Electrocatalyst materials for fuel cells based on the polyoxometalates [PMo(12 − n)VnO40](3 + n)− (n = 0-3)

We report on the use of the polyoxometalate acids of the series [PMo(12 − n)VnO40](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 V3+/4+ couple. With a platinum reference wire in contact with the anode, polarization curves are obtained withVOC 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,VOC = 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.