The oxygen reduction activity and methanol tolerance of a range of transition metal sulfide electrocatalysts have been evaluated in half-cell experiments and in a liquid-feed solid polymer electrolyte direct methanol fuel cell. These catalysts were prepared in high surface area form by direct synthesis onto various surface-functionalized carbon blacks. Of the materials tested, mixed-metal catalysts based on ReRuS and MoRuS were observed to give the best oxygen reduction activities. In addition, significant increases in performance were observed when employing sulfur-functionalized carbon black, which were attributed to the preferential deposition of active Ru sites in the catalyst-preparation process.Although the intrinsic activity of the best material tested, namely, Mo2Ru5S5 on sulfur-treated XC-72, was lower than Pt (by Ca. 155 mV throughout the entire polarization curve), its activity relative to Pt increased significantly in methanolcontaminated electrolytes. This was due to methanol oxidation side reactions reducing the net activity of the Pt, especially at low overpotentials.

The effect of carbon functionality on the electrocatalytic performance of carbon black-supported, Pt..based, direct methanol fuel cell cathodes was investigated. Polarization data show that cathodes with nitrogen and sulfur functionality have enhanced catalytic activity toward oxygen reduction. Transmission electron microscopy results indicate that this behavior may be ascribed to a platinum particle size effect.

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