Effect of Pt-Ru alloy composition on high-temperature methanol electro-oxidation

The structure, chemistry and morphology of unsupported Pt---Ru electro-catalysts of various compositions were investigated by X-ray diffraction (XRD), energy-dispersive analysis by X-rays and X-ray photoelectron spectroscopy. The metal surface-area of Pt---Ru catalysts prepared in an identical manner increased significantly with the increase in Ru content. The electro-catalytic activity of the catalysts towards methanol oxidation in direct methanol fuel cells (DMFC) was studied at 130 °C. A volcano-shape curve was obtained as a function of alloy composition for both mass and specific activities with a maximum occurring for the Pt:Ru (1:1) electro-catalyst. At low anodic overpotentials, an increase in both mass and specific activities as a function of bulk composition was found up to 50 at.% Ru, corresponding to about 40% Ru on the surface. These results indicate that the bifunctional mechanism governs the methanol electro-oxidation on Pt---Ru in the high temperature range, similarly to conventional DMFC operation (60–90 °C).