Electrocatalyst materials for fuel cells based on the polyoxometalates [PMo (12 − n)V nO 40] (3 + n)− ( n = 0–3)

Abstract

We report on the use of the polyoxometalate acids of the series [PMo (12 − n )V n O 40] (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 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.