THE CHEMICAL STATE OF Ru IN Pt-Ru DIRECT METHANOL FUEL CELL ANODE ELECTROCATALYSTS

摘要

Bulk and surface analyses of commercial, as-received direct methanol fuel cell Pt-Ru electrocatalysts indicate that a significant portion of the Ru exists as RuO_2 and/or a hydrous oxide. A consistent picture of the chemical state of these catalysts arises from their characterization by glow discharge mass spectroscopy, x-ray photoelectron spectroscopy, thermal gravimetric and differential thermal analysis and x-ray absorption near-edge structure spectroscopy. In two of the commercial Pt-Ru catalysts examined, the amount of Ru present as oxidized Ru was approx 95 and 75 atom percent. In addition, significant quantities of various transition metal and light element impurities are incorporated in the as-received catalysts. The ramifications of these findings are discussed with regard to the existence of metal alloy, the state of the surfaces that form the catalyst-ionomer-reductant interphase, the degree of catalyst activity and the methanol decomposition mechanism.