METHANOL OXIDATION ON CARBON-SUPPORTED PLATINUM-TIN ELECTRODES IN SULFURIC-ACID

A study is made of the electrooxidation of methanol in sulfuric acid o n carbon-supported electrodes containing platinum-tin bimetal catalyst s that are prepared by an in situ potentiometric-characterization rout e. The catalysts are investigated by employing chemical analyses, X-ra y diffraction (XRD), X-ray absorption-near-edge spectroscopy (XANES) a nd X-ray photoelectron spectroscopy (XPS) data in conjunction with ele ctrochemical measurements. From the electrochemical data, it is inferr ed that while an electrode with (3:1) Pt-Sn/C catalyst involves a two- electron rate-limiting step akin to platinum-on-carbon electrodes, it is shifted to a one-electron mechanism on electrodes with (3:2)Pt-Sn/C , (3:3)Pt-Sn/C, and (3:4)Pt-Sn/C catalysts. The study suggests that th e tin content in the platinum-tin bimetal catalyst produces: (i) a cha rge transfer from tin to platinum; (ii) an increase in the coverage of adsorbed methanolic residues with increase in the tin content, as ind icated by the shift in rest potential of the electrodes towards the re versible value for oxidation of methanol (0.043 V versus SHE), and (ii i) a decrease in the overall content of higher valent platinum sites i n the catalyst.