甲醇在欠电位沉积Sn/Pt电极上催化氧化

在欠电位沉积（upd）锡修饰的铂电极（upd-Sn/Pt）上,对甲醇电化学催化氧化过程进行了研究.发现当Pt表面upd-Sn的覆盖率在20％附近时,对甲醇的催化氧化的增强作用最为明显；在电位低于0.35 V （vs RHE）时,甲醇在Pt与upd-Sn/Pt电极上氧化只进行到脱氢生成CO的步骤;在0.35 V以后,表面Sn－OH形成,反应Sn－OH＋COads=Sn＋CO2＋H＋＋e有利于表面CO的去除;而Pt电极上,只有0.6 V以后,才有反应Pt－OH＋COads=Pt＋CO2＋H＋＋e发生.因此,Sn的存在有利于甲醇在较低的电位下氧化; Pt电极上CH3OH脱氢并释放出电子的过程是一个快速的过程,表面CO的去除是甲醇氧化过程的控制步骤;甲醇氧化产生的表面吸附态CO 以线式吸附为主,少量的桥式吸附态CO在反应初期即达到吸附饱和; Pt表面上upd-Sn表现的催化增强作用,在光亮铂电极和在高分散铂黑电极上是一致的.

Methanol Electroxidation on Upd-Sn Modified Platinum Electrodes

The electro oxidation of CH3OH on underpotentially deposited tin modified platinum electrode (upd Sn/Pt) has been studied.In this study,weaimed 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 availabe 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.