A study of methanol electro-oxidation reactions in carbon membrane electrodes and structural properties of Pt alloy electro-catalysts by EXAFS

The transition metal alloy electro-catalysts were evaluated as low cost alt ernatives to direct oxidation of methanol fuel cells (DMFCs) and compared w ith the generally accepted noble metal and alloy catalysts using cyclic vol tammetry and X-ray absorption spectroscopy techniques. The effect of methan ol concentration in sulfuric acid, temperature, and catalyst surface area w ere evaluated and matched with the proper electro-oxidation mechanisms. The alloy catalyst Pt-Co/C was found to be a better catalyst for methanol oxid ation in acid solution compared with other transition metal alloys. The obs erved current oscillations in Pt-Cu/C in low and medium temperature regions were due to the dual role played by the surface reaction between MOH and P t-CO. Pt/C/Nafion(R) showed the highest resistance (10(6) Omega cm(-2)) com pared with Pt-Ru/C (280 m Omega cm(-2)). The observed unfavorable electroch emical performance of the bimetallic Pt-Ru catalysts call be correlated wit h the observed variations in geometric structural information obtained from EXAFS and XANES measurements. The bimetallic catalysts investigated in thi s study must have formed as a Pt cluster covered with Ru and may not be in the expected alloy composition, which probably leads to the poor electroche mical performance. (C) 2000 Elsevier Science S.A. All rights reserved.