Pt / C Electrode Doping Of Sno <sub> 2 </ Sub> On The Methanol Electro-catalytic Oxidation Performance

In recent years, the direct methanol fuel cell (DMFC) has been paid more and more attention due to its many advantages such as the mobile power sources. However, it has some key problems. One of them is that the Pt, which is the normally used anodic catalyst, has the low electrocatalytic activity for the CH3OH oxidation and is easy to be poisoned with the intermediate of the methanol oxidation. Many investigations show that the Pt catalyst doping some metal oxides improves its electrocatalytic performance. This is due to the formation of more OHads on the surface of the doped metal oxides. It accelerates the desorption of the COads which is an intermediate product in the CH3OH oxidation. In this work, the kinetics and mechanism of the CH3OH oxidation on Pt/C and Pt-Ru/C electrodes have been studied. In addition, we synthesized the Pt-SnO₂/C catalysts through the liquid-saturated method. SnO₂ are tetrahedral rutile structure and excellent conductivity, their excess electrones on the orbit d of Sn atom can move to the Pt catalyst. So high electrocatalytic activities and the CO tolerance were found by changing the sequence of the Pt and SnO₂ and choosing different active carbons for the supported catalysts.The kinetic and mechanism of the CH3OH oxidation was studied by cyclic voltammetry(CV) and chronopotentiometry(CP). It was found that the rate of the CH3OH oxidation depends on various adsorbates such as CHOHads, COads, OHads and Oads on the electrode surface.When the coverage of both COads and OHads is relatively high, an autocatalysis occurs by oxidizing the bridge-bonded adsorbates, which produces more vacant sites. The anodic current increase with the decreasing of the potential, and both the formation of the OHads and desorption of the COads are a couple of competitive reactions.For the preparation order of SnO₂/C and Pt-SnO₂/C, the Pt-SnO₂/C(Pt:SnO₂=1:1, quality ratio) catalyst gave the best results in electrocatalytic activity and the CO tolerance, and the lower the content of the SnO₂ was, the lower the electrocatalytic activity and the CO tolerance became. On the other hand, the Pt-SnO₂/C(Pt:SnO₂=20:1, quality ratio) showed the best electrocatalytic activity and the CO tolerance for the preparation order of Pt/C and Pt-SnO₂/C, the higher the content of the SnO₂ was, the lower the electrocatalytic activity and the CO tolerance...