Electrocatalyst Materials for Fuel Cells Based on the Polyoxometalates [PMo/sub (12-n)/V/sub n/O/sub 40/]/sup (3+n)-/ (n=0-3)

We report on the use of the polyoxometalate acids of the series [PMo _{(12- n)}V_nO₄₀]^{(3 + n)-} (n = 0-3) as electrocatalysts in both the anode and the cathode of polymer-electrolyte membrane (PEM) fuel cells. The heteropolyacids were incorporated as catalysts in a commercial gas diffusion electrode based on Vulcan XC-72 carbon which strongly adsorbed a low loading of the catalyst, ca. 0.1 mg/cm². The moderate activity observed was independent of the number of vanadium atoms in the polyoxometalate. In the anode the electrochemistry is dominated by the V^3+/4+ couple. With a platinum reference wire in contact with the anode, polarization curves are obtained with V_OC of 650 mV and current densities of 10 mA cm^-2 at 100 mV at 80°C. These catalysts showed an order of magnitude more activity on the cathode after moderate heat treatment than on the anode, V_OC = 750 mV, current densities of 140 mA cm^-2 at 100 mV. The temperature dependence of the catalysts was also investigated and showed increasing current densities could be achieved on the anode up to 139°C and the cathode to 100°C showing the potential for these materials to work at elevated temperatures.