ORDERED POROUS CARBON SUPPORTED NANO-PLATINUM ELECTROCATALYST FOR DIRECT METHANOL FUEL CELL APPLICATIONS

Abstract

Fuel cells are considered as the future energy conversion device for wide variety of applications. Fuel cells can power almost any portable device or machine that uses batteries. Unlike a typical battery, which eventually goes dead, a fuel cell continues to produce energy as long as fuel and oxidant are supplied. Laptop, computers, cellular phones, video recorders, and hearing aids could be powered by portable fuel cells. Fuel cells have strong benefits over conventional combustion-based technologies currently used in many power plants and cars. They produce much smaller quantities of greenhouse gases and none of the air pollutants that create smog and cause health problems. If pure hydrogen is used as a fuel, fuel cells emit only heat and water as a byproduct. Hydrogen-powered fuel cells are also far more energy efficient than traditional combustion technologies. Among the different types of fuel cells, the PEM (Polymer electrolyte membrane) fuel cells employing hydrogen as the fuel and the DMFC (Direct methanol fuel cell) employing methanol as the fuel are under development for successful commercialization. The commercialization of fuel cells is delayed mainly because of the high cost of the catalyst layer which needs expensive noble metal such as platinum and its alloys. The sluggish kinetics of oxygen reduction reaction in H2 based PEMFC and both oxygen reduction and methanol oxidation reactions in DMFC, have caused concern. Even a slight enhancement in the activity and durability of these catalysts can bring down the cost significantly. The typical catalyst mostly used in fuel cell electrodes is Pt dispersed on carbon black support, for both anode and cathode electrodes. Hydrogen is the most potential and promising fuel due to its high energy density and the maximum attainable voltage (Eºmax =1.15 V), which is closer to the theoretical value (Eºtheor = 1.23 V). But hydrogen fuel cell encounters challenges of hydrogen production, storage and transportation, whereas DMFC uses a liquid methanol as a fuel, which can be easily stored, handled and transported. Carbon materials are the most widely used support for fuel cell electro catalyst due to its various properties. These properties include corrosion resistance, anisotropic electronic property, formation of intercalation compounds, strong covalent bond formation with variety of surface modifiers and adsorbing capacity of wide variety of materials. The nature of the carbon determines the electrochemical performance of electrode catalysts. Interactions between the noble metal and the support may increase the catalyst performance. Carbon black, Vulcan XC-72 is the most common support material for fuel cell electro catalyst. But nowadays various carbon materials have been investigated as electro-catalyst support like carbon nanofibers, carbon nanotubes, carbon aerogels and ordered nanoporous carbon (micro and mesoporous carbon). Micro porous carbons, having very high surface area are of great technological interest for the development of catalytic, electro catalytic and hydrogen storage systems. Ordered microporous carbons have been prepared by nanocasting method. i.e., CNI-1 and NCNI-1 have been synthesized by carbonization of furfuryl alcohol and pyrrole respectively within the pores of mordenite. The inorganic templates were then removed by HF treatment, followed by filtration, washing and drying to obtain the microporous carbons. All the carbon samples were systematically characterized by various analytical and spectroscopic techniques including, XRD, XPS, SEM and N2 sorption measurements. Subsequently, 10 and 20 wt % Pt were loaded on the microporous carbons using H2PtCl6.6H2O acid. The prepared platinum catalysts were systematically characterized by XRD, XPS and TEM. The prepared catalysts were evaluated for their catalytic activity for methanol electro oxidation reaction. Electrochemical oxidation of methanol over the microporous carbon supported platinum catalysts was studied by cyclic voltammetry at room temperature. The electrochemical measurements performed using 1 M H2SO4 + 1 M CH3OH indicate that the prepared catalysts exhibit excellent electrochemical activity as well as better CO tolerance compare to commercial Pt catalyst. The stability of the catalysts was studied by chronoamperometry (CA) measurement. Prepared microporous carbon supported Pt catalysts showed better stability compare to commercial Pt catalyst. It is therefore, concluded that platinum supported on ordered microporous carbon catalysts are promising electrode materials for methanol fuel cell applications.