ELECTROOXIDATION MECHANISMS OF METHANOL AND FORMIC-ACID ON PT-RU ALLOY SURFACES

Voltammetry combined with single-potential alteration infrared spectro scopy (SPAIRS) were used to study the extent of adsorbed CO produced a t Pt, Ru and Pt-Ru alloy electrodes during methanol and formic acid ox idation in acidic supporting electrolyte. The addition of even small a tomic fractions of Ru to Pt surfaces caused a decrease in the quasi-st eady-state level of CO on the surface for both reactions. This result is consistent with the bifunctional mechanism proposed previously: Ru sites nucleate oxygen containing species at approximate to 0.2-0.3 V l ower potential than on the pure Pt surface; the adsorption of methanol occurs on Pt ensembles producing adsorbed CO; in the case of formic a cid, adsorption is equally facile at Pt-Pt, Pt-Ru and Ru-Ru sites, wit h dehydration producing adsorbed CO; the further electro-oxidation of CO is catalyzed by oxygen-containing species nucleated onto nearby by Ru atoms. The improved efficiency of the alloy surfaces for oxidation of adsorbed CO at low potential shifts the rate limiting step to the a dsorption step, which results in very low coverages of the surfaces by adsorbed CO.