Oxygen reduction on Ru1.92Mo0.08SeO4, Ru/carbon, and Pt/carbon in pure andmethanol-containing electrolytes

The oxygen reduction reaction (ORR) activity of a Ru1.92Mo0.08SeO4 catalyst , a Vulcan XC72-supDortcd Ru catalyst and, for comparison, a Vulcan XC72-su pported Pt catalyst was studied with a rotating ring-disk electrode. The ve ry similar reaction characteristics of the two Ru catalysts in pure and CH3 OH-containing H2SO4 electrolyte, which differ markedly from those of the Pt catalyst, indicate that the reactive centers in both Ru catalysts must be identical. They are highly selective (>95%) toward reduction to H2O (four e lectron pathway), independent of the presence of methanol. In the latter ca se, they are 100% selective toward the ORR, i.e., completely methanol toler ant, while the ORR on Pt catalysts is accompanied by significant CH3OH oxid ation. Based on mass specific current densities, however, the Ru catalysts are significantly less active than the standard Pt catalysts. Only at metha nol concentrations above 10-30 mM does their methanol tolerance make them m ore active than Pt/Vulcan. Implications for their use as cathode catalysts in a direct methanol fuel cell are discussed. (C) 2000 The Electrochemical Society.