Performance and Durability of Chalcogenide-Modified Ruthenium Catalysts for Oxygen Reduction: Hydrogen-Air MEA and RRDE Studies

The ORR performance of a Se/Ru catalyst has been evaluated by RRDE measurements and in fuel cell tests. The catalyst was prepared by adding aqueous SeO2 to metallic Ru black, then bubbling H2 through the mixture. The Tafel slope (80{plus minus}5 mV decade-1 at low overpotential) and activation energy (25{plus minus}3 kJ mol-1 at 0.40 V overpotential) indicate that this Se/Ru catalyst behaves mechanistically in a similar way to pure noble metal catalysts (e.g., Pt and Ru). In comparison to other Se/Ru catalysts, the sample shows higher activity, presumably due to the greater number of Ru sites uncovered by Se available for reaction with oxygen, as estimated by CO stripping. Fuel cell tests demonstrate that Se/Ru is superior to Ru black at low current densities, thanks to the inhibiting effect of Se on the oxidation of Ru to inactive species. The stability of Se under aqueous and fuel cell conditions is also discussed.