Technoeconomic Analysis of Photoelectrochemical (PEC) Hydrogen Production

Abstract

Photoelectrochemical (PEC) production of hydrogen is a promising renewable energy technology for generation of hydrogen for use in the future hydrogen economy. PEC systems use solar photons to generate a voltage in an electrolysis cell sufficient to electrolyze water, producing H2 and O2 gases. A major advantage of PEC systems is that they involve relatively simple processes steps as compared to many other H2 production systems. Additionally, they possess a wide operating temperature ranges, with no intrinsic upper temperature limit and a lower temperature of slightly below 0oC without a warm-up period, and well below 0oC with a warm-up period dependent on outside temperature. The primary challenges for PEC are to develop materials with sufficient photovoltage to electrolyze water, to minimize internal resistance losses, to have long lifetime (particularly corrosion life), to maximize photon utilization efficiencies, and to reduce plant capital cost. Under contract to the US Department of Energy, Directed Technologies Inc. (DTI) has conducted a techno-economic evaluation of conceptual PEC hydrogen production systems. Four basic system configurations are chosen by DOE’s PEC Working Group to encompass the technology spread of potential future PEC production systems. Overall system designs and parameters, costs of implementation, and costs of the output hydrogen were determined for each of the four conceptual systems. Each system consisted of a PEC reactor that generates H2 and O2, a gas processing system that compresses and purifies the output gas stream, and ancillary equipment. The first two of the four system configurations examined utilize aqueous reactor beds containing colloidal suspensions of PV-active nanoparticles, each nanoparticle being composed of the appropriate layered PV materials to achieve sufficient bandgap voltage to carry out the electrolysis reaction. The third and fourth system configurations use multi-layer planar PV cells in electrical contact with a small electrolyte reservoir and produce oxygen gas on the anode face and hydrogen gas on the cathode face. They are positioned in fixed or steered arrays facing the sun. The four specific system types conceptually designed and evaluated in the report are: Type-1: A single electrolyte -filled reactor bed containing a colloidal suspension of PEC nanoparticles which produce a mixture of H2 and O2 product gases. Type-2: Dual electrolyte-filled reactor beds containing colloidal suspensions of PEC nanoparticles, with one bed carrying out the H2O => ½ O2 + 2 H+ half-reaction, the other bed carrying out the 2H+ => H2 half-reaction, and including a mechanism for circulating the ions between beds. Type-3: A fixed PEC planar array tilted toward the sun at local latitude angle, using multijunction PV/PEC cells immersed in an electrolyte reservoir. Type-4: A PEC solar concentrator system, using reflectors to focus the solar flux at a 10:1 intensity ratio onto multi-junction PV/PEC cell receivers immersed in an electrolyte reservoir and pressurized to 300 psi.