PLATINUM ALLOY ELECTRODES BONDED TO SOLID POLYMER ELECTROLYTE FOR ENHANCEMENT OF METHANOL ELECTROOXIDATION AND ITS REACTION-MECHANISM

Enhancement of methanol electro-oxidation was observed on Pt alloy-SPE (solid polymer electrolyte) electrodes in a sulfuric acid solution, on which the catalytic activity was higher than that on a plain Pt-SPE or a second metal-electrodeposited Pt-SPE. Such Pt alloy-SPEs were prepared by a reducing agent penetration method; the reducing agent penetrated from one face of the SPE membrane to the other face, which contacted the mixture of metal ion solutions. Then, at the latter face of the SPE membrane, Pt alloy was formed, which was confirmed by x-ray diffraction. Such Pt alloy on SPE exhibited a partly amorphous character in the case of PtSn and PtRu alloy-SPEs. The electrodes studied were PtAuRu, PtRu, PtSn, and PtRuSn alloy-SPEs. For a specific alloy system, it was found that amorphous Pt alloy-SPEs exhibited the higher catalytic activity than the crystalline ones. The order of catalytic activity among them was cPtRuSn > aPtSn > aPtAuRu at 50-degrees-C, where a and c denote amorphous and crystalline, respectively. The kinetic parameters were observed to be different among the Pt alloy-SPEs. It was discussed from those parameters that the adsorption state of the adsorbed intermediate from a methanol molecule depended on the kind of electrode. The highest activities were observed on PtRuSn alloy-SPE at 50 and 60-degrees-C, which were 33 mA.cm-2 and 50 mA.cm-2 at 0.4 V vs. RHE in 1M CH3OH + 0.5M H2SO4 as apparent current densities, or 90 and 130-mu-A.cm-2 as true current densities with respect to the surface of Pt, respectively.