very small hydrated clusters makes the materials function as a selective membrane that is not permeable to dissolved gases (including O2), thus preventing back reactions. (156, 158) There is a possibility to utilize this functionality to protect the surface from poisoning because this membrane function also insulates various redox-active species. (157) Development of shell materials that make the OER catalyst selective is also ongoing.
It is interesting to note that overall photocatalytic efficiency may be further improved by having better HER or OER electrocatalysts under all conditions. Based on this charge-up theory, enhancements in the rate of reduction or oxidation improve the overall efficiency of water splitting, which is determined by the photon flux and the efficiency of carrier transport from the photocatalyst to the redox catalysts because accelerated electron or hole processes affect the potential, which in turn perturbs the rates of the process on the opposite side. (161) Because electron and hole transport are parallel reactions, the overall photocatalysis process does not have a single rate-determining step unlike the case of half-reaction electrocatalysis). (44, 161) In other words, further improvement for electron consumption (HER) or hole consumption (OER) should improve overall efficiencies. Fast consumption of electrons will cause hole accumulation on the OER side, further enhancing the overall rate, or vice versa. (162, 163) It is also effective to analyze the sensitivity of HER or OER performance to overall photocatalysis performance, which can be evaluated using photocatalysis with isotope effects (44) or effectively comparing electrocatalytic reactions under dark conditions. (164)
Mass Transfer (Ion Diffusion)
After decades of studying photocatalysis for water splitting, the efficiency of this process has been tremendously improved. (165) The primary focus of photosynthetic reactions is still based on managing photons in the bulk and on the surfaces of photon absorber materials, as mentioned previously. The research in this field has therefore been largely oriented by the synthesis of efficient photon absorber materials, including their electrocatalyst decorations. Nevertheless, when reaching commercially viable efficiency is considered, the mass transfer of reactants and ions in addition to solution resistance can no longer be ignored during electrocatalysis or photocatalysis. (150) Much research is focused on systems that work at room temperature, and under such conditions, it is often the case that the diffusion of ions contributes to the overall efficiency by creating a concentration overpotential; an additional loss originates from the depletion of reactants. This is certainly the case when photocatalytic remediation of low-concentration substances is the target reaction. (12) The rigorous and quantitative determination of parameters in such a process is essentially possible using the thermodynamic and kinetic information that can be generated using electrochemistry.
At a given current, sources of potentials are classified into kinetic overpotential (dependent on catalyst), concentration overpotential (independent of catalyst), and solution resistance. The contributions of the concentration overpotential and solution resistance can be quantitatively obtained by using the physical properties of the solution. Detailed quantification and methodology was reviewed in previous literature. Mass transport phenomena in electrochemistry are described by the Nernst–Planck equation with terms for (in this order) diffusion, migration, and convection (for species i in the x-direction): (1)
(15)where J is the flux, D is the diffusion coefficient, z is the charge number and v is the velocity of the forces in the solution. (1) The Stokes–Einstein model gives the diffusion coefficient as
(16)where k is the Boltzmann constant, d is the effective diameter of the ion in the hydrated form (Stokes diameter), and μ is the viscosity of the solution. (166) Therefore, the parameters governing mass transport flux are the effective size of the species, viscosity of the solution, and activity (or fugacity) of the species. Moreover, solubility of dissolved gases, another quantifiable parameter, is greatly influenced by the identity and molarity of the supporting electrolyte, which correlates with reverse reaction of products going back to water, or hydrogen oxidation reaction (HOR), and oxygen reduction reaction (ORR). (167) These physical properties can be obtained separately, often from a database, (168) and the contribution of mass transport is thus quantifiable. Under relevant reaction conditions, the benchmark STH efficiency of 10% corresponds to a hydrogen production rate of ∼154 μmol H2 cm–2 h–1 and a corresponding current of ∼8.3 mA cm–2 (assuming that a single semiconductor (or tandem semiconductors) is achieving the overall water splitting). Under static conditions (no convection) at 25 °C, even hydronium (proton) and hydroxide ions can face diffusion-limiting currents, causing “reactant switching”: pH values of ∼1.6 or lower (for hydronium ion) and ∼12.3 or higher (for hydroxide ion) are necessary in unbuffered conditions. Outside this range of pH (unbuffered, near-neutral pH), reactant switching between H+ (HER) and OH– (OER) to H2O must occur, causing additional kinetic overpotential. (150) Obviously, this activity of the reactants, together with minimized solution resistance, is one reason why extreme pH conditions are chosen for the electrolysis of water. In addition, the HER causes an increase in the pH, and the OER causes a decrease in the pH, so the complete isolation of ions in a two-compartment cell will lead to a high concentration overpotential (shifting the thermodynamic potential by 59 mV pH–1), which causes additional loss of overall efficiency. The use of an ion-exchangeable membrane is mandatory to separate H2 and O2 while minimizing these concentration overpotentials. (169) Nafion or an alkaline membrane typically works in media with extreme pH, (170) although some membranes that may be used as neutral pH values have been recently developed. (171) One of the most significant benefits of coproducing an H2/O2 mixture is avoiding the use of membranes and minimizing solution resistance and the pH gradient (i.e., the concentration overpotential). (169) However, this process occurs at the expense of producing an explosive gas mixture (H2 and O2). (169)
(15)where J is the flux, D is the diffusion coefficient, z is the charge number and v is the velocity of the forces in the solution. (1) The Stokes–Einstein model gives the diffusion coefficient as(16)where k is the Boltzmann constant, d is the effective diameter of the ion in the hydrated form (Stokes diameter), and μ is the viscosity of the solution. (166) Therefore, the parameters governing mass transport flux are the effective size of the species, viscosity of the solution, and activity (or fugacity) of the species. Moreover, solubility of dissolved gases, another quantifiable parameter, is greatly influenced by the identity and molarity of the supporting electrolyte, which correlates with reverse reaction of products going back to water, or hydrogen oxidation reaction (HOR), and oxygen reduction reaction (ORR). (167) These physical properties can be obtained separately, often from a database, (168) and the contribution of mass transport is thus quantifiable. Under relevant reaction conditions, the benchmark STH efficiency of 10% corresponds to a hydrogen production rate of ∼154 μmol H2 cm–2 h–1 and a corresponding current of ∼8.3 mA cm–2 (assuming that a single semiconductor (or tandem semiconductors) is achieving the overall water splitting). Under static conditions (no convection) at 25 °C, even hydronium (proton) and hydroxide ions can face diffusion-limiting currents, causing “reactant switching”: pH values of ∼1.6 or lower (for hydronium ion) and ∼12.3 or higher (for hydroxide ion) are necessary in unbuffered conditions. Outside this range of pH (unbuffered, near-neutral pH), reactant switching between H+ (HER) and OH– (OER) to H2O must occur, causing additional kinetic overpotential. (150) Obviously, this activity of the reactants, together with minimized solution resistance, is one reason why extreme pH conditions are chosen for the electrolysis of water. In addition, the HER causes an increase in the pH, and the OER causes a decrease in the pH, so the complete isolation of ions in a two-compartment cell will lead to a high concentration overpotential (shifting the thermodynamic potential by 59 mV pH–1), which causes additional loss of overall efficiency. The use of an ion-exchangeable membrane is mandatory to separate H2 and O2 while minimizing these concentration overpotentials. (169) Nafion or an alkaline membrane typically works in media with extreme pH, (170) although some membranes that may be used as neutral pH values have been recently developed. (171) One of the most significant benefits of coproducing an H2/O2 mixture is avoiding the use of membranes and minimizing solution resistance and the pH gradient (i.e., the concentration overpotential). (169) However, this process occurs at the expense of producing an explosive gas mixture (H2 and O2). (169)Near-neutral pH conditions makes it possible to use many materials for stable photocatalytic water splitting. Under neutral pH conditions, buffering ions are commonly used to maintain local pH values by utilizing their buffering action. (172) In addition to the role of the supporting electrolyte in minimizing solution resistance (iR drop), the buffer ions significantly influence electrocatalysis. The buffer’s counteranion is a carrier for H+ and thus plays a role in transporting the H+ reactant to cathode or abstracting the H+ products from the anode. (173-175) At relevant current densities and under ambient conditions, the diffusion of buffer ions may therefore result in substantial concentration overpotentials. For example, using an excellent catalyst, such as Pt, for HER in NaH2PO4, the optimum buffer concentrations for the HER appear to be as high as 1.5–2.0 M at 25 °C. (174) It has also been recently determined that some OER catalysts also suffer from concentration overpotentials, or mass-transfer limitation of buffering ions, which can be seen because the rotating-disk electrode current depends on its rotation speed. (174) This fact is often neglected in the photocatalysis and photoelectrochemistry community.
Another interesting consideration of the activity of the reactants is the use of water vapor as a reactant (liquid water vs water vapor). Using vapor-phase water has advantages such as the ability to easily control its supply and the use of simple reactor designs, e.g., a fixed bed for powder systems. (175) However, using water vapor as a reactant encounters considerable difficulties due to an additional term for the adsorption of water vapor at low partial pressures, which may strongly decrease the overall efficiency. In contrast, using liquid-phase water (close to unity) or the associated ions (H+ or OH–) as reactants can result in high activities, effectively utilizing the electric field applied at the double-layer region.
In static photoelectrochemical water splitting, high efficiency (currents) of photoelectrodes leads to additional efficiency loss due to the generated gas bubbles blocking the surface. It was reported that hydrophilic surface is preferred to detach the generated bubbles, which was also confirmed by the fact that introduction of surfactant was thus effective to remove gas bubbles. Contact angle at gas-surface interface is known to be correlated, but the details can be found elsewhere. (176) For photocatalyst powder systems, the gas bubble problems seem absent in the literature, yet probably because of low efficiency of the powder suspension system. Since the photocatalytic performance is being improved, one must consider the final form of photocatalyst samples, whether they should be immobilized in which substrates, and types of convective flow of liquids. Associated with this, the temperature of the reactant water may be considered, which impacts not only catalytic rates but also the mass transport which also has activation energy with Arrhenius relation.
Discussion and Perspectives
ARTICLE SECTIONS
This contribution identified a number of quantifiable parameters associated with the complex processes that occur during photocatalytic water splitting. The processes are sequentially and often coherently connected in the following order and operate at different time scales as the six-gear concept as shown in Figure 2. These parameters and relevant useful information are summarized in Table 1. Strategy should be adequately planned to investigate photocatalytic materials and reactions. In photoelectrochemical water splitting study, there are some suggested guidelines in the literature, (177) which are also useful for investigating photocatalytic water splitting as many phenomena function in common principles. Most of the constants and the quantifiable variables are listed in Table 2. By identifying these “quantities”, one may predict efficiencies using various established equations and thus help directing the researches. For further details regarding the equations, the readers are referred to previous reviews for semiconductor study, (25, 107, 178) and electrochemistry study, (173) and literature cited therein. One may want to check the absorption coefficient (Gear 1), especially close to band edges, the exciton binding energy (Gear 2) and carrier lifetime (Gear 3). Next is to describe carrier diffusion (Gear 3) and transport (Gear 4). In simple cases, simulation can currently estimate maximum photocatalytic quantum efficiencies based on the quantified values of bulk semiconductor parameters. This will be the first assessment whether the bulk semiconductor properties should be ever suitable for efficient photocatalysis. The guidance obtained is whether the material itself should be altered, the synthesis protocol should be improved (crystallinity), or electrocatalyst decoration should be improved in terms of dispersion and loading, etc.
Table 1. List of Events, Parameters, Variables, Relevant Theories, and Useful Characterization Techniques for Photocatalysis Investigation
| events | parameters/variables | theory | characterization techniques |
|---|---|---|---|
| 1. photon absorption | absorptance/reflectance/scattering | Franck–Condon principle | X-ray diffraction |
| absorption coefficient | Lambert–Beer’s law | UV–vis-NIR spectroscopy | |
| absorption depth | electromagnetic wave propagation | spectroradiometer | |
| density of state | Maxwell curl equations | ||
| 2. exciton separation | effective mass | electrostatic force | transient absorption spectroscopy |
| dielectric constant/dielectric loss | Mott–Wannier type | photoemission spectroscopy | |
| refractive index | Frenkel type | optical absorption spectroscopy | |
| exciton binding energy | photoconductivity screening potential spectroscopy | ||
| magneto-optical spectroscopy | |||
| 3. carrier diffusion | carrier mobility | recombination models (srh, Auger) | van der Pauw technique with Hall measurement |
| diffusion coefficient | Poisson equation | time-resolved spectroscopy | |
| carrier lifetime | drift and diffusion equations | THz and microwave spectroscopies | |
| carrier diffusion length | continuity equations | ||
| carrier concentrations | Boltzmann transport equation | ||
| charge recombination kinetics | semiconductor devices equations | ||
| 4. carrier transport | electric field | Einstein relation | conductivity measurement |
| drift current | Mott–Schottky analysis | photoemission spectroscopy (in air) | |
| depletion layer width | Schottky/ohmic contact | ultraviolet photoemission spectroscopy | |
| flatband potential/workfunction/redox potential (potential-determining ion) | electrochemistry (aqueous nonaqueous) | ||
| barrier height | intensity modulated photocurrent/photovoltage spectroscopy | ||
| Fermi level pinning | ambient-pressure X-ray photoelectron spectroscopy | ||
| density of surface states | |||
| kinetics of charge transfer and recombination | |||
| 5. electrochemistry | exchange current density (charge transfer resistance) | Butler–Volmer analysis | voltammetry, Tafel analysis |
| charge/electron transfer coefficient | Tafel equation | impedance spectroscopy | |
| conductivity | |||
| Tafel slope | |||
| activation energy | |||
| 6. mass transfer | diffusion coefficient (ion size viscosity activity coefficient) | Nernst–Planck–Poisson equation | Koutechy–Levich analysis |
| solution resistance | Fick’s law | viscometer | |
| Einstein–Smoluchowski equation | pH meter | ||
| Cottrell/Koutechy–Levich equation | conductivity/impedance | ||
| other parameters/variables and characterization techniques | temperature | scanning electron microscope | |
| activity/fugacity (of reactant and products) | transmission electron microscope | ||
| photon flux and photon distribution | X-ray diffraction | ||
| durability | X-ray photoelectron spectroscopy |
Table 2. Major Constants and Variables Involved in Photocatalysis
| constants | ||
|---|---|---|
| symbol | unit | description |
| e | C | elementary charge |
| kB | J K–1 | Boltzmann constant |
| h | J s | Planck constant |
| ε0 | F m–1 | vacuum permittivity |
| me | kg | electron mass |
| R | J mol–1 K–1 | gas constant |
| F | C mol–1 | Faraday constant |
| variables for semiconductor equations | ||
|---|---|---|
| symbol | unit | description |
| T | K | temperature |
| εr(s) | relative permittivity (dielectric constant) of semiconductor | |
| n, p | m–3 | electron and hole concentration |
| ni | m–3 | intrinsic carrier concentration |
| n0, p0 | m–3 | quasi-equilibrium carrier density |
| NC, NV | m–3 | effective density of states in the conduction and valence band |
| μn, μp | m2 V–1 s–1 | electron and hole mobility |
| τn, τp | s | electron and hole lifetime |
| τc | s | collision time |
| Dn, Dp | m2 s–1 | electron and hole diffusion coefficient |
| L | m | diffusion length |
| P0 | m2 s–1 | photons absorbed from AM 1.5G |
| α(λ) | m–1 | absorption coefficient |
| λ | m | wavelength of photon |
| x | m | depth into the bulk of a semiconductor |
| ρ | m | surface of the semiconductor |
| r0, rs | m | catalyst and semiconductor particle size (diameter) |
| χ | eV | semiconductor electron affinity |
| Eg | eV | band gap |
| EC | eV | conduction band edge |
| EV | eV | valence band edge |
| m*n, m*p | effective electron and hole mass | |
| A*n, A*p | A m–2 K–2 | effective Richardson constant for electrons and holes |
| variables for electrochemical parameters | ||
|---|---|---|
| symbol | unit | description |
| n | number of electrons in reaction | |
| ai | thermodynamic activity (of species i) | |
| γ± | activity coefficient | |
| Di | m2 s–1 | diffusion coefficient (of species i) |
| δ | m | diffusion layer thickness |
| u | m2 s–1 V–1 | ion mobility |
| a | m | Stokes radius |
| μ | Pa s | viscosity of solution |
| ν | m2 s–1 | kinematic viscosity of solution |
| εr(l) | relative permittivity (dielectric constant) of solution | |
| η | V | overpotential |
| α | transfer coefficient | |
| j0 | A cm–2 | exchange current density |
| θ | surface coverage | |
| k | (depending on elementary steps) | rate constant |
| A | (depending on elementary steps) | preexponential factor |
| Ea | kJ mol–1 | activation energy |
In a typical example, Si is widely available already in a commercial scale, and, upon purchasing, many parameters mentioned in the first part (Gears 1–4) are effectively quantified. Si wafers are commercially available with known dopant concentration and conductivity/resistivity. A μm-order diffusion length is accordingly obtainable, so the strategy is to focus on the further improvement in optical enhancement and surface charge separation with dispersed catalyst decoration. A deconvolution of such properties (including Gear 4–6) for 3D structure p-Si photocathode was well reported by Esposito and co-workers. (176) On the contrary, for another example, nonoxide materials, such as Ta3N5 used as a visible-light-responsive photocatalyst, have many parameters unknown and remain uncertainties to the semiconductor properties. Such quantities of the parameters were summarized in the literature for Ta3N5. (179) This type of (oxy)nitride materials is synthesized at each laboratory usually via nitridation of oxide precursors in NH3 flow at high temperatures. Nonstoichiometry due to remaining oxygen as well as anion vacancy associated with Ta5+ reduction to Ta3+ in the bulk structure is also recognized. (180) From the literature, despite the efforts for the surface alteration and catalyst decoration essential to enhance photocatalytic performance, there remain a lot to do to improve bulk properties and improve carrier lifetimes. (107) Diffusion lengths can be as short as a few nm when carrier trapping of Ta3N5 happens in a picosecond-order (181, 182) (although a part of carriers that have longer lifetimes was also reported for Ta3N5). (183, 184) It is still important that the synthesis protocol should be improved for prolong carrier lifetime and resultant diffusion lengths (e.g., flux-assisted protocols for improved crystallinity).
It is also time to thoroughly discuss the actual reaction conditions with practical reactor design for photocatalysis (pressure, temperature, activity, etc.), (185-189) because they will affect the photovoltage, electrocatalytic kinetics, the diffusion of ions, and so on. As a result, the performance/durability ranking of photocatalytic/electrocatalytic materials may be different from investigations at room temperature under low pressures. Accordingly, the era has come for solar fuel production study to seriously consider the practical photoreactor design together with reaction conditions. (186) In a photoreactor in large-scale application under solar irradiation, temperature may substantially rise by design, which may be beneficial because many photocatalytic systems are reported to have positive activation energy, (11) and kinetic isotope effects from D2O experiments; (189, 190) that is, surface electrocatalysis may be sluggish enough to influence overall efficiency. It is desired to maintain small density and high dispersion of the catalysts on the photon absorber not to absorb photons by the catalysts themselves. Such small quantities of the catalysts, especially when the efficiency is improved, prefers high temperature to catch up the electrocatalysis. Choice of materials should also be conducted based on durability and robustness of the photocatalyst materials under the operational reaction conditions.
This contribution may serve as a set of guidelines to help identify the kinetic bottleneck with “quantities” that limit the overall efficiency of photocatalysis and to help intentionally improve specific properties: steps forward toward “photocatalysis by design” concept. Finally, the concepts shown here are not limited to this reaction and may be applied to, e.g., photocatalytic CO2 reduction or even environmental remediation. To develop a commercial level of photocatalytic efficiency, consolidated efforts to achieve commercial solar energy conversion processes based on an understanding at the microscopic and macroscopic levels should be made.
Author Information
ARTICLE SECTIONS
- Kazuhiro Takanabe - King Abdullah University of Science and Technology (KAUST), KAUST Catalysis Center (KCC) and Physical Sciences and Engineering Division (PSE), 4700 KAUST, Thuwal 23955-6900, Saudi Arabia;
http://orcid.org/0000-0001-5374-9451;
Acknowledgment
ARTICLE SECTIONS
The research reported in this publication was supported by King Abdullah University of Science and Technology (KAUST). The author appreciates Dr. Angel T. Garcia-Esparza for thorough discussion on simulation data related to Figure 7.
References
ARTICLE SECTIONS
This article references 190 other publications.
- 1Electrochemical Methods, 2nd ed.; Bard, A. J., Faulkner, L. R., Eds.; John Wiley & Sons, Inc.: Hoboken, NJ, 2001; pp 736– 768.Google ScholarThere is no corresponding record for this reference.
- 2Kraeutler, B.; Bard, A. J. J. Am. Chem. Soc. 1978, 100, 2239– 2240 DOI: 10.1021/ja00475a049
- 3Calvo, E. J. In Electrode Kinetics: Principles and Methodology, Bamford, C. H.; Tipper, C. F. H.; Compton, R. G., Eds.; Elsevier: Amsterdam, 1986; Vol. 26, pp 1– 74.Google ScholarThere is no corresponding record for this reference.
- 4Shaner, M. R.; Atwater, H. A.; Lewis, N. S.; McFarland, E. W. Energy Environ. Sci. 2016, 9, 2354– 2371 DOI: 10.1039/C5EE02573G
- 5Lewis, N. S. Science 2016, 351, Article No. aad1920 DOI: 10.1126/science.aad1920
- 6Nakamura, A.; Ota, Y.; Koike, K.; Hidaka, Y.; Nishioka, K.; Sugiyama, M.; Fujii, K. Appl. Phys. Express 2015, 8, 107101 DOI: 10.7567/APEX.8.107101[Crossref], [CAS], Google Scholar6https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xis1Kit74%253D&md5=9574eff0586bc41a2e474cb18e005650A 24.4% solar to hydrogen energy conversion efficiency by combining concentrator photovoltaic modules and electrochemical cellsNakamura, Akihiro; Ota, Yasuyuki; Koike, Kayo; Hidaka, Yoshihide; Nishioka, Kensuke; Sugiyama, Masakazu; Fujii, KatsushiApplied Physics Express (2015), 8 (10), 107101/1-107101/4CODEN: APEPC4; ISSN:1882-0786. (IOP Publishing Ltd.)The highest efficiency of 24.4% for the solar-to-hydrogen (STH) energy conversion was obtained in an outdoor field test by combining concentrator photovoltaic (CPV) modules with InGaP/GaAs/Ge three-junction cells and polymer-electrolyte electrochem. (EC) cells. The high efficiency was obtained by using the high-efficiency CPV modules (∼31% under the present operation conditions) and the direct connection between the CPV modules and the EC cells with an almost optimized no. of elements in series. The STH efficiency bottleneck was clarified to be the efficiency of the CPV modules, the over-potential of the EC cells, and matching of the operation point to the maximal-power point of the CPV modules.
- 7Khaselev, O.; Turner, J. A. Science 1998, 280, 425– 427 DOI: 10.1126/science.280.5362.425
- 8Nocera, D. G. Acc. Chem. Res. 2012, 45, 767– 776 DOI: 10.1021/ar2003013[ACS Full Text
], [CAS], Google Scholar8https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XltVylu7k%253D&md5=c7ae917b44e8c4be8a38bf2be8f384d0The Artificial LeafNocera, Daniel G.Accounts of Chemical Research (2012), 45 (5), 767-776CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)A review. To convert the energy of sunlight into chem. energy, the leaf splits H2O via the photosynthetic process to produce mol. O and H, which is in a form of sepd. protons and electrons. The primary steps of natural photosynthesis involve the absorption of sunlight and its conversion into spatially sepd. electron-hole pairs. The holes of this wireless current are captured by the O evolving complex (OEC) of photosystem II (PSII) to oxidize H2O to O. The electrons and protons produced as a byproduct of the OEC reaction are captured by ferrodoxin of photosystem I. With the aid of ferrodoxin-NADP+ reductase, they are used to produce H as NADPH. For a synthetic material to realize the solar energy conversion function of the leaf, the light-absorbing material must capture a solar photon to generate a wireless current that is harnessed by catalysts, which drive the 4 electron/hole fuel-forming H2O-splitting reaction under benign conditions and under 1 sun (100 mW/cm2) illumination. This Account describes the construction of an artificial leaf comprising earth-abundant elements by interfacing a triple junction, amorphous Si photovoltaic with H- and O-evolving catalysts made from a ternary alloy (NiMoZn) and a Co-phosphate cluster (Co-OEC), resp. The latter captures the structural and functional attributes of the PSII-OEC. Similar to the PSII-OEC, the Co-OEC self-assembles upon oxidn. of an earth-abundant metal ion from 2+ to 3+, may operate in natural H2O at room temp., and is self-healing. The Co-OEC also activates H2O by a p-coupled electron transfer mechanism in which the Co-OEC is increased by 4 hole equiv. akin to the S-state pumping of the Kok cycle of PSII. X-ray absorption spectroscopy studies established that the Co-OEC is a structural relative of Mn3CaO4-Mn cubane of the PSII-OEC, where Co replaces Mn and the cubane is extended in a corner-sharing, head-to-tail dimer. The ability to perform the O-evolving reaction in H2O at neutral or near-neutral conditions has several consequences for the construction of the artificial leaf. The NiMoZn alloy may be used in place of Pt to generate H. To stabilize Si in H2O, its surface is coated with a conducting metal oxide onto which the Co-OEC may be deposited. The net result is that immersing a triple-junction Si wafer coated with NiMoZn and Co-OEC in H2O and holding it up to sunlight can effect direct solar energy conversion via H2O splitting. By constructing a simple, stand-alone device composed of earth-abundant materials, the artificial leaf provides a means for an inexpensive and highly distributed solar-to-fuels system that employs low-cost systems engineering and manufg. Through this type of system, solar energy can become a viable energy supply to those in the non-legacy world. - 9Sun, K.; Saadi, F. H.; Lichterman, M. F.; Hale, W. G.; Wang, H.-P.; Zhou, X.; Plymale, N. T.; Omelchenko, S. T.; He, J.-H; Papadantonakis, K. M.; Brunschwig, B. S.; Lewis, N. S. Proc. Natl. Acad. Sci. U.S.A. 2015, 112, 3612– 3617 DOI: 10.1073/pnas.1423034112
- 10Kageshima, Y.; Shinagawa, T.; Kuwata, T.; Nakata, J.; Minegishi, T.; Takanabe, K.; Domen, K. Sci. Rep. 2016, 6, 24633 DOI: 10.1038/srep24633[Crossref], [PubMed], [CAS], Google Scholar10https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xmt1ens7k%253D&md5=2f2a12e88ba48d056a9ee2d5e2ea1bd7A miniature solar device for overall water splitting consisting of series-connected spherical silicon solar cellsKageshima, Yosuke; Shinagawa, Tatsuya; Kuwata, Takaaki; Nakata, Josuke; Minegishi, Tsutomu; Takanabe, Kazuhiro; Domen, KazunariScientific Reports (2016), 6 (), 24633CODEN: SRCEC3; ISSN:2045-2322. (Nature Publishing Group)A novel "photovoltaics (PV) + electrolyzer" concept is presented using a simple, small, and completely stand-alone non-biased device for solar-driven overall water splitting. Three or four spherical-shaped p-n junction silicon balls were successfully connected in series, named "SPHELAR.". SPHELAR possessed small projected areas of 0.20 (3PVs) and 0.26 cm2 (4PVs) and exhibited working voltages sufficient for water electrolysis. Impacts of the configuration on the PV module performance were carefully analyzed, revealing that a drastic increase in the photocurrent (≈20%) was attained by the effective utilization of a reflective sheet. Sep. investigations on the electrocatalyst performance showed that non-noble metal based materials with reasonably small sizes (<0.80 cm2) exhibited substantial currents at the PV working voltage. By combining the observations of the PV characteristics, light management and electrocatalyst performance, solar-driven overall water splitting was readily achieved, reaching solar-to-hydrogen efficiencies of 7.4% (3PVs) and 6.4% (4PVs).
- 11Wang, Q.; Hisatomi, T.; Jia, Q.; Tokudome, H.; Zhong, M.; Wang, C.; Pan, Z.; Takata, T.; Nakabayashi, M.; Shibata, N.; Li, Y.; Sharp, I. D.; Kudo, A.; Yamada, T.; Domen, K. Nat. Mater. 2016, 15, 611– 615 DOI: 10.1038/nmat4589[Crossref], [PubMed], [CAS], Google Scholar11https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XktVamsb4%253D&md5=f8f0b57c75ad424efc58155932f3e0cfScalable water splitting on particulate photocatalyst sheets with a solar-to-hydrogen energy conversion efficiency exceeding 1%Wang, Qian; Hisatomi, Takashi; Jia, Qingxin; Tokudome, Hiromasa; Zhong, Miao; Wang, Chizhong; Pan, Zhenhua; Takata, Tsuyoshi; Nakabayashi, Mamiko; Shibata, Naoya; Li, Yanbo; Sharp, Ian D.; Kudo, Akihiko; Yamada, Taro; Domen, KazunariNature Materials (2016), 15 (6), 611-615CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)Photocatalytic H2O splitting using particulate semiconductors is a potentially scalable and economically feasible technol. for converting solar energy into H. Z-scheme systems based on 2-step photoexcitation of a H evolution photocatalyst (HEP) and an O evolution photocatalyst (OEP) are suited to harvesting of sunlight because semiconductors with either H2O redn. or oxidn. activity can be applied to the H2O splitting reaction. However, it is challenging to achieve efficient transfer of electrons between HEP and OEP particles. Here, the authors present photocatalyst sheets based on La- and Rh-codoped SrTiO3 (SrTiO3:La, Rh; ref. ) and Mo-doped BiVO4 (BiVO4:Mo) powders embedded into a Au layer. Enhancement of the electron relay by annealing and suppression of undesirable reactions through surface modification allow pure H2O (pH 6.8) splitting with a solar-to-H energy conversion efficiency of 1.1% and an apparent quantum yield of over 30% at 419 nm. The photocatalyst sheet design enables efficient and scalable H2O splitting using particulate semiconductors.
- 12Osterloh, F. E. ACS Energy Lett. 2017, 2, 445– 453 DOI: 10.1021/acsenergylett.6b00665[ACS Full Text], [CAS], Google Scholar12https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtFKltL0%253D&md5=3811453d758dc57a3b3c5d86709271abPhotocatalysis versus Photosynthesis: A Sensitivity Analysis of Devices for Solar Energy Conversion and Chemical TransformationsOsterloh, Frank E.ACS Energy Letters (2017), 2 (2), 445-453CODEN: AELCCP; ISSN:2380-8195. (American Chemical Society)A review. The chem. literature often does not differentiate between photocatalytic (PC) and photosynthetic (PS) processes (including artificial photosynthesis) even though these reactions differ in their thermodn. Photocatalytic processes are thermodynamically downhill (ΔG < 0) and are merely accelerated by the catalyst, whereas photosynthetic processes are thermodynamically unfavorable (ΔG > 0) and require photochem. energy input to occur. The authors apply this differentiation to analyze the basic functions of PC and PS devices and to formulate design criteria for improved performance. As will be shown, the corresponding devices exhibit distinctly different sensitivities to their functional parameters. For example, under conditions of optimal light absorption, carrier lifetimes, and electrochem. rates, the performance of PCs is limited only by their surface area, while type 1 PS devices are limited by their carrier mobility and mass transport, and type 2 PS devices are limited by electrochem. charge-transfer selectivity. Strategies for the optimization of type 1 and 2 photosynthetic devices and photocatalysts are also discussed.
- 13Mills, A.; Wang, J. J. Photochem. Photobiol., A 1999, 127, 123– 134 DOI: 10.1016/S1010-6030(99)00143-4[Crossref], [CAS], Google Scholar13https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1MXmtlSlt7s%253D&md5=8729cdb8f5dbb14f328b805e248d06dbPhotobleaching of Methylene blue sensitized by TiO2: an ambiguous system?Mills, A.; Wang, J.Journal of Photochemistry and Photobiology, A: Chemistry (1999), 127 (1-3), 123-134CODEN: JPPCEJ; ISSN:1010-6030. (Elsevier Science S.A.)The photobleaching of Methylene blue (MB), sensitized by TiO2, in an aq. soln. is studied in the absence and presence of oxygen. In the absence of oxygen and in the presence of a sacrificial electron acceptor (SED), MB is photoreduced to its colorless leuco form, LMB, by the TiO2 photocatalyst. This photoredn. process is obsd. even if an SED is not present, indicating that MB itself can act as an SED. The oxidn. of LMB by oxygen to regenerate MB is significantly slower if the aq. soln. is acidified (0.01 mol-dm-3 HClO4) and, at low partial pressures, the rate of reaction depends directly upon the concn. of dissolved oxygen. The TiO2-sensitized photobleaching of MB is irreversible in an oxygen-satd. aq. soln., as expected, since the bleaching was due to an oxidative process. However, in an acidified soln. (0.01 mol-dm-3 HClO4), the photobleaching process, in an oxygen-satd. soln., generates LMB initially. The latter situation arises because, under acidic conditions, LMB reacts only very slowly with oxygen to form MB. The significance of these findings with respect to the popular use of photobleaching of MB as a demonstration of semiconductor photomineralization is discussed.
- 14Yan, X.; Ohno, T.; Nishijima, K.; Abe, R.; Ohtani, B. Chem. Phys. Lett. 2006, 429, 606– 610 DOI: 10.1016/j.cplett.2006.08.081
- 15Ohtani, B. Chem. Lett. 2008, 37, 216– 229 DOI: 10.1246/cl.2008.216
- 16Mills, A. Appl. Catal., B 2012, 128, 144– 149 DOI: 10.1016/j.apcatb.2012.01.019[Crossref], [CAS], Google Scholar16https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38Xhs1KjsL7N&md5=44dafaeea1a2b76b6af5521f1af7ca0fAn overview of the methylene blue ISO test for assessing the activities of photocatalytic filmsMills, AndrewApplied Catalysis, B: Environmental (2012), 128 (), 144-149CODEN: ACBEE3; ISSN:0926-3373. (Elsevier B.V.)The main features are described of the ISO published std.: 10678:2010, namely the Detn. of photocatalytic activity of surfaces in an aq. medium by degrdn. of methylene blue'. The main underlying assumptions of the std. are considered, namely: (i) dye purity, (ii) adsorption and pH, (iii) light source, (iv) stirring and diffusion, (v) reaction mechanism and (vi) kinetics. Possible sources of errors arising form these assumptions are identified and changes to the std.'s protocol suggested. The major suggested changes are: (i) a source of MB+ of known and proven on site high purity (>90%) should be used to make up the std. test soln., which should have a referenced absorbance, 0.74, at 665 nm; (ii) the conditioning soln. should be the same concn. as the std. test soln., (iii) the initial pH of the reaction soln. should lie in the range: 5.5-6.0; (iv) a BLB UVA light with a europium-doped strontium fluoroborate or borate phosphor should be used; (v) the reaction soln. should be vigorously and continuously stirred if possible; (vi) the soln. height should be the min. recommended value of 2 cm, and the photoreactor cylinder i.d., 4.7 cm; (vii) after the 3 h irradn. the reaction soln. should be left stirring overnight to check that no dye photoreductive bleaching has occurred. Application of most of these suggestions should improve considerably the std.'s reported current poor percentage errors for repeatability within a lab (9.2%) and reproducibility between labs (30.6%).
- 17Kisch, H. Angew. Chem., Int. Ed. 2013, 52, 812– 847 DOI: 10.1002/anie.201201200
- 18Buriak, J. M.; Kamat, P. V.; Schanze, K. S. ACS Appl. Mater. Interfaces 2014, 6, 11815– 11816 DOI: 10.1021/am504389z
- 19Buriak, J. M. Chem. Mater. 2014, 26, 2211– 2213 DOI: 10.1021/cm5010449
- 20Kisch, H.; Bahnemann, D. J. Phys. Chem. Lett. 2015, 6, 1907– 1910 DOI: 10.1021/acs.jpclett.5b00521[ACS Full Text], [CAS], Google Scholar20https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXnvFCks7k%253D&md5=855fb32d3777fd93518080635531fdcbBest Practice in Photocatalysis: Comparing Rates or Apparent Quantum Yields?Kisch, Horst; Bahnemann, DetlefJournal of Physical Chemistry Letters (2015), 6 (10), 1907-1910CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)There is no expanded citation for this reference.
- 21Coridan, R. H.; Nielander, A. C.; Francis, S. A.; McDowell, M. T.; Dix, V.; Chatman, S. M.; Lewis, N. S. Energy Environ. Sci. 2015, 8, 2886– 2901 DOI: 10.1039/C5EE00777A
- 22Buriak, J. M.; Jones, C. W.; Kamat, P. V.; Schanze, K. S.; Schatz, G. C.; Scholes, G. D.; Weiss, P. S. Chem. Mater. 2016, 28, 3525– 3526 DOI: 10.1021/acs.chemmater.6b01854
- 23Qureshi, M.; Takanabe, K. Chem. Mater. 2017, 29, 158– 167 DOI: 10.1021/acs.chemmater.6b02907
- 24Takanabe, K.; Domen, K. ChemCatChem 2012, 4, 1485– 1497 DOI: 10.1002/cctc.201200324
- 25Takanabe, K. Top. Curr. Chem. 2015, 371, 73– 103 DOI: 10.1007/128_2015_646
- 26Nozik, A. J. Annu. Rev. Phys. Chem. 1978, 29, 189– 222 DOI: 10.1146/annurev.pc.29.100178.001201
- 27Nosaka, Y.; Ishizuka, Y.; Miyama, H. Ber. Bunsenges. Phys. Chem. 1986, 90, 1199– 1204 DOI: 10.1002/bbpc.19860901216
- 28Memming, R. Top. Curr. Chem. 1988, 143, 79– 112 DOI: 10.1007/BFb0018072
- 29Hagfeldt, A.; Grätzel, M. Chem. Rev. 1995, 95, 49– 68 DOI: 10.1021/cr00033a003
- 30Photocatalysis Science and Technology; Kaneko, M.; Okura, I., Eds.; Kodansha-Springer: Tokyo-New York, 2002, : pp 1– 360.Google ScholarThere is no corresponding record for this reference.
- 31Domen, K. In Photocatalysis—Heterogeneous. Encyclopedia of Catalysis; Horvath, I. T., Ed., Wiley: Weinheim, 2002.Google ScholarThere is no corresponding record for this reference.
- 32Maeda, K.; Domen, K. J. Phys. Chem. C 2007, 111, 7851– 7861 DOI: 10.1021/jp070911w
- 33Kamat, P. V. J. Phys. Chem. C 2007, 111, 2834– 2860 DOI: 10.1021/jp066952u
- 34Osterloh, F. E. Chem. Mater. 2008, 20, 35– 54 DOI: 10.1021/cm7024203
- 35Kudo, A.; Miseki, Y. Chem. Soc. Rev. 2009, 38, 253– 278 DOI: 10.1039/B800489G[Crossref], [PubMed], [CAS], Google Scholar35https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXhsFWjtL3P&md5=21d808dac82a11a649988f31a9231941Heterogeneous photocatalyst materials for water splittingKudo, Akihiko; Miseki, YugoChemical Society Reviews (2009), 38 (1), 253-278CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)This crit. review shows the basis of photocatalytic water splitting and exptl. points, and surveys heterogeneous photocatalyst materials for water splitting into H2 and O2, and H2 or O2 evolution from an aq. soln. contg. a sacrificial reagent. Many oxides consisting of metal cations with d0 and d10 configurations, metal (oxy)sulfide and metal (oxy)nitride photocatalysts have been reported, esp. during the latest decade. The fruitful photocatalyst library gives important information on factors affecting photocatalytic performances and design of new materials. Photocatalytic water splitting and H2 evolution using abundant compds. as electron donors are expected to contribute to construction of a clean and simple system for solar hydrogen prodn., and a soln. of global energy and environmental issues in the future (361 refs.).
- 36Inoue, Y. Energy Environ. Sci. 2009, 2, 364– 386 DOI: 10.1039/b816677n
- 37Walter, M. G.; Warren, E. L.; McKone, J. R.; Boettcher, S. W.; Mi, Q.; Santori, E. A.; Lewis, N. S. Chem. Rev. 2010, 110, 6446– 6473 DOI: 10.1021/cr1002326[ACS Full Text], [CAS], Google Scholar37https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXhtl2lsbvF&md5=e805b03c6896be7e34d8f64bfe299a87Solar Water Splitting CellsWalter, Michael G.; Warren, Emily L.; McKone, James R.; Boettcher, Shannon W.; Mi, Qixi; Santori, Elizabeth A.; Lewis, Nathan S.Chemical Reviews (Washington, DC, United States) (2010), 110 (11), 6446-6473CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)A review on the efforts to develop an efficient semiconductor-based photoelectrochem. water splitting device in which the only inputs are sunlight and water. The fundamental principles of photoinduced electron-transfer mechanisms at a semiconductor/liq. junction, and optimization of such processes, are summarized. A wide range of both p- and n-type semiconductor photoelectrode materials that have been studied for photoelectrochem. water splitting cells are then described. In addn., heterogeneous electrocatalysts used to facilitate the oxidn. and redn. reactions in electrochem. and in photoelectrochem. water splitting systems are reviewed. Finally, efforts to combine photoanode, photocathode, and photovoltaic-assisted coupled configurations in both single and dual band gap photoelectrolysis cells are examd. in terms of their solar-to-hydrogen efficiency, stability, and expected viability. Strategies to optimize solar-to-chem. energy-conversion efficiencies by optimization of light harvesting structured semiconductors, photoinduced electron transfer and transport, and surface catalysis are also described.
- 38Maeda, K.; Domen, K. J. Phys. Chem. Lett. 2010, 1, 2655– 2661 DOI: 10.1021/jz1007966[ACS Full Text], [CAS], Google Scholar38https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXhtVOmt7vE&md5=44835af453de055197cbf0715ddb73f7Photocatalytic Water Splitting: Recent Progress and Future ChallengesMaeda, Kazuhiko; Domen, KazunariJournal of Physical Chemistry Letters (2010), 1 (18), 2655-2661CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)A review. H2O splitting to form H and O using solar energy in the presence of semiconductor photocatalysts has long been studied as a potential means of clean, large-scale fuel prodn. In general, overall H2O splitting can be achieved when a photocatalyst is modified with a suitable cocatalyst. It is therefore important to develop both photocatalysts and cocatalysts. In the past 5 years, there was significant progress in H2O splitting photocatalysis, esp. in the development of cocatalysts and related phys. and materials chem. This work describes the state of the art and future challenges in photocatalytic H2O splitting, with a focus on the recent progress of own research.
- 39Hisatomi, T.; Minegishi, T.; Domen, K. Bull. Chem. Soc. Jpn. 2012, 85, 647– 655 DOI: 10.1246/bcsj.20120058
- 40Tong, H.; Ouyang, S.; Bi, Y.; Umezawa, N.; Oshikiri, M.; Ye, J. Adv. Mater. 2012, 24, 229– 251 DOI: 10.1002/adma.201102752
- 41Tachibana, Y.; Vayssieres, L.; Durrant, J. R. Nat. Photonics 2012, 6, 511– 518 DOI: 10.1038/nphoton.2012.175[Crossref], [CAS], Google Scholar41https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XhtFWjtLfN&md5=b98a6de15072b768fe7403a6e3f91012Artificial photosynthesis for solar water-splittingTachibana, Yasuhiro; Vayssieres, Lionel; Durrant, James R.Nature Photonics (2012), 6 (8), 511-518CODEN: NPAHBY; ISSN:1749-4885. (Nature Publishing Group)A review. Hydrogen generated from solar-driven water-splitting has the potential to be a clean, sustainable and abundant energy source. Inspired by natural photosynthesis, artificial solar water-splitting devices are now being designed and tested. Recent developments based on mol. and/or nanostructure designs have led to advances in our understanding of light-induced charge sepn. and subsequent catalytic water oxidn. and redn. reactions. Here we review some of the recent progress towards developing artificial photosynthetic devices, together with their analogies to biol. photosynthesis, including technologies that focus on the development of visible-light active hetero-nanostructures and require an understanding of the underlying interfacial carrier dynamics. Finally, we propose a vision for a future sustainable hydrogen fuel community based on artificial photosynthesis.
- 42Osterloh, F. E. Chem. Soc. Rev. 2013, 42, 2294– 2320 DOI: 10.1039/C2CS35266D
- 43Hisatomi, T.; Kubota, J.; Domen, K. Chem. Soc. Rev. 2014, 43, 7520– 7535 DOI: 10.1039/C3CS60378D
- 44Hisatomi, T.; Takanabe, K.; Domen, K. Catal. Lett. 2015, 145, 95– 108 DOI: 10.1007/s10562-014-1397-z
- 45Sivula, K.; van de Krol, R. Nat. Rev. Mater. 2016, 1, 15010 DOI: 10.1038/natrevmats.2015.10[Crossref], [CAS], Google Scholar45https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtVertrw%253D&md5=b12daf57f62282682a10cb4866778d93Semiconducting materials for photoelectrochemical energy conversionSivula, Kevin; van de Krol, RoelNature Reviews Materials (2016), 1 (2), 15010CODEN: NRMADL; ISSN:2058-8437. (Nature Publishing Group)To achieve a sustainable society with an energy mix primarily based on solar energy, we need methods of storing energy from sunlight as chem. fuels. Photoelectrochem. (PEC) devices offer the promise of solar fuel prodn. through artificial photosynthesis. Although the idea of a carbon-neutral energy economy powered by such 'artificial leaves' is intriguing, viable PEC energy conversion on a global scale requires the development of devices that are highly efficient, stable and simple in design. In this Review, recently developed semiconductor materials for the direct conversion of light into fuels are scrutinized with respect to their at. constitution, electronic structure and potential for practical performance as photoelectrodes in PEC cells. The processes of light absorption, charge sepn. and transport, and suitable energetics for energy conversion in PEC devices are emphasized. Both the advantageous and unfavorable aspects of multinary oxides, oxynitrides, chalcogenides, classic semiconductors and carbon-based semiconductors are critically considered on the basis of their exptl. demonstrated performance and predicted properties.
- 46Sato, N. Electrochemistry at Metal and Semiconductor Electrodes; Sato, N., Ed.; Elsevier, Amsterdam, 1998, : pp 1– 396.Google ScholarThere is no corresponding record for this reference.
- 47Modern Molecular Photochemistry of Organic Molecules; Turro, N. J.; Ramamurthy, V.; Scaiano, J. C., Eds.; University Science Books: Sausalito, CA, 2010; pp 1– 38.Google ScholarThere is no corresponding record for this reference.
- 48Polman, A.; Atwater, H. A. Nat. Mater. 2012, 11, 174– 177 DOI: 10.1038/nmat3263
- 49Osterloh, F. E. J. Phys. Chem. Lett. 2014, 5, 3354– 3359 DOI: 10.1021/jz501740n[ACS Full Text], [CAS], Google Scholar49https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhsFWjs7rM&md5=bf3df327c8119a0ec3bbe92fb081d0ceMaximum Theoretical Efficiency Limit of Photovoltaic Devices: Effect of Band Structure on Excited State EntropyOsterloh, Frank E.Journal of Physical Chemistry Letters (2014), 5 (19), 3354-3359CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)The Shockley-Queisser anal. provides a theor. limit for the max. energy conversion efficiency of single junction photovoltaic cells. But besides the semiconductor bandgap no other semiconductor properties are considered in the anal. Here, we show that the max. conversion efficiency is limited further by the excited state entropy of the semiconductors. The entropy loss can be estd. with the modified Sackur-Tetrode equation as a function of the curvature of the bands, the degeneracy of states near the band edges, the illumination intensity, the temp., and the band gap. The application of the second law of thermodn. to semiconductors provides a simple explanation for the obsd. high performance of Group IV, III-V, and II-VI materials with strong covalent bonding and for the lower efficiency of transition metal oxides contg. weakly interacting metal d orbitals. The model also predicts efficient energy conversion with quantum confined and mol. structures in the presence of a light harvesting mechanism.
- 50Omelchenko, S. T.; Tolstova, Y.; Atwater, H. A.; Lewis, N. S. ACS Energy Lett. 2017, 2, 431– 437 DOI: 10.1021/acsenergylett.6b00704[ACS Full Text], [CAS], Google Scholar50https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXht1eiurk%253D&md5=7915aa5154404136e5a187df4d26979bExcitonic Effects in Emerging Photovoltaic Materials: A Case Study in Cu2OOmelchenko, Stefan T.; Tolstova, Yulia; Atwater, Harry A.; Lewis, Nathan S.ACS Energy Letters (2017), 2 (2), 431-437CODEN: AELCCP; ISSN:2380-8195. (American Chemical Society)Excitonic effects account for a fundamental photoconversion and charge transport mechanism in Cu2O; hence, the universally adopted "free carrier" model substantially underestimates the photovoltaic efficiency for such devices. The quasi-equil. branching ratio between excitons and free carriers in Cu2O indicates that up to 28% of photogenerated carriers during photovoltaic operation are excitons. These large exciton densities were directly obsd. in photoluminescence and spectral response measurements. The results of a device physics simulation using a model that includes excitonic effects agree well with exptl. measured current-voltage characteristics of Cu2O-based photovoltaics. In the case of Cu2O, the free carrier model underestimates the efficiency of a Cu2O solar cell by as much as 1.9 abs. percent at room temp.
- 51National Renewable Energy Laboratory (NREL). Website: http://rredc.nrel.gov/solar/spectra/am1.5.Google ScholarThere is no corresponding record for this reference.
- 52Takanabe, K.; Domen, K. Green 2011, 1, 313– 322 DOI: 10.1515/GREEN.2011.030[Crossref], [CAS], Google Scholar52https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhtlOktbbO&md5=fbb3919c5dc8e60502156ee4d8e680b8Toward visible light response: overall water splitting using heterogeneous photocatalystsTakanabe, Kazuhiro; Domen, KazunariGreen (2011), 1 (5-6), 313-322CODEN: GREECH; ISSN:1869-876X. (Walter de Gruyter GmbH & Co. KG)A review. Extensive energy conversion of solar energy can only be achieved by large-scale collection of solar flux. The technol. that satisfies this requirement must be as simple as possible to reduce capital cost. Overall water splitting by powder-form photocatalysts directly produces a mixt. of H2 and O2 (chem. energy) in a single reactor, which does not require any complicated parabolic mirrors and electronic devices. Because of its simplicity and low capital cost, it has tremendous potential to become the major technol. of solar energy conversion. Development of highly efficient photocatalysts is desired. This review addresses why visible light responsive photocatalysts are essential to be developed. The state of the art for the photocatalysts for overall water splitting is briefly described. Moreover, various fundamental aspects for developing efficient photocatalysts, such as particle size of photocatalysts, cocatalysts, and reaction kinetics are discussed.
- 53Chen, Z.; Dinh, H. N.; Miller, E. Photoelectrochemical Water Splitting Standards, Experimental Methods, and Protocols; Springer: New York. 2013.
- 54Wemple, S. H.; Seman, J. A. Appl. Opt. 1973, 12, 2947– 2949 DOI: 10.1364/AO.12.002947[Crossref], [PubMed], [CAS], Google Scholar54https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC3c%252FnvFKgtQ%253D%253D&md5=2c3055a403dc01a449016f46e580961eOptical transmission through multilayered structuresWemple S H; Seman J AApplied optics (1973), 12 (12), 2947-9 ISSN:0003-6935.A simple procedure is presented for computing optical transmission through planar layered structures when interference effects can be neglected, but all multiple internal reflections are taken into account. Closed form solutions are given for a single absorbing layer on a nonabsorbing substrate and for two identical absorbing layers on either side of a nonabsorbing substrate.
- 55Di Giulio, M.; Micocci, G.; Rella, R.; Siciliano, P.; Tepore, A. Phys. Stat. Sol. a 1993, 136, K101– K104 DOI: 10.1002/pssa.2211360236
- 56Lodenquai, J. F. Sol. Energy 1994, 53, 209– 210 DOI: 10.1016/0038-092X(94)90483-9
- 57Absorption and Scattering of Light by Small Particles; Bohren, C. F.; Huffman, D. R., Eds.; Wiley-VCH, Weinheim, 2004, : pp 1– 476.Google ScholarThere is no corresponding record for this reference.
- 58Interpreting Diffuse Reflectance and Transmittance; Dahm, D. J.; Dahm, K. D., Eds.; NIR Publications: West Sussex, 2007, : pp 1– 286.Google ScholarThere is no corresponding record for this reference.
- 59Light Scattering by Particles in Water, Jonasz, M.; Fournier, G. R., Eds.; Academic Press: Oxford, 2007, : pp 145– 558.
- 60Bae, D.; Pedersen, T.; Seger, B.; Malizia, M.; Kuznetsov, A.; Hansen, O.; Chorkendorff, I.; Vesborg, P. C. K. Energy Environ. Sci. 2015, 8, 650– 660 DOI: 10.1039/C4EE03723E
- 61Le Bahers, T.; Rérat, M.; Sautet, P. J. Phys. Chem. C 2014, 118, 5997– 6008 DOI: 10.1021/jp409724c
- 62Green, M. A. Sol. Energy Mater. Sol. Cells 2008, 92, 1305– 1310 DOI: 10.1016/j.solmat.2008.06.009[Crossref], [CAS], Google Scholar62https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXhtVGksbbI&md5=767829b037109986978cb974d333b6ecSelf-consistent optical parameters of intrinsic silicon at 300 K including temperature coefficientsGreen, Martin A.Solar Energy Materials & Solar Cells (2008), 92 (11), 1305-1310CODEN: SEMCEQ; ISSN:0927-0248. (Elsevier B.V.)An updated tabulation is presented of the optical properties of intrinsic Si, of particular interest in solar cell calcns. Improved values of absorption coeff., refractive index and extinction coeff. at 300 K are tabulated over the 0.25-1.45 μm wavelength range at 0.01 μm intervals. The self-consistent tabulation was derived from Kramers-Kronig anal. of updated reflectance data deduced from the literature. The inclusion of normalized temp. coeffs. allows extrapolation over a wide temp. range, with accuracy similar to that of available exptl. data demonstrated over the -24° to 200° range.
- 63Franck, J.; Dymond, E. G. Trans. Faraday Soc. 1926, 21, 536– 542 DOI: 10.1039/tf9262100536
- 64Condon, E. Phys. Rev. 1926, 28, 1182– 1201 DOI: 10.1103/PhysRev.28.1182[Crossref], [CAS], Google Scholar64https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaB2sXovV2i&md5=e84d9659e9f76759fea0962e1208351eTheory of intensity distribution in band systemsCondon, EdwardPhysical Review (1926), 28 (), 1182-1201CODEN: PHRVAO; ISSN:0031-899X.There is no expanded citation for this reference.
- 65Džimbeg-Malčić, V.; Barbarić-Mikočević, Ž.; Itrić, K. Technical Gazette 2011, 18, 117Google ScholarThere is no corresponding record for this reference.
- 66Kurik, M. V. Phys. Stat. Sol. a 1971, 8, 9– 45 DOI: 10.1002/pssa.2210080102[Crossref], [CAS], Google Scholar66https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaE38XltF2qsw%253D%253D&md5=196c4cae2ef8ac8dc23e0bd87046e7b5Urbach ruleKurik, M. V.Physica Status Solidi A: Applied Research (1971), 8 (1), 9-45CODEN: PSSABA; ISSN:0031-8965.A review with 181 refs.
- 67Introduction to Solid State Physics, 8th ed.; Kittel, C., Ed.; Wiley: Weinheim, 2005, : pp 1– 704.Google ScholarThere is no corresponding record for this reference.
- 68Bastard, G.; Mendez, E. E.; Chang, L. L.; Esaki, L. Phys. Rev. B: Condens. Matter Mater. Phys. 1982, 26, 1974– 1979 DOI: 10.1103/PhysRevB.26.1974
- 69Semiconductors: Data Handbook, 3rd ed.; Madelung, O., Ed.; Springer: New York, 2004.
- 70Melissen, S.; Le Bahers, T.; Steinmann, S. N.; Sautet, P. J. Phys. Chem. C 2015, 119, 25188– 25196 DOI: 10.1021/acs.jpcc.5b07059
- 71Shockley, W.; Read, W. T., Jr. Phys. Rev. 1952, 87, 835– 842 DOI: 10.1103/PhysRev.87.835
- 72Hall, R. N. Phys. Rev. 1952, 87, 387 DOI: 10.1103/PhysRev.87.387
- 73Auger, P. Comptes Rendus de l'Académie des Sciences 1952, 177, 169Google ScholarThere is no corresponding record for this reference.
- 74Leng, W. H.; Barnes, P. R. F.; Juozapavicius, M.; O’Regan, B. C.; Durrant, J. R. J. Phys. Chem. Lett. 2010, 1, 967– 972 DOI: 10.1021/jz100051q[ACS Full Text], [CAS], Google Scholar74https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXisFGntb0%253D&md5=9a3f3d6cdc9a540b35da60329cd4a3b1Electron Diffusion Length in Mesoporous Nanocrystalline TiO2 Photoelectrodes during Water OxidationLeng, W. H.; Barnes, Piers R. F.; Juozapavicius, Mindaugas; O'Regan, Brian C.; Durrant, James R.Journal of Physical Chemistry Letters (2010), 1 (6), 967-972CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)A long electron diffusion length (L) relative to film thickness is required for efficient collection of charge in photoelectrodes. L was measured in a nanocryst., mesoporous TiO2 electrode during photochem. water splitting by two independent methods: (a) analyzing the ratio of incident photon conversion efficiency measured under back and front side illumination, and (b) analyzing transient photovoltage increase and decay measurements. These gave values of L that agreed (L = 8.5-12.5 μm between -0.15 and 0.1 V vs. Ag/AgCl 3M KCl at pH 2). The transient measurements were consistent with trap limited transport and recombination of electrons as previously obsd. in dye-sensitized solar cells. L of ∼10 μm is sufficient to collect sepd. electrons with minor electrolyte recombination losses in thin electrodes. However, charge collection may limit performance in doped mesoporous electrodes with weak visible light absorption where thicker films are required.
- 75Law, M. E.; Solley, E.; Liang, M.; Burk, D. E. IEEE Electron Device Lett. 1991, 12, 401– 403 DOI: 10.1109/55.119145
- 76Ito, H.; Furuta, T.; Ishibashi, T. Appl. Phys. Lett. 1991, 58, 2936– 2938 DOI: 10.1063/1.104727
- 77Cohen, R.; Lyahovitskaya, V.; Poles, E.; Liu, A.; Rosenwaks, Y. Appl. Phys. Lett. 1998, 73, 1400– 1402 DOI: 10.1063/1.122169
- 78Kuciauskas, D.; Kanevce, A.; Dippo, P.; Seyedmohammadi, S.; Malik, R. IEEE J. Photovoltaics 2015, 5, 366– 371 DOI: 10.1109/JPHOTOV.2014.2359738
- 79Rosenwaks, Y.; Shapira, Y.; Huppert, D. Phys. Rev. B: Condens. Matter Mater. Phys. 1992, 45, 9108– 9119 DOI: 10.1103/PhysRevB.45.9108
- 80Casey, H. C., Jr.; Miller, B. I.; Pinkas, E. J. Appl. Phys. 1973, 44, 1281– 1287 DOI: 10.1063/1.1662340[Crossref], [CAS], Google Scholar80https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaE3sXhtFKrsb8%253D&md5=91c7489236636ff1b9e1d0c98e70f1b7Variation of minority-carrier diffusion length with carrier concentration in gallium arsenide liquid-phase epitaxial layersCasey, H. C., Jr.; Miller, B. I.; Pinkas, E.Journal of Applied Physics (1973), 44 (3), 1281-7CODEN: JAPIAU; ISSN:0021-8979.Minority-carrier diffusion lengths in GaAs at 298°K were detd. in Ge-doped p-type layers and Sn-doped n-type layers by short-circuit photocurrent measurements. The layers were grown by liq.-phase epitaxy and utilized a 1-to 2-μ top layer fo A10.5Ga0.5As to eliminate surface recombination. Electron diffusion lengths Ln of 7-8 μ were obtained at concns. <1 × 1018 holes/cm3 with a decrease to 0.8μ at 1 × 1019 holes/ cm3. Hole diffusion lengths Lp of 2-4 μ were obtained at concns. <1 × 1018 electrons/cm3 with a decrease to 0.3 μ at 6 × 1018 electrons/cm3. The relatively const. diffusion length in p- and n-type layers below concns. of 1 × 1018 cm-3 is detd. by nonradiative recombination. At hole concns. >1 × 1018 cm-3, the radiative recombination contributes to the decrease in Lp. For the n-type layers, the rapid decrease in Lp above concns. of 1 × 1018 cm-3 results from an increase in nonradiative recombination at high donor concns.
- 81Lewis, N. S. Inorg. Chem. 2005, 44, 6900– 6911 DOI: 10.1021/ic051118p
- 82Zhuravlev, L. T. Colloids Surf., A 2000, 173, 1– 38 DOI: 10.1016/S0927-7757(00)00556-2[Crossref], [CAS], Google Scholar82https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXmsFKktLk%253D&md5=1168cec5b4a06a146674273c1781d0dbThe surface chemistry of amorphous silica. Zhuravlev modelZhuravlev, L. T.Colloids and Surfaces, A: Physicochemical and Engineering Aspects (2000), 173 (1-3), 1-38CODEN: CPEAEH; ISSN:0927-7757. (Elsevier Science B.V.)A review, with 347 refs. on the author's own results on the properties of amorphous SiO2 surface. In any description of the surface SiO2 the hydroxylation of the surface is of crit. importance. An anal. was made of the processes of dehydration (the removal of phys. adsorbed water), dehydroxylation (the removal of silanol groups from the SiO2 surface), and rehydroxylation (the restoration of the hydroxyl covering). For each of these processes a probable mechanism is suggested. The results of exptl. and theor. studies permitted to construct the original model (Zhuravlev model-1 and model-2) for describing the surface chem. of amorphous SiO2. The main advantage of this physico-chem. model lies in the possibility to det. the concn. and the distribution of different types of silanol and siloxane groups and to characterize the energetic heterogeneity of the SiO2 surface as a function of the pretreatment temp. of SiO2 samples. The model makes it possible to det. the kind of the chemisorption of water (rapid, weakly activated or slow, strongly activated) under the restoration of the hydroxyl covering and also to assess of OH groups inside the SiO2 skeleton. The magnitude of the silanol no., i.e., the no. of OH groups per unit surface area, αOH, when the surface is hydroxylated to the max. degree, is considered to be a physico-chem. const. This const. has a numerical value: αOH,AVER = 4.6 (least-squares method) and αOH,AVER = 4.9 OH nm-2 (arithmetical mean) and is known in literature as the Kiselev-Zhuravlev const. Adsorption and other surface properties per unit surface area of SiO2 are identical (except for very fine pores). On the basis of data published in the literature, this model was found to be useful in solving various applied and theor. problems in the field of adsorption, catalysis, chromatog., chem. modification, etc. The Brunauer-Emmett-Teller (BET) method is the correct method and gives the opportunity to measure the real phys. magnitude of the sp. surface area, SKr (by low temp. adsorption of Kr), for SiO2s and other oxide dispersed solids.
- 83Yoneyama, H. Crit. Rev. Solid State Mater. Sci. 1993, 18, 69– 111 DOI: 10.1080/10408439308243416[Crossref], [CAS], Google Scholar83https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3sXksF2ntLs%253D&md5=6aa23e192921c2b07b976452a799d2bcElectrochemical aspects of light-induced heterogeneous reactions on semiconductorsYoneyama, HiroshiCritical Reviews in Solid State and Materials Sciences (1993), 18 (1), 69-111CODEN: CCRSDA; ISSN:1040-8436.Working mechanisms as photocatalyst of semiconductor particles suspended in soln. are reviewed with emphasis on photoelectrochem. aspects. Several techniques useful for the detn. of of electronic energy levels of the photocatalysts and for enhancing apparent photocatalytic activities are described, and their utilities are shown in the photodecompn. of water on various kinds of semiconductor particles. Studies on the detoxification of inorg. and org. wastes are collected as a promising application field of suspended semiconductor photocatalysts. Finally, significance of the use of quantized semiconductor particles as photocatalysts is discussed. 432 Refs.
- 84Fukasawa, Y.; Takanabe, K.; Shimojima, A.; Antonietti, M.; Domen, K.; Okubo, T. Chem. - Asian J. 2011, 6, 103– 109 DOI: 10.1002/asia.201000523[Crossref], [PubMed], [CAS], Google Scholar84https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXhs1WnsbvK&md5=5311851878d116d323cf76bb9809c697Synthesis of Ordered Porous Graphitic-C3N4 and Regularly Arranged Ta3N5 Nanoparticles by Using Self-Assembled Silica Nanospheres as a Primary TemplateFukasawa, Yuki; Takanabe, Kazuhiro; Shimojima, Atsushi; Antonietti, Markus; Domen, Kazunari; Okubo, TatsuyaChemistry - An Asian Journal (2011), 6 (1), 103-109CODEN: CAAJBI; ISSN:1861-4728. (Wiley-VCH Verlag GmbH & Co. KGaA)Uniform-sized silica nanospheres (SNSs) assembled into close-packed structures were used as a primary template for ordered porous graphitic carbon nitride (g-C3N4), which was subsequently used as a hard template to generate regularly arranged Ta3N5 nanoparticles of well-controlled size. Inverse opal g-C3N4 structures with the uniform pore size of 20-80 nm were synthesized by polymn. of cyanamide and subsequent dissoln. of the SNSs with an aq. HF soln. Back-filling of the C3N4 pores with tantalum precursors, followed by nitridation in an NH3 flow gave regularly arranged, cryst. Ta3N5 nanoparticles that are connected with each other. The surface areas of the Ta3N5 samples were as high as 60 m2 g-1, and their particle size was tunable from 20 to 80 nm, which reflects the pore size of g-C3N4. Polycryst. hollow nanoparticles of Ta3N5 were also obtained by infiltration of a reduced amt. of the tantalum source into the g-C3N4 template. An improved photocatalytic activity for H2 evolution on the assembly of the Ta3N5 nanoparticles under visible-light irradn. was attained as compared with that on a conventional Ta3N5 bulk material with low surface area.
- 85Gerischer, H. J. Phys. Chem. 1984, 88, 6096– 6097 DOI: 10.1021/j150669a007
- 86van der Pauw, L. J. Philips Res. Rep. 1958, 13, 1Google ScholarThere is no corresponding record for this reference.
- 87Heaney, M. B. The Measurement, Instrumentation and Sensors Handbook; CRC, Boca Raton, 2000.Google ScholarThere is no corresponding record for this reference.
- 88Tung, R. T. Appl. Phys. Rev. 2014, 1, 011304 DOI: 10.1063/1.4858400[Crossref], [CAS], Google Scholar88https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXlslSktbc%253D&md5=abc66bf33acc918d3481972fba7b1057The physics and chemistry of the Schottky barrier heightTung, Raymond T.Applied Physics Reviews (2014), 1 (1), 011304/1-011304/54CODEN: APRPG5; ISSN:1931-9401. (American Institute of Physics)A review. The formation of the Schottky barrier height (SBH) is a complex problem because of the dependence of the SBH on the at. structure of the metal-semiconductor (MS) interface. Existing models of the SBH are too simple to realistically treat the chem. exhibited at MS interfaces. This article points out, through examn. of available exptl. and theor. results, that a comprehensive, quantum-mechanics-based picture of SBH formation can already be constructed, although no simple equations can emerge, which are applicable for all MS interfaces. Important concepts and principles in physics and chem. that govern the formation of the SBH are described in detail, from which the exptl. and theor. results for individual MS interfaces can be understood. Strategies used and results obtained from recent investigations to systematically modify the SBH are also examd. from the perspective of the phys. and chem. principles of the MS interface. (c) 2014 American Institute of Physics.
- 89Physics of Semiconductor Devices, 3rd ed., Sze, S. M.; Ng, K. K., Eds.; Wiley: New York, 2006, : pp 134– 196.
- 90Kurtin, S.; McGill, T. C.; Mead, C. A. Phys. Rev. Lett. 1969, 22, 1433– 1436 DOI: 10.1103/PhysRevLett.22.1433
- 91Esposito, D. V.; Levin, I.; Moffat, T. P.; Talin, A. A. Nat. Mater. 2013, 12, 562– 568 DOI: 10.1038/nmat3626
- 92Ham, Y.; Minegishi, T.; Hisatomi, T.; Domen, K. Chem. Commun. 2016, 52, 5011– 5014 DOI: 10.1039/C6CC00497K[Crossref], [PubMed], [CAS], Google Scholar92https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XktVagsL0%253D&md5=71ba5de24187f84da96327a6c2fb04faA SrTiO3 photoanode prepared by the particle transfer method for oxygen evolution from water with high quantum efficienciesHam, Y.; Minegishi, T.; Hisatomi, T.; Domen, K.Chemical Communications (Cambridge, United Kingdom) (2016), 52 (28), 5011-5014CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)A photoanode prepd. from flux-synthesized Al-doped SrTiO3 by the particle transfer method with a Ta contact layer exhibited a high IPCE of 69% at 320 nm. The photocatalytic activity of SrTiO3 particles was very sensitive to the synthesis method used to make the SrTiO3 particles, while its photoelectrochem. performance was not.
- 93Minegishi, T.; Nishimura, N.; Kubota, J.; Domen, K. Chem. Sci. 2013, 4, 1120– 1124 DOI: 10.1039/c2sc21845c[Crossref], [CAS], Google Scholar93https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhvFGqu7s%253D&md5=8d2d4c404c64c5a124a013e52a15ed5cPhotoelectrochemical properties of LaTiO2N electrodes prepared by particle transfer for sunlight-driven water splittingMinegishi, Tsutomu; Nishimura, Naoyuki; Kubota, Jun; Domen, KazunariChemical Science (2013), 4 (3), 1120-1124CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)Photoelectrochem. (PEC) water splitting is a promising technol. for the prodn. of renewable solar hydrogen from water. A method of fabricating photoelectrodes from semiconductor particles for efficient water splitting was investigated using LaTiO2N as a test case. When a Ti conductor electrode with the back side covered with LaTiO2N particles was constructed by radio-frequency magnetron sputtering, the LaTiO2N photoelectrode generated a remarkable photoanodic current and evolved O2. The insertion of a Ta or Nb interlayer between the Ti conductor and the LaTiO2N particles enhanced the photocurrent. This method of fabricating photoelectrodes from semiconductor particles enables the use of simple powder semiconductors in solar energy conversion systems.
- 94Paracchino, A.; Laporte, V.; Sivula, K.; Grätzel, M.; Thimsen, E. Nat. Mater. 2011, 10, 456– 461 DOI: 10.1038/nmat3017
- 95Gerischer, H. Electrochim. Acta 1990, 35, 1677– 1699 DOI: 10.1016/0013-4686(90)87067-C
- 96Zhang, Z.; Yates, J. T., Jr. Chem. Rev. 2012, 112, 5520– 5551 DOI: 10.1021/cr3000626[ACS Full Text], [CAS], Google Scholar96https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XhtVWhtLrP&md5=d384840181ca78fc90506d35b75708cbBand bending in semiconductors: Chemical and physical consequences at surfaces and interfacesZhang, Zhen; Yates, John T., Jr.Chemical Reviews (Washington, DC, United States) (2012), 112 (10), 5520-5551CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)A review. Topics include band bending by metal/semiconductor contact; field-effect surface-state; adsorption. Space charge region at infinite metal/semiconductor interface and finite metal/semiconductor interface. Applications of the band bending concepts in ion diffusion in metal oxides and chemicurrent measurements. Measurements of band bending at semiconductor surfaces by photoelectron spectroscopy; photoluminescence spectroscopy surface photovoltage, scanning probe microscopy; and related methods; STM and STS; local barrier height measurement; ballistic electron emission microscopy; O2 photostimulated and electron-stimulated desorption. Effects of band bending on photochem. (size effect, elec. field effect, surface structure, gas adsorption).
- 97Grätzel, M. Nature 2001, 414, 338– 344 DOI: 10.1038/35104607[Crossref], [PubMed], [CAS], Google Scholar97https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3MXovFGitr8%253D&md5=2b0390f22ab99b07caec95b79454a7ebPhotoelectrochemical cellsGratzel, MichaelNature (London, United Kingdom) (2001), 414 (6861), 338-344CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)A review discussing the historical background, and present status and development prospects of new generation of photoelectrochem. cells.
- 98Chamousis, R. L.; Osterloh, F. E. Energy Environ. Sci. 2014, 7, 736– 743 DOI: 10.1039/C3EE42993H
- 99Butler, M. A.; Ginley, D. S. J. Electrochem. Soc. 1978, 125, 228– 232 DOI: 10.1149/1.2131419[Crossref], [CAS], Google Scholar99https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaE1cXhtFant78%253D&md5=00169bc0cf9ce0b7524d3a196ede9c61Prediction of flatband potentials at semiconductor-electrolyte interfaces from atomic electronegativitiesButler, M. A.; Ginley, D. S.Journal of the Electrochemical Society (1978), 125 (2), 228-32CODEN: JESOAN; ISSN:0013-4651.The electron affinities of several metal oxide semiconductors that are used as anodes in photoelectrochem. cells are calcd. using the at. electronegs. of the constituent atoms. These electron affinities are quant. related to the measured flatband potentials by considering the effects of specific adsorption of potential-detg. ions (for metal oxides used in photoelectrolysis, these are usually OH- and H+). Methods are discussed for detg.pH at which net adsorbed surface charge and thus potential across the Helmholtz layer is zero (point of zero zeta potential). This pH value is shown to correlate with the electronegativity of the metal oxides. The application of these ideas to other semiconductor-electrolyte systems is discussed.
- 100Green, M. A.; Hishikawa, Y.; Warta, W.; Dunlop, E. W.; Levi, D. H.; Hohl-Ebinger, J.; Ho-Baillie, A. W. H. Prog. Photovoltaics 2017, 25, 668– 676 DOI: 10.1002/pip.2909
- 101Turner, J. A. J. Chem. Educ. 1983, 60, 327– 329 DOI: 10.1021/ed060p327
- 102Lewis, N. S. J. Electrochem. Soc. 1984, 131, 2496– 2503 DOI: 10.1149/1.2115347
- 103Rossi, R. C.; Tan, M. X.; Lewis, N. S. Appl. Phys. Lett. 2000, 77, 2698– 2700 DOI: 10.1063/1.1319534
- 104Rossi, R. C.; Lewis, N. S. J. Phys. Chem. B 2001, 105, 12303– 12318 DOI: 10.1021/jp011861c
- 105Bisquert, J.; Cendula, P.; Bertoluzzi, L.; Gimenez, S. J. Phys. Chem. Lett. 2014, 5, 205– 207 DOI: 10.1021/jz402703d[ACS Full Text], [CAS], Google Scholar105https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhvFKhtrrO&md5=4c91dcefb23c697dbc2b83804993b08fEnergy Diagram of Semiconductor/Electrolyte JunctionsBisquert, Juan; Cendula, Peter; Bertoluzzi, Luca; Gimenez, SixtoJournal of Physical Chemistry Letters (2014), 5 (1), 205-207CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)The energy diagram of an n-type semiconductor electrode in contact with electrolyte is studied. A set of math. relationships that allow us to relate the different expressions of voltage and energies such as the flatband potential and the energy (or potential) of semiconductor conduction band at the surface.
- 106Xiang, C.; Weber, A. Z.; Ardo, S.; Berger, A.; Chen, Y.; Coridan, R.; Fountaine, K. T.; Haussener, S.; Hu, S.; Liu, R.; Lewis, N. S.; Modestino, M. A.; Shaner, M. M.; Singh, M. R.; Stevens, J. C.; Sun, K.; Walczak, K. Angew. Chem., Int. Ed. 2016, 55, 12974– 12988 DOI: 10.1002/anie.201510463
- 107Garcia-Esparza, A. T.; Takanabe, K. J. Mater. Chem. A 2016, 4, 2894– 2908 DOI: 10.1039/C5TA06983A[Crossref], [CAS], Google Scholar107https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhs1Sit7rF&md5=467c98b431ca40da7848c64e4e81760aA simplified theoretical guideline for overall water splitting using photocatalyst particlesGarcia-Esparza, Angel T.; Takanabe, KazuhiroJournal of Materials Chemistry A: Materials for Energy and Sustainability (2016), 4 (8), 2894-2908CODEN: JMCAET; ISSN:2050-7496. (Royal Society of Chemistry)Particulate photocatalytic water splitting is the most disruptive and competitive soln. for the direct prodn. of solar fuels. Despite more than four decades of work in the field of photocatalysis using powd. semiconductors decorated with catalyst particles, there is no clear consensus on the factors limiting the solar-to-hydrogen efficiency (STH). To understand the intrinsic limitations of the system, we numerically simulated simplified two-dimensional photocatalytic models using classical semiconductor device equations. This work presents the sensitivity of quantum efficiency (QE) to the various semiconductor properties, such as absorption properties and carrier mobilities, and to the dispersion of catalyst particles, which create heterojunctions, the driving force for charge sepn. As a result, a pinch-off effect was prevalent underneath the hydrogen evolution site, suggesting an undesired energetic barrier for electron diffusion to the catalyst. The simulation using the values reported in the literature revealed that the QE was exclusively governed by recombination in the bulk of the photocatalyst particles, hindering the charge sepn. efficiency before reaching the catalysts on the surface. Using some of the reported parameters, our simulation shows that a typical defective n-type semiconductor particle (∼100 nm) ideally exhibits a QE of <5% in the visible light range per particle, which reaches only approx. 10% in a slurry after 4 consecutive absorbing units (1.4% STH, from simulated solar irradn.). Although the present model contains rigid limitations, we use these trends as an initial guideline to pursue photocatalysis by a design strategy, which may result in possible alternatives to achieve higher efficiencies.
- 108Cendula, P.; Tilley, S. D.; Gimenez, S.; Bisquert, J.; Schmid, M.; Grätzel, M.; Schumacher, J. O. J. Phys. Chem. C 2014, 118, 29599– 29607 DOI: 10.1021/jp509719d
- 109Mills, T. J.; Lin, F.; Boettcher, S. W. Phys. Rev. Lett. 2014, 112, 148304 DOI: 10.1103/PhysRevLett.112.148304
- 110Lin, F.; Boettcher, S. W. Nat. Mater. 2014, 13, 81– 86 DOI: 10.1038/nmat3811
- 111Lichterman, M. F.; Hu, S.; Richter, M. H.; Crumlin, E. J.; Axnanda, S.; Favaro, M.; Drisdell, W.; Hussain, Z.; Mayer, T.; Brunschwig, B. S.; Lewis, N. S.; Liu, Z.; Lewerenz, H. J. Energy Environ. Sci. 2015, 8, 2409– 2416 DOI: 10.1039/C5EE01014D
- 112Laskowski, F. A. L.; Nellist, M. R.; Venkatkarthick, R.; Boettcher, S. W. Energy Environ. Sci. 2017, 10, 570– 579 DOI: 10.1039/C6EE03505A
- 113Hu, S.; Shaner, M. R.; Beardslee, J. A.; Lichterman, M.; Brunschwig, B. S.; Lewis, N. S. Science 2014, 344, 1005– 1009 DOI: 10.1126/science.1251428[Crossref], [PubMed], [CAS], Google Scholar113https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXosFSmuro%253D&md5=9de5f3032f2f33d9db97a9759ed0307bAmorphous TiO2 coatings stabilize Si, GaAs, and GaP photoanodes for efficient water oxidationHu, Shu; Shaner, Matthew R.; Beardslee, Joseph A.; Lichterman, Michael; Brunschwig, Bruce S.; Lewis, Nathan S.Science (Washington, DC, United States) (2014), 344 (6187), 1005-1009CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)Although semiconductors such as silicon (Si), gallium arsenide (GaAs), and gallium phosphide (GaP) have band gaps that make them efficient photoanodes for solar fuel prodn., these materials are unstable in aq. media. TiO2 coatings (4 to 143 nm thick) grown by at. layer deposition prevent corrosion, have electronic defects that promote hole conduction, and are sufficiently transparent to reach the light-limited performance of protected semiconductors. In conjunction with a thin layer or islands of Ni oxide electrocatalysts, Si photoanodes exhibited continuous oxidn. of 1.0M aq. KOH to O2 for >100 h at photocurrent densities of >30 mA per square centimeter and ~100% faradaic efficiency. TiO2-coated GaAs and GaP photoelectrodes exhibited photovoltages of 0.81 and 0.59 V and light-limiting photocurrent densities of 14.3 and 3.4 mA per square centimeter, resp., for water oxidn.
- 114Verlage, E.; Hu, S.; Liu, R.; Jones, R. J. R.; Sun, K.; Xiang, C.; Lewis, N. S.; Atwater, H. A. Energy Environ. Sci. 2015, 8, 3166– 3172 DOI: 10.1039/C5EE01786F[Crossref], [CAS], Google Scholar114https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhtlKnsLfE&md5=e548bf4d84d606a21052c9eef1da43efA monolithically integrated, intrinsically safe, 10% efficient, solar-driven water-splitting system based on active, stable earth-abundant electrocatalysts in conjunction with tandem III-V light absorbers protected by amorphous TiO2 filmsVerlage, Erik; Hu, Shu; Liu, Rui; Jones, Ryan J. R.; Sun, Ke; Xiang, Chengxiang; Lewis, Nathan S.; Atwater, Harry A.Energy & Environmental Science (2015), 8 (11), 3166-3172CODEN: EESNBY; ISSN:1754-5706. (Royal Society of Chemistry)A monolithically integrated device consisting of a tandem-junction GaAs/InGaP photoanode coated by an amorphous TiO2 stabilization layer, in conjunction with Ni-based, earth-abundant active electrocatalysts for the hydrogen-evolution and oxygen-evolution reactions, was used to effect unassisted, solar-driven water splitting in 1.0 M KOH(aq). When connected to a Ni-Mo-coated counterelectrode in a two-electrode cell configuration, the TiO2-protected III-V tandem device exhibited a solar-to-hydrogen conversion efficiency, ηSTH, of 10.5% under 1 sun illumination, with stable performance for >40 h of continuous operation at an efficiency of ηSTH > 10%. The protected tandem device also formed the basis for a monolithically integrated, intrinsically safe solar-hydrogen prototype system (1 cm2) driven by a NiMo/GaAs/InGaP/TiO2/Ni structure. The intrinsically safe system exhibited a hydrogen prodn. rate of 0.81 μL s-1 and a solar-to-hydrogen conversion efficiency of 8.6% under 1 sun illumination in 1.0 M KOH(aq), with minimal product gas crossover while allowing for beneficial collection of sep. streams of H2(g) and O2(g).
- 115Zhou, X.; Liu, R.; Sun, K.; Chen, Y.; Verlage, E.; Francis, S. A.; Lewis, N. S.; Xiang, C. ACS Energy Lett. 2016, 1, 764– 770 DOI: 10.1021/acsenergylett.6b00317[ACS Full Text], [CAS], Google Scholar115https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhsV2hs77J&md5=ce1fce3fa43e3a3711ed47debe205586Solar-Driven Reduction of 1 atm of CO2 to Formate at 10% Energy-Conversion Efficiency by Use of a TiO2-Protected III-V Tandem Photoanode in Conjunction with a Bipolar Membrane and a Pd/C CathodeZhou, Xinghao; Liu, Rui; Sun, Ke; Chen, Yikai; Verlage, Erik; Francis, Sonja A.; Lewis, Nathan S.; Xiang, ChengxiangACS Energy Letters (2016), 1 (4), 764-770CODEN: AELCCP; ISSN:2380-8195. (American Chemical Society)A solar-driven CO2 redn. (CO2R) cell was constructed, consisting of a tandem GaAs/InGaP/TiO2/Ni photoanode in 1.0M KOH(aq) (pH = 13.7) to facilitate the oxygen-evolution reaction (OER), a Pd/C nanoparticle-coated Ti mesh cathode in 2.8M KHCO3(aq) (pH = 8.0) to perform the CO2R reaction, and a bipolar membrane to allow for steady-state operation of the catholyte and anolyte at different bulk pH values. At the operational c.d. of 8.5 mA cm-2, in 2.8M KHCO3(aq), the cathode exhibited <100 mV overpotential and >94% faradaic efficiency for the redn. of 1 atm of CO2(g) to formate. The anode exhibited a 320 ± 7 mV overpotential for the OER in 1.0M KOH(aq), and the bipolar membrane exhibited ∼480 mV voltage loss with minimal product crossovers and >90 and >95% selectivity for protons and hydroxide ions, resp. The bipolar membrane facilitated coupling between two electrodes and electrolytes, one for the CO2R reaction and one for the OER, that typically operate at mutually different pH values and produced a lower total cell overvoltage than known single-electrolyte CO2R systems while exhibiting ∼10% solar-to-fuels energy-conversion efficiency.
- 116Ding, C.; Shi, J.; Wang, Z.; Li, C. ACS Catal. 2017, 7, 675– 688 DOI: 10.1021/acscatal.6b03107[ACS Full Text], [CAS], Google Scholar116https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XitVGitbnP&md5=3a34e10643d75a34ccc54fa67b1fcf25Photoelectrocatalytic Water Splitting: Significance of Cocatalysts, Electrolyte, and InterfacesDing, Chunmei; Shi, Jingying; Wang, Zhiliang; Li, CanACS Catalysis (2017), 7 (1), 675-688CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)A review is given. The efficiency of photoelectrocatalytic (PEC) water splitting is limited by the serious recombination of photogenerated charges, high overpotential, and sluggish kinetics of surface reaction. We describe the recent progress on engineering the electrode-electrolyte and semiconductor-cocatalyst interfaces with cocatalysts, electrolytes, and interfacial layers (interlayers) to increase the PEC efficiency. Introducing cocatalysts has been demonstrated to be the most efficient way to lower the reaction barrier and promote charge injection to the reactants. It has been found that electrolyte ions can influence the surface catalysis remarkably. Electrolyte cations on the surface can influence the water splitting and backward reactions, and anions may take part in the proton transfer processes, indicating that fine-tuning of the electrolyte parameters turns out to be an important strategy for enhancing the PEC efficiency. Careful modification of the interface between the cocatalysts and the semiconductor via suitable interlayers is crit. for promoting charge sepn. and transfer, which can indirectly influence the surface catalysis. The mechanisms of surface catalysis are assumed to involve transfer of photogenerated holes to the surface active sites to form high-valent species, which then oxidize the water mols. Many key scientific issues about the generation of photovoltage, the sepn., storage, and transfer of carriers, the function of cocatalysts, the roles of electrolyte ions, and the influences of other parameters during PEC water splitting are discussed with some perspective views.
- 117Hill, J. C.; Landers, A. T.; Switzer, J. A. Nat. Mater. 2015, 14, 1150– 1156 DOI: 10.1038/nmat4408
- 118Digdaya, I. A.; Adhyaksa, G.; Trzesniewski, B. J.; Garnett, E.; Smith, W. A. Nat. Commun. 2017, 8, 15968 DOI: 10.1038/ncomms15968[Crossref], [PubMed], [CAS], Google Scholar118https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtVyqtrjJ&md5=333b23f5370f39355ca681925fdeb60dInterfacial engineering of metal-insulator-semiconductor junctions for efficient and stable photoelectrochemical water oxidationDigdaya, Ibadillah A.; Adhyaksa, Gede W. P.; Trzesniewski, Bartek J.; Garnett, Erik C.; Smith, Wilson A.Nature Communications (2017), 8 (), 15968CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)Solar-assisted water splitting can potentially provide an efficient route for large-scale renewable energy conversion and storage. It is essential for such a system to provide a sufficiently high photocurrent and photovoltage to drive the water oxidn. reaction. Here we demonstrate a photoanode that is capable of achieving a high photovoltage by engineering the interfacial energetics of metal-insulator-semiconductor junctions. We evaluate the importance of using two metals to decouple the functionalities for a Schottky contact and a highly efficient catalyst. We also illustrate the improvement of the photovoltage upon incidental oxidn. of the metallic surface layer in KOH soln. Addnl., we analyze the role of the thin insulating layer to the pinning and depinning of Fermi level that is responsible to the resulting photovoltage. Finally, we report the advantage of using dual metal overlayers as a simple protection route for highly efficient metal-insulator-semiconductor photoanodes by showing over 200 h of operational stability.
- 119Kamat, P. V. Pure Appl. Chem. 2002, 74, 1693– 1706 DOI: 10.1351/pac200274091693
- 120Jakob, M.; Levanon, H.; Kamat, P. V. Nano Lett. 2003, 3, 353– 358 DOI: 10.1021/nl0340071
- 121Subramanian, V.; Wolf, E. E.; Kamat, P. V. J. Am. Chem. Soc. 2004, 126, 4943– 4950 DOI: 10.1021/ja0315199
- 122Yoshida, M.; Yamakata, A.; Takanabe, K.; Kubota, J.; Osawa, M.; Domen, K. J. Am. Chem. Soc. 2009, 131, 13218– 13219 DOI: 10.1021/ja904991p
- 123Lu, X.; Bandara, A.; Katayama, M.; Yamakata, A.; Kubota, J.; Domen, K. J. Phys. Chem. C 2011, 115, 23902– 23907 DOI: 10.1021/jp207484q
- 124Stamenkovic, V. R.; Strmcnik, D.; Lopes, P. P.; Markovic, N. M. Nat. Mater. 2017, 16, 57– 69 DOI: 10.1038/nmat4738[Crossref], [CAS], Google Scholar124https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XitFamu73M&md5=ce9089ad76dcd6f4fd98d5c539c790c6Energy and fuels from electrochemical interfacesStamenkovic, Vojislav R.; Strmcnik, Dusan; Lopes, Pietro P.; Markovic, Nenad M.Nature Materials (2017), 16 (1), 57-69CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)Advances in electrocatalysis at solid-liq. interfaces are vital for driving the technol. innovations that are needed to deliver reliable, affordable and environmentally friendly energy. Here, we highlight the key achievements in the development of new materials for efficient hydrogen and oxygen prodn. in electrolyzers and, in reverse, their use in fuel cells. A key issue addressed here is the degree to which the fundamental understanding of the synergy between covalent and non-covalent interactions can form the basis for any predictive ability in tailor-making real-world catalysts. Common descriptors such as the substrate-hydroxide binding energy and the interactions in the double layer between hydroxide-oxides and H---OH are found to control individual parts of the hydrogen and oxygen electrochem. that govern the efficiency of water-based energy conversion and storage systems. Links between aq.- and org.-based environments are also established, encouraging the 'fuel cell' and 'battery' communities to move forward together.
- 125Suntivich, J.; Perry, E. E.; Gasteiger, H. A.; Shao-Horn, Y. Electrocatalysis 2013, 4, 49– 55 DOI: 10.1007/s12678-012-0118-x
- 126Fuel Cell Catalysis, A Surface Science Approach; Koper, M. T. M., Ed.; John Wiley & Sons, Inc.: Hoboken, NJ, 2009, : pp 1– 158.
- 127Shinagawa, T.; Garcia-Esparza, A. T.; Takanabe, K. Sci. Rep. 2015, 5, 13801 DOI: 10.1038/srep13801[Crossref], [PubMed], [CAS], Google Scholar127https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC283gsFeluw%253D%253D&md5=ac27784a48ec67e4bea1ac3d6c62a416Insight on Tafel slopes from a microkinetic analysis of aqueous electrocatalysis for energy conversionShinagawa Tatsuya; Garcia-Esparza Angel T; Takanabe KazuhiroScientific reports (2015), 5 (), 13801 ISSN:.Microkinetic analyses of aqueous electrochemistry involving gaseous H2 or O2, i.e., hydrogen evolution reaction (HER), hydrogen oxidation reaction (HOR), oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), are revisited. The Tafel slopes used to evaluate the rate determining steps generally assume extreme coverage of the adsorbed species (θ≈0 or ≈1), although, in practice, the slopes are coverage-dependent. We conducted detailed kinetic analyses describing the coverage-dependent Tafel slopes for the aforementioned reactions. Our careful analyses provide a general benchmark for experimentally observed Tafel slopes that can be assigned to specific rate determining steps. The Tafel analysis is a powerful tool for discussing the rate determining steps involved in electrocatalysis, but our study also demonstrated that overly simplified assumptions led to an inaccurate description of the surface electrocatalysis. Additionally, in many studies, Tafel analyses have been performed in conjunction with the Butler-Volmer equation, where its applicability regarding only electron transfer kinetics is often overlooked. Based on the derived kinetic description of the HER/HOR as an example, the limitation of Butler-Volmer expression in electrocatalysis is also discussed in this report.
- 128Trasatti, S. J. Electroanal. Chem. Interfacial Electrochem. 1972, 39, 163– 184 DOI: 10.1016/S0022-0728(72)80485-6[Crossref], [CAS], Google Scholar128https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaE38XltVyks7g%253D&md5=c0f43ebc002ad058af7e6c7d4b6c0d0fWork function, electronegativity, and electrochemical behavior of metals. III. Electrolytic hydrogen evolution in acid solutionsTrasatti, SergioJournal of Electroanalytical Chemistry and Interfacial Electrochemistry (1972), 39 (1), 163-84CODEN: JEIEBC; ISSN:0022-0728.Various attempts to interpret the electrochem. behavior of an electrode during H evolution are reviewed. The general behavior of a metal is apt to be related to its work function, the energy with which electrons near the Fermi level are bound to the interior of the solid. The use of this work function in developing a single theory to explain exptl. data on H discharge for all metals is considered.
- 129Greeley, J.; Jaramillo, T. F.; Bonde, J.; Chorkendorff, I.; Nørskov, J. K. Nat. Mater. 2006, 5, 909– 913 DOI: 10.1038/nmat1752[Crossref], [PubMed], [CAS], Google Scholar129https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28XhtFCqu73N&md5=bffaed56805e7732d1a12a9f68d9fe1eComputational high-throughput screening of electrocatalytic materials for hydrogen evolutionGreeley, Jeff; Jaramillo, Thomas F.; Bonde, Jacob; Chorkendorff, Ib; Norskov, Jens K.Nature Materials (2006), 5 (11), 909-913CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)The pace of materials discovery for heterogeneous catalysts and electrocatalysts could, in principle, be accelerated by the development of efficient computational screening methods. This would require an integrated approach, where the catalytic activity and stability of new materials are evaluated and where predictions are benchmarked by careful synthesis and exptl. tests. In this contribution, the authors present a d. functional theory-based, high-throughput screening scheme that successfully uses these strategies to identify a new electrocatalyst for the hydrogen evolution reaction (HER). The activity of over 700 binary surface alloys is evaluated theor.; the stability of each alloy in electrochem. environments is also estd. BiPt has a predicted activity comparable to, or even better than, pure Pt, the archetypical HER catalyst. This alloy is synthesized and tested exptl. and shows improved HER performance compared with pure Pt, in agreement with the computational screening results.
- 130Matsumoto, Y.; Sato, E. Mater. Chem. Phys. 1986, 14, 397– 426 DOI: 10.1016/0254-0584(86)90045-3[Crossref], [CAS], Google Scholar130https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL28XktFCjsbg%253D&md5=927a8b77c648b5b9cb8ab79f61debc4dElectrocatalytic properties of transition metal oxides for oxygen evolution reactionMatsumoto, Y.; Sato, E.Materials Chemistry and Physics (1986), 14 (5), 397-26CODEN: MCHPDR; ISSN:0254-0584.A review with 143 refs. is given on electrocatalysis of the transition metal oxides for the O2 evolution reaction. Many transition metal oxides tested as the anode material for the O evolution reaction are summarized.
- 131Man, I. C.; Su, H.-Y.; Calle-Vallejo, F.; Hansen, H. A.; Martinez, J. I.; Inoglu, N. G.; Kitchin, J.; Jaramillo, T. F.; Nørskov, J. K.; Rossmeisl, J. ChemCatChem 2011, 3, 1159– 1165 DOI: 10.1002/cctc.201000397[Crossref], [CAS], Google Scholar131https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXotFyjsb0%253D&md5=f4103e77db6bcd3ba840b6376b33315aUniversality in Oxygen Evolution Electrocatalysis on Oxide SurfacesMan, Isabela C.; Su, Hai-Yan; Calle-Vallejo, Federico; Hansen, Heine A.; Martinez, Jose I.; Inoglu, Nilay G.; Kitchin, John; Jaramillo, Thomas F.; Noerskov, Jens K.; Rossmeisl, JanChemCatChem (2011), 3 (7), 1159-1165CODEN: CHEMK3; ISSN:1867-3880. (Wiley-VCH Verlag GmbH & Co. KGaA)Trends in electrocatalytic activity of the O evolution reaction (OER) were studied from a large database of HO* and HOO* adsorption energies on oxide surfaces. The theor. overpotential was calcd. by applying std. d. functional theory in combination with the computational std. H electrode (SHE) model. By the discovery of a universal scaling relation between the adsorption energies of HOO* vs. HO*, it is possible to analyze the reaction free energy diagrams of all the oxides in a general way. This gave rise to an activity volcano that was the same for a wide variety of oxide catalyst materials and a universal descriptor for the O evolution activity, which suggests a fundamental limitation on the max. O evolution activity of planar oxide catalysts.
- 132Grimaud, A.; May, K. J.; Carlton, C. E.; Lee, Y. L.; Risch, M.; Hong, W. T.; Zhou, J.; Shao-Horn, Y. Nat. Commun. 2013, 4, 3439 DOI: 10.1038/ncomms3439[Crossref], [CAS], Google Scholar132https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhs1egsrzE&md5=71f102bc006bb4346bf7da233d79e499Double perovskites as a family of highly active catalysts for oxygen evolution in alkaline solutionGrimaud, Alexis; May, Kevin J.; Carlton, Christopher E.; Lee, Yueh-Lin; Risch, Marcel; Hong, Wesley T.; Zhou, Jigang; Shao-Horn, YangNature Communications (2013), 4 (), 3439, 7 pp.CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)The electronic structure of transition metal oxides governs the catalysis of many central reactions for energy storage applications such as oxygen electrocatalysis. Here we exploit the versatility of the perovskite structure to search for oxide catalysts that are both active and stable. We report double perovskites (Ln0.5Ba0.5)CoO3-δ (Ln = Pr, Sm, Gd and Ho) as a family of highly active catalysts for the oxygen evolution reaction upon water oxidn. in alk. soln. These double perovskites are stable unlike pseudocubic perovskites with comparable activities such as Ba0.5Sr0.5Co0.8Fe0.2O3-δ which readily amorphize during the oxygen evolution reaction. The high activity and stability of these double perovskites can be explained by having the O p-band center neither too close nor too far from the Fermi level, which is computed from ab initio studies.
- 133Popczun, E. J.; McKone, J. R.; Read, C. G.; Biacchi, A. J.; Wiltrout, A. M.; Lewis, N. S.; Schaak, R. E. J. Am. Chem. Soc. 2013, 135, 9267– 9270 DOI: 10.1021/ja403440e[ACS Full Text], [CAS], Google Scholar133https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXpsVehtrY%253D&md5=1f90d9dff7e66e7a97301477bdd4dc00Nanostructured Nickel Phosphide as an Electrocatalyst for the Hydrogen Evolution ReactionPopczun, Eric J.; McKone, James R.; Read, Carlos G.; Biacchi, Adam J.; Wiltrout, Alex M.; Lewis, Nathan S.; Schaak, Raymond E.Journal of the American Chemical Society (2013), 135 (25), 9267-9270CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Nanoparticles of nickel phosphide (Ni2P) have been investigated for electrocatalytic activity and stability for the hydrogen evolution reaction (HER) in acidic solns., under which proton exchange membrane-based electrolysis is operational. The catalytically active Ni2P nanoparticles were hollow and faceted to expose a high d. of the Ni2P(001) surface, which has previously been predicted based on theory to be an active HER catalyst. The Ni2P nanoparticles had among the highest HER activity of any non-noble metal electrocatalyst reported to date, producing H2(g) with nearly quant. faradaic yield, while also affording stability in aq. acidic media.
- 134Jiang, P.; Liu, Q.; Liang, Y.; Tian, J.; Asiri, A. M.; Sun, X. Angew. Chem., Int. Ed. 2014, 53, 12855– 12859 DOI: 10.1002/anie.201406848[Crossref], [CAS], Google Scholar134https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhvV2mtrvN&md5=e8b5bed1d364d872ee0799a30210b5edA Cost-Effective 3D Hydrogen Evolution Cathode with High Catalytic Activity: FeP Nanowire Array as the Active PhaseJiang, Ping; Liu, Qian; Liang, Yanhui; Tian, Jingqi; Asiri, Abdullah M.; Sun, XupingAngewandte Chemie, International Edition (2014), 53 (47), 12855-12859CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)Iron is the cheapest and one of the most abundant transition metals. Natural [FeFe]-hydrogenases exhibit remarkably high activity in hydrogen evolution, but they suffer from high oxygen sensitivity and difficulty in scale-up. Herein, an FeP nanowire array was developed on Ti plate (FeP NA/Ti) from its β-FeOOH NA/Ti precursor through a low-temp. phosphidation reaction. When applied as self-supported 3D hydrogen evolution cathode, the FeP NA/Ti electrode shows exceptionally high catalytic activity and good durability, and it only requires overpotentials of 55 and 127 mV to afford current densities of 10 and 100 mA cm2, resp. The excellent electrocatalytic performance is promising for applications as non-noble-metal HER catalyst with a high performance-price ratio in electrochem. water splitting for large-scale hydrogen fuel prodn.
- 135Popczun, E. J.; Read, C. G.; Roske, C. W.; Lewis, N. S.; Schaak, R. E. Angew. Chem., Int. Ed. 2014, 53, 5427– 5430 DOI: 10.1002/anie.201402646[Crossref], [CAS], Google Scholar135https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXmt1ahsr4%253D&md5=afaedbccf5033d70a4ddcf2d32c432f8Highly active electrocatalysis of the hydrogen evolution reaction by cobalt phosphide nanoparticlesPopczun, Eric J.; Read, Carlos G.; Roske, Christopher W.; Lewis, Nathan S.; Schaak, Raymond E.Angewandte Chemie, International Edition (2014), 53 (21), 5427-5430CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)Nanoparticles of cobalt phosphide, CoP, have been prepd. and evaluated as electrocatalysts for the hydrogen evolution reaction (HER) under strongly acidic conditions (0.50M H2SO4, pH 0.3). Uniform, multi-faceted CoP nanoparticles were synthesized by reacting Co nanoparticles with trioctylphosphine. Electrodes comprised of CoP nanoparticles on a Ti support (2 mg cm-2 mass loading) produced a cathodic c.d. of 20 mA cm-2 at an overpotential of -85 mV. The CoP/Ti electrodes were stable over 24 h of sustained hydrogen prodn. in 0.50M H2SO4. The activity was essentially unchanged after 400 cyclic voltammetric sweeps, suggesting long-term viability under operating conditions. CoP is therefore amongst the most active, acid-stable, earth-abundant HER electrocatalysts reported to date.
- 136Smith, R. D. L.; Prévot, M. S.; Fagan, R. D.; Zhang, Z.; Sedach, P. A.; Siu, J. M. K.; Trudel, S.; Berlinguette, C. P. Science 2013, 340, 60– 63 DOI: 10.1126/science.1233638
- 137Gong, M.; Li, Y.; Wang, H.; Liang, Y.; Wu, J. Z.; Zhou, J.; Wang, J.; Regier, T.; Wei, F.; Dai, H. J. Am. Chem. Soc. 2013, 135, 8452– 8455 DOI: 10.1021/ja4027715
- 138Gong, M.; Zhou, W.; Tsai, M. C.; Zhou, J.; Guan, M.; Lin, M. C.; Zhang, B.; Hu, Y.; Wang, D. Y.; Yang, J.; Pennycook, S. J.; Hwang, B. J.; Dai, H. Nat. Commun. 2014, 5, 5695 DOI: 10.1038/ncomms5695
- 139Suntivich, J.; May, K. J.; Gasteiger, H. A.; Goodenough, J. B.; Shao-Horn, Y. Science 2011, 334, 1383– 1385 DOI: 10.1126/science.1212858[Crossref], [PubMed], [CAS], Google Scholar139https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXhsFOjt73K&md5=34d8b657e052d2f31c5aa3773b5e6f80A Perovskite Oxide Optimized for Oxygen Evolution Catalysis from Molecular Orbital PrinciplesSuntivich, Jin; May, Kevin J.; Gasteiger, Hubert A.; Goodenough, John B.; Shao-Horn, YangScience (Washington, DC, United States) (2011), 334 (6061), 1383-1385CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)The efficiency of many energy storage technologies, such as rechargeable metal-air batteries and H prodn. from H2O splitting, is limited by the slow kinetics of the O evolution reaction (OER). Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) catalyzes the OER with intrinsic activity that is at least an order of magnitude higher than that of the state-of-the-art Ir oxide catalyst in alk. media. The high activity of BSCF was predicted from a design principle established by systematic examn. of >10 transition metal oxides, which showed that the intrinsic OER activity exhibits a volcano-shaped dependence on the occupancy of the 3d electron with an eg symmetry of surface transition metal cations in an oxide. The peak OER activity was predicted to be at an eg occupancy close to unity, with high covalency of transition metal-O bonds.
- 140Wei, C.; Feng, Z.; Scherer, G. G.; Barber, J.; Shao-Horn, Y.; Xu, Z. J. Adv. Mater. 2017, 29, 1606800 DOI: 10.1002/adma.201606800
- 141Kanan, M. W.; Nocera, D. G. Science 2008, 321, 1072– 1075 DOI: 10.1126/science.1162018[Crossref], [PubMed], [CAS], Google Scholar141https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXhtVSitrbP&md5=dbeea0b08710b7d24acf4046a56424d8In Situ Formation of an Oxygen-Evolving Catalyst in Neutral Water Containing Phosphate and Co2+Kanan, Matthew W.; Nocera, Daniel G.Science (Washington, DC, United States) (2008), 321 (5892), 1072-1075CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)The utilization of solar energy on a large scale requires its storage. In natural photosynthesis, energy from sunlight is used to rearrange the bonds of water to oxygen and hydrogen equiv. The realization of artificial systems that perform "water splitting" requires catalysts that produce oxygen from water without the need for excessive driving potentials. Here we report such a catalyst that forms upon the oxidative polarization of an inert indium tin oxide electrode in phosphate-buffered water contg. cobalt (II) ions. A variety of anal. techniques indicates the presence of phosphate in an approx. 1:2 ratio with cobalt in this material. The pH dependence of the catalytic activity also implicates the hydrogen phosphate ion as the proton acceptor in the oxygen-producing reaction. This catalyst not only forms in situ from earth-abundant materials but also operates in neutral water under ambient conditions.
- 142Lutterman, D. A.; Surendranath, Y.; Nocera, D. G. J. Am. Chem. Soc. 2009, 131, 3838– 3839 DOI: 10.1021/ja900023k
- 143Dinca, M.; Surendranath, Y.; Nocera, D. G. Proc. Natl. Acad. Sci. U. S. A. 2010, 107, 10337– 10341 DOI: 10.1073/pnas.1001859107
- 144Kuang, Y.; Jia, Q.; Ma, G.; Hisatomi, T.; Minegishi, T.; Nishiyama, H.; Nakabayashi, M.; Shibata, N.; Yamada, T.; Kudo, A.; Domen, K. Nat. Energy 2016, 2, 16191 DOI: 10.1038/nenergy.2016.191
- 145Shinagawa, T.; Ng, M. T.-K.; Takanabe, K. Angew. Chem., Int. Ed. 2017, 56, 5061– 5065 DOI: 10.1002/anie.201701642
- 146Shinagawa, T.; Takanabe, K. J. Phys. Chem. C 2016, 120, 24187– 24196 DOI: 10.1021/acs.jpcc.6b07954
- 147Electrochemistry, 2nd ed.; Hamann, C. H.; Hamnett, A.; Vielstich, W., Eds.; Wiley-VCH: Weinheim, 2007; pp 397– 438.Google ScholarThere is no corresponding record for this reference.
- 148Kato, H.; Asakura, K.; Kudo, A. J. Am. Chem. Soc. 2003, 125, 3082– 3089 DOI: 10.1021/ja027751g
- 149Sakata, Y.; Matsuda, Y.; Nakagawa, T.; Yasunaga, R.; Imamura, H.; Teramura, K. ChemSusChem 2011, 4, 181– 184 DOI: 10.1002/cssc.201000258
- 150Shinagawa, T.; Garcia-Esparza, A. T.; Takanabe, K. ChemElectroChem 2014, 1, 1497– 1507 DOI: 10.1002/celc.201402085
- 151Subbaraman, R.; Tripkovic, D.; Chang, K. C.; Strmcnik, D.; Paulikas, A. P.; Hirunsit, P.; Chan, M.; Greeley, J.; Stamenkovic, V.; Markovic, N. M. Nat. Mater. 2012, 11, 550– 557 DOI: 10.1038/nmat3313[Crossref], [PubMed], [CAS], Google Scholar151https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XmsFOqsb8%253D&md5=6579cb7fc048f54d4c8d2b12be343727Trends in activity for the water electrolyzer reactions on 3d M(Ni,Co,Fe,Mn) hydro(oxy)oxide catalystsSubbaraman, Ram; Tripkovic, Dusan; Chang, Kee-Chul; Strmcnik, Dusan; Paulikas, Arvydas P.; Hirunsit, Pussana; Chan, Maria; Greeley, Jeff; Stamenkovic, Vojislav; Markovic, Nenad M.Nature Materials (2012), 11 (6), 550-557CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)Design and synthesis of materials for efficient electrochem. transformation of H2O to H2 and of hydroxyl ions to O in alk. environments is of paramount importance in reducing energy losses in H2O-alkali electrolyzers. Here, using 3d-M hydr(oxy)oxides, with distinct stoichiometries and morphologies in the H evolution reaction (HER) and the O evolution reaction (OER) regions, the authors establish the overall catalytic activities for these reaction as a function of a more fundamental property, a descriptor, OH-M2+δ bond strength (0 ≤ δ ≤ 1.5). This relation exhibits trends in reactivity (Mn < Fe < Co < Ni), which is governed by the strength of the OH-M2+δ energetic (Ni < Co < Fe < Mn). These trends are independent of the source of the OH, either the supporting electrolyte (for the OER) or the H2O dissocn. product (for the HER). The successful identification of these electrocatalytic trends provides the foundation for rational design of active sites' for practical alk. HER and OER electrocatalysts.
- 152Yang, J.; Cooper, J. K.; Toma, F. M.; Walczak, K. A.; Favaro, M.; Beeman, J. W.; Hess, L. H.; Wang, C.; Zhu, C.; Gul, S.; Yano, J.; Kisielowski, C.; Schwartzberg, A.; Sharp, I. D. Nat. Mater. 2017, 16, 335– 341 DOI: 10.1038/nmat4794[Crossref], [PubMed], [CAS], Google Scholar152https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xhsl2gsLfJ&md5=44e1cf123f39c9067433cf7d181432b0A multifunctional biphasic water splitting catalyst tailored for integration with high-performance semiconductor photoanodesYang, Jinhui; Cooper, Jason K.; Toma, Francesca M.; Walczak, Karl A.; Favaro, Marco; Beeman, Jeffrey W.; Hess, Lucas H.; Wang, Cheng; Zhu, Chenhui; Gul, Sheraz; Yano, Junko; Kisielowski, Christian; Schwartzberg, Adam; Sharp, Ian D.Nature Materials (2017), 16 (3), 335-341CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)Artificial photosystems are advanced by the development of conformal catalytic materials that promote desired chem. transformations, while also maintaining stability and minimizing parasitic light absorption for integration on surfaces of semiconductor light absorbers. Here, we demonstrate that multifunctional, nanoscale catalysts that enable high-performance photoelectrochem. energy conversion can be engineered by plasma-enhanced at. layer deposition. The collective properties of tailored Co3O4/Co(OH)2 thin films simultaneously provide high activity for water splitting, permit efficient interfacial charge transport from semiconductor substrates, and enhance durability of chem. sensitive interfaces. These films comprise compact and continuous nanocryst. Co3O4 spinel that is impervious to phase transformation and impermeable to ions, thereby providing effective protection of the underlying substrate. Moreover, a secondary phase of structurally disordered and chem. labile Co(OH)2 is introduced to ensure a high concn. of catalytically active sites. Application of this coating to photovoltaic p+n-Si junctions yields best reported performance characteristics for cryst. Si photoanodes.
- 153Seitz, L. C.; Chen, Z.; Forman, A. J.; Pinaud, B. A.; Benck, J. D.; Jaramillo, T. F. ChemSusChem 2014, 7, 1372– 1385 DOI: 10.1002/cssc.201301030
- 154Maeda, K.; Teramura, K.; Lu, D.; Saito, N.; Inoue, Y.; Domen, K. Angew. Chem., Int. Ed. 2006, 45, 7806– 7809 DOI: 10.1002/anie.200602473
- 155Maeda, K.; Domen, K. Top. Curr. Chem. 2011, 303, 95– 119 DOI: 10.1007/128_2011_138
- 156Yoshida, M.; Takanabe, K.; Maeda, K.; Ishikawa, A.; Kubota, J.; Sakata, Y.; Ikezawa, Y.; Domen, K. J. Phys. Chem. C 2009, 113, 10151– 10157 DOI: 10.1021/jp901418u
- 157Qureshi, M.; Shinagawa, T.; Tsiapis, N.; Takanabe, K. ACS Sustainable Chem. Eng. 2017, 5, 8079– 8088 DOI: 10.1021/acssuschemeng.7b01704[ACS Full Text], [CAS], Google Scholar157https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXht12mt7vO&md5=8d8c68253064ee964a5404bddad97db2Exclusive Hydrogen Generation by Electrocatalysts Coated with an Amorphous Chromium-Based Layer Achieving Efficient Overall Water SplittingQureshi, Muhammad; Shinagawa, Tatsuya; Tsiapis, Nikolaos; Takanabe, KazuhiroACS Sustainable Chemistry & Engineering (2017), 5 (9), 8079-8088CODEN: ASCECG; ISSN:2168-0485. (American Chemical Society)Successful conversion of renewable energy to useful chems. requires efficient devices that can electrocatalyze or photocatalyze redox reactions, e.g., overall water splitting. Excellent electrocatalysts for the hydrogen evolution reaction (HER), such as Pt, can also cause other side-reactions, including the water-forming back-reaction from H2 and O2 products. A Cr-based amorphous layer coated on catalysts can work as a successful surface modifier that avoids the back-reaction, but its capabilities and limitations toward other species have not been studied. Herein, we investigated the Cr-based layer on Pt from perspectives of both electrocatalysis and photocatalysis using redox-active mols./ions (O2, ferricyanide, IO3-, S2O82-, H2O2, and CO gas). Our systematic study revealed that utilization of the Cr-based layer realized an exclusive cathodic reaction only to HER, even in the presence of the aforementioned reactive species, suggesting that Cr-based layers work as membranes, as well as corrosion and poison inhibition layers. However, the Cr-based layer experienced self-oxidn. and dissolved into the aq. phase when a strong oxidizing agent or low pH was present. Presented herein are fundamental and crit. aspects of the Cr-based modifier, which is essential for the successful and practical development of solar fuel prodn. systems.
- 158Garcia-Esparza, A. T.; Shinagawa, T.; Ould-Chikh, S.; Qureshi, M.; Peng, X.; Wei, N.; Anjum, D. H.; Clo, A.; Weng, T.-C.; Nordlund, D.; Sokaras, D.; Kubota, J.; Domen, K.; Takanabe, K. Angew. Chem., Int. Ed. 2017, 56, 5780– 5784 DOI: 10.1002/anie.201701861
- 159Pan, C.; Takata, T.; Nakabayashi, M.; Matsumoto, T.; Shibata, N.; Ikuhara, Y.; Domen, K. Angew. Chem., Int. Ed. 2015, 54, 2955– 2959 DOI: 10.1002/anie.201410961
- 160Yoshida, M.; Maeda, K.; Lu, D.; Kubota, J.; Domen, K. J. Phys. Chem. C 2013, 117, 14000– 14006 DOI: 10.1021/jp402240d[ACS Full Text], [CAS], Google Scholar160https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXpslKgsLw%253D&md5=f790d4e3d7af421474663ceca43ab726Lanthanoid Oxide Layers on Rhodium-Loaded (Ga1-xZnx)(N1-xOx) Photocatalyst as a Modifier for Overall Water Splitting under Visible-Light IrradiationYoshida, Masaaki; Maeda, Kazuhiko; Lu, Daling; Kubota, Jun; Domen, KazunariJournal of Physical Chemistry C (2013), 117 (27), 14000-14006CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)Lanthanoid oxide modifier layers were applied to Rh metal nanoparticles on (Ga1-xZnx)(N1-xOx) photocatalyst for overall water splitting under visible-light irradn. Structural anal. by transmission electron microscopy, energy-dispersive X-ray spectroscopy, XPS, and X-ray absorption spectroscopy revealed that lanthanoid(III) oxide layers coated the Rh nanoparticles on (Ga1-xZnx)(N1-xOx), although they were also deposited directly on the (Ga1-xZnx)(N1-xOx) surface. Certain lanthanoid oxide layers (La, Pr, Sm, Gd, and Dy) functioned as modifiers for Rh-metal/(Ga1-xZnx)(N1-xOx) to produce H2 and O2 gases, although the Rh-metal/(Ga1-xZnx)(N1-xOx) photocatalyst exhibited little activity for overall water splitting due to rapid water formation from H2 and O2 on Rh. Ce and Eu oxide layers showed no photocatalytic activity, most likely due to their ability to capture photoexcited electrons from Rh-metal/(Ga1-xZnx)(N1-xOx). The enhancement of photocatalytic activity by lanthanoid oxide loading was shown to be dependent on the formation of redox-inactive lanthanoid(III) oxide layers on the Rh nanoparticles, which effectively suppresses the backward water formation reaction to enable H2 evolution on Rh.
- 161Hisatomi, T.; Maeda, K.; Takanabe, K.; Kubota, J.; Domen, K. J. Phys. Chem. C 2009, 113, 21458– 21466 DOI: 10.1021/jp9079662
- 162Maeda, K.; Xiong, A.; Yoshinaga, T.; Ikeda, T.; Sakamoto, N.; Hisatomi, T.; Takashima, M.; Lu, D.; Kanehara, M.; Setoyama, T.; Teranishi, T.; Domen, K. Angew. Chem., Int. Ed. 2010, 49, 4096– 4099 DOI: 10.1002/anie.201001259
- 163Townsend, T. K.; Browning, N. D.; Osterloh, F. E. Energy Environ. Sci. 2012, 5, 9543– 9550 DOI: 10.1039/c2ee22665k
- 164Takanabe, K. In Nanotechnology in Catalysis: Applications in the Chemical Industry, Energy Development, and Environment Protection; Sels, B.; Voorde, M. V., Eds.; Wiley-VCH: Weinheim, 2017; pp 891– 906.
- 165Rajeshwar, K. J. Phys. Chem. Lett. 2011, 2, 1301– 1309 DOI: 10.1021/jz200396h[ACS Full Text], [CAS], Google Scholar165https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXmtFSisL0%253D&md5=f4252f4bd99bcd5d5714fc3710ced443Solar Energy Conversion and Environmental Remediation Using Inorganic Semiconductor-Liquid Interfaces: The Road Traveled and the Way ForwardRajeshwar, KrishnanJournal of Physical Chemistry Letters (2011), 2 (11), 1301-1309CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)Unlike their solid-state counterparts, semiconductor-liq. junctions are versatile in that the incident solar energy can be stored in the form of chem. fuels. Another attractive application is the use of irradiated oxide semiconductor-coated surfaces for self-cleaning and antifogging. The theme of this history-tinged Guest Commentary centers on the question of what has been accomplished in the above "photoelectrochem." schemes over the 35 yr time frame from 1975 to 2010. Progress in this field was aided by the infusion of new concepts and contributions from the materials chem. and physics communities. A related aspect of discussion is how the active semiconductor material has evolved both chem. and morphol. in these applications. It is shown that despite impressive research advances, only a handful of the above concepts (e.g., dye-sensitized solar photon conversion and self-cleaning and antifogging surfaces) have made the successful transition from the lab. to the marketplace.
- 166Atkins, P.; Paula, J. D. Atkins’ Physical Chemistry, 10th ed.; W. H. Freeman and Company: New York, 2014.Google ScholarThere is no corresponding record for this reference.
- 167Shinagawa, T.; Takanabe, K. J. Power Sources 2015, 287, 465– 471 DOI: 10.1016/j.jpowsour.2015.04.091
- 168Haynes, W. M.; Lide, D. R. Handbook of Chemistry and Physics, 92nd ed.; CRC Press: Boca Raton, FL, 2011.Google ScholarThere is no corresponding record for this reference.
- 169Jin, J.; Walczak, K.; Singh, M. R.; Karp, C.; Lewis, N. S.; Xiang, C. Energy Environ. Sci. 2014, 7, 3371– 3380 DOI: 10.1039/C4EE01824A
- 170Chabi, S.; Papadantonakis, K. M.; Lewis, N. S.; Freund, M. S. Energy Environ. Sci. 2017, 10, 1320– 1338 DOI: 10.1039/C7EE00294G
- 171Kutz, R. B.; Chen, Q.; Yang, H.; Sajjad, S. D.; Liu, Z.; Masel, I. R. Energy Technol. 2017, 5, 929– 936 DOI: 10.1002/ente.201600636[Crossref], [CAS], Google Scholar171https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXpvVSltLg%253D&md5=957477e23a3affd0052f38514329b436Sustainion Imidazolium-Functionalized Polymers for Carbon Dioxide ElectrolysisKutz, Robert B.; Chen, Qingmei; Yang, Hongzhou; Sajjad, Syed D.; Liu, Zengcai; Masel, I. RichardEnergy Technology (Weinheim, Germany) (2017), 5 (6), 929-936CODEN: ETNEFN; ISSN:2194-4296. (Wiley-VCH Verlag GmbH & Co. KGaA)CO2 electrolysis is a key step in CO2 conversion into fuels and chems. as a way of mitigating climate change. We report the synthesis and testing of a series of new anion-conductive membranes (tradenamed Sustainion®) for use in CO2 electrolysis. These membranes incorporate the functional character of imidazolium-based ionic liqs. as co-catalysts in CO2 redn. into a solid membrane with a styrene backbone. We find that the addn. of an imidazolium group onto the styrene side-chains increases the selectivity of the reaction from approx. 25% to approx. 95%. The current at 3 V is increased by a factor of 14. So far we have been able to tune these parameters to achieve stable cells that provide current densities higher than 100 mA cm-2 at 3 V cell potential with a CO product selectivity over 98%. Stable performance was obsd. for 6 mo of continuous operation (>150 000 000 turnovers). These results demonstrate that imidazolium polymers are ideal membranes for CO2 electrolysis.
- 172Klingan, K.; Ringleb, F.; Zaharieva, I.; Heidkamp, J.; Chernev, P.; Gonzalez-Flores, D.; Risch, M.; Fischer, A.; Dau, H. ChemSusChem 2014, 7, 1301– 1310 DOI: 10.1002/cssc.201301019
- 173Shinagawa, T.; Takanabe, K. ChemSusChem 2017, 10, 1318– 1336 DOI: 10.1002/cssc.201601583
- 174Shinagawa, T.; Ng, M. T.-K.; Takanabe, K. ChemSusChem, DOI: DOI: 10.1002/cssc.201701266 .
- 175Dionigi, F.; Vesborg, P. C. K.; Pedersen, T.; Hansen, O.; Dahl, S.; Xiong, A.; Maeda, K.; Domen, K.; Chorkendorff, I. Energy Environ. Sci. 2011, 4, 2937– 2942 DOI: 10.1039/c1ee01242h
- 176Esposito, D. V.; Lee, Y.; Yoon, H.; Haney, P. M.; Labrador, N. y.; Moffat, T. P.; Talin, A. A.; Szalai, V. A. Sustainable Energy Fuels 2017, 1, 154– 173 DOI: 10.1039/C6SE00073H[Crossref], [CAS], Google Scholar176https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhs1Crs77N&md5=c8ddc6c357c9cfc09f4b99bcb60eadd8Deconvoluting the influences of 3D structure on the performance of photoelectrodes for solar-driven water splittingEsposito, Daniel V.; Lee, Youngmin; Yoon, Heayoung; Haney, Paul M.; Labrador, Natalie Y.; Moffat, Thomas P.; Talin, A. Alec; Szalai, Veronika A.Sustainable Energy & Fuels (2017), 1 (1), 154-173CODEN: SEFUA7; ISSN:2398-4902. (Royal Society of Chemistry)Three-dimensionally (3D) structured photoelectrodes offer a no. of potential benefits for solar fuel prodn. compared to conventional planar photoelectrodes, including decreased optical losses, higher surface area for catalysis, easier removal of product species, and enhanced carrier collection efficiency. However, 3D structures can also present challenges, such as lower photovoltage and larger surface recombination. Quantifying and understanding the advantages and disadvantages of 3D structuring can maximize benefits, but this goal is not trivial because the factors that affect photoelectrode performance are intertwined. In this article, we provide an overview of the benefits and challenges of using 3D photoelectrode structures and present a systematic approach for deconvoluting the most common effects of 3D structure on photoelectrode performance. As a basis for this study, metal-insulator-semiconductor (MIS) photoelectrodes consisting of p-Si micro-pillar arrays with well-defined diam., pitch, and height were fabricated by reactive ion etching (RIE). A general framework for modeling the influences of 3D structure on photoelectrode current-potential performance is presented, and a comparison of the loss mechanisms in 3D and planar photoelectrodes is illustrated using loss anal. diagrams. We expect that most of the measurements and analyses that we demonstrate for MIS photoelectrodes can be applied with equal success to liq.-junction and p-n junction 3D structured photoelectrodes.
- 177Chen, Z.; Jaramillo, T. F.; Deutsch, T. G.; Kleiman-Shwarsctein, A.; Forman, A. J.; Gaillard, N.; Garland, R.; Takanabe, K.; Heske, C.; Sunkara, M.; McFarland, E. W.; Domen, K.; Miller, E. L.; Turner, J. A.; Dinh, H. N. J. Mater. Res. 2010, 25, 3– 16 DOI: 10.1557/JMR.2010.0020[Crossref], [CAS], Google Scholar177https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXhtlKmsLw%253D&md5=70cf3c6595a9d9a1f489b028475e09aaAccelerating materials development for photoelectrochemical hydrogen production: standards for methods, definitions, and reporting protocolsChen, Zhebo; Jaramillo, Thomas F.; Deutsch, Todd G.; Kleiman-Shwarsctein, Alan; Forman, Arnold J.; Gaillard, Nicolas; Garland, Roxanne; Takanabe, Kazuhiro; Heske, Clemens; Sunkara, Mahendra; McFarland, Eric W.; Domen, Kazunari; Miller, Eric L.; Turner, John A.; Dinh, Huyen N.Journal of Materials Research (2010), 25 (1), 3-16CODEN: JMREEE; ISSN:0884-2914. (Materials Research Society)A review. Photoelectrochem. (PEC) H2O splitting for H prodn. is a promising technol. that uses sunlight and H2O to produce renewable H with O as a byproduct. In the expanding field of PEC H prodn., the use of standardized screening methods and reporting has emerged as a necessity. This article is intended to provide guidance on key practices in characterization of PEC materials and proper reporting of efficiencies. Presented here are the definitions of various efficiency values that pertain to PEC, with an emphasis on the importance of solar-to-H efficiency, as well as a flow chart with std. procedures for PEC characterization techniques for planar photoelectrode materials (i.e., not suspensions of particles) with a focus on single band gap absorbers. These guidelines serve as a foundation and prelude to a much more complete and in-depth discussion of PEC techniques and procedures presented elsewhere.
- 178van de Krol, R.; Grätzel, M. Photoelectrochemical Hydrogen Production; Springer: Berlin, 2012.
- 179Nurlaela, E.; Ziani, A.; Takanabe, K. Mater. Renew. Sustainable Energy 2016, 5, 18 DOI: 10.1007/s40243-016-0083-z
- 180Nurlaela, E.; Ould-Chikh, S.; Harb, M.; del Gobbo, S.; Aouine, M.; Puzenat, E.; Sautet, P.; Domen, K.; Basset, J.-M.; Takanabe, K. Chem. Mater. 2014, 26, 4812– 4825 DOI: 10.1021/cm502015q
- 181Ziani, A.; Nurlaela, E.; Dhawale, D. S.; Silva, D.; Alarousu, E.; Mohammed, O. F.; Takanabe, K. Phys. Chem. Chem. Phys. 2015, 17, 2670– 2677 DOI: 10.1039/C4CP05616G
- 182Nurlaela, E.; Wang, H.; Shinagawa, T.; Flanagan, S.; Ould-Chikh, S.; Qureshi, M.; Mics, Z.; Sautet, P.; Le Bahers, T.; Cánovas, E.; Bonn, M.; Takanabe, K. ACS Catal. 2016, 6, 4117– 4126 DOI: 10.1021/acscatal.6b00508[ACS Full Text], [CAS], Google Scholar182https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XosVSjtLY%253D&md5=d9525dcdd19ecb10b88d138dcc4084dcEnhanced Kinetics of Hole Transfer and Electrocatalysis during Photocatalytic Oxygen Evolution by Cocatalyst TuningNurlaela, Ela; Wang, Hai; Shinagawa, Tatsuya; Flanagan, Sean; Ould-Chikh, Samy; Qureshi, Muhammad; Mics, Zoltan; Sautet, Philippe; Le Bahers, Tangui; Canovas, Enrique; Bonn, Mischa; Takanabe, KazuhiroACS Catalysis (2016), 6 (7), 4117-4126CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)Understanding photophys. and electrocatalytic processes during photocatalysis in a powder suspension system is crucial for developing efficient solar energy conversion systems. We report a substantial enhancement by a factor of 3 in photocatalytic efficiency for the oxygen evolution reaction (OER) by adding trace amts. (∼0.05 wt %) of noble metals (Rh and Ru) to a 2 wt % cobalt oxide modified Ta3N5 photocatalyst particulate. The optimized system exhibited high quantum efficiencies (QEs) of up to 28 and 8.4% at 500 and 600 nm in 0.1 M Na2S2O8 at pH 14. By isolation of the electrochem. components to generate doped cobalt oxide electrodes, the electrocatalytic activity of cobalt oxide on doping with Ru or Rh was improved in comparison with cobalt oxide, as evidenced by the onset shift for electrochem. OER. D. functional theory (DFT) calcns. show that the effect of a second metal addn. is to perturb the electronic structure and redox properties in such a way that both hole transfer kinetics and electrocatalytic rates improve. Time-resolved terahertz spectroscopy (TRTS) measurement provides evidence of long-lived electron populations (>1 ns; with mobilities μe ≈ 0.1-3 cm2 V-1 s-1), which are not perturbed by the addn. of CoOx-related phases. Furthermore, we find that Ta3N5 phases alone suffer ultrafast hole trapping (within 10 ps); the CoOx and M/CoOx decorations most likely induce a kinetic competition between hole transfer toward the CoOx-related phases and trapping in the Ta3N5 phase, which is consistent with the improved OER rates. The present work not only provides a novel way to improve electrocatalytic and photocatalytic performance but also gives addnl. tools and insight into understand the characteristics of photocatalysts that can be used in a suspension system.
- 183de Respinis, M.; Fravventura, M.; Abdi, F. F.; Schreuders, H.; Savenije, T. J.; Smith, W. A.; Dam, B.; van de Krol, R. Chem. Mater. 2015, 27, 7091– 7099 DOI: 10.1021/acs.chemmater.5b02938
- 184Vequizo, J. J. M.; Hojamberdiev, M.; Teshima, K.; Yamakata, A. J. Photochem. Photobiol., A 2017, DOI: 10.1016/j.jphotochem.2017.09.005
- 185Xing, Z.; Zong, X.; Pan, J.; Wang, L. Chem. Eng. Sci. 2013, 104, 125– 146 DOI: 10.1016/j.ces.2013.08.039[Crossref], [CAS], Google Scholar185https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhvFWit7vO&md5=6ae40e40757445367c583efbcc68114bOn the engineering part of solar hydrogen production from water splitting: Photoreactor designXing, Zheng; Zong, Xu; Pan, Jian; Wang, LianzhouChemical Engineering Science (2013), 104 (), 125-146CODEN: CESCAC; ISSN:0009-2509. (Elsevier Ltd.)A review. Water splitting under sunlight illumination in the presence of semiconductor photocatalyst is a promising way to produce clean hydrogen fuel. Solar hydrogen can be obtained in two routes: photoelectrochem. (PEC) water splitting based on immobilized photocatalysts in thin films and photocatalytic (photochem.) water splitting based on powder photocatalysts in slurry system. Over the past several decades, tremendous research work was devoted to exploring new semiconductor materials suitable for PEC and photochem. systems and understanding the underlying mechanism of the water splitting process. However, much less attention was paid to the design of photocatalytic reaction systems or reactors, which is indeed critically important for the overall solar energy conversion performance. This paper summarizes the basic working mechanisms of both PEC and photochem. systems, and gives an overview of a variety of photoreactor design and development.
- 186Setoyama, T.; Takewaki, T.; Domen, K.; Tatsumi, T. Faraday Discuss. 2017, 198, 509– 527 DOI: 10.1039/C6FD00196C
- 187Singh, M. R.; Xiang, C.; Lewis, N. S. Sustain. Energy Fuels 2017, 1, 458– 466 DOI: 10.1039/C7SE00062F
- 188Pinaud, B. A.; Benck, J. D.; Seitz, L. C.; Forman, A. J.; Chen, Z.; Deutsch, T. G.; James, B. D.; Baum, K. N.; Baum, G. N.; Ardo, S.; Wang, H.; Miller, E.; Jaramillo, T. F. Energy Environ. Sci. 2013, 6, 1983– 2002 DOI: 10.1039/c3ee40831k
- 189Hisatomi, T.; Miyazaki, K.; Takanabe, K.; Maeda, K.; Kubota, J.; Sakata, Y.; Domen, K. Chem. Phys. Lett. 2010, 486, 144– 146 DOI: 10.1016/j.cplett.2010.01.006
- 190Hisatomi, T.; Maeda, K.; Takanabe, K.; Kubota, J.; Domen, K. J. Phys. Chem. C 2009, 113, 21458– 21466 DOI: 10.1021/jp9079662
Cited By
This article is cited by 545 publications.
- Tengfei Jiang, Jingying Wei, Jianyang Li, Huaiguo Xue, Jingqi Tian, Romain Gautier. Rapid Identification of Efficient Photocatalysts by Visualizing the Spatial Distribution of Photoinduced Charge Carriers. ACS Catalysis 2023, 13 (7) , 4168-4177. https://doi.org/10.1021/acscatal.3c00149
- Masato Takeuchi, Tadateru Kikuchi, Atsushi Kondo, Ryo Kurosawa, Junichi Ryu, Masaya Matsuoka. Near-Infrared Spectroscopic Analysis─Formation of Ca(OH)2 and Ca(OD)2 by Hydration of CaO with H2O and D2O. The Journal of Physical Chemistry C 2023, 127 (13) , 6406-6413. https://doi.org/10.1021/acs.jpcc.3c00285
- Emmanuel N. Musa, Sumandeep Kaur, Trenton C. Gallagher, Thao Mi Anthony, William F. Stickle, Líney Árnadóttir, Kyriakos C. Stylianou. Two Birds, One Stone: Coupling Hydrogen Production with Herbicide Degradation over Metal–Organic Framework-Derived Titanium Dioxide. ACS Catalysis 2023, 13 (6) , 3710-3722. https://doi.org/10.1021/acscatal.3c00265
- Yosuke Kageshima, So Kato, Sota Shiga, Fumiaki Takagi, Hikari Minamisawa, Masaomi Horita, Tomohiko Yamakami, Katsuya Teshima, Kazunari Domen, Hiromasa Nishikiori. Impact of Ball Milling on the Hydrogen Evolution Performance of Cu2Sn0.38Ge0.62S3 Photocatalytic Particles Synthesized via a Flux Method. ACS Applied Materials & Interfaces 2023, 15 (10) , 13108-13120. https://doi.org/10.1021/acsami.2c23103
- Shimpei Naniwa, Kosaku Kato, Akira Yamamoto, Hisao Yoshida, Akira Yamakata. Particle Size Dependent Trap States of Photoexcited Carriers in Anatase TiO2 Nanoparticles. The Journal of Physical Chemistry C 2023, 127 (8) , 4295-4302. https://doi.org/10.1021/acs.jpcc.2c08125
- Celal Avcıoǧlu, Suna Avcıoǧlu, Maged F. Bekheet, Aleksander Gurlo. Photocatalytic Overall Water Splitting by SrTiO3: Progress Report and Design Strategies. ACS Applied Energy Materials 2023, 6 (3) , 1134-1154. https://doi.org/10.1021/acsaem.2c03280
- Van-Huy Trinh, Jeongsuk Seo. Porous Cuboidal SrNbO2N Crystals Grown on a Nb Substrate as an Active Photoanode for Neutral Seawater Splitting under Sunlight. ACS Sustainable Chemistry & Engineering 2023, 11 (5) , 1655-1665. https://doi.org/10.1021/acssuschemeng.2c05261
- Rohit Mann, Deepa Khushalani. Role of Seawater Ions in Forming an Effective Interface between Photocatalyst/Cocatalyst. ACS Applied Materials & Interfaces 2023, 15 (1) , 1219-1226. https://doi.org/10.1021/acsami.2c17919
- Riza Ariyani Nur Khasanah, Chi-Hung Lee, Yi Chen Li, Chang-Heng Chen, Tsong-Shin Lim, Chang-Ren Wang, Po-Ya Chang, Hwo-Shuenn Sheu, Forest Shih-Sen Chien. Enhancement of Photocatalytic Activity of Electrodeposited Cu2O by Reducing Oxygen Vacancy Density. ACS Applied Energy Materials 2022, 5 (12) , 15326-15332. https://doi.org/10.1021/acsaem.2c02963
- Bramhaiah Kommula, Pandiselvi Durairaj, Samita Mishra, Subhajit Kar, Adhra Sury, Amit Kumar, Arijit K. De, Sunandan Sarkar, Santanu Bhattacharyya. Self-Assembled Oligothiophenes for Photocatalytic Hydrogen Production and Simultaneous Organic Transformation. ACS Applied Nano Materials 2022, 5 (10) , 14746-14758. https://doi.org/10.1021/acsanm.2c03061
- Mian Zahid Hussain, Zhuxian Yang, Bart van der Linden, Werner R. Heinz, Mounib Bahri, Ovidiu Ersen, Quanli Jia, Roland A. Fischer, Yanqiu Zhu, Yongde Xia. MOF-Derived Multi-heterostructured Composites for Enhanced Photocatalytic Hydrogen Evolution: Deciphering the Roles of Different Components. Energy & Fuels 2022, 36 (19) , 12212-12225. https://doi.org/10.1021/acs.energyfuels.2c02319
- Zachary J. Baum, Leilani Lotti Diaz, Tatyana Konovalova, Qiongqiong Angela Zhou. Materials Research Directions Toward a Green Hydrogen Economy: A Review. ACS Omega 2022, 7 (37) , 32908-32935. https://doi.org/10.1021/acsomega.2c03996
- Takuya Suguro, Fuminao Kishimoto, Kazuhiro Takanabe. Photocatalytic Hydrogen Production under Water Vapor Feeding─A Minireview. Energy & Fuels 2022, 36 (16) , 8978-8994. https://doi.org/10.1021/acs.energyfuels.2c01478
- Aloka Kumar Sahu, Meenakshi Pokhriyal, Sreedevi Upadhyayula, Xiu Song Zhao. Modulating Charge Carrier Dynamics among Anisotropic Crystal Facets of Cu2O for Enhanced CO2 Photoreduction. The Journal of Physical Chemistry C 2022, 126 (31) , 13094-13104. https://doi.org/10.1021/acs.jpcc.2c02306
- Yiqiang He, Cailing Chen, Yuxin Liu, Yilin Yang, Chunguang Li, Zhan Shi, Yu Han, Shouhua Feng. Quantitative Evaluation of Carrier Dynamics in Full-Spectrum Responsive Metallic ZnIn2S4 with Indium Vacancies for Boosting Photocatalytic CO2 Reduction. Nano Letters 2022, 22 (12) , 4970-4978. https://doi.org/10.1021/acs.nanolett.2c01666
- Hyunho Park, Soo Young Park. Enhancing the Alkaline Hydrogen Evolution Reaction of Graphene Quantum Dots by Ethylenediamine Functionalization. ACS Applied Materials & Interfaces 2022, 14 (23) , 26733-26741. https://doi.org/10.1021/acsami.2c04703
- Sebastian Pios, Wolfgang Domcke. Ab Initio Electronic Structure Study of the Photoinduced Reduction of Carbon Dioxide with the Heptazinyl Radical. The Journal of Physical Chemistry A 2022, 126 (18) , 2778-2787. https://doi.org/10.1021/acs.jpca.2c00615
- Haiyun Wang, Hao Cheng, Haifeng Lv, Hangxun Xu, Xiaojun Wu, Jinlong Yang. Molecular Design of Two-Dimensional Covalent Heptazine Frameworks for Photocatalytic Overall Water Splitting under Visible Light. The Journal of Physical Chemistry Letters 2022, 13 (17) , 3949-3956. https://doi.org/10.1021/acs.jpclett.2c00819
- Bing Han, Yunchao Lou, Zhe Liu, Chutong Zhou, Zhiyu Wang, Guodong Qian. O,N-Codoped CeF3 Upconversion Nanoparticles for Efficient Photocatalytic Oxygen Evolution under Visible Light. ACS Applied Nano Materials 2022, 5 (4) , 5096-5102. https://doi.org/10.1021/acsanm.2c00140
- Wolfgang Domcke, Andrzej L. Sobolewski. Water Oxidation and Hydrogen Evolution with Organic Photooxidants: A Theoretical Perspective. The Journal of Physical Chemistry B 2022, 126 (15) , 2777-2788. https://doi.org/10.1021/acs.jpcb.2c00705
- Maria Bouri, Nicolas Niederhauser, Benjamin Künzli, Maximilian Amsler, Ulrich Aschauer. Oxygen Evolution Reaction Activity of Sr2Ta2O7 and Sr2Nb2O7 Surfaces. The Journal of Physical Chemistry C 2022, 126 (15) , 6556-6563. https://doi.org/10.1021/acs.jpcc.2c00649
- Xuesong Lu, Jeannie Z. Y. Tan, M. Mercedes Maroto-Valer. Investigation of CO2 Photoreduction in an Annular Fluidized Bed Photoreactor by MP-PIC Simulation. Industrial & Engineering Chemistry Research 2022, 61 (8) , 3123-3136. https://doi.org/10.1021/acs.iecr.1c04035
- Hong-Jia Wang, Jia-Sheng Lin, Hua Zhang, Yue-Jiao Zhang, Jian-Feng Li. Plasmonic Core–Shell Materials: Synthesis, Spectroscopic Characterization, and Photocatalytic Applications. Accounts of Materials Research 2022, 3 (2) , 187-198. https://doi.org/10.1021/accountsmr.1c00217
- Rito Yanagi, Tianshuo Zhao, Devan Solanki, Zhenhua Pan, Shu Hu. Charge Separation in Photocatalysts: Mechanisms, Physical Parameters, and Design Principles. ACS Energy Letters 2022, 7 (1) , 432-452. https://doi.org/10.1021/acsenergylett.1c02516
- Hajime Suzuki, Masanobu Higashi, Osamu Tomita, Yusuke Ishii, Takafumi Yamamoto, Daichi Kato, Tetsu Kotani, Daichi Ozaki, Shunsuke Nozawa, Kouichi Nakashima, Koji Fujita, Akinori Saeki, Hiroshi Kageyama, Ryu Abe. PbBi3O4X3 (X = Cl, Br) with Single/Double Halogen Layers as a Photocatalyst for Visible-Light-Driven Water Splitting: Impact of a Halogen Layer on the Band Structure and Stability. Chemistry of Materials 2021, 33 (24) , 9580-9587. https://doi.org/10.1021/acs.chemmater.1c02876
- Xiao Li, Shanlin Pan. Transparent Ultramicroelectrodes for Studying Interfacial Charge-Transfer Kinetics of Photoelectrochemical Water Oxidation at TiO2 Nanorods with Scanning Electrochemical Microscopy. Analytical Chemistry 2021, 93 (48) , 15886-15896. https://doi.org/10.1021/acs.analchem.1c02598
- Areen Sherryna, Muhammad Tahir. Role of Ti3C2 MXene as Prominent Schottky Barriers in Driving Hydrogen Production through Photoinduced Water Splitting: A Comprehensive Review. ACS Applied Energy Materials 2021, 4 (11) , 11982-12006. https://doi.org/10.1021/acsaem.1c02241
- Yang Liu, Chensi Tang, Min Cheng, Ming Chen, Sha Chen, Lei Lei, Yashi Chen, Huan Yi, Yukui Fu, Ling Li. [email protected]–Organic Framework Composites as Effective Photocatalysts. ACS Catalysis 2021, 11 (21) , 13374-13396. https://doi.org/10.1021/acscatal.1c03866
- Hiromasa Nishikiori, Yosuke Kageshima, Nasrin Hooshmand, Mostafa A. El-Sayed, Katsuya Teshima. Observation of Excited State Proton Transfer between the Titania Surface and Dye Molecule by Time-Resolved Fluorescence Spectroscopy. The Journal of Physical Chemistry C 2021, 125 (40) , 21958-21963. https://doi.org/10.1021/acs.jpcc.1c05843
- Mirabbos Hojamberdiev, J. Manuel Mora-Hernandez, Ronald Vargas, Akira Yamakata, Kunio Yubuta, Eva Maria Heppke, Leticia M. Torres-Martínez, Katsuya Teshima, Martin Lerch. Time-Retrenched Synthesis of BaTaO2N by Localizing an NH3 Delivery System for Visible-Light-Driven Photoelectrochemical Water Oxidation at Neutral pH: Solid-State Reaction or Flux Method?. ACS Applied Energy Materials 2021, 4 (9) , 9315-9327. https://doi.org/10.1021/acsaem.1c01539
- Kai Han, Diane M. Haiber, Julius Knöppel, Caroline Lievens, Serhiy Cherevko, Peter Crozier, Guido Mul, Bastian Mei. CrOx-Mediated Performance Enhancement of Ni/NiO-Mg:SrTiO3 in Photocatalytic Water Splitting. ACS Catalysis 2021, 11 (17) , 11049-11058. https://doi.org/10.1021/acscatal.1c03104
- Yosuke Kageshima, Yui Gomyo, Hikaru Matsuoka, Hiroto Inuzuka, Hajime Suzuki, Ryu Abe, Katsuya Teshima, Kazunari Domen, Hiromasa Nishikiori. Z-Scheme Overall Water Splitting Using ZnxCd1–xSe Particles Coated with Metal Cyanoferrates as Hydrogen Evolution Photocatalysts. ACS Catalysis 2021, 11 (13) , 8004-8014. https://doi.org/10.1021/acscatal.1c01187
- Leo Diehl, Douglas H. Fabini, Nella M. Vargas-Barbosa, Alberto Jiménez-Solano, Theresa Block, Viola Duppel, Igor Moudrakovski, Kathrin Küster, Rainer Pöttgen, Bettina V. Lotsch. Interplay between Valence Band Tuning and Redox Stability in SnTiO3: Implications for Directed Design of Photocatalysts. Chemistry of Materials 2021, 33 (8) , 2824-2836. https://doi.org/10.1021/acs.chemmater.0c04886
- Yosuke Kageshima, Sota Shiga, Tatsuki Ode, Fumiaki Takagi, Hiromasa Shiiba, Myo Than Htay, Yoshio Hashimoto, Katsuya Teshima, Kazunari Domen, Hiromasa Nishikiori. Photocatalytic and Photoelectrochemical Hydrogen Evolution from Water over Cu2SnxGe1–xS3 Particles. Journal of the American Chemical Society 2021, 143 (15) , 5698-5708. https://doi.org/10.1021/jacs.0c12140
- Yudai Kawase, Tomohiro Higashi, Masao Katayama, Kazunari Domen, Kazuhiro Takanabe. Maximizing Oxygen Evolution Performance on a Transparent NiFeOx/Ta3N5 Photoelectrode Fabricated on an Insulator. ACS Applied Materials & Interfaces 2021, 13 (14) , 16317-16325. https://doi.org/10.1021/acsami.1c00826
- Akinobu Miyoshi, Akihide Kuwabara, Kazuhiko Maeda. Effects of Nitrogen/Fluorine Codoping on Photocatalytic Rutile TiO2 Crystal Studied by First-Principles Calculations. Inorganic Chemistry 2021, 60 (4) , 2381-2389. https://doi.org/10.1021/acs.inorgchem.0c03262
- Yanuo Shi, Luyao Wang, Ziyu Wang, Giovanni Vinai, Luca Braglia, Piero Torelli, Carmela Aruta, Enrico Traversa, Weimin Liu, Nan Yang. Defect Engineering for Tuning the Photoresponse of Ceria-Based Solid Oxide Photoelectrochemical Cells. ACS Applied Materials & Interfaces 2021, 13 (1) , 541-551. https://doi.org/10.1021/acsami.0c17921
- Alberto Piccioni, Daniele Catone, Alessandra Paladini, Patrick O’Keeffe, Alex Boschi, Alessandro Kovtun, Maria Katsikini, Federico Boscherini, Luca Pasquini. Ultrafast Charge Carrier Dynamics in Vanadium-Modified TiO2 Thin Films and Its Relation to Their Photoelectrocatalytic Efficiency for Water Splitting. The Journal of Physical Chemistry C 2020, 124 (49) , 26572-26582. https://doi.org/10.1021/acs.jpcc.0c06790
- Run-Dong Zhao, Yi-Man Zhang, Qing-Lu Liu, Zong-Yan Zhao. Effects of the Preparation Process on the Photocatalytic Performance of Delafossite CuCrO2. Inorganic Chemistry 2020, 59 (22) , 16679-16689. https://doi.org/10.1021/acs.inorgchem.0c02678
- L. Piccolo, P. Afanasiev, F. Morfin, T. Len, C. Dessal, J. L. Rousset, M. Aouine, F. Bourgain, A. Aguilar-Tapia, O. Proux, Y. Chen, L. Soler, J. Llorca. Operando X-ray Absorption Spectroscopy Investigation of Photocatalytic Hydrogen Evolution over Ultradispersed Pt/TiO2 Catalysts. ACS Catalysis 2020, 10 (21) , 12696-12705. https://doi.org/10.1021/acscatal.0c03464
- Danila Vasilchenko, Polina Topchiyan, Alphiya Tsygankova, Tatyana Asanova, Boris Kolesov, Andrey Bukhtiyarov, Anna Kurenkova, Ekaterina Kozlova. Photoinduced Deposition of Platinum from (Bu4N)2[Pt(NO3)6] for a Low Pt-Loading Pt/TiO2 Hydrogen Photogeneration Catalyst. ACS Applied Materials & Interfaces 2020, 12 (43) , 48631-48641. https://doi.org/10.1021/acsami.0c14361
- Ananth Govind Rajan, John Mark P. Martirez, Emily A. Carter. Why Do We Use the Materials and Operating Conditions We Use for Heterogeneous (Photo)Electrochemical Water Splitting?. ACS Catalysis 2020, 10 (19) , 11177-11234. https://doi.org/10.1021/acscatal.0c01862
- Kang Rui Garrick Lim, Albertus D. Handoko, Srinivasa Kartik Nemani, Brian Wyatt, Hai-Ying Jiang, Junwang Tang, Babak Anasori, Zhi Wei Seh. Rational Design of Two-Dimensional Transition Metal Carbide/Nitride (MXene) Hybrids and Nanocomposites for Catalytic Energy Storage and Conversion. ACS Nano 2020, 14 (9) , 10834-10864. https://doi.org/10.1021/acsnano.0c05482
- Divya Priyadarshani, Pradipkumar Leuaa, Rajan Maurya, Anil Kottantharayil, Manoj Neergat. Semiconductor-to-Metal-like Behavior of Si with Dopant Concentration—An Electrochemical Investigation and Illustration with Surface Hydride Formation and Hydrogen Evolution Reaction. The Journal of Physical Chemistry C 2020, 124 (37) , 19990-19999. https://doi.org/10.1021/acs.jpcc.0c05616
- Ashish Kumar, Ajay Kumar, Venkata Krishnan. Perovskite Oxide Based Materials for Energy and Environment-Oriented Photocatalysis. ACS Catalysis 2020, 10 (17) , 10253-10315. https://doi.org/10.1021/acscatal.0c02947
- Ton Nu Quynh Trang, Nguyen Dang Nam, Le Thi Ngoc Tu, Hau Pham Quoc, Tran Van Man, Van Thi Thanh Ho, Vu Thi Hanh Thu. In Situ Spatial Charge Separation of an [email protected] Multiphase Photosystem toward Highly Efficient Photocatalytic Performance of Hydrogen Production. The Journal of Physical Chemistry C 2020, 124 (31) , 16961-16974. https://doi.org/10.1021/acs.jpcc.0c03590
- Riddhiman Medhi, Maria D. Marquez, T. Randall Lee. Visible-Light-Active Doped Metal Oxide Nanoparticles: Review of their Synthesis, Properties, and Applications. ACS Applied Nano Materials 2020, 3 (7) , 6156-6185. https://doi.org/10.1021/acsanm.0c01035
- Amgad R. Rezk, Heba Ahmed, Tarra L. Brain, Jasmine O. Castro, Ming K. Tan, Julien Langley, Nicholas Cox, Joydip Mondal, Wu Li, Muthupandian Ashokkumar, Leslie Y. Yeo. Free Radical Generation from High-Frequency Electromechanical Dissociation of Pure Water. The Journal of Physical Chemistry Letters 2020, 11 (12) , 4655-4661. https://doi.org/10.1021/acs.jpclett.0c01227
- Yunhong Pi, Xuanyu Feng, Yang Song, Ziwan Xu, Zhong Li, Wenbin Lin. Metal–Organic Frameworks Integrate Cu Photosensitizers and Secondary Building Unit-Supported Fe Catalysts for Photocatalytic Hydrogen Evolution. Journal of the American Chemical Society 2020, 142 (23) , 10302-10307. https://doi.org/10.1021/jacs.0c03906
- Ángel Morales-García, Rosendo Valero, Francesc Illas. Morphology of TiO2 Nanoparticles as a Fingerprint for the Transient Absorption Spectra: Implications for Photocatalysis. The Journal of Physical Chemistry C 2020, 124 (22) , 11819-11824. https://doi.org/10.1021/acs.jpcc.0c02946
- Jiawei Sun, Weiwei Xia, Qian Zheng, Xianghua Zeng, Wei Liu, Gang Liu, Pengdi Wang. Increased Active Sites on Irregular Morphological α-Fe2O3 Nanorods for Enhanced Photoelectrochemical Performance. ACS Omega 2020, 5 (21) , 12339-12345. https://doi.org/10.1021/acsomega.0c01072
- Hajime Suzuki, Shohei Kanno, Masahiko Hada, Ryu Abe, Akinori Saeki. Exploring the Relationship between Effective Mass, Transient Photoconductivity, and Photocatalytic Activity of SrxPb1–xBiO2Cl (x = 0–1) Oxyhalides. Chemistry of Materials 2020, 32 (10) , 4166-4173. https://doi.org/10.1021/acs.chemmater.9b05366
- Xunfu Zhou, Yuxuan Fang, Xin Cai, Shengsen Zhang, Siyuan Yang, Hongqiang Wang, Xinhua Zhong, Yueping Fang. In Situ Photodeposited Construction of Pt–CdS/g-C3N4–MnOx Composite Photocatalyst for Efficient Visible-Light-Driven Overall Water Splitting. ACS Applied Materials & Interfaces 2020, 12 (18) , 20579-20588. https://doi.org/10.1021/acsami.0c04241
- Shuai Chen, Scott Prins, Aicheng Chen. Patterning of BiVO4 Surfaces and Monitoring of Localized Catalytic Activity Using Scanning Photoelectrochemical Microscopy. ACS Applied Materials & Interfaces 2020, 12 (15) , 18065-18073. https://doi.org/10.1021/acsami.9b22605
- Constantin A. Walenta, Carla Courtois, Sebastian L. Kollmannsberger, Moritz Eder, Martin Tschurl, Ueli Heiz. Surface Species in Photocatalytic Methanol Reforming on Pt/TiO2(110): Learning from Surface Science Experiments for Catalytically Relevant Conditions. ACS Catalysis 2020, 10 (7) , 4080-4091. https://doi.org/10.1021/acscatal.0c00260
- Warren Athol Thompson, Eva Sanchez Fernandez, M. Mercedes Maroto-Valer. Review and Analysis of CO2 Photoreduction Kinetics. ACS Sustainable Chemistry & Engineering 2020, 8 (12) , 4677-4692. https://doi.org/10.1021/acssuschemeng.9b06170
- Kamonchanok Roongraung, Surawut Chuangchote, Navadol Laosiripojana, Takashi Sagawa. Electrospun Ag-TiO2 Nanofibers for Photocatalytic Glucose Conversion to High-Value Chemicals. ACS Omega 2020, 5 (11) , 5862-5872. https://doi.org/10.1021/acsomega.9b04076
- Yi Huang, Cuibo Liu, Mengyang Li, Huizhi Li, Yongwang Li, Ren Su, Bin Zhang. Photoimmobilized Ni Clusters Boost Photodehydrogenative Coupling of Amines to Imines via Enhanced Hydrogen Evolution Kinetics. ACS Catalysis 2020, 10 (6) , 3904-3910. https://doi.org/10.1021/acscatal.0c00282
- Qian Wang, Kazunari Domen. Particulate Photocatalysts for Light-Driven Water Splitting: Mechanisms, Challenges, and Design Strategies. Chemical Reviews 2020, 120 (2) , 919-985. https://doi.org/10.1021/acs.chemrev.9b00201
- Deobrat Singh, Sudip Chakraborty, Rajeev Ahuja. Emergence of Si2BN Monolayer as Efficient HER Catalyst under Co-functionalization Influence. ACS Applied Energy Materials 2019, 2 (12) , 8441-8448. https://doi.org/10.1021/acsaem.9b01292
- Sabari Ghosh, Ankit Kumar Srivastava, Radha Govu, Ujjwal Pal, Samudranil Pal. A Diuranyl(VI) Complex and Its Application in Electrocatalytic and Photocatalytic Hydrogen Evolution from Neutral Aqueous Medium. Inorganic Chemistry 2019, 58 (21) , 14410-14419. https://doi.org/10.1021/acs.inorgchem.9b01726
- Lei Zhang, Xin Mao, Sri Kasi Matta, Yuantong Gu, Aijun Du. Two-Dimensional CuTe2X (X = Cl, Br, and I): Potential Photocatalysts for Water Splitting under the Visible/Infrared Light. The Journal of Physical Chemistry C 2019, 123 (42) , 25543-25548. https://doi.org/10.1021/acs.jpcc.9b06116
- Yong-Jun Yuan, Zhi-Kai Shen, Shixin Song, Jie Guan, Liang Bao, Lang Pei, Yibing Su, Shiting Wu, Wangfeng Bai, Zhen-Tao Yu, Zhenguo Ji, Zhigang Zou. Co–P Bonds as Atomic-Level Charge Transfer Channel To Boost Photocatalytic H2 Production of Co2P/Black Phosphorus Nanosheets Photocatalyst. ACS Catalysis 2019, 9 (9) , 7801-7807. https://doi.org/10.1021/acscatal.9b02274
- Jie Liu, Jingnan Zhang, Ding Wang, Deyuan Li, Jun Ke, Shaobin Wang, Shaomin Liu, Huining Xiao, Rujie Wang. Highly Dispersed NiCo2O4 Nanodots Decorated Three-Dimensional g-C3N4 for Enhanced Photocatalytic H2 Generation. ACS Sustainable Chemistry & Engineering 2019, 7 (14) , 12428-12438. https://doi.org/10.1021/acssuschemeng.9b01965
- Hajime Suzuki, Masanobu Higashi, Hironobu Kunioku, Ryu Abe, Akinori Saeki. Photoconductivity–Lifetime Product Correlates Well with the Photocatalytic Activity of Oxyhalides Bi4TaO8Cl and PbBiO2Cl: An Approach to Boost Their O2 Evolution Rates. ACS Energy Letters 2019, 4 (7) , 1572-1578. https://doi.org/10.1021/acsenergylett.9b00793
- David S. D. Gunn, Jonathan M. Skelton, Lee A. Burton, Sebastian Metz, Stephen C. Parker. Thermodynamics, Electronic Structure, and Vibrational Properties of Snn(S1–xSex)m Solid Solutions for Energy Applications. Chemistry of Materials 2019, 31 (10) , 3672-3685. https://doi.org/10.1021/acs.chemmater.9b00362
- Amal BaQais, Nina Tymińska, Tangui Le Bahers, Kazuhiro Takanabe. Optoelectronic Structure and Photocatalytic Applications of Na(Bi,La)S2 Solid Solutions with Tunable Band Gaps. Chemistry of Materials 2019, 31 (9) , 3211-3220. https://doi.org/10.1021/acs.chemmater.9b00031
- Mamta Devi Sharma, Chavi Mahala, Mrinmoyee Basu. Shape-Controlled Hematite: An Efficient Photoanode for Photoelectrochemical Water Splitting. Industrial & Engineering Chemistry Research 2019, 58 (17) , 7200-7208. https://doi.org/10.1021/acs.iecr.9b00739
- Kento Yamada, Hajime Suzuki, Ryu Abe, Akinori Saeki. Complex Photoconductivity Reveals How the Nonstoichiometric Sr/Ti Affects the Charge Dynamics of a SrTiO3 Photocatalyst. The Journal of Physical Chemistry Letters 2019, 10 (8) , 1986-1991. https://doi.org/10.1021/acs.jpclett.9b00880
- Yu Bai, Yueer Zhou, Jing Zhang, Xuebing Chen, Yonghui Zhang, Jifa Liu, Jian Wang, Fangfang Wang, Changdong Chen, Chun Li, Rengui Li, Can Li. Homophase Junction for Promoting Spatial Charge Separation in Photocatalytic Water Splitting. ACS Catalysis 2019, 9 (4) , 3242-3252. https://doi.org/10.1021/acscatal.8b05050
- Ossama Elbanna, Mingshan Zhu, Mamoru Fujitsuka, Tetsuro Majima. Black Phosphorus Sensitized TiO2 Mesocrystal Photocatalyst for Hydrogen Evolution with Visible and Near-Infrared Light Irradiation. ACS Catalysis 2019, 9 (4) , 3618-3626. https://doi.org/10.1021/acscatal.8b05081
- Ying Wang, Shaoqi Zhan, Mårten S. G. Ahlquist. Nucleophilic Attack by OH2 or OH–: A Detailed Investigation on pH-Dependent Performance of a Ru Catalyst. Organometallics 2019, 38 (6) , 1264-1268. https://doi.org/10.1021/acs.organomet.8b00544
- Junsang Cho, Aaron Sheng, Nuwanthi Suwandaratne, Linda Wangoh, Justin L. Andrews, Peihong Zhang, Louis F. J. Piper, David F. Watson, Sarbajit Banerjee. The Middle Road Less Taken: Electronic-Structure-Inspired Design of Hybrid Photocatalytic Platforms for Solar Fuel Generation. Accounts of Chemical Research 2019, 52 (3) , 645-655. https://doi.org/10.1021/acs.accounts.8b00378
- Deqian Zeng, Ting Zhou, Wee-Jun Ong, Mingda Wu, Xiaoguang Duan, Wanjie Xu, Yuanzhi Chen, Yi-An Zhu, Dong-Liang Peng. Sub-5 nm Ultra-Fine FeP Nanodots as Efficient Co-Catalysts Modified Porous g-C3N4 for Precious-Metal-Free Photocatalytic Hydrogen Evolution under Visible Light. ACS Applied Materials & Interfaces 2019, 11 (6) , 5651-5660. https://doi.org/10.1021/acsami.8b20958
- Yosuke Kageshima, Tsutomu Minegishi, Sho Sugisaki, Yosuke Goto, Hiroyuki Kaneko, Mamiko Nakabayashi, Naoya Shibata, Kazunari Domen. Surface Protective and Catalytic Layer Consisting of RuO2 and Pt for Stable Production of Methylcyclohexane Using Solar Energy. ACS Applied Materials & Interfaces 2018, 10 (51) , 44396-44402. https://doi.org/10.1021/acsami.8b14814
- Xiaogang Yang, Dunwei Wang. Photocatalysis: From Fundamental Principles to Materials and Applications. ACS Applied Energy Materials 2018, 1 (12) , 6657-6693. https://doi.org/10.1021/acsaem.8b01345
- Justin L. Andrews, Junsang Cho, Linda Wangoh, Nuwanthi Suwandaratne, Aaron Sheng, Saurabh Chauhan, Kelly Nieto, Alec Mohr, Karthika J. Kadassery, Melissa R. Popeil, Pardeep K. Thakur, Matthew Sfeir, David C. Lacy, Tien-Lin Lee, Peihong Zhang, David F. Watson, Louis F. J. Piper, Sarbajit Banerjee. Hole Extraction by Design in Photocatalytic Architectures Interfacing CdSe Quantum Dots with Topochemically Stabilized Tin Vanadium Oxide. Journal of the American Chemical Society 2018, 140 (49) , 17163-17174. https://doi.org/10.1021/jacs.8b09924
- Hamidreza Hajiyani, Rossitza Pentcheva. Surface Termination and Composition Control of Activity of the CoxNi1–xFe2O4(001) Surface for Water Oxidation: Insights from DFT+U Calculations. ACS Catalysis 2018, 8 (12) , 11773-11782. https://doi.org/10.1021/acscatal.8b00574
- Tae Hwa Jeon, Min Seok Koo, Hyejin Kim, Wonyong Choi. Dual-Functional Photocatalytic and Photoelectrocatalytic Systems for Energy- and Resource-Recovering Water Treatment. ACS Catalysis 2018, 8 (12) , 11542-11563. https://doi.org/10.1021/acscatal.8b03521
- Hwan Lee, D. Amaranatha Reddy, Yujin Kim, So Yeon Chun, Rory Ma, D. Praveen Kumar, Jae Kyu Song, Tae Kyu Kim. Drastic Improvement of 1D-CdS Solar-Driven Photocatalytic Hydrogen Evolution Rate by Integrating with NiFe Layered Double Hydroxide Nanosheets Synthesized by Liquid-Phase Pulsed-Laser Ablation. ACS Sustainable Chemistry & Engineering 2018, 6 (12) , 16734-16743. https://doi.org/10.1021/acssuschemeng.8b04000
- Dandan Cui, Liang Wang, Yi Du, Weichang Hao, Jun Chen. Photocatalytic Reduction on Bismuth-Based p-Block Semiconductors. ACS Sustainable Chemistry & Engineering 2018, 6 (12) , 15936-15953. https://doi.org/10.1021/acssuschemeng.8b04977
- Bastian Mei, Kai Han, Guido Mul. Driving Surface Redox Reactions in Heterogeneous Photocatalysis: The Active State of Illuminated Semiconductor-Supported Nanoparticles during Overall Water-Splitting. ACS Catalysis 2018, 8 (10) , 9154-9164. https://doi.org/10.1021/acscatal.8b02215
- Amitava Banerjee, Sudip Chakraborty, Naresh K. Jena, Rajeev Ahuja. Scrupulous Probing of Bifunctional Catalytic Activity of Borophene Monolayer: Mapping Reaction Coordinate with Charge Transfer. ACS Applied Energy Materials 2018, 1 (8) , 3571-3576. https://doi.org/10.1021/acsaem.8b00813
- Ghazal Salehi, Reza Abazari, Ali Reza Mahjoub. Visible-Light-Induced Graphitic–[email protected]–Aluminum Layered Double Hydroxide Nanocomposites with Enhanced Photocatalytic Activity for Removal of Dyes in Water. Inorganic Chemistry 2018, 57 (14) , 8681-8691. https://doi.org/10.1021/acs.inorgchem.8b01636
- Saher Hamid, Ralf Dillert, Detlef W. Bahnemann. Photocatalytic Reforming of Aqueous Acetic Acid into Molecular Hydrogen and Hydrocarbons over Co-catalyst-Loaded TiO2: Shifting the Product Distribution. The Journal of Physical Chemistry C 2018, 122 (24) , 12792-12809. https://doi.org/10.1021/acs.jpcc.8b02691
- Xiang Gao, Yuanjing Wen, Dan Qu, Li An, Shiliang Luan, Wenshuai Jiang, Xupeng Zong, Xingyuan Liu, Zaicheng Sun. Interference Effect of Alcohol on Nessler’s Reagent in Photocatalytic Nitrogen Fixation. ACS Sustainable Chemistry & Engineering 2018, 6 (4) , 5342-5348. https://doi.org/10.1021/acssuschemeng.8b00110
- Xiaoqing Yan, Mengyang Xia, Hanxuan Liu, Bin Zhang, Chunran Chang, Lianzhou Wang, Guidong Yang. An electron-hole rich dual-site nickel catalyst for efficient photocatalytic overall water splitting. Nature Communications 2023, 14 (1) https://doi.org/10.1038/s41467-023-37358-3
- Anqiang Jiang, Heng Guo, Shan Yu, Fengying Zhang, Tingyu Shuai, Yubin Ke, Peng Yang, Ying Zhou. Dual charge-accepting engineering modified AgIn5S8/CdS quantum dots for efficient photocatalytic hydrogen evolution overall H2S splitting. Applied Catalysis B: Environmental 2023, 332 , 122747. https://doi.org/10.1016/j.apcatb.2023.122747
- Shufang Chang, Li Shi, Jinxing Yu, Ran Wang, Xiaoxiang Xu, Gang Liu. Boosted Z-scheme photocatalytic overall water splitting with faceted Bi4TaO8Cl crystals as water oxidation photocatalyst. Applied Catalysis B: Environmental 2023, 328 , 122541. https://doi.org/10.1016/j.apcatb.2023.122541
- Driss Mazkad, Nour-eddine Lazar, Abdellah Benzaouak, Ali Moussadik, Mohamed El Habib Hitar, Noureddine Touach, Mohammed El Mahi, El Mostapha Lotfi. Photocatalytic properties insight of Sm-doped LiNbO3 in ferroelectric Li1− xNbSm1/3xO3 system. Journal of Environmental Chemical Engineering 2023, 11 (3) , 109732. https://doi.org/10.1016/j.jece.2023.109732
- Alberto Puga. Photocatalytic Hydrogen Production in the Context of Sustainable Energy. 2023, 1-18. https://doi.org/10.1002/9783527835423.ch1
- Alberto Puga. Photocatalytic Overall Water Splitting and Related Processes for Strategic Energy Storage into Hydrogen. 2023, 63-93. https://doi.org/10.1002/9783527835423.ch4
- Mariano Curti, Yamen AlSalka, Osama Al‐Madanat, Detlef W. Bahnemann. Isotopic Substitution to Unravel the Mechanisms of Photocatalytic Hydrogen Production. 2023, 35-61. https://doi.org/10.1002/9783527835423.ch3
- Kai Yu, Tianyang Zhang, Yingming Wang, Jie Wu, Hui Huang, Kui Yin, Fan Liao, Yang Liu, Zhenhui Kang. Anchoring Co3O4 on CdZnS to accelerate hole migration for highly stable photocatalytic overall water splitting. Applied Catalysis B: Environmental 2023, 324 , 122228. https://doi.org/10.1016/j.apcatb.2022.122228
- Guoan Lin, Xiaoqin Sun, Xiaoxiang Xu. Mg modified LaTiO2N with ameliorated photocarrier separation for solar water splitting. Applied Catalysis B: Environmental 2023, 324 , 122258. https://doi.org/10.1016/j.apcatb.2022.122258
- Zhiyun Long, Xiaohang Yang, Xuyang Huo, Xuanze Li, Qiuju Qi, Xingbo Bian, Qiyao Wang, Fengjian Yang, WeilunYu, Lei Jiang. Bioinspired Z-scheme In2O3/C3N4 heterojunctions with tunable nanorod lengths for enhanced photocatalytic hydrogen evolution. Chemical Engineering Journal 2023, 461 , 141893. https://doi.org/10.1016/j.cej.2023.141893
- Chitiphon Chuaicham, Yuto Noguchi, Sulakshana Shenoy, Kaiqian Shu, Jirawat Trakulmututa, Assadawoot Srikhaow, Karthikeyan Sekar, Keiko Sasaki. Simultaneous Photocatalytic Sugar Conversion and Hydrogen Production Using Pd Nanoparticles Decorated on Iron-Doped Hydroxyapatite. Catalysts 2023, 13 (4) , 675. https://doi.org/10.3390/catal13040675
- P. Velusamy, Xinghui Liu, M. Sathiya, Norah Salem Alsaiari, Fatimah Mohammed Alzahrani, M. Tariq Nazir, Elangovan Elamurugu, M. Senthil Pandian, Fuchun Zhang. Investigate the suitability of g-C3N4 nanosheets ornamented with BiOI nanoflowers for photocatalytic dye degradation and PEC water splitting. Chemosphere 2023, 321 , 138007. https://doi.org/10.1016/j.chemosphere.2023.138007
- Xunfu Zhou, Meng Li, Pai Wang, Minfu Wu, Bei Jin, Jin Luo, Meifeng Chen, Xiaoqin Zhou, Yanning Zhang, Xiaosong Zhou. Synergistic effect of phosphorus doping and MoS2 co-catalysts on g-C3N4 photocatalysts for enhanced solar water splitting. Journal of Materials Science & Technology 2023, 120 https://doi.org/10.1016/j.jmst.2023.02.041
- Xiang Xie, Peng Ge, Ruiting Xue, Hongfei Lv, Wenhua Xue, Enzhou Liu. Enhanced photocatalytic H2 evolution and anti-photocorrosion of sulfide photocatalyst by improving surface reaction: A review. International Journal of Hydrogen Energy 2023, 417 https://doi.org/10.1016/j.ijhydene.2023.03.193
Abstract
Figure 1
Figure 1. Schematic image of the photocatalytic water splitting process. The gear with the number indicates the order of the photocatalytic process to be successful for overall water splitting. For a detailed description, please refer to the text.
Figure 2
Figure 2. Parameters associated with photocatalysis. Overall water splitting is only successful for high efficiencies of all six gears depicted in the scheme. The different time scales of the reactions are also displayed.
Figure 3
Figure 3. Bandgap structure of oxide and oxynitride semiconductors for photoelectrochemical applications. Contribution of metal cation and oxygen anion states to the conduction and valence bands. The bandgap energy (red for n-type, black for p-type) is shown with respect to the reversible hydrogen electrode and the water redox energy levels (assuming Nernstian behavior four the band-edge energies with respect to electrolyte pH). Reprinted with permission from ref 45. Copyright 2016 Macmillan Publishers Limited.
Figure 4
Figure 4. (A) Hole and (B) electron lifetimes in heavily doped n-type and p-type silicon, respectively. Reprinted with permission from ref 75. Copyright 1991 Institute of Electrical and Electronics Engineers.
Figure 5
Figure 5. Rough estimation of the ratios of the numbers between the active surface sites (assuming ∼4 nm–2 hydroxylated surface as maximum) (82) to the bulk carrier. The cubic particle of 100 nm diameter is used as an example.
Figure 6
Figure 6. (A) Barrier height versus electronegativity of metals deposited on Si, GaSe, and SiO2. (B) Index of interface behavior S as a function of the electronegativity difference of the semiconductors. Reprinted with permission from ref 89. Copyright 2006 John Wiley & Sons, Inc.
Figure 7
Figure 7. (A) Geometric model schemes using n-type semiconductor with HER catalyst decoration with the boundary conditions and the assumptions used for the simulations. (B) Potential gradients under the HER catalyst (red dotted line in A) at different donor concentrations, carrier mobility, and carrier lifetime. The x-direction represents the depth from surface (left) into the bulk (right) of the semiconductor. An ohmic junction was assumed for the HER catalyst in contact with the semiconductor, whereas a Schottky contact was assumed to calculate the electrolyte interface. The potential difference between HER site and OER site is assumed to be 1.53 eV. Reprinted with permission from ref 107. Copyright 2016 Royal Society of Chemistry.
References
ARTICLE SECTIONSThis article references 190 other publications.
- 1Electrochemical Methods, 2nd ed.; Bard, A. J., Faulkner, L. R., Eds.; John Wiley & Sons, Inc.: Hoboken, NJ, 2001; pp 736– 768.Google ScholarThere is no corresponding record for this reference.
- 2Kraeutler, B.; Bard, A. J. J. Am. Chem. Soc. 1978, 100, 2239– 2240 DOI: 10.1021/ja00475a049
- 3Calvo, E. J. In Electrode Kinetics: Principles and Methodology, Bamford, C. H.; Tipper, C. F. H.; Compton, R. G., Eds.; Elsevier: Amsterdam, 1986; Vol. 26, pp 1– 74.Google ScholarThere is no corresponding record for this reference.
- 4Shaner, M. R.; Atwater, H. A.; Lewis, N. S.; McFarland, E. W. Energy Environ. Sci. 2016, 9, 2354– 2371 DOI: 10.1039/C5EE02573G
- 5Lewis, N. S. Science 2016, 351, Article No. aad1920 DOI: 10.1126/science.aad1920
- 6Nakamura, A.; Ota, Y.; Koike, K.; Hidaka, Y.; Nishioka, K.; Sugiyama, M.; Fujii, K. Appl. Phys. Express 2015, 8, 107101 DOI: 10.7567/APEX.8.107101[Crossref], [CAS], Google Scholar6https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xis1Kit74%253D&md5=9574eff0586bc41a2e474cb18e005650A 24.4% solar to hydrogen energy conversion efficiency by combining concentrator photovoltaic modules and electrochemical cellsNakamura, Akihiro; Ota, Yasuyuki; Koike, Kayo; Hidaka, Yoshihide; Nishioka, Kensuke; Sugiyama, Masakazu; Fujii, KatsushiApplied Physics Express (2015), 8 (10), 107101/1-107101/4CODEN: APEPC4; ISSN:1882-0786. (IOP Publishing Ltd.)The highest efficiency of 24.4% for the solar-to-hydrogen (STH) energy conversion was obtained in an outdoor field test by combining concentrator photovoltaic (CPV) modules with InGaP/GaAs/Ge three-junction cells and polymer-electrolyte electrochem. (EC) cells. The high efficiency was obtained by using the high-efficiency CPV modules (∼31% under the present operation conditions) and the direct connection between the CPV modules and the EC cells with an almost optimized no. of elements in series. The STH efficiency bottleneck was clarified to be the efficiency of the CPV modules, the over-potential of the EC cells, and matching of the operation point to the maximal-power point of the CPV modules.
- 7Khaselev, O.; Turner, J. A. Science 1998, 280, 425– 427 DOI: 10.1126/science.280.5362.425
- 8Nocera, D. G. Acc. Chem. Res. 2012, 45, 767– 776 DOI: 10.1021/ar2003013[ACS Full Text], [CAS], Google Scholar8https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XltVylu7k%253D&md5=c7ae917b44e8c4be8a38bf2be8f384d0The Artificial LeafNocera, Daniel G.Accounts of Chemical Research (2012), 45 (5), 767-776CODEN: ACHRE4; ISSN:0001-4842. (American Chemical Society)A review. To convert the energy of sunlight into chem. energy, the leaf splits H2O via the photosynthetic process to produce mol. O and H, which is in a form of sepd. protons and electrons. The primary steps of natural photosynthesis involve the absorption of sunlight and its conversion into spatially sepd. electron-hole pairs. The holes of this wireless current are captured by the O evolving complex (OEC) of photosystem II (PSII) to oxidize H2O to O. The electrons and protons produced as a byproduct of the OEC reaction are captured by ferrodoxin of photosystem I. With the aid of ferrodoxin-NADP+ reductase, they are used to produce H as NADPH. For a synthetic material to realize the solar energy conversion function of the leaf, the light-absorbing material must capture a solar photon to generate a wireless current that is harnessed by catalysts, which drive the 4 electron/hole fuel-forming H2O-splitting reaction under benign conditions and under 1 sun (100 mW/cm2) illumination. This Account describes the construction of an artificial leaf comprising earth-abundant elements by interfacing a triple junction, amorphous Si photovoltaic with H- and O-evolving catalysts made from a ternary alloy (NiMoZn) and a Co-phosphate cluster (Co-OEC), resp. The latter captures the structural and functional attributes of the PSII-OEC. Similar to the PSII-OEC, the Co-OEC self-assembles upon oxidn. of an earth-abundant metal ion from 2+ to 3+, may operate in natural H2O at room temp., and is self-healing. The Co-OEC also activates H2O by a p-coupled electron transfer mechanism in which the Co-OEC is increased by 4 hole equiv. akin to the S-state pumping of the Kok cycle of PSII. X-ray absorption spectroscopy studies established that the Co-OEC is a structural relative of Mn3CaO4-Mn cubane of the PSII-OEC, where Co replaces Mn and the cubane is extended in a corner-sharing, head-to-tail dimer. The ability to perform the O-evolving reaction in H2O at neutral or near-neutral conditions has several consequences for the construction of the artificial leaf. The NiMoZn alloy may be used in place of Pt to generate H. To stabilize Si in H2O, its surface is coated with a conducting metal oxide onto which the Co-OEC may be deposited. The net result is that immersing a triple-junction Si wafer coated with NiMoZn and Co-OEC in H2O and holding it up to sunlight can effect direct solar energy conversion via H2O splitting. By constructing a simple, stand-alone device composed of earth-abundant materials, the artificial leaf provides a means for an inexpensive and highly distributed solar-to-fuels system that employs low-cost systems engineering and manufg. Through this type of system, solar energy can become a viable energy supply to those in the non-legacy world.
- 9Sun, K.; Saadi, F. H.; Lichterman, M. F.; Hale, W. G.; Wang, H.-P.; Zhou, X.; Plymale, N. T.; Omelchenko, S. T.; He, J.-H; Papadantonakis, K. M.; Brunschwig, B. S.; Lewis, N. S. Proc. Natl. Acad. Sci. U.S.A. 2015, 112, 3612– 3617 DOI: 10.1073/pnas.1423034112
- 10Kageshima, Y.; Shinagawa, T.; Kuwata, T.; Nakata, J.; Minegishi, T.; Takanabe, K.; Domen, K. Sci. Rep. 2016, 6, 24633 DOI: 10.1038/srep24633[Crossref], [PubMed], [CAS], Google Scholar10https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xmt1ens7k%253D&md5=2f2a12e88ba48d056a9ee2d5e2ea1bd7A miniature solar device for overall water splitting consisting of series-connected spherical silicon solar cellsKageshima, Yosuke; Shinagawa, Tatsuya; Kuwata, Takaaki; Nakata, Josuke; Minegishi, Tsutomu; Takanabe, Kazuhiro; Domen, KazunariScientific Reports (2016), 6 (), 24633CODEN: SRCEC3; ISSN:2045-2322. (Nature Publishing Group)A novel "photovoltaics (PV) + electrolyzer" concept is presented using a simple, small, and completely stand-alone non-biased device for solar-driven overall water splitting. Three or four spherical-shaped p-n junction silicon balls were successfully connected in series, named "SPHELAR.". SPHELAR possessed small projected areas of 0.20 (3PVs) and 0.26 cm2 (4PVs) and exhibited working voltages sufficient for water electrolysis. Impacts of the configuration on the PV module performance were carefully analyzed, revealing that a drastic increase in the photocurrent (≈20%) was attained by the effective utilization of a reflective sheet. Sep. investigations on the electrocatalyst performance showed that non-noble metal based materials with reasonably small sizes (<0.80 cm2) exhibited substantial currents at the PV working voltage. By combining the observations of the PV characteristics, light management and electrocatalyst performance, solar-driven overall water splitting was readily achieved, reaching solar-to-hydrogen efficiencies of 7.4% (3PVs) and 6.4% (4PVs).
- 11Wang, Q.; Hisatomi, T.; Jia, Q.; Tokudome, H.; Zhong, M.; Wang, C.; Pan, Z.; Takata, T.; Nakabayashi, M.; Shibata, N.; Li, Y.; Sharp, I. D.; Kudo, A.; Yamada, T.; Domen, K. Nat. Mater. 2016, 15, 611– 615 DOI: 10.1038/nmat4589[Crossref], [PubMed], [CAS], Google Scholar11https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XktVamsb4%253D&md5=f8f0b57c75ad424efc58155932f3e0cfScalable water splitting on particulate photocatalyst sheets with a solar-to-hydrogen energy conversion efficiency exceeding 1%Wang, Qian; Hisatomi, Takashi; Jia, Qingxin; Tokudome, Hiromasa; Zhong, Miao; Wang, Chizhong; Pan, Zhenhua; Takata, Tsuyoshi; Nakabayashi, Mamiko; Shibata, Naoya; Li, Yanbo; Sharp, Ian D.; Kudo, Akihiko; Yamada, Taro; Domen, KazunariNature Materials (2016), 15 (6), 611-615CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)Photocatalytic H2O splitting using particulate semiconductors is a potentially scalable and economically feasible technol. for converting solar energy into H. Z-scheme systems based on 2-step photoexcitation of a H evolution photocatalyst (HEP) and an O evolution photocatalyst (OEP) are suited to harvesting of sunlight because semiconductors with either H2O redn. or oxidn. activity can be applied to the H2O splitting reaction. However, it is challenging to achieve efficient transfer of electrons between HEP and OEP particles. Here, the authors present photocatalyst sheets based on La- and Rh-codoped SrTiO3 (SrTiO3:La, Rh; ref. ) and Mo-doped BiVO4 (BiVO4:Mo) powders embedded into a Au layer. Enhancement of the electron relay by annealing and suppression of undesirable reactions through surface modification allow pure H2O (pH 6.8) splitting with a solar-to-H energy conversion efficiency of 1.1% and an apparent quantum yield of over 30% at 419 nm. The photocatalyst sheet design enables efficient and scalable H2O splitting using particulate semiconductors.
- 12Osterloh, F. E. ACS Energy Lett. 2017, 2, 445– 453 DOI: 10.1021/acsenergylett.6b00665[ACS Full Text], [CAS], Google Scholar12https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtFKltL0%253D&md5=3811453d758dc57a3b3c5d86709271abPhotocatalysis versus Photosynthesis: A Sensitivity Analysis of Devices for Solar Energy Conversion and Chemical TransformationsOsterloh, Frank E.ACS Energy Letters (2017), 2 (2), 445-453CODEN: AELCCP; ISSN:2380-8195. (American Chemical Society)A review. The chem. literature often does not differentiate between photocatalytic (PC) and photosynthetic (PS) processes (including artificial photosynthesis) even though these reactions differ in their thermodn. Photocatalytic processes are thermodynamically downhill (ΔG < 0) and are merely accelerated by the catalyst, whereas photosynthetic processes are thermodynamically unfavorable (ΔG > 0) and require photochem. energy input to occur. The authors apply this differentiation to analyze the basic functions of PC and PS devices and to formulate design criteria for improved performance. As will be shown, the corresponding devices exhibit distinctly different sensitivities to their functional parameters. For example, under conditions of optimal light absorption, carrier lifetimes, and electrochem. rates, the performance of PCs is limited only by their surface area, while type 1 PS devices are limited by their carrier mobility and mass transport, and type 2 PS devices are limited by electrochem. charge-transfer selectivity. Strategies for the optimization of type 1 and 2 photosynthetic devices and photocatalysts are also discussed.
- 13Mills, A.; Wang, J. J. Photochem. Photobiol., A 1999, 127, 123– 134 DOI: 10.1016/S1010-6030(99)00143-4[Crossref], [CAS], Google Scholar13https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1MXmtlSlt7s%253D&md5=8729cdb8f5dbb14f328b805e248d06dbPhotobleaching of Methylene blue sensitized by TiO2: an ambiguous system?Mills, A.; Wang, J.Journal of Photochemistry and Photobiology, A: Chemistry (1999), 127 (1-3), 123-134CODEN: JPPCEJ; ISSN:1010-6030. (Elsevier Science S.A.)The photobleaching of Methylene blue (MB), sensitized by TiO2, in an aq. soln. is studied in the absence and presence of oxygen. In the absence of oxygen and in the presence of a sacrificial electron acceptor (SED), MB is photoreduced to its colorless leuco form, LMB, by the TiO2 photocatalyst. This photoredn. process is obsd. even if an SED is not present, indicating that MB itself can act as an SED. The oxidn. of LMB by oxygen to regenerate MB is significantly slower if the aq. soln. is acidified (0.01 mol-dm-3 HClO4) and, at low partial pressures, the rate of reaction depends directly upon the concn. of dissolved oxygen. The TiO2-sensitized photobleaching of MB is irreversible in an oxygen-satd. aq. soln., as expected, since the bleaching was due to an oxidative process. However, in an acidified soln. (0.01 mol-dm-3 HClO4), the photobleaching process, in an oxygen-satd. soln., generates LMB initially. The latter situation arises because, under acidic conditions, LMB reacts only very slowly with oxygen to form MB. The significance of these findings with respect to the popular use of photobleaching of MB as a demonstration of semiconductor photomineralization is discussed.
- 14Yan, X.; Ohno, T.; Nishijima, K.; Abe, R.; Ohtani, B. Chem. Phys. Lett. 2006, 429, 606– 610 DOI: 10.1016/j.cplett.2006.08.081
- 15Ohtani, B. Chem. Lett. 2008, 37, 216– 229 DOI: 10.1246/cl.2008.216
- 16Mills, A. Appl. Catal., B 2012, 128, 144– 149 DOI: 10.1016/j.apcatb.2012.01.019[Crossref], [CAS], Google Scholar16https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38Xhs1KjsL7N&md5=44dafaeea1a2b76b6af5521f1af7ca0fAn overview of the methylene blue ISO test for assessing the activities of photocatalytic filmsMills, AndrewApplied Catalysis, B: Environmental (2012), 128 (), 144-149CODEN: ACBEE3; ISSN:0926-3373. (Elsevier B.V.)The main features are described of the ISO published std.: 10678:2010, namely the Detn. of photocatalytic activity of surfaces in an aq. medium by degrdn. of methylene blue'. The main underlying assumptions of the std. are considered, namely: (i) dye purity, (ii) adsorption and pH, (iii) light source, (iv) stirring and diffusion, (v) reaction mechanism and (vi) kinetics. Possible sources of errors arising form these assumptions are identified and changes to the std.'s protocol suggested. The major suggested changes are: (i) a source of MB+ of known and proven on site high purity (>90%) should be used to make up the std. test soln., which should have a referenced absorbance, 0.74, at 665 nm; (ii) the conditioning soln. should be the same concn. as the std. test soln., (iii) the initial pH of the reaction soln. should lie in the range: 5.5-6.0; (iv) a BLB UVA light with a europium-doped strontium fluoroborate or borate phosphor should be used; (v) the reaction soln. should be vigorously and continuously stirred if possible; (vi) the soln. height should be the min. recommended value of 2 cm, and the photoreactor cylinder i.d., 4.7 cm; (vii) after the 3 h irradn. the reaction soln. should be left stirring overnight to check that no dye photoreductive bleaching has occurred. Application of most of these suggestions should improve considerably the std.'s reported current poor percentage errors for repeatability within a lab (9.2%) and reproducibility between labs (30.6%).
- 17Kisch, H. Angew. Chem., Int. Ed. 2013, 52, 812– 847 DOI: 10.1002/anie.201201200
- 18Buriak, J. M.; Kamat, P. V.; Schanze, K. S. ACS Appl. Mater. Interfaces 2014, 6, 11815– 11816 DOI: 10.1021/am504389z
- 19Buriak, J. M. Chem. Mater. 2014, 26, 2211– 2213 DOI: 10.1021/cm5010449
- 20Kisch, H.; Bahnemann, D. J. Phys. Chem. Lett. 2015, 6, 1907– 1910 DOI: 10.1021/acs.jpclett.5b00521[ACS Full Text], [CAS], Google Scholar20https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXnvFCks7k%253D&md5=855fb32d3777fd93518080635531fdcbBest Practice in Photocatalysis: Comparing Rates or Apparent Quantum Yields?Kisch, Horst; Bahnemann, DetlefJournal of Physical Chemistry Letters (2015), 6 (10), 1907-1910CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)There is no expanded citation for this reference.
- 21Coridan, R. H.; Nielander, A. C.; Francis, S. A.; McDowell, M. T.; Dix, V.; Chatman, S. M.; Lewis, N. S. Energy Environ. Sci. 2015, 8, 2886– 2901 DOI: 10.1039/C5EE00777A
- 22Buriak, J. M.; Jones, C. W.; Kamat, P. V.; Schanze, K. S.; Schatz, G. C.; Scholes, G. D.; Weiss, P. S. Chem. Mater. 2016, 28, 3525– 3526 DOI: 10.1021/acs.chemmater.6b01854
- 23Qureshi, M.; Takanabe, K. Chem. Mater. 2017, 29, 158– 167 DOI: 10.1021/acs.chemmater.6b02907
- 24Takanabe, K.; Domen, K. ChemCatChem 2012, 4, 1485– 1497 DOI: 10.1002/cctc.201200324
- 25Takanabe, K. Top. Curr. Chem. 2015, 371, 73– 103 DOI: 10.1007/128_2015_646
- 26Nozik, A. J. Annu. Rev. Phys. Chem. 1978, 29, 189– 222 DOI: 10.1146/annurev.pc.29.100178.001201
- 27Nosaka, Y.; Ishizuka, Y.; Miyama, H. Ber. Bunsenges. Phys. Chem. 1986, 90, 1199– 1204 DOI: 10.1002/bbpc.19860901216
- 28Memming, R. Top. Curr. Chem. 1988, 143, 79– 112 DOI: 10.1007/BFb0018072
- 29Hagfeldt, A.; Grätzel, M. Chem. Rev. 1995, 95, 49– 68 DOI: 10.1021/cr00033a003
- 30Photocatalysis Science and Technology; Kaneko, M.; Okura, I., Eds.; Kodansha-Springer: Tokyo-New York, 2002, : pp 1– 360.Google ScholarThere is no corresponding record for this reference.
- 31Domen, K. In Photocatalysis—Heterogeneous. Encyclopedia of Catalysis; Horvath, I. T., Ed., Wiley: Weinheim, 2002.Google ScholarThere is no corresponding record for this reference.
- 32Maeda, K.; Domen, K. J. Phys. Chem. C 2007, 111, 7851– 7861 DOI: 10.1021/jp070911w
- 33Kamat, P. V. J. Phys. Chem. C 2007, 111, 2834– 2860 DOI: 10.1021/jp066952u
- 34Osterloh, F. E. Chem. Mater. 2008, 20, 35– 54 DOI: 10.1021/cm7024203
- 35Kudo, A.; Miseki, Y. Chem. Soc. Rev. 2009, 38, 253– 278 DOI: 10.1039/B800489G[Crossref], [PubMed], [CAS], Google Scholar35https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXhsFWjtL3P&md5=21d808dac82a11a649988f31a9231941Heterogeneous photocatalyst materials for water splittingKudo, Akihiko; Miseki, YugoChemical Society Reviews (2009), 38 (1), 253-278CODEN: CSRVBR; ISSN:0306-0012. (Royal Society of Chemistry)This crit. review shows the basis of photocatalytic water splitting and exptl. points, and surveys heterogeneous photocatalyst materials for water splitting into H2 and O2, and H2 or O2 evolution from an aq. soln. contg. a sacrificial reagent. Many oxides consisting of metal cations with d0 and d10 configurations, metal (oxy)sulfide and metal (oxy)nitride photocatalysts have been reported, esp. during the latest decade. The fruitful photocatalyst library gives important information on factors affecting photocatalytic performances and design of new materials. Photocatalytic water splitting and H2 evolution using abundant compds. as electron donors are expected to contribute to construction of a clean and simple system for solar hydrogen prodn., and a soln. of global energy and environmental issues in the future (361 refs.).
- 36Inoue, Y. Energy Environ. Sci. 2009, 2, 364– 386 DOI: 10.1039/b816677n
- 37Walter, M. G.; Warren, E. L.; McKone, J. R.; Boettcher, S. W.; Mi, Q.; Santori, E. A.; Lewis, N. S. Chem. Rev. 2010, 110, 6446– 6473 DOI: 10.1021/cr1002326[ACS Full Text], [CAS], Google Scholar37https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXhtl2lsbvF&md5=e805b03c6896be7e34d8f64bfe299a87Solar Water Splitting CellsWalter, Michael G.; Warren, Emily L.; McKone, James R.; Boettcher, Shannon W.; Mi, Qixi; Santori, Elizabeth A.; Lewis, Nathan S.Chemical Reviews (Washington, DC, United States) (2010), 110 (11), 6446-6473CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)A review on the efforts to develop an efficient semiconductor-based photoelectrochem. water splitting device in which the only inputs are sunlight and water. The fundamental principles of photoinduced electron-transfer mechanisms at a semiconductor/liq. junction, and optimization of such processes, are summarized. A wide range of both p- and n-type semiconductor photoelectrode materials that have been studied for photoelectrochem. water splitting cells are then described. In addn., heterogeneous electrocatalysts used to facilitate the oxidn. and redn. reactions in electrochem. and in photoelectrochem. water splitting systems are reviewed. Finally, efforts to combine photoanode, photocathode, and photovoltaic-assisted coupled configurations in both single and dual band gap photoelectrolysis cells are examd. in terms of their solar-to-hydrogen efficiency, stability, and expected viability. Strategies to optimize solar-to-chem. energy-conversion efficiencies by optimization of light harvesting structured semiconductors, photoinduced electron transfer and transport, and surface catalysis are also described.
- 38Maeda, K.; Domen, K. J. Phys. Chem. Lett. 2010, 1, 2655– 2661 DOI: 10.1021/jz1007966[ACS Full Text], [CAS], Google Scholar38https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXhtVOmt7vE&md5=44835af453de055197cbf0715ddb73f7Photocatalytic Water Splitting: Recent Progress and Future ChallengesMaeda, Kazuhiko; Domen, KazunariJournal of Physical Chemistry Letters (2010), 1 (18), 2655-2661CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)A review. H2O splitting to form H and O using solar energy in the presence of semiconductor photocatalysts has long been studied as a potential means of clean, large-scale fuel prodn. In general, overall H2O splitting can be achieved when a photocatalyst is modified with a suitable cocatalyst. It is therefore important to develop both photocatalysts and cocatalysts. In the past 5 years, there was significant progress in H2O splitting photocatalysis, esp. in the development of cocatalysts and related phys. and materials chem. This work describes the state of the art and future challenges in photocatalytic H2O splitting, with a focus on the recent progress of own research.
- 39Hisatomi, T.; Minegishi, T.; Domen, K. Bull. Chem. Soc. Jpn. 2012, 85, 647– 655 DOI: 10.1246/bcsj.20120058
- 40Tong, H.; Ouyang, S.; Bi, Y.; Umezawa, N.; Oshikiri, M.; Ye, J. Adv. Mater. 2012, 24, 229– 251 DOI: 10.1002/adma.201102752
- 41Tachibana, Y.; Vayssieres, L.; Durrant, J. R. Nat. Photonics 2012, 6, 511– 518 DOI: 10.1038/nphoton.2012.175[Crossref], [CAS], Google Scholar41https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XhtFWjtLfN&md5=b98a6de15072b768fe7403a6e3f91012Artificial photosynthesis for solar water-splittingTachibana, Yasuhiro; Vayssieres, Lionel; Durrant, James R.Nature Photonics (2012), 6 (8), 511-518CODEN: NPAHBY; ISSN:1749-4885. (Nature Publishing Group)A review. Hydrogen generated from solar-driven water-splitting has the potential to be a clean, sustainable and abundant energy source. Inspired by natural photosynthesis, artificial solar water-splitting devices are now being designed and tested. Recent developments based on mol. and/or nanostructure designs have led to advances in our understanding of light-induced charge sepn. and subsequent catalytic water oxidn. and redn. reactions. Here we review some of the recent progress towards developing artificial photosynthetic devices, together with their analogies to biol. photosynthesis, including technologies that focus on the development of visible-light active hetero-nanostructures and require an understanding of the underlying interfacial carrier dynamics. Finally, we propose a vision for a future sustainable hydrogen fuel community based on artificial photosynthesis.
- 42Osterloh, F. E. Chem. Soc. Rev. 2013, 42, 2294– 2320 DOI: 10.1039/C2CS35266D
- 43Hisatomi, T.; Kubota, J.; Domen, K. Chem. Soc. Rev. 2014, 43, 7520– 7535 DOI: 10.1039/C3CS60378D
- 44Hisatomi, T.; Takanabe, K.; Domen, K. Catal. Lett. 2015, 145, 95– 108 DOI: 10.1007/s10562-014-1397-z
- 45Sivula, K.; van de Krol, R. Nat. Rev. Mater. 2016, 1, 15010 DOI: 10.1038/natrevmats.2015.10[Crossref], [CAS], Google Scholar45https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtVertrw%253D&md5=b12daf57f62282682a10cb4866778d93Semiconducting materials for photoelectrochemical energy conversionSivula, Kevin; van de Krol, RoelNature Reviews Materials (2016), 1 (2), 15010CODEN: NRMADL; ISSN:2058-8437. (Nature Publishing Group)To achieve a sustainable society with an energy mix primarily based on solar energy, we need methods of storing energy from sunlight as chem. fuels. Photoelectrochem. (PEC) devices offer the promise of solar fuel prodn. through artificial photosynthesis. Although the idea of a carbon-neutral energy economy powered by such 'artificial leaves' is intriguing, viable PEC energy conversion on a global scale requires the development of devices that are highly efficient, stable and simple in design. In this Review, recently developed semiconductor materials for the direct conversion of light into fuels are scrutinized with respect to their at. constitution, electronic structure and potential for practical performance as photoelectrodes in PEC cells. The processes of light absorption, charge sepn. and transport, and suitable energetics for energy conversion in PEC devices are emphasized. Both the advantageous and unfavorable aspects of multinary oxides, oxynitrides, chalcogenides, classic semiconductors and carbon-based semiconductors are critically considered on the basis of their exptl. demonstrated performance and predicted properties.
- 46Sato, N. Electrochemistry at Metal and Semiconductor Electrodes; Sato, N., Ed.; Elsevier, Amsterdam, 1998, : pp 1– 396.Google ScholarThere is no corresponding record for this reference.
- 47Modern Molecular Photochemistry of Organic Molecules; Turro, N. J.; Ramamurthy, V.; Scaiano, J. C., Eds.; University Science Books: Sausalito, CA, 2010; pp 1– 38.Google ScholarThere is no corresponding record for this reference.
- 48Polman, A.; Atwater, H. A. Nat. Mater. 2012, 11, 174– 177 DOI: 10.1038/nmat3263
- 49Osterloh, F. E. J. Phys. Chem. Lett. 2014, 5, 3354– 3359 DOI: 10.1021/jz501740n[ACS Full Text], [CAS], Google Scholar49https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhsFWjs7rM&md5=bf3df327c8119a0ec3bbe92fb081d0ceMaximum Theoretical Efficiency Limit of Photovoltaic Devices: Effect of Band Structure on Excited State EntropyOsterloh, Frank E.Journal of Physical Chemistry Letters (2014), 5 (19), 3354-3359CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)The Shockley-Queisser anal. provides a theor. limit for the max. energy conversion efficiency of single junction photovoltaic cells. But besides the semiconductor bandgap no other semiconductor properties are considered in the anal. Here, we show that the max. conversion efficiency is limited further by the excited state entropy of the semiconductors. The entropy loss can be estd. with the modified Sackur-Tetrode equation as a function of the curvature of the bands, the degeneracy of states near the band edges, the illumination intensity, the temp., and the band gap. The application of the second law of thermodn. to semiconductors provides a simple explanation for the obsd. high performance of Group IV, III-V, and II-VI materials with strong covalent bonding and for the lower efficiency of transition metal oxides contg. weakly interacting metal d orbitals. The model also predicts efficient energy conversion with quantum confined and mol. structures in the presence of a light harvesting mechanism.
- 50Omelchenko, S. T.; Tolstova, Y.; Atwater, H. A.; Lewis, N. S. ACS Energy Lett. 2017, 2, 431– 437 DOI: 10.1021/acsenergylett.6b00704[ACS Full Text], [CAS], Google Scholar50https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXht1eiurk%253D&md5=7915aa5154404136e5a187df4d26979bExcitonic Effects in Emerging Photovoltaic Materials: A Case Study in Cu2OOmelchenko, Stefan T.; Tolstova, Yulia; Atwater, Harry A.; Lewis, Nathan S.ACS Energy Letters (2017), 2 (2), 431-437CODEN: AELCCP; ISSN:2380-8195. (American Chemical Society)Excitonic effects account for a fundamental photoconversion and charge transport mechanism in Cu2O; hence, the universally adopted "free carrier" model substantially underestimates the photovoltaic efficiency for such devices. The quasi-equil. branching ratio between excitons and free carriers in Cu2O indicates that up to 28% of photogenerated carriers during photovoltaic operation are excitons. These large exciton densities were directly obsd. in photoluminescence and spectral response measurements. The results of a device physics simulation using a model that includes excitonic effects agree well with exptl. measured current-voltage characteristics of Cu2O-based photovoltaics. In the case of Cu2O, the free carrier model underestimates the efficiency of a Cu2O solar cell by as much as 1.9 abs. percent at room temp.
- 51National Renewable Energy Laboratory (NREL). Website: http://rredc.nrel.gov/solar/spectra/am1.5.Google ScholarThere is no corresponding record for this reference.
- 52Takanabe, K.; Domen, K. Green 2011, 1, 313– 322 DOI: 10.1515/GREEN.2011.030[Crossref], [CAS], Google Scholar52https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhtlOktbbO&md5=fbb3919c5dc8e60502156ee4d8e680b8Toward visible light response: overall water splitting using heterogeneous photocatalystsTakanabe, Kazuhiro; Domen, KazunariGreen (2011), 1 (5-6), 313-322CODEN: GREECH; ISSN:1869-876X. (Walter de Gruyter GmbH & Co. KG)A review. Extensive energy conversion of solar energy can only be achieved by large-scale collection of solar flux. The technol. that satisfies this requirement must be as simple as possible to reduce capital cost. Overall water splitting by powder-form photocatalysts directly produces a mixt. of H2 and O2 (chem. energy) in a single reactor, which does not require any complicated parabolic mirrors and electronic devices. Because of its simplicity and low capital cost, it has tremendous potential to become the major technol. of solar energy conversion. Development of highly efficient photocatalysts is desired. This review addresses why visible light responsive photocatalysts are essential to be developed. The state of the art for the photocatalysts for overall water splitting is briefly described. Moreover, various fundamental aspects for developing efficient photocatalysts, such as particle size of photocatalysts, cocatalysts, and reaction kinetics are discussed.
- 53Chen, Z.; Dinh, H. N.; Miller, E. Photoelectrochemical Water Splitting Standards, Experimental Methods, and Protocols; Springer: New York. 2013.
- 54Wemple, S. H.; Seman, J. A. Appl. Opt. 1973, 12, 2947– 2949 DOI: 10.1364/AO.12.002947[Crossref], [PubMed], [CAS], Google Scholar54https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC3c%252FnvFKgtQ%253D%253D&md5=2c3055a403dc01a449016f46e580961eOptical transmission through multilayered structuresWemple S H; Seman J AApplied optics (1973), 12 (12), 2947-9 ISSN:0003-6935.A simple procedure is presented for computing optical transmission through planar layered structures when interference effects can be neglected, but all multiple internal reflections are taken into account. Closed form solutions are given for a single absorbing layer on a nonabsorbing substrate and for two identical absorbing layers on either side of a nonabsorbing substrate.
- 55Di Giulio, M.; Micocci, G.; Rella, R.; Siciliano, P.; Tepore, A. Phys. Stat. Sol. a 1993, 136, K101– K104 DOI: 10.1002/pssa.2211360236
- 56Lodenquai, J. F. Sol. Energy 1994, 53, 209– 210 DOI: 10.1016/0038-092X(94)90483-9
- 57Absorption and Scattering of Light by Small Particles; Bohren, C. F.; Huffman, D. R., Eds.; Wiley-VCH, Weinheim, 2004, : pp 1– 476.Google ScholarThere is no corresponding record for this reference.
- 58Interpreting Diffuse Reflectance and Transmittance; Dahm, D. J.; Dahm, K. D., Eds.; NIR Publications: West Sussex, 2007, : pp 1– 286.Google ScholarThere is no corresponding record for this reference.
- 59Light Scattering by Particles in Water, Jonasz, M.; Fournier, G. R., Eds.; Academic Press: Oxford, 2007, : pp 145– 558.
- 60Bae, D.; Pedersen, T.; Seger, B.; Malizia, M.; Kuznetsov, A.; Hansen, O.; Chorkendorff, I.; Vesborg, P. C. K. Energy Environ. Sci. 2015, 8, 650– 660 DOI: 10.1039/C4EE03723E
- 61Le Bahers, T.; Rérat, M.; Sautet, P. J. Phys. Chem. C 2014, 118, 5997– 6008 DOI: 10.1021/jp409724c
- 62Green, M. A. Sol. Energy Mater. Sol. Cells 2008, 92, 1305– 1310 DOI: 10.1016/j.solmat.2008.06.009[Crossref], [CAS], Google Scholar62https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXhtVGksbbI&md5=767829b037109986978cb974d333b6ecSelf-consistent optical parameters of intrinsic silicon at 300 K including temperature coefficientsGreen, Martin A.Solar Energy Materials & Solar Cells (2008), 92 (11), 1305-1310CODEN: SEMCEQ; ISSN:0927-0248. (Elsevier B.V.)An updated tabulation is presented of the optical properties of intrinsic Si, of particular interest in solar cell calcns. Improved values of absorption coeff., refractive index and extinction coeff. at 300 K are tabulated over the 0.25-1.45 μm wavelength range at 0.01 μm intervals. The self-consistent tabulation was derived from Kramers-Kronig anal. of updated reflectance data deduced from the literature. The inclusion of normalized temp. coeffs. allows extrapolation over a wide temp. range, with accuracy similar to that of available exptl. data demonstrated over the -24° to 200° range.
- 63Franck, J.; Dymond, E. G. Trans. Faraday Soc. 1926, 21, 536– 542 DOI: 10.1039/tf9262100536
- 64Condon, E. Phys. Rev. 1926, 28, 1182– 1201 DOI: 10.1103/PhysRev.28.1182[Crossref], [CAS], Google Scholar64https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaB2sXovV2i&md5=e84d9659e9f76759fea0962e1208351eTheory of intensity distribution in band systemsCondon, EdwardPhysical Review (1926), 28 (), 1182-1201CODEN: PHRVAO; ISSN:0031-899X.There is no expanded citation for this reference.
- 65Džimbeg-Malčić, V.; Barbarić-Mikočević, Ž.; Itrić, K. Technical Gazette 2011, 18, 117Google ScholarThere is no corresponding record for this reference.
- 66Kurik, M. V. Phys. Stat. Sol. a 1971, 8, 9– 45 DOI: 10.1002/pssa.2210080102[Crossref], [CAS], Google Scholar66https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaE38XltF2qsw%253D%253D&md5=196c4cae2ef8ac8dc23e0bd87046e7b5Urbach ruleKurik, M. V.Physica Status Solidi A: Applied Research (1971), 8 (1), 9-45CODEN: PSSABA; ISSN:0031-8965.A review with 181 refs.
- 67Introduction to Solid State Physics, 8th ed.; Kittel, C., Ed.; Wiley: Weinheim, 2005, : pp 1– 704.Google ScholarThere is no corresponding record for this reference.
- 68Bastard, G.; Mendez, E. E.; Chang, L. L.; Esaki, L. Phys. Rev. B: Condens. Matter Mater. Phys. 1982, 26, 1974– 1979 DOI: 10.1103/PhysRevB.26.1974
- 69Semiconductors: Data Handbook, 3rd ed.; Madelung, O., Ed.; Springer: New York, 2004.
- 70Melissen, S.; Le Bahers, T.; Steinmann, S. N.; Sautet, P. J. Phys. Chem. C 2015, 119, 25188– 25196 DOI: 10.1021/acs.jpcc.5b07059
- 71Shockley, W.; Read, W. T., Jr. Phys. Rev. 1952, 87, 835– 842 DOI: 10.1103/PhysRev.87.835
- 72Hall, R. N. Phys. Rev. 1952, 87, 387 DOI: 10.1103/PhysRev.87.387
- 73Auger, P. Comptes Rendus de l'Académie des Sciences 1952, 177, 169Google ScholarThere is no corresponding record for this reference.
- 74Leng, W. H.; Barnes, P. R. F.; Juozapavicius, M.; O’Regan, B. C.; Durrant, J. R. J. Phys. Chem. Lett. 2010, 1, 967– 972 DOI: 10.1021/jz100051q[ACS Full Text], [CAS], Google Scholar74https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXisFGntb0%253D&md5=9a3f3d6cdc9a540b35da60329cd4a3b1Electron Diffusion Length in Mesoporous Nanocrystalline TiO2 Photoelectrodes during Water OxidationLeng, W. H.; Barnes, Piers R. F.; Juozapavicius, Mindaugas; O'Regan, Brian C.; Durrant, James R.Journal of Physical Chemistry Letters (2010), 1 (6), 967-972CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)A long electron diffusion length (L) relative to film thickness is required for efficient collection of charge in photoelectrodes. L was measured in a nanocryst., mesoporous TiO2 electrode during photochem. water splitting by two independent methods: (a) analyzing the ratio of incident photon conversion efficiency measured under back and front side illumination, and (b) analyzing transient photovoltage increase and decay measurements. These gave values of L that agreed (L = 8.5-12.5 μm between -0.15 and 0.1 V vs. Ag/AgCl 3M KCl at pH 2). The transient measurements were consistent with trap limited transport and recombination of electrons as previously obsd. in dye-sensitized solar cells. L of ∼10 μm is sufficient to collect sepd. electrons with minor electrolyte recombination losses in thin electrodes. However, charge collection may limit performance in doped mesoporous electrodes with weak visible light absorption where thicker films are required.
- 75Law, M. E.; Solley, E.; Liang, M.; Burk, D. E. IEEE Electron Device Lett. 1991, 12, 401– 403 DOI: 10.1109/55.119145
- 76Ito, H.; Furuta, T.; Ishibashi, T. Appl. Phys. Lett. 1991, 58, 2936– 2938 DOI: 10.1063/1.104727
- 77Cohen, R.; Lyahovitskaya, V.; Poles, E.; Liu, A.; Rosenwaks, Y. Appl. Phys. Lett. 1998, 73, 1400– 1402 DOI: 10.1063/1.122169
- 78Kuciauskas, D.; Kanevce, A.; Dippo, P.; Seyedmohammadi, S.; Malik, R. IEEE J. Photovoltaics 2015, 5, 366– 371 DOI: 10.1109/JPHOTOV.2014.2359738
- 79Rosenwaks, Y.; Shapira, Y.; Huppert, D. Phys. Rev. B: Condens. Matter Mater. Phys. 1992, 45, 9108– 9119 DOI: 10.1103/PhysRevB.45.9108
- 80Casey, H. C., Jr.; Miller, B. I.; Pinkas, E. J. Appl. Phys. 1973, 44, 1281– 1287 DOI: 10.1063/1.1662340[Crossref], [CAS], Google Scholar80https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaE3sXhtFKrsb8%253D&md5=91c7489236636ff1b9e1d0c98e70f1b7Variation of minority-carrier diffusion length with carrier concentration in gallium arsenide liquid-phase epitaxial layersCasey, H. C., Jr.; Miller, B. I.; Pinkas, E.Journal of Applied Physics (1973), 44 (3), 1281-7CODEN: JAPIAU; ISSN:0021-8979.Minority-carrier diffusion lengths in GaAs at 298°K were detd. in Ge-doped p-type layers and Sn-doped n-type layers by short-circuit photocurrent measurements. The layers were grown by liq.-phase epitaxy and utilized a 1-to 2-μ top layer fo A10.5Ga0.5As to eliminate surface recombination. Electron diffusion lengths Ln of 7-8 μ were obtained at concns. <1 × 1018 holes/cm3 with a decrease to 0.8μ at 1 × 1019 holes/ cm3. Hole diffusion lengths Lp of 2-4 μ were obtained at concns. <1 × 1018 electrons/cm3 with a decrease to 0.3 μ at 6 × 1018 electrons/cm3. The relatively const. diffusion length in p- and n-type layers below concns. of 1 × 1018 cm-3 is detd. by nonradiative recombination. At hole concns. >1 × 1018 cm-3, the radiative recombination contributes to the decrease in Lp. For the n-type layers, the rapid decrease in Lp above concns. of 1 × 1018 cm-3 results from an increase in nonradiative recombination at high donor concns.
- 81Lewis, N. S. Inorg. Chem. 2005, 44, 6900– 6911 DOI: 10.1021/ic051118p
- 82Zhuravlev, L. T. Colloids Surf., A 2000, 173, 1– 38 DOI: 10.1016/S0927-7757(00)00556-2[Crossref], [CAS], Google Scholar82https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3cXmsFKktLk%253D&md5=1168cec5b4a06a146674273c1781d0dbThe surface chemistry of amorphous silica. Zhuravlev modelZhuravlev, L. T.Colloids and Surfaces, A: Physicochemical and Engineering Aspects (2000), 173 (1-3), 1-38CODEN: CPEAEH; ISSN:0927-7757. (Elsevier Science B.V.)A review, with 347 refs. on the author's own results on the properties of amorphous SiO2 surface. In any description of the surface SiO2 the hydroxylation of the surface is of crit. importance. An anal. was made of the processes of dehydration (the removal of phys. adsorbed water), dehydroxylation (the removal of silanol groups from the SiO2 surface), and rehydroxylation (the restoration of the hydroxyl covering). For each of these processes a probable mechanism is suggested. The results of exptl. and theor. studies permitted to construct the original model (Zhuravlev model-1 and model-2) for describing the surface chem. of amorphous SiO2. The main advantage of this physico-chem. model lies in the possibility to det. the concn. and the distribution of different types of silanol and siloxane groups and to characterize the energetic heterogeneity of the SiO2 surface as a function of the pretreatment temp. of SiO2 samples. The model makes it possible to det. the kind of the chemisorption of water (rapid, weakly activated or slow, strongly activated) under the restoration of the hydroxyl covering and also to assess of OH groups inside the SiO2 skeleton. The magnitude of the silanol no., i.e., the no. of OH groups per unit surface area, αOH, when the surface is hydroxylated to the max. degree, is considered to be a physico-chem. const. This const. has a numerical value: αOH,AVER = 4.6 (least-squares method) and αOH,AVER = 4.9 OH nm-2 (arithmetical mean) and is known in literature as the Kiselev-Zhuravlev const. Adsorption and other surface properties per unit surface area of SiO2 are identical (except for very fine pores). On the basis of data published in the literature, this model was found to be useful in solving various applied and theor. problems in the field of adsorption, catalysis, chromatog., chem. modification, etc. The Brunauer-Emmett-Teller (BET) method is the correct method and gives the opportunity to measure the real phys. magnitude of the sp. surface area, SKr (by low temp. adsorption of Kr), for SiO2s and other oxide dispersed solids.
- 83Yoneyama, H. Crit. Rev. Solid State Mater. Sci. 1993, 18, 69– 111 DOI: 10.1080/10408439308243416[Crossref], [CAS], Google Scholar83https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK3sXksF2ntLs%253D&md5=6aa23e192921c2b07b976452a799d2bcElectrochemical aspects of light-induced heterogeneous reactions on semiconductorsYoneyama, HiroshiCritical Reviews in Solid State and Materials Sciences (1993), 18 (1), 69-111CODEN: CCRSDA; ISSN:1040-8436.Working mechanisms as photocatalyst of semiconductor particles suspended in soln. are reviewed with emphasis on photoelectrochem. aspects. Several techniques useful for the detn. of of electronic energy levels of the photocatalysts and for enhancing apparent photocatalytic activities are described, and their utilities are shown in the photodecompn. of water on various kinds of semiconductor particles. Studies on the detoxification of inorg. and org. wastes are collected as a promising application field of suspended semiconductor photocatalysts. Finally, significance of the use of quantized semiconductor particles as photocatalysts is discussed. 432 Refs.
- 84Fukasawa, Y.; Takanabe, K.; Shimojima, A.; Antonietti, M.; Domen, K.; Okubo, T. Chem. - Asian J. 2011, 6, 103– 109 DOI: 10.1002/asia.201000523[Crossref], [PubMed], [CAS], Google Scholar84https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXhs1WnsbvK&md5=5311851878d116d323cf76bb9809c697Synthesis of Ordered Porous Graphitic-C3N4 and Regularly Arranged Ta3N5 Nanoparticles by Using Self-Assembled Silica Nanospheres as a Primary TemplateFukasawa, Yuki; Takanabe, Kazuhiro; Shimojima, Atsushi; Antonietti, Markus; Domen, Kazunari; Okubo, TatsuyaChemistry - An Asian Journal (2011), 6 (1), 103-109CODEN: CAAJBI; ISSN:1861-4728. (Wiley-VCH Verlag GmbH & Co. KGaA)Uniform-sized silica nanospheres (SNSs) assembled into close-packed structures were used as a primary template for ordered porous graphitic carbon nitride (g-C3N4), which was subsequently used as a hard template to generate regularly arranged Ta3N5 nanoparticles of well-controlled size. Inverse opal g-C3N4 structures with the uniform pore size of 20-80 nm were synthesized by polymn. of cyanamide and subsequent dissoln. of the SNSs with an aq. HF soln. Back-filling of the C3N4 pores with tantalum precursors, followed by nitridation in an NH3 flow gave regularly arranged, cryst. Ta3N5 nanoparticles that are connected with each other. The surface areas of the Ta3N5 samples were as high as 60 m2 g-1, and their particle size was tunable from 20 to 80 nm, which reflects the pore size of g-C3N4. Polycryst. hollow nanoparticles of Ta3N5 were also obtained by infiltration of a reduced amt. of the tantalum source into the g-C3N4 template. An improved photocatalytic activity for H2 evolution on the assembly of the Ta3N5 nanoparticles under visible-light irradn. was attained as compared with that on a conventional Ta3N5 bulk material with low surface area.
- 85Gerischer, H. J. Phys. Chem. 1984, 88, 6096– 6097 DOI: 10.1021/j150669a007
- 86van der Pauw, L. J. Philips Res. Rep. 1958, 13, 1Google ScholarThere is no corresponding record for this reference.
- 87Heaney, M. B. The Measurement, Instrumentation and Sensors Handbook; CRC, Boca Raton, 2000.Google ScholarThere is no corresponding record for this reference.
- 88Tung, R. T. Appl. Phys. Rev. 2014, 1, 011304 DOI: 10.1063/1.4858400[Crossref], [CAS], Google Scholar88https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXlslSktbc%253D&md5=abc66bf33acc918d3481972fba7b1057The physics and chemistry of the Schottky barrier heightTung, Raymond T.Applied Physics Reviews (2014), 1 (1), 011304/1-011304/54CODEN: APRPG5; ISSN:1931-9401. (American Institute of Physics)A review. The formation of the Schottky barrier height (SBH) is a complex problem because of the dependence of the SBH on the at. structure of the metal-semiconductor (MS) interface. Existing models of the SBH are too simple to realistically treat the chem. exhibited at MS interfaces. This article points out, through examn. of available exptl. and theor. results, that a comprehensive, quantum-mechanics-based picture of SBH formation can already be constructed, although no simple equations can emerge, which are applicable for all MS interfaces. Important concepts and principles in physics and chem. that govern the formation of the SBH are described in detail, from which the exptl. and theor. results for individual MS interfaces can be understood. Strategies used and results obtained from recent investigations to systematically modify the SBH are also examd. from the perspective of the phys. and chem. principles of the MS interface. (c) 2014 American Institute of Physics.
- 89Physics of Semiconductor Devices, 3rd ed., Sze, S. M.; Ng, K. K., Eds.; Wiley: New York, 2006, : pp 134– 196.
- 90Kurtin, S.; McGill, T. C.; Mead, C. A. Phys. Rev. Lett. 1969, 22, 1433– 1436 DOI: 10.1103/PhysRevLett.22.1433
- 91Esposito, D. V.; Levin, I.; Moffat, T. P.; Talin, A. A. Nat. Mater. 2013, 12, 562– 568 DOI: 10.1038/nmat3626
- 92Ham, Y.; Minegishi, T.; Hisatomi, T.; Domen, K. Chem. Commun. 2016, 52, 5011– 5014 DOI: 10.1039/C6CC00497K[Crossref], [PubMed], [CAS], Google Scholar92https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XktVagsL0%253D&md5=71ba5de24187f84da96327a6c2fb04faA SrTiO3 photoanode prepared by the particle transfer method for oxygen evolution from water with high quantum efficienciesHam, Y.; Minegishi, T.; Hisatomi, T.; Domen, K.Chemical Communications (Cambridge, United Kingdom) (2016), 52 (28), 5011-5014CODEN: CHCOFS; ISSN:1359-7345. (Royal Society of Chemistry)A photoanode prepd. from flux-synthesized Al-doped SrTiO3 by the particle transfer method with a Ta contact layer exhibited a high IPCE of 69% at 320 nm. The photocatalytic activity of SrTiO3 particles was very sensitive to the synthesis method used to make the SrTiO3 particles, while its photoelectrochem. performance was not.
- 93Minegishi, T.; Nishimura, N.; Kubota, J.; Domen, K. Chem. Sci. 2013, 4, 1120– 1124 DOI: 10.1039/c2sc21845c[Crossref], [CAS], Google Scholar93https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhvFGqu7s%253D&md5=8d2d4c404c64c5a124a013e52a15ed5cPhotoelectrochemical properties of LaTiO2N electrodes prepared by particle transfer for sunlight-driven water splittingMinegishi, Tsutomu; Nishimura, Naoyuki; Kubota, Jun; Domen, KazunariChemical Science (2013), 4 (3), 1120-1124CODEN: CSHCCN; ISSN:2041-6520. (Royal Society of Chemistry)Photoelectrochem. (PEC) water splitting is a promising technol. for the prodn. of renewable solar hydrogen from water. A method of fabricating photoelectrodes from semiconductor particles for efficient water splitting was investigated using LaTiO2N as a test case. When a Ti conductor electrode with the back side covered with LaTiO2N particles was constructed by radio-frequency magnetron sputtering, the LaTiO2N photoelectrode generated a remarkable photoanodic current and evolved O2. The insertion of a Ta or Nb interlayer between the Ti conductor and the LaTiO2N particles enhanced the photocurrent. This method of fabricating photoelectrodes from semiconductor particles enables the use of simple powder semiconductors in solar energy conversion systems.
- 94Paracchino, A.; Laporte, V.; Sivula, K.; Grätzel, M.; Thimsen, E. Nat. Mater. 2011, 10, 456– 461 DOI: 10.1038/nmat3017
- 95Gerischer, H. Electrochim. Acta 1990, 35, 1677– 1699 DOI: 10.1016/0013-4686(90)87067-C
- 96Zhang, Z.; Yates, J. T., Jr. Chem. Rev. 2012, 112, 5520– 5551 DOI: 10.1021/cr3000626[ACS Full Text], [CAS], Google Scholar96https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XhtVWhtLrP&md5=d384840181ca78fc90506d35b75708cbBand bending in semiconductors: Chemical and physical consequences at surfaces and interfacesZhang, Zhen; Yates, John T., Jr.Chemical Reviews (Washington, DC, United States) (2012), 112 (10), 5520-5551CODEN: CHREAY; ISSN:0009-2665. (American Chemical Society)A review. Topics include band bending by metal/semiconductor contact; field-effect surface-state; adsorption. Space charge region at infinite metal/semiconductor interface and finite metal/semiconductor interface. Applications of the band bending concepts in ion diffusion in metal oxides and chemicurrent measurements. Measurements of band bending at semiconductor surfaces by photoelectron spectroscopy; photoluminescence spectroscopy surface photovoltage, scanning probe microscopy; and related methods; STM and STS; local barrier height measurement; ballistic electron emission microscopy; O2 photostimulated and electron-stimulated desorption. Effects of band bending on photochem. (size effect, elec. field effect, surface structure, gas adsorption).
- 97Grätzel, M. Nature 2001, 414, 338– 344 DOI: 10.1038/35104607[Crossref], [PubMed], [CAS], Google Scholar97https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3MXovFGitr8%253D&md5=2b0390f22ab99b07caec95b79454a7ebPhotoelectrochemical cellsGratzel, MichaelNature (London, United Kingdom) (2001), 414 (6861), 338-344CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)A review discussing the historical background, and present status and development prospects of new generation of photoelectrochem. cells.
- 98Chamousis, R. L.; Osterloh, F. E. Energy Environ. Sci. 2014, 7, 736– 743 DOI: 10.1039/C3EE42993H
- 99Butler, M. A.; Ginley, D. S. J. Electrochem. Soc. 1978, 125, 228– 232 DOI: 10.1149/1.2131419[Crossref], [CAS], Google Scholar99https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaE1cXhtFant78%253D&md5=00169bc0cf9ce0b7524d3a196ede9c61Prediction of flatband potentials at semiconductor-electrolyte interfaces from atomic electronegativitiesButler, M. A.; Ginley, D. S.Journal of the Electrochemical Society (1978), 125 (2), 228-32CODEN: JESOAN; ISSN:0013-4651.The electron affinities of several metal oxide semiconductors that are used as anodes in photoelectrochem. cells are calcd. using the at. electronegs. of the constituent atoms. These electron affinities are quant. related to the measured flatband potentials by considering the effects of specific adsorption of potential-detg. ions (for metal oxides used in photoelectrolysis, these are usually OH- and H+). Methods are discussed for detg.pH at which net adsorbed surface charge and thus potential across the Helmholtz layer is zero (point of zero zeta potential). This pH value is shown to correlate with the electronegativity of the metal oxides. The application of these ideas to other semiconductor-electrolyte systems is discussed.
- 100Green, M. A.; Hishikawa, Y.; Warta, W.; Dunlop, E. W.; Levi, D. H.; Hohl-Ebinger, J.; Ho-Baillie, A. W. H. Prog. Photovoltaics 2017, 25, 668– 676 DOI: 10.1002/pip.2909
- 101Turner, J. A. J. Chem. Educ. 1983, 60, 327– 329 DOI: 10.1021/ed060p327
- 102Lewis, N. S. J. Electrochem. Soc. 1984, 131, 2496– 2503 DOI: 10.1149/1.2115347
- 103Rossi, R. C.; Tan, M. X.; Lewis, N. S. Appl. Phys. Lett. 2000, 77, 2698– 2700 DOI: 10.1063/1.1319534
- 104Rossi, R. C.; Lewis, N. S. J. Phys. Chem. B 2001, 105, 12303– 12318 DOI: 10.1021/jp011861c
- 105Bisquert, J.; Cendula, P.; Bertoluzzi, L.; Gimenez, S. J. Phys. Chem. Lett. 2014, 5, 205– 207 DOI: 10.1021/jz402703d[ACS Full Text], [CAS], Google Scholar105https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhvFKhtrrO&md5=4c91dcefb23c697dbc2b83804993b08fEnergy Diagram of Semiconductor/Electrolyte JunctionsBisquert, Juan; Cendula, Peter; Bertoluzzi, Luca; Gimenez, SixtoJournal of Physical Chemistry Letters (2014), 5 (1), 205-207CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)The energy diagram of an n-type semiconductor electrode in contact with electrolyte is studied. A set of math. relationships that allow us to relate the different expressions of voltage and energies such as the flatband potential and the energy (or potential) of semiconductor conduction band at the surface.
- 106Xiang, C.; Weber, A. Z.; Ardo, S.; Berger, A.; Chen, Y.; Coridan, R.; Fountaine, K. T.; Haussener, S.; Hu, S.; Liu, R.; Lewis, N. S.; Modestino, M. A.; Shaner, M. M.; Singh, M. R.; Stevens, J. C.; Sun, K.; Walczak, K. Angew. Chem., Int. Ed. 2016, 55, 12974– 12988 DOI: 10.1002/anie.201510463
- 107Garcia-Esparza, A. T.; Takanabe, K. J. Mater. Chem. A 2016, 4, 2894– 2908 DOI: 10.1039/C5TA06983A[Crossref], [CAS], Google Scholar107https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhs1Sit7rF&md5=467c98b431ca40da7848c64e4e81760aA simplified theoretical guideline for overall water splitting using photocatalyst particlesGarcia-Esparza, Angel T.; Takanabe, KazuhiroJournal of Materials Chemistry A: Materials for Energy and Sustainability (2016), 4 (8), 2894-2908CODEN: JMCAET; ISSN:2050-7496. (Royal Society of Chemistry)Particulate photocatalytic water splitting is the most disruptive and competitive soln. for the direct prodn. of solar fuels. Despite more than four decades of work in the field of photocatalysis using powd. semiconductors decorated with catalyst particles, there is no clear consensus on the factors limiting the solar-to-hydrogen efficiency (STH). To understand the intrinsic limitations of the system, we numerically simulated simplified two-dimensional photocatalytic models using classical semiconductor device equations. This work presents the sensitivity of quantum efficiency (QE) to the various semiconductor properties, such as absorption properties and carrier mobilities, and to the dispersion of catalyst particles, which create heterojunctions, the driving force for charge sepn. As a result, a pinch-off effect was prevalent underneath the hydrogen evolution site, suggesting an undesired energetic barrier for electron diffusion to the catalyst. The simulation using the values reported in the literature revealed that the QE was exclusively governed by recombination in the bulk of the photocatalyst particles, hindering the charge sepn. efficiency before reaching the catalysts on the surface. Using some of the reported parameters, our simulation shows that a typical defective n-type semiconductor particle (∼100 nm) ideally exhibits a QE of <5% in the visible light range per particle, which reaches only approx. 10% in a slurry after 4 consecutive absorbing units (1.4% STH, from simulated solar irradn.). Although the present model contains rigid limitations, we use these trends as an initial guideline to pursue photocatalysis by a design strategy, which may result in possible alternatives to achieve higher efficiencies.
- 108Cendula, P.; Tilley, S. D.; Gimenez, S.; Bisquert, J.; Schmid, M.; Grätzel, M.; Schumacher, J. O. J. Phys. Chem. C 2014, 118, 29599– 29607 DOI: 10.1021/jp509719d
- 109Mills, T. J.; Lin, F.; Boettcher, S. W. Phys. Rev. Lett. 2014, 112, 148304 DOI: 10.1103/PhysRevLett.112.148304
- 110Lin, F.; Boettcher, S. W. Nat. Mater. 2014, 13, 81– 86 DOI: 10.1038/nmat3811
- 111Lichterman, M. F.; Hu, S.; Richter, M. H.; Crumlin, E. J.; Axnanda, S.; Favaro, M.; Drisdell, W.; Hussain, Z.; Mayer, T.; Brunschwig, B. S.; Lewis, N. S.; Liu, Z.; Lewerenz, H. J. Energy Environ. Sci. 2015, 8, 2409– 2416 DOI: 10.1039/C5EE01014D
- 112Laskowski, F. A. L.; Nellist, M. R.; Venkatkarthick, R.; Boettcher, S. W. Energy Environ. Sci. 2017, 10, 570– 579 DOI: 10.1039/C6EE03505A
- 113Hu, S.; Shaner, M. R.; Beardslee, J. A.; Lichterman, M.; Brunschwig, B. S.; Lewis, N. S. Science 2014, 344, 1005– 1009 DOI: 10.1126/science.1251428[Crossref], [PubMed], [CAS], Google Scholar113https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXosFSmuro%253D&md5=9de5f3032f2f33d9db97a9759ed0307bAmorphous TiO2 coatings stabilize Si, GaAs, and GaP photoanodes for efficient water oxidationHu, Shu; Shaner, Matthew R.; Beardslee, Joseph A.; Lichterman, Michael; Brunschwig, Bruce S.; Lewis, Nathan S.Science (Washington, DC, United States) (2014), 344 (6187), 1005-1009CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)Although semiconductors such as silicon (Si), gallium arsenide (GaAs), and gallium phosphide (GaP) have band gaps that make them efficient photoanodes for solar fuel prodn., these materials are unstable in aq. media. TiO2 coatings (4 to 143 nm thick) grown by at. layer deposition prevent corrosion, have electronic defects that promote hole conduction, and are sufficiently transparent to reach the light-limited performance of protected semiconductors. In conjunction with a thin layer or islands of Ni oxide electrocatalysts, Si photoanodes exhibited continuous oxidn. of 1.0M aq. KOH to O2 for >100 h at photocurrent densities of >30 mA per square centimeter and ~100% faradaic efficiency. TiO2-coated GaAs and GaP photoelectrodes exhibited photovoltages of 0.81 and 0.59 V and light-limiting photocurrent densities of 14.3 and 3.4 mA per square centimeter, resp., for water oxidn.
- 114Verlage, E.; Hu, S.; Liu, R.; Jones, R. J. R.; Sun, K.; Xiang, C.; Lewis, N. S.; Atwater, H. A. Energy Environ. Sci. 2015, 8, 3166– 3172 DOI: 10.1039/C5EE01786F[Crossref], [CAS], Google Scholar114https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhtlKnsLfE&md5=e548bf4d84d606a21052c9eef1da43efA monolithically integrated, intrinsically safe, 10% efficient, solar-driven water-splitting system based on active, stable earth-abundant electrocatalysts in conjunction with tandem III-V light absorbers protected by amorphous TiO2 filmsVerlage, Erik; Hu, Shu; Liu, Rui; Jones, Ryan J. R.; Sun, Ke; Xiang, Chengxiang; Lewis, Nathan S.; Atwater, Harry A.Energy & Environmental Science (2015), 8 (11), 3166-3172CODEN: EESNBY; ISSN:1754-5706. (Royal Society of Chemistry)A monolithically integrated device consisting of a tandem-junction GaAs/InGaP photoanode coated by an amorphous TiO2 stabilization layer, in conjunction with Ni-based, earth-abundant active electrocatalysts for the hydrogen-evolution and oxygen-evolution reactions, was used to effect unassisted, solar-driven water splitting in 1.0 M KOH(aq). When connected to a Ni-Mo-coated counterelectrode in a two-electrode cell configuration, the TiO2-protected III-V tandem device exhibited a solar-to-hydrogen conversion efficiency, ηSTH, of 10.5% under 1 sun illumination, with stable performance for >40 h of continuous operation at an efficiency of ηSTH > 10%. The protected tandem device also formed the basis for a monolithically integrated, intrinsically safe solar-hydrogen prototype system (1 cm2) driven by a NiMo/GaAs/InGaP/TiO2/Ni structure. The intrinsically safe system exhibited a hydrogen prodn. rate of 0.81 μL s-1 and a solar-to-hydrogen conversion efficiency of 8.6% under 1 sun illumination in 1.0 M KOH(aq), with minimal product gas crossover while allowing for beneficial collection of sep. streams of H2(g) and O2(g).
- 115Zhou, X.; Liu, R.; Sun, K.; Chen, Y.; Verlage, E.; Francis, S. A.; Lewis, N. S.; Xiang, C. ACS Energy Lett. 2016, 1, 764– 770 DOI: 10.1021/acsenergylett.6b00317[ACS Full Text], [CAS], Google Scholar115https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhsV2hs77J&md5=ce1fce3fa43e3a3711ed47debe205586Solar-Driven Reduction of 1 atm of CO2 to Formate at 10% Energy-Conversion Efficiency by Use of a TiO2-Protected III-V Tandem Photoanode in Conjunction with a Bipolar Membrane and a Pd/C CathodeZhou, Xinghao; Liu, Rui; Sun, Ke; Chen, Yikai; Verlage, Erik; Francis, Sonja A.; Lewis, Nathan S.; Xiang, ChengxiangACS Energy Letters (2016), 1 (4), 764-770CODEN: AELCCP; ISSN:2380-8195. (American Chemical Society)A solar-driven CO2 redn. (CO2R) cell was constructed, consisting of a tandem GaAs/InGaP/TiO2/Ni photoanode in 1.0M KOH(aq) (pH = 13.7) to facilitate the oxygen-evolution reaction (OER), a Pd/C nanoparticle-coated Ti mesh cathode in 2.8M KHCO3(aq) (pH = 8.0) to perform the CO2R reaction, and a bipolar membrane to allow for steady-state operation of the catholyte and anolyte at different bulk pH values. At the operational c.d. of 8.5 mA cm-2, in 2.8M KHCO3(aq), the cathode exhibited <100 mV overpotential and >94% faradaic efficiency for the redn. of 1 atm of CO2(g) to formate. The anode exhibited a 320 ± 7 mV overpotential for the OER in 1.0M KOH(aq), and the bipolar membrane exhibited ∼480 mV voltage loss with minimal product crossovers and >90 and >95% selectivity for protons and hydroxide ions, resp. The bipolar membrane facilitated coupling between two electrodes and electrolytes, one for the CO2R reaction and one for the OER, that typically operate at mutually different pH values and produced a lower total cell overvoltage than known single-electrolyte CO2R systems while exhibiting ∼10% solar-to-fuels energy-conversion efficiency.
- 116Ding, C.; Shi, J.; Wang, Z.; Li, C. ACS Catal. 2017, 7, 675– 688 DOI: 10.1021/acscatal.6b03107[ACS Full Text], [CAS], Google Scholar116https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XitVGitbnP&md5=3a34e10643d75a34ccc54fa67b1fcf25Photoelectrocatalytic Water Splitting: Significance of Cocatalysts, Electrolyte, and InterfacesDing, Chunmei; Shi, Jingying; Wang, Zhiliang; Li, CanACS Catalysis (2017), 7 (1), 675-688CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)A review is given. The efficiency of photoelectrocatalytic (PEC) water splitting is limited by the serious recombination of photogenerated charges, high overpotential, and sluggish kinetics of surface reaction. We describe the recent progress on engineering the electrode-electrolyte and semiconductor-cocatalyst interfaces with cocatalysts, electrolytes, and interfacial layers (interlayers) to increase the PEC efficiency. Introducing cocatalysts has been demonstrated to be the most efficient way to lower the reaction barrier and promote charge injection to the reactants. It has been found that electrolyte ions can influence the surface catalysis remarkably. Electrolyte cations on the surface can influence the water splitting and backward reactions, and anions may take part in the proton transfer processes, indicating that fine-tuning of the electrolyte parameters turns out to be an important strategy for enhancing the PEC efficiency. Careful modification of the interface between the cocatalysts and the semiconductor via suitable interlayers is crit. for promoting charge sepn. and transfer, which can indirectly influence the surface catalysis. The mechanisms of surface catalysis are assumed to involve transfer of photogenerated holes to the surface active sites to form high-valent species, which then oxidize the water mols. Many key scientific issues about the generation of photovoltage, the sepn., storage, and transfer of carriers, the function of cocatalysts, the roles of electrolyte ions, and the influences of other parameters during PEC water splitting are discussed with some perspective views.
- 117Hill, J. C.; Landers, A. T.; Switzer, J. A. Nat. Mater. 2015, 14, 1150– 1156 DOI: 10.1038/nmat4408
- 118Digdaya, I. A.; Adhyaksa, G.; Trzesniewski, B. J.; Garnett, E.; Smith, W. A. Nat. Commun. 2017, 8, 15968 DOI: 10.1038/ncomms15968[Crossref], [PubMed], [CAS], Google Scholar118https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhtVyqtrjJ&md5=333b23f5370f39355ca681925fdeb60dInterfacial engineering of metal-insulator-semiconductor junctions for efficient and stable photoelectrochemical water oxidationDigdaya, Ibadillah A.; Adhyaksa, Gede W. P.; Trzesniewski, Bartek J.; Garnett, Erik C.; Smith, Wilson A.Nature Communications (2017), 8 (), 15968CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)Solar-assisted water splitting can potentially provide an efficient route for large-scale renewable energy conversion and storage. It is essential for such a system to provide a sufficiently high photocurrent and photovoltage to drive the water oxidn. reaction. Here we demonstrate a photoanode that is capable of achieving a high photovoltage by engineering the interfacial energetics of metal-insulator-semiconductor junctions. We evaluate the importance of using two metals to decouple the functionalities for a Schottky contact and a highly efficient catalyst. We also illustrate the improvement of the photovoltage upon incidental oxidn. of the metallic surface layer in KOH soln. Addnl., we analyze the role of the thin insulating layer to the pinning and depinning of Fermi level that is responsible to the resulting photovoltage. Finally, we report the advantage of using dual metal overlayers as a simple protection route for highly efficient metal-insulator-semiconductor photoanodes by showing over 200 h of operational stability.
- 119Kamat, P. V. Pure Appl. Chem. 2002, 74, 1693– 1706 DOI: 10.1351/pac200274091693
- 120Jakob, M.; Levanon, H.; Kamat, P. V. Nano Lett. 2003, 3, 353– 358 DOI: 10.1021/nl0340071
- 121Subramanian, V.; Wolf, E. E.; Kamat, P. V. J. Am. Chem. Soc. 2004, 126, 4943– 4950 DOI: 10.1021/ja0315199
- 122Yoshida, M.; Yamakata, A.; Takanabe, K.; Kubota, J.; Osawa, M.; Domen, K. J. Am. Chem. Soc. 2009, 131, 13218– 13219 DOI: 10.1021/ja904991p
- 123Lu, X.; Bandara, A.; Katayama, M.; Yamakata, A.; Kubota, J.; Domen, K. J. Phys. Chem. C 2011, 115, 23902– 23907 DOI: 10.1021/jp207484q
- 124Stamenkovic, V. R.; Strmcnik, D.; Lopes, P. P.; Markovic, N. M. Nat. Mater. 2017, 16, 57– 69 DOI: 10.1038/nmat4738[Crossref], [CAS], Google Scholar124https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XitFamu73M&md5=ce9089ad76dcd6f4fd98d5c539c790c6Energy and fuels from electrochemical interfacesStamenkovic, Vojislav R.; Strmcnik, Dusan; Lopes, Pietro P.; Markovic, Nenad M.Nature Materials (2017), 16 (1), 57-69CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)Advances in electrocatalysis at solid-liq. interfaces are vital for driving the technol. innovations that are needed to deliver reliable, affordable and environmentally friendly energy. Here, we highlight the key achievements in the development of new materials for efficient hydrogen and oxygen prodn. in electrolyzers and, in reverse, their use in fuel cells. A key issue addressed here is the degree to which the fundamental understanding of the synergy between covalent and non-covalent interactions can form the basis for any predictive ability in tailor-making real-world catalysts. Common descriptors such as the substrate-hydroxide binding energy and the interactions in the double layer between hydroxide-oxides and H---OH are found to control individual parts of the hydrogen and oxygen electrochem. that govern the efficiency of water-based energy conversion and storage systems. Links between aq.- and org.-based environments are also established, encouraging the 'fuel cell' and 'battery' communities to move forward together.
- 125Suntivich, J.; Perry, E. E.; Gasteiger, H. A.; Shao-Horn, Y. Electrocatalysis 2013, 4, 49– 55 DOI: 10.1007/s12678-012-0118-x
- 126Fuel Cell Catalysis, A Surface Science Approach; Koper, M. T. M., Ed.; John Wiley & Sons, Inc.: Hoboken, NJ, 2009, : pp 1– 158.
- 127Shinagawa, T.; Garcia-Esparza, A. T.; Takanabe, K. Sci. Rep. 2015, 5, 13801 DOI: 10.1038/srep13801[Crossref], [PubMed], [CAS], Google Scholar127https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC283gsFeluw%253D%253D&md5=ac27784a48ec67e4bea1ac3d6c62a416Insight on Tafel slopes from a microkinetic analysis of aqueous electrocatalysis for energy conversionShinagawa Tatsuya; Garcia-Esparza Angel T; Takanabe KazuhiroScientific reports (2015), 5 (), 13801 ISSN:.Microkinetic analyses of aqueous electrochemistry involving gaseous H2 or O2, i.e., hydrogen evolution reaction (HER), hydrogen oxidation reaction (HOR), oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), are revisited. The Tafel slopes used to evaluate the rate determining steps generally assume extreme coverage of the adsorbed species (θ≈0 or ≈1), although, in practice, the slopes are coverage-dependent. We conducted detailed kinetic analyses describing the coverage-dependent Tafel slopes for the aforementioned reactions. Our careful analyses provide a general benchmark for experimentally observed Tafel slopes that can be assigned to specific rate determining steps. The Tafel analysis is a powerful tool for discussing the rate determining steps involved in electrocatalysis, but our study also demonstrated that overly simplified assumptions led to an inaccurate description of the surface electrocatalysis. Additionally, in many studies, Tafel analyses have been performed in conjunction with the Butler-Volmer equation, where its applicability regarding only electron transfer kinetics is often overlooked. Based on the derived kinetic description of the HER/HOR as an example, the limitation of Butler-Volmer expression in electrocatalysis is also discussed in this report.
- 128Trasatti, S. J. Electroanal. Chem. Interfacial Electrochem. 1972, 39, 163– 184 DOI: 10.1016/S0022-0728(72)80485-6[Crossref], [CAS], Google Scholar128https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaE38XltVyks7g%253D&md5=c0f43ebc002ad058af7e6c7d4b6c0d0fWork function, electronegativity, and electrochemical behavior of metals. III. Electrolytic hydrogen evolution in acid solutionsTrasatti, SergioJournal of Electroanalytical Chemistry and Interfacial Electrochemistry (1972), 39 (1), 163-84CODEN: JEIEBC; ISSN:0022-0728.Various attempts to interpret the electrochem. behavior of an electrode during H evolution are reviewed. The general behavior of a metal is apt to be related to its work function, the energy with which electrons near the Fermi level are bound to the interior of the solid. The use of this work function in developing a single theory to explain exptl. data on H discharge for all metals is considered.
- 129Greeley, J.; Jaramillo, T. F.; Bonde, J.; Chorkendorff, I.; Nørskov, J. K. Nat. Mater. 2006, 5, 909– 913 DOI: 10.1038/nmat1752[Crossref], [PubMed], [CAS], Google Scholar129https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28XhtFCqu73N&md5=bffaed56805e7732d1a12a9f68d9fe1eComputational high-throughput screening of electrocatalytic materials for hydrogen evolutionGreeley, Jeff; Jaramillo, Thomas F.; Bonde, Jacob; Chorkendorff, Ib; Norskov, Jens K.Nature Materials (2006), 5 (11), 909-913CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)The pace of materials discovery for heterogeneous catalysts and electrocatalysts could, in principle, be accelerated by the development of efficient computational screening methods. This would require an integrated approach, where the catalytic activity and stability of new materials are evaluated and where predictions are benchmarked by careful synthesis and exptl. tests. In this contribution, the authors present a d. functional theory-based, high-throughput screening scheme that successfully uses these strategies to identify a new electrocatalyst for the hydrogen evolution reaction (HER). The activity of over 700 binary surface alloys is evaluated theor.; the stability of each alloy in electrochem. environments is also estd. BiPt has a predicted activity comparable to, or even better than, pure Pt, the archetypical HER catalyst. This alloy is synthesized and tested exptl. and shows improved HER performance compared with pure Pt, in agreement with the computational screening results.
- 130Matsumoto, Y.; Sato, E. Mater. Chem. Phys. 1986, 14, 397– 426 DOI: 10.1016/0254-0584(86)90045-3[Crossref], [CAS], Google Scholar130https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL28XktFCjsbg%253D&md5=927a8b77c648b5b9cb8ab79f61debc4dElectrocatalytic properties of transition metal oxides for oxygen evolution reactionMatsumoto, Y.; Sato, E.Materials Chemistry and Physics (1986), 14 (5), 397-26CODEN: MCHPDR; ISSN:0254-0584.A review with 143 refs. is given on electrocatalysis of the transition metal oxides for the O2 evolution reaction. Many transition metal oxides tested as the anode material for the O evolution reaction are summarized.
- 131Man, I. C.; Su, H.-Y.; Calle-Vallejo, F.; Hansen, H. A.; Martinez, J. I.; Inoglu, N. G.; Kitchin, J.; Jaramillo, T. F.; Nørskov, J. K.; Rossmeisl, J. ChemCatChem 2011, 3, 1159– 1165 DOI: 10.1002/cctc.201000397[Crossref], [CAS], Google Scholar131https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXotFyjsb0%253D&md5=f4103e77db6bcd3ba840b6376b33315aUniversality in Oxygen Evolution Electrocatalysis on Oxide SurfacesMan, Isabela C.; Su, Hai-Yan; Calle-Vallejo, Federico; Hansen, Heine A.; Martinez, Jose I.; Inoglu, Nilay G.; Kitchin, John; Jaramillo, Thomas F.; Noerskov, Jens K.; Rossmeisl, JanChemCatChem (2011), 3 (7), 1159-1165CODEN: CHEMK3; ISSN:1867-3880. (Wiley-VCH Verlag GmbH & Co. KGaA)Trends in electrocatalytic activity of the O evolution reaction (OER) were studied from a large database of HO* and HOO* adsorption energies on oxide surfaces. The theor. overpotential was calcd. by applying std. d. functional theory in combination with the computational std. H electrode (SHE) model. By the discovery of a universal scaling relation between the adsorption energies of HOO* vs. HO*, it is possible to analyze the reaction free energy diagrams of all the oxides in a general way. This gave rise to an activity volcano that was the same for a wide variety of oxide catalyst materials and a universal descriptor for the O evolution activity, which suggests a fundamental limitation on the max. O evolution activity of planar oxide catalysts.
- 132Grimaud, A.; May, K. J.; Carlton, C. E.; Lee, Y. L.; Risch, M.; Hong, W. T.; Zhou, J.; Shao-Horn, Y. Nat. Commun. 2013, 4, 3439 DOI: 10.1038/ncomms3439[Crossref], [CAS], Google Scholar132https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhs1egsrzE&md5=71f102bc006bb4346bf7da233d79e499Double perovskites as a family of highly active catalysts for oxygen evolution in alkaline solutionGrimaud, Alexis; May, Kevin J.; Carlton, Christopher E.; Lee, Yueh-Lin; Risch, Marcel; Hong, Wesley T.; Zhou, Jigang; Shao-Horn, YangNature Communications (2013), 4 (), 3439, 7 pp.CODEN: NCAOBW; ISSN:2041-1723. (Nature Publishing Group)The electronic structure of transition metal oxides governs the catalysis of many central reactions for energy storage applications such as oxygen electrocatalysis. Here we exploit the versatility of the perovskite structure to search for oxide catalysts that are both active and stable. We report double perovskites (Ln0.5Ba0.5)CoO3-δ (Ln = Pr, Sm, Gd and Ho) as a family of highly active catalysts for the oxygen evolution reaction upon water oxidn. in alk. soln. These double perovskites are stable unlike pseudocubic perovskites with comparable activities such as Ba0.5Sr0.5Co0.8Fe0.2O3-δ which readily amorphize during the oxygen evolution reaction. The high activity and stability of these double perovskites can be explained by having the O p-band center neither too close nor too far from the Fermi level, which is computed from ab initio studies.
- 133Popczun, E. J.; McKone, J. R.; Read, C. G.; Biacchi, A. J.; Wiltrout, A. M.; Lewis, N. S.; Schaak, R. E. J. Am. Chem. Soc. 2013, 135, 9267– 9270 DOI: 10.1021/ja403440e[ACS Full Text], [CAS], Google Scholar133https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXpsVehtrY%253D&md5=1f90d9dff7e66e7a97301477bdd4dc00Nanostructured Nickel Phosphide as an Electrocatalyst for the Hydrogen Evolution ReactionPopczun, Eric J.; McKone, James R.; Read, Carlos G.; Biacchi, Adam J.; Wiltrout, Alex M.; Lewis, Nathan S.; Schaak, Raymond E.Journal of the American Chemical Society (2013), 135 (25), 9267-9270CODEN: JACSAT; ISSN:0002-7863. (American Chemical Society)Nanoparticles of nickel phosphide (Ni2P) have been investigated for electrocatalytic activity and stability for the hydrogen evolution reaction (HER) in acidic solns., under which proton exchange membrane-based electrolysis is operational. The catalytically active Ni2P nanoparticles were hollow and faceted to expose a high d. of the Ni2P(001) surface, which has previously been predicted based on theory to be an active HER catalyst. The Ni2P nanoparticles had among the highest HER activity of any non-noble metal electrocatalyst reported to date, producing H2(g) with nearly quant. faradaic yield, while also affording stability in aq. acidic media.
- 134Jiang, P.; Liu, Q.; Liang, Y.; Tian, J.; Asiri, A. M.; Sun, X. Angew. Chem., Int. Ed. 2014, 53, 12855– 12859 DOI: 10.1002/anie.201406848[Crossref], [CAS], Google Scholar134https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhvV2mtrvN&md5=e8b5bed1d364d872ee0799a30210b5edA Cost-Effective 3D Hydrogen Evolution Cathode with High Catalytic Activity: FeP Nanowire Array as the Active PhaseJiang, Ping; Liu, Qian; Liang, Yanhui; Tian, Jingqi; Asiri, Abdullah M.; Sun, XupingAngewandte Chemie, International Edition (2014), 53 (47), 12855-12859CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)Iron is the cheapest and one of the most abundant transition metals. Natural [FeFe]-hydrogenases exhibit remarkably high activity in hydrogen evolution, but they suffer from high oxygen sensitivity and difficulty in scale-up. Herein, an FeP nanowire array was developed on Ti plate (FeP NA/Ti) from its β-FeOOH NA/Ti precursor through a low-temp. phosphidation reaction. When applied as self-supported 3D hydrogen evolution cathode, the FeP NA/Ti electrode shows exceptionally high catalytic activity and good durability, and it only requires overpotentials of 55 and 127 mV to afford current densities of 10 and 100 mA cm2, resp. The excellent electrocatalytic performance is promising for applications as non-noble-metal HER catalyst with a high performance-price ratio in electrochem. water splitting for large-scale hydrogen fuel prodn.
- 135Popczun, E. J.; Read, C. G.; Roske, C. W.; Lewis, N. S.; Schaak, R. E. Angew. Chem., Int. Ed. 2014, 53, 5427– 5430 DOI: 10.1002/anie.201402646[Crossref], [CAS], Google Scholar135https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXmt1ahsr4%253D&md5=afaedbccf5033d70a4ddcf2d32c432f8Highly active electrocatalysis of the hydrogen evolution reaction by cobalt phosphide nanoparticlesPopczun, Eric J.; Read, Carlos G.; Roske, Christopher W.; Lewis, Nathan S.; Schaak, Raymond E.Angewandte Chemie, International Edition (2014), 53 (21), 5427-5430CODEN: ACIEF5; ISSN:1433-7851. (Wiley-VCH Verlag GmbH & Co. KGaA)Nanoparticles of cobalt phosphide, CoP, have been prepd. and evaluated as electrocatalysts for the hydrogen evolution reaction (HER) under strongly acidic conditions (0.50M H2SO4, pH 0.3). Uniform, multi-faceted CoP nanoparticles were synthesized by reacting Co nanoparticles with trioctylphosphine. Electrodes comprised of CoP nanoparticles on a Ti support (2 mg cm-2 mass loading) produced a cathodic c.d. of 20 mA cm-2 at an overpotential of -85 mV. The CoP/Ti electrodes were stable over 24 h of sustained hydrogen prodn. in 0.50M H2SO4. The activity was essentially unchanged after 400 cyclic voltammetric sweeps, suggesting long-term viability under operating conditions. CoP is therefore amongst the most active, acid-stable, earth-abundant HER electrocatalysts reported to date.
- 136Smith, R. D. L.; Prévot, M. S.; Fagan, R. D.; Zhang, Z.; Sedach, P. A.; Siu, J. M. K.; Trudel, S.; Berlinguette, C. P. Science 2013, 340, 60– 63 DOI: 10.1126/science.1233638
- 137Gong, M.; Li, Y.; Wang, H.; Liang, Y.; Wu, J. Z.; Zhou, J.; Wang, J.; Regier, T.; Wei, F.; Dai, H. J. Am. Chem. Soc. 2013, 135, 8452– 8455 DOI: 10.1021/ja4027715
- 138Gong, M.; Zhou, W.; Tsai, M. C.; Zhou, J.; Guan, M.; Lin, M. C.; Zhang, B.; Hu, Y.; Wang, D. Y.; Yang, J.; Pennycook, S. J.; Hwang, B. J.; Dai, H. Nat. Commun. 2014, 5, 5695 DOI: 10.1038/ncomms5695
- 139Suntivich, J.; May, K. J.; Gasteiger, H. A.; Goodenough, J. B.; Shao-Horn, Y. Science 2011, 334, 1383– 1385 DOI: 10.1126/science.1212858[Crossref], [PubMed], [CAS], Google Scholar139https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXhsFOjt73K&md5=34d8b657e052d2f31c5aa3773b5e6f80A Perovskite Oxide Optimized for Oxygen Evolution Catalysis from Molecular Orbital PrinciplesSuntivich, Jin; May, Kevin J.; Gasteiger, Hubert A.; Goodenough, John B.; Shao-Horn, YangScience (Washington, DC, United States) (2011), 334 (6061), 1383-1385CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)The efficiency of many energy storage technologies, such as rechargeable metal-air batteries and H prodn. from H2O splitting, is limited by the slow kinetics of the O evolution reaction (OER). Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) catalyzes the OER with intrinsic activity that is at least an order of magnitude higher than that of the state-of-the-art Ir oxide catalyst in alk. media. The high activity of BSCF was predicted from a design principle established by systematic examn. of >10 transition metal oxides, which showed that the intrinsic OER activity exhibits a volcano-shaped dependence on the occupancy of the 3d electron with an eg symmetry of surface transition metal cations in an oxide. The peak OER activity was predicted to be at an eg occupancy close to unity, with high covalency of transition metal-O bonds.
- 140Wei, C.; Feng, Z.; Scherer, G. G.; Barber, J.; Shao-Horn, Y.; Xu, Z. J. Adv. Mater. 2017, 29, 1606800 DOI: 10.1002/adma.201606800
- 141Kanan, M. W.; Nocera, D. G. Science 2008, 321, 1072– 1075 DOI: 10.1126/science.1162018[Crossref], [PubMed], [CAS], Google Scholar141https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXhtVSitrbP&md5=dbeea0b08710b7d24acf4046a56424d8In Situ Formation of an Oxygen-Evolving Catalyst in Neutral Water Containing Phosphate and Co2+Kanan, Matthew W.; Nocera, Daniel G.Science (Washington, DC, United States) (2008), 321 (5892), 1072-1075CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)The utilization of solar energy on a large scale requires its storage. In natural photosynthesis, energy from sunlight is used to rearrange the bonds of water to oxygen and hydrogen equiv. The realization of artificial systems that perform "water splitting" requires catalysts that produce oxygen from water without the need for excessive driving potentials. Here we report such a catalyst that forms upon the oxidative polarization of an inert indium tin oxide electrode in phosphate-buffered water contg. cobalt (II) ions. A variety of anal. techniques indicates the presence of phosphate in an approx. 1:2 ratio with cobalt in this material. The pH dependence of the catalytic activity also implicates the hydrogen phosphate ion as the proton acceptor in the oxygen-producing reaction. This catalyst not only forms in situ from earth-abundant materials but also operates in neutral water under ambient conditions.
- 142Lutterman, D. A.; Surendranath, Y.; Nocera, D. G. J. Am. Chem. Soc. 2009, 131, 3838– 3839 DOI: 10.1021/ja900023k
- 143Dinca, M.; Surendranath, Y.; Nocera, D. G. Proc. Natl. Acad. Sci. U. S. A. 2010, 107, 10337– 10341 DOI: 10.1073/pnas.1001859107
- 144Kuang, Y.; Jia, Q.; Ma, G.; Hisatomi, T.; Minegishi, T.; Nishiyama, H.; Nakabayashi, M.; Shibata, N.; Yamada, T.; Kudo, A.; Domen, K. Nat. Energy 2016, 2, 16191 DOI: 10.1038/nenergy.2016.191
- 145Shinagawa, T.; Ng, M. T.-K.; Takanabe, K. Angew. Chem., Int. Ed. 2017, 56, 5061– 5065 DOI: 10.1002/anie.201701642
- 146Shinagawa, T.; Takanabe, K. J. Phys. Chem. C 2016, 120, 24187– 24196 DOI: 10.1021/acs.jpcc.6b07954
- 147Electrochemistry, 2nd ed.; Hamann, C. H.; Hamnett, A.; Vielstich, W., Eds.; Wiley-VCH: Weinheim, 2007; pp 397– 438.Google ScholarThere is no corresponding record for this reference.
- 148Kato, H.; Asakura, K.; Kudo, A. J. Am. Chem. Soc. 2003, 125, 3082– 3089 DOI: 10.1021/ja027751g
- 149Sakata, Y.; Matsuda, Y.; Nakagawa, T.; Yasunaga, R.; Imamura, H.; Teramura, K. ChemSusChem 2011, 4, 181– 184 DOI: 10.1002/cssc.201000258
- 150Shinagawa, T.; Garcia-Esparza, A. T.; Takanabe, K. ChemElectroChem 2014, 1, 1497– 1507 DOI: 10.1002/celc.201402085
- 151Subbaraman, R.; Tripkovic, D.; Chang, K. C.; Strmcnik, D.; Paulikas, A. P.; Hirunsit, P.; Chan, M.; Greeley, J.; Stamenkovic, V.; Markovic, N. M. Nat. Mater. 2012, 11, 550– 557 DOI: 10.1038/nmat3313[Crossref], [PubMed], [CAS], Google Scholar151https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XmsFOqsb8%253D&md5=6579cb7fc048f54d4c8d2b12be343727Trends in activity for the water electrolyzer reactions on 3d M(Ni,Co,Fe,Mn) hydro(oxy)oxide catalystsSubbaraman, Ram; Tripkovic, Dusan; Chang, Kee-Chul; Strmcnik, Dusan; Paulikas, Arvydas P.; Hirunsit, Pussana; Chan, Maria; Greeley, Jeff; Stamenkovic, Vojislav; Markovic, Nenad M.Nature Materials (2012), 11 (6), 550-557CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)Design and synthesis of materials for efficient electrochem. transformation of H2O to H2 and of hydroxyl ions to O in alk. environments is of paramount importance in reducing energy losses in H2O-alkali electrolyzers. Here, using 3d-M hydr(oxy)oxides, with distinct stoichiometries and morphologies in the H evolution reaction (HER) and the O evolution reaction (OER) regions, the authors establish the overall catalytic activities for these reaction as a function of a more fundamental property, a descriptor, OH-M2+δ bond strength (0 ≤ δ ≤ 1.5). This relation exhibits trends in reactivity (Mn < Fe < Co < Ni), which is governed by the strength of the OH-M2+δ energetic (Ni < Co < Fe < Mn). These trends are independent of the source of the OH, either the supporting electrolyte (for the OER) or the H2O dissocn. product (for the HER). The successful identification of these electrocatalytic trends provides the foundation for rational design of active sites' for practical alk. HER and OER electrocatalysts.
- 152Yang, J.; Cooper, J. K.; Toma, F. M.; Walczak, K. A.; Favaro, M.; Beeman, J. W.; Hess, L. H.; Wang, C.; Zhu, C.; Gul, S.; Yano, J.; Kisielowski, C.; Schwartzberg, A.; Sharp, I. D. Nat. Mater. 2017, 16, 335– 341 DOI: 10.1038/nmat4794[Crossref], [PubMed], [CAS], Google Scholar152https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xhsl2gsLfJ&md5=44e1cf123f39c9067433cf7d181432b0A multifunctional biphasic water splitting catalyst tailored for integration with high-performance semiconductor photoanodesYang, Jinhui; Cooper, Jason K.; Toma, Francesca M.; Walczak, Karl A.; Favaro, Marco; Beeman, Jeffrey W.; Hess, Lucas H.; Wang, Cheng; Zhu, Chenhui; Gul, Sheraz; Yano, Junko; Kisielowski, Christian; Schwartzberg, Adam; Sharp, Ian D.Nature Materials (2017), 16 (3), 335-341CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)Artificial photosystems are advanced by the development of conformal catalytic materials that promote desired chem. transformations, while also maintaining stability and minimizing parasitic light absorption for integration on surfaces of semiconductor light absorbers. Here, we demonstrate that multifunctional, nanoscale catalysts that enable high-performance photoelectrochem. energy conversion can be engineered by plasma-enhanced at. layer deposition. The collective properties of tailored Co3O4/Co(OH)2 thin films simultaneously provide high activity for water splitting, permit efficient interfacial charge transport from semiconductor substrates, and enhance durability of chem. sensitive interfaces. These films comprise compact and continuous nanocryst. Co3O4 spinel that is impervious to phase transformation and impermeable to ions, thereby providing effective protection of the underlying substrate. Moreover, a secondary phase of structurally disordered and chem. labile Co(OH)2 is introduced to ensure a high concn. of catalytically active sites. Application of this coating to photovoltaic p+n-Si junctions yields best reported performance characteristics for cryst. Si photoanodes.
- 153Seitz, L. C.; Chen, Z.; Forman, A. J.; Pinaud, B. A.; Benck, J. D.; Jaramillo, T. F. ChemSusChem 2014, 7, 1372– 1385 DOI: 10.1002/cssc.201301030
- 154Maeda, K.; Teramura, K.; Lu, D.; Saito, N.; Inoue, Y.; Domen, K. Angew. Chem., Int. Ed. 2006, 45, 7806– 7809 DOI: 10.1002/anie.200602473
- 155Maeda, K.; Domen, K. Top. Curr. Chem. 2011, 303, 95– 119 DOI: 10.1007/128_2011_138
- 156Yoshida, M.; Takanabe, K.; Maeda, K.; Ishikawa, A.; Kubota, J.; Sakata, Y.; Ikezawa, Y.; Domen, K. J. Phys. Chem. C 2009, 113, 10151– 10157 DOI: 10.1021/jp901418u
- 157Qureshi, M.; Shinagawa, T.; Tsiapis, N.; Takanabe, K. ACS Sustainable Chem. Eng. 2017, 5, 8079– 8088 DOI: 10.1021/acssuschemeng.7b01704[ACS Full Text], [CAS], Google Scholar157https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXht12mt7vO&md5=8d8c68253064ee964a5404bddad97db2Exclusive Hydrogen Generation by Electrocatalysts Coated with an Amorphous Chromium-Based Layer Achieving Efficient Overall Water SplittingQureshi, Muhammad; Shinagawa, Tatsuya; Tsiapis, Nikolaos; Takanabe, KazuhiroACS Sustainable Chemistry & Engineering (2017), 5 (9), 8079-8088CODEN: ASCECG; ISSN:2168-0485. (American Chemical Society)Successful conversion of renewable energy to useful chems. requires efficient devices that can electrocatalyze or photocatalyze redox reactions, e.g., overall water splitting. Excellent electrocatalysts for the hydrogen evolution reaction (HER), such as Pt, can also cause other side-reactions, including the water-forming back-reaction from H2 and O2 products. A Cr-based amorphous layer coated on catalysts can work as a successful surface modifier that avoids the back-reaction, but its capabilities and limitations toward other species have not been studied. Herein, we investigated the Cr-based layer on Pt from perspectives of both electrocatalysis and photocatalysis using redox-active mols./ions (O2, ferricyanide, IO3-, S2O82-, H2O2, and CO gas). Our systematic study revealed that utilization of the Cr-based layer realized an exclusive cathodic reaction only to HER, even in the presence of the aforementioned reactive species, suggesting that Cr-based layers work as membranes, as well as corrosion and poison inhibition layers. However, the Cr-based layer experienced self-oxidn. and dissolved into the aq. phase when a strong oxidizing agent or low pH was present. Presented herein are fundamental and crit. aspects of the Cr-based modifier, which is essential for the successful and practical development of solar fuel prodn. systems.
- 158Garcia-Esparza, A. T.; Shinagawa, T.; Ould-Chikh, S.; Qureshi, M.; Peng, X.; Wei, N.; Anjum, D. H.; Clo, A.; Weng, T.-C.; Nordlund, D.; Sokaras, D.; Kubota, J.; Domen, K.; Takanabe, K. Angew. Chem., Int. Ed. 2017, 56, 5780– 5784 DOI: 10.1002/anie.201701861
- 159Pan, C.; Takata, T.; Nakabayashi, M.; Matsumoto, T.; Shibata, N.; Ikuhara, Y.; Domen, K. Angew. Chem., Int. Ed. 2015, 54, 2955– 2959 DOI: 10.1002/anie.201410961
- 160Yoshida, M.; Maeda, K.; Lu, D.; Kubota, J.; Domen, K. J. Phys. Chem. C 2013, 117, 14000– 14006 DOI: 10.1021/jp402240d[ACS Full Text], [CAS], Google Scholar160https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXpslKgsLw%253D&md5=f790d4e3d7af421474663ceca43ab726Lanthanoid Oxide Layers on Rhodium-Loaded (Ga1-xZnx)(N1-xOx) Photocatalyst as a Modifier for Overall Water Splitting under Visible-Light IrradiationYoshida, Masaaki; Maeda, Kazuhiko; Lu, Daling; Kubota, Jun; Domen, KazunariJournal of Physical Chemistry C (2013), 117 (27), 14000-14006CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)Lanthanoid oxide modifier layers were applied to Rh metal nanoparticles on (Ga1-xZnx)(N1-xOx) photocatalyst for overall water splitting under visible-light irradn. Structural anal. by transmission electron microscopy, energy-dispersive X-ray spectroscopy, XPS, and X-ray absorption spectroscopy revealed that lanthanoid(III) oxide layers coated the Rh nanoparticles on (Ga1-xZnx)(N1-xOx), although they were also deposited directly on the (Ga1-xZnx)(N1-xOx) surface. Certain lanthanoid oxide layers (La, Pr, Sm, Gd, and Dy) functioned as modifiers for Rh-metal/(Ga1-xZnx)(N1-xOx) to produce H2 and O2 gases, although the Rh-metal/(Ga1-xZnx)(N1-xOx) photocatalyst exhibited little activity for overall water splitting due to rapid water formation from H2 and O2 on Rh. Ce and Eu oxide layers showed no photocatalytic activity, most likely due to their ability to capture photoexcited electrons from Rh-metal/(Ga1-xZnx)(N1-xOx). The enhancement of photocatalytic activity by lanthanoid oxide loading was shown to be dependent on the formation of redox-inactive lanthanoid(III) oxide layers on the Rh nanoparticles, which effectively suppresses the backward water formation reaction to enable H2 evolution on Rh.
- 161Hisatomi, T.; Maeda, K.; Takanabe, K.; Kubota, J.; Domen, K. J. Phys. Chem. C 2009, 113, 21458– 21466 DOI: 10.1021/jp9079662
- 162Maeda, K.; Xiong, A.; Yoshinaga, T.; Ikeda, T.; Sakamoto, N.; Hisatomi, T.; Takashima, M.; Lu, D.; Kanehara, M.; Setoyama, T.; Teranishi, T.; Domen, K. Angew. Chem., Int. Ed. 2010, 49, 4096– 4099 DOI: 10.1002/anie.201001259
- 163Townsend, T. K.; Browning, N. D.; Osterloh, F. E. Energy Environ. Sci. 2012, 5, 9543– 9550 DOI: 10.1039/c2ee22665k
- 164Takanabe, K. In Nanotechnology in Catalysis: Applications in the Chemical Industry, Energy Development, and Environment Protection; Sels, B.; Voorde, M. V., Eds.; Wiley-VCH: Weinheim, 2017; pp 891– 906.
- 165Rajeshwar, K. J. Phys. Chem. Lett. 2011, 2, 1301– 1309 DOI: 10.1021/jz200396h[ACS Full Text], [CAS], Google Scholar165https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXmtFSisL0%253D&md5=f4252f4bd99bcd5d5714fc3710ced443Solar Energy Conversion and Environmental Remediation Using Inorganic Semiconductor-Liquid Interfaces: The Road Traveled and the Way ForwardRajeshwar, KrishnanJournal of Physical Chemistry Letters (2011), 2 (11), 1301-1309CODEN: JPCLCD; ISSN:1948-7185. (American Chemical Society)Unlike their solid-state counterparts, semiconductor-liq. junctions are versatile in that the incident solar energy can be stored in the form of chem. fuels. Another attractive application is the use of irradiated oxide semiconductor-coated surfaces for self-cleaning and antifogging. The theme of this history-tinged Guest Commentary centers on the question of what has been accomplished in the above "photoelectrochem." schemes over the 35 yr time frame from 1975 to 2010. Progress in this field was aided by the infusion of new concepts and contributions from the materials chem. and physics communities. A related aspect of discussion is how the active semiconductor material has evolved both chem. and morphol. in these applications. It is shown that despite impressive research advances, only a handful of the above concepts (e.g., dye-sensitized solar photon conversion and self-cleaning and antifogging surfaces) have made the successful transition from the lab. to the marketplace.
- 166Atkins, P.; Paula, J. D. Atkins’ Physical Chemistry, 10th ed.; W. H. Freeman and Company: New York, 2014.Google ScholarThere is no corresponding record for this reference.
- 167Shinagawa, T.; Takanabe, K. J. Power Sources 2015, 287, 465– 471 DOI: 10.1016/j.jpowsour.2015.04.091
- 168Haynes, W. M.; Lide, D. R. Handbook of Chemistry and Physics, 92nd ed.; CRC Press: Boca Raton, FL, 2011.Google ScholarThere is no corresponding record for this reference.
- 169Jin, J.; Walczak, K.; Singh, M. R.; Karp, C.; Lewis, N. S.; Xiang, C. Energy Environ. Sci. 2014, 7, 3371– 3380 DOI: 10.1039/C4EE01824A
- 170Chabi, S.; Papadantonakis, K. M.; Lewis, N. S.; Freund, M. S. Energy Environ. Sci. 2017, 10, 1320– 1338 DOI: 10.1039/C7EE00294G
- 171Kutz, R. B.; Chen, Q.; Yang, H.; Sajjad, S. D.; Liu, Z.; Masel, I. R. Energy Technol. 2017, 5, 929– 936 DOI: 10.1002/ente.201600636[Crossref], [CAS], Google Scholar171https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXpvVSltLg%253D&md5=957477e23a3affd0052f38514329b436Sustainion Imidazolium-Functionalized Polymers for Carbon Dioxide ElectrolysisKutz, Robert B.; Chen, Qingmei; Yang, Hongzhou; Sajjad, Syed D.; Liu, Zengcai; Masel, I. RichardEnergy Technology (Weinheim, Germany) (2017), 5 (6), 929-936CODEN: ETNEFN; ISSN:2194-4296. (Wiley-VCH Verlag GmbH & Co. KGaA)CO2 electrolysis is a key step in CO2 conversion into fuels and chems. as a way of mitigating climate change. We report the synthesis and testing of a series of new anion-conductive membranes (tradenamed Sustainion®) for use in CO2 electrolysis. These membranes incorporate the functional character of imidazolium-based ionic liqs. as co-catalysts in CO2 redn. into a solid membrane with a styrene backbone. We find that the addn. of an imidazolium group onto the styrene side-chains increases the selectivity of the reaction from approx. 25% to approx. 95%. The current at 3 V is increased by a factor of 14. So far we have been able to tune these parameters to achieve stable cells that provide current densities higher than 100 mA cm-2 at 3 V cell potential with a CO product selectivity over 98%. Stable performance was obsd. for 6 mo of continuous operation (>150 000 000 turnovers). These results demonstrate that imidazolium polymers are ideal membranes for CO2 electrolysis.
- 172Klingan, K.; Ringleb, F.; Zaharieva, I.; Heidkamp, J.; Chernev, P.; Gonzalez-Flores, D.; Risch, M.; Fischer, A.; Dau, H. ChemSusChem 2014, 7, 1301– 1310 DOI: 10.1002/cssc.201301019
- 173Shinagawa, T.; Takanabe, K. ChemSusChem 2017, 10, 1318– 1336 DOI: 10.1002/cssc.201601583
- 174Shinagawa, T.; Ng, M. T.-K.; Takanabe, K. ChemSusChem, DOI: DOI: 10.1002/cssc.201701266 .
- 175Dionigi, F.; Vesborg, P. C. K.; Pedersen, T.; Hansen, O.; Dahl, S.; Xiong, A.; Maeda, K.; Domen, K.; Chorkendorff, I. Energy Environ. Sci. 2011, 4, 2937– 2942 DOI: 10.1039/c1ee01242h
- 176Esposito, D. V.; Lee, Y.; Yoon, H.; Haney, P. M.; Labrador, N. y.; Moffat, T. P.; Talin, A. A.; Szalai, V. A. Sustainable Energy Fuels 2017, 1, 154– 173 DOI: 10.1039/C6SE00073H[Crossref], [CAS], Google Scholar176https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXhs1Crs77N&md5=c8ddc6c357c9cfc09f4b99bcb60eadd8Deconvoluting the influences of 3D structure on the performance of photoelectrodes for solar-driven water splittingEsposito, Daniel V.; Lee, Youngmin; Yoon, Heayoung; Haney, Paul M.; Labrador, Natalie Y.; Moffat, Thomas P.; Talin, A. Alec; Szalai, Veronika A.Sustainable Energy & Fuels (2017), 1 (1), 154-173CODEN: SEFUA7; ISSN:2398-4902. (Royal Society of Chemistry)Three-dimensionally (3D) structured photoelectrodes offer a no. of potential benefits for solar fuel prodn. compared to conventional planar photoelectrodes, including decreased optical losses, higher surface area for catalysis, easier removal of product species, and enhanced carrier collection efficiency. However, 3D structures can also present challenges, such as lower photovoltage and larger surface recombination. Quantifying and understanding the advantages and disadvantages of 3D structuring can maximize benefits, but this goal is not trivial because the factors that affect photoelectrode performance are intertwined. In this article, we provide an overview of the benefits and challenges of using 3D photoelectrode structures and present a systematic approach for deconvoluting the most common effects of 3D structure on photoelectrode performance. As a basis for this study, metal-insulator-semiconductor (MIS) photoelectrodes consisting of p-Si micro-pillar arrays with well-defined diam., pitch, and height were fabricated by reactive ion etching (RIE). A general framework for modeling the influences of 3D structure on photoelectrode current-potential performance is presented, and a comparison of the loss mechanisms in 3D and planar photoelectrodes is illustrated using loss anal. diagrams. We expect that most of the measurements and analyses that we demonstrate for MIS photoelectrodes can be applied with equal success to liq.-junction and p-n junction 3D structured photoelectrodes.
- 177Chen, Z.; Jaramillo, T. F.; Deutsch, T. G.; Kleiman-Shwarsctein, A.; Forman, A. J.; Gaillard, N.; Garland, R.; Takanabe, K.; Heske, C.; Sunkara, M.; McFarland, E. W.; Domen, K.; Miller, E. L.; Turner, J. A.; Dinh, H. N. J. Mater. Res. 2010, 25, 3– 16 DOI: 10.1557/JMR.2010.0020[Crossref], [CAS], Google Scholar177https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXhtlKmsLw%253D&md5=70cf3c6595a9d9a1f489b028475e09aaAccelerating materials development for photoelectrochemical hydrogen production: standards for methods, definitions, and reporting protocolsChen, Zhebo; Jaramillo, Thomas F.; Deutsch, Todd G.; Kleiman-Shwarsctein, Alan; Forman, Arnold J.; Gaillard, Nicolas; Garland, Roxanne; Takanabe, Kazuhiro; Heske, Clemens; Sunkara, Mahendra; McFarland, Eric W.; Domen, Kazunari; Miller, Eric L.; Turner, John A.; Dinh, Huyen N.Journal of Materials Research (2010), 25 (1), 3-16CODEN: JMREEE; ISSN:0884-2914. (Materials Research Society)A review. Photoelectrochem. (PEC) H2O splitting for H prodn. is a promising technol. that uses sunlight and H2O to produce renewable H with O as a byproduct. In the expanding field of PEC H prodn., the use of standardized screening methods and reporting has emerged as a necessity. This article is intended to provide guidance on key practices in characterization of PEC materials and proper reporting of efficiencies. Presented here are the definitions of various efficiency values that pertain to PEC, with an emphasis on the importance of solar-to-H efficiency, as well as a flow chart with std. procedures for PEC characterization techniques for planar photoelectrode materials (i.e., not suspensions of particles) with a focus on single band gap absorbers. These guidelines serve as a foundation and prelude to a much more complete and in-depth discussion of PEC techniques and procedures presented elsewhere.
- 178van de Krol, R.; Grätzel, M. Photoelectrochemical Hydrogen Production; Springer: Berlin, 2012.
- 179Nurlaela, E.; Ziani, A.; Takanabe, K. Mater. Renew. Sustainable Energy 2016, 5, 18 DOI: 10.1007/s40243-016-0083-z
- 180Nurlaela, E.; Ould-Chikh, S.; Harb, M.; del Gobbo, S.; Aouine, M.; Puzenat, E.; Sautet, P.; Domen, K.; Basset, J.-M.; Takanabe, K. Chem. Mater. 2014, 26, 4812– 4825 DOI: 10.1021/cm502015q
- 181Ziani, A.; Nurlaela, E.; Dhawale, D. S.; Silva, D.; Alarousu, E.; Mohammed, O. F.; Takanabe, K. Phys. Chem. Chem. Phys. 2015, 17, 2670– 2677 DOI: 10.1039/C4CP05616G
- 182Nurlaela, E.; Wang, H.; Shinagawa, T.; Flanagan, S.; Ould-Chikh, S.; Qureshi, M.; Mics, Z.; Sautet, P.; Le Bahers, T.; Cánovas, E.; Bonn, M.; Takanabe, K. ACS Catal. 2016, 6, 4117– 4126 DOI: 10.1021/acscatal.6b00508[ACS Full Text], [CAS], Google Scholar182https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XosVSjtLY%253D&md5=d9525dcdd19ecb10b88d138dcc4084dcEnhanced Kinetics of Hole Transfer and Electrocatalysis during Photocatalytic Oxygen Evolution by Cocatalyst TuningNurlaela, Ela; Wang, Hai; Shinagawa, Tatsuya; Flanagan, Sean; Ould-Chikh, Samy; Qureshi, Muhammad; Mics, Zoltan; Sautet, Philippe; Le Bahers, Tangui; Canovas, Enrique; Bonn, Mischa; Takanabe, KazuhiroACS Catalysis (2016), 6 (7), 4117-4126CODEN: ACCACS; ISSN:2155-5435. (American Chemical Society)Understanding photophys. and electrocatalytic processes during photocatalysis in a powder suspension system is crucial for developing efficient solar energy conversion systems. We report a substantial enhancement by a factor of 3 in photocatalytic efficiency for the oxygen evolution reaction (OER) by adding trace amts. (∼0.05 wt %) of noble metals (Rh and Ru) to a 2 wt % cobalt oxide modified Ta3N5 photocatalyst particulate. The optimized system exhibited high quantum efficiencies (QEs) of up to 28 and 8.4% at 500 and 600 nm in 0.1 M Na2S2O8 at pH 14. By isolation of the electrochem. components to generate doped cobalt oxide electrodes, the electrocatalytic activity of cobalt oxide on doping with Ru or Rh was improved in comparison with cobalt oxide, as evidenced by the onset shift for electrochem. OER. D. functional theory (DFT) calcns. show that the effect of a second metal addn. is to perturb the electronic structure and redox properties in such a way that both hole transfer kinetics and electrocatalytic rates improve. Time-resolved terahertz spectroscopy (TRTS) measurement provides evidence of long-lived electron populations (>1 ns; with mobilities μe ≈ 0.1-3 cm2 V-1 s-1), which are not perturbed by the addn. of CoOx-related phases. Furthermore, we find that Ta3N5 phases alone suffer ultrafast hole trapping (within 10 ps); the CoOx and M/CoOx decorations most likely induce a kinetic competition between hole transfer toward the CoOx-related phases and trapping in the Ta3N5 phase, which is consistent with the improved OER rates. The present work not only provides a novel way to improve electrocatalytic and photocatalytic performance but also gives addnl. tools and insight into understand the characteristics of photocatalysts that can be used in a suspension system.
- 183de Respinis, M.; Fravventura, M.; Abdi, F. F.; Schreuders, H.; Savenije, T. J.; Smith, W. A.; Dam, B.; van de Krol, R. Chem. Mater. 2015, 27, 7091– 7099 DOI: 10.1021/acs.chemmater.5b02938
- 184Vequizo, J. J. M.; Hojamberdiev, M.; Teshima, K.; Yamakata, A. J. Photochem. Photobiol., A 2017, DOI: 10.1016/j.jphotochem.2017.09.005
- 185Xing, Z.; Zong, X.; Pan, J.; Wang, L. Chem. Eng. Sci. 2013, 104, 125– 146 DOI: 10.1016/j.ces.2013.08.039[Crossref], [CAS], Google Scholar185https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXhvFWit7vO&md5=6ae40e40757445367c583efbcc68114bOn the engineering part of solar hydrogen production from water splitting: Photoreactor designXing, Zheng; Zong, Xu; Pan, Jian; Wang, LianzhouChemical Engineering Science (2013), 104 (), 125-146CODEN: CESCAC; ISSN:0009-2509. (Elsevier Ltd.)A review. Water splitting under sunlight illumination in the presence of semiconductor photocatalyst is a promising way to produce clean hydrogen fuel. Solar hydrogen can be obtained in two routes: photoelectrochem. (PEC) water splitting based on immobilized photocatalysts in thin films and photocatalytic (photochem.) water splitting based on powder photocatalysts in slurry system. Over the past several decades, tremendous research work was devoted to exploring new semiconductor materials suitable for PEC and photochem. systems and understanding the underlying mechanism of the water splitting process. However, much less attention was paid to the design of photocatalytic reaction systems or reactors, which is indeed critically important for the overall solar energy conversion performance. This paper summarizes the basic working mechanisms of both PEC and photochem. systems, and gives an overview of a variety of photoreactor design and development.
- 186Setoyama, T.; Takewaki, T.; Domen, K.; Tatsumi, T. Faraday Discuss. 2017, 198, 509– 527 DOI: 10.1039/C6FD00196C
- 187Singh, M. R.; Xiang, C.; Lewis, N. S. Sustain. Energy Fuels 2017, 1, 458– 466 DOI: 10.1039/C7SE00062F
- 188Pinaud, B. A.; Benck, J. D.; Seitz, L. C.; Forman, A. J.; Chen, Z.; Deutsch, T. G.; James, B. D.; Baum, K. N.; Baum, G. N.; Ardo, S.; Wang, H.; Miller, E.; Jaramillo, T. F. Energy Environ. Sci. 2013, 6, 1983– 2002 DOI: 10.1039/c3ee40831k
- 189Hisatomi, T.; Miyazaki, K.; Takanabe, K.; Maeda, K.; Kubota, J.; Sakata, Y.; Domen, K. Chem. Phys. Lett. 2010, 486, 144– 146 DOI: 10.1016/j.cplett.2010.01.006
- 190Hisatomi, T.; Maeda, K.; Takanabe, K.; Kubota, J.; Domen, K. J. Phys. Chem. C 2009, 113, 21458– 21466 DOI: 10.1021/jp9079662