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/cm(2). 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 with V-OC of 650 mV and current densities of 10 mA cm(-2) at 100 mV at 80degreesC. 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 139degreesC and the cathode to 100degreesC showing the potential for these materials to work at elevated temperatures. (C) 2004 Elsevier Ltd. All rights reserved.