Abstract: The electro-oxidation of CH3OH on underpotentially-deposited-tin-modified platinum electrode (upd-Sn/Pt) has been studied. In this study, we aimed to clarify the role of tin playing in methanol electroxidation by using electrochemical techniques and surface-enhanced infrared absorption spectroscopy (SEIRAS). The following points have been obtained through the study. The upd-Sn modified Pt electrode with coverage around 0.20 shows a remarkably enhanced activity for the electro-oxidation of CH3OH; As long as the potential is lower than 0.35 V (vs RHE),regardless of a pure Pt or the upd-Sn/ Pt electrode, the direct electro-oxidation of methanol only can reach the stage of COads formation,i.e.CH3OH/Pt=COads＋4H＋＋4e(Pt) (a). When the rate of the accumulation of COads exceeds the rate of the following reaction: Sn－OH＋COads = CO2＋H＋＋e (Sn) (b), the reaction (a) will slow down. When the surface of pure Pt is completely covered by COads, the reaction (a) will totally stop. There will be no current to be output until reaction (b) removes COads from the electrode surface. The more the sites of Pt occupied by Sn adatoms, the fewer the sites available for reaction (a). That is why an unduly high coverage of Sn will lead to the reduction of catalysis of upd-Sn/Pt electrode. The enhanced effect of tin on the methanol electroxidation is observed on both the bright platinum and the platinized platinum.

Key words: Direct methanol fuel cells (DMFC), Methanol oxidation, Underpotential deposition, Pt-Sn alloy