Carbonyl Clusters Ways Preparation Of Direct Methanol Fuel Cell Anode Catalyst

The fuel cell has been paid more and more attention because of the shortage of fossil fuels and environmental pollution produced using fossil fuels. Among the fuel cells, people attaches more and more important to the direct methanol fuel cell (DMFC) using methanol as liquid fuel. However, the performances of DMFC are still limited by several problems. One problem is that commonly used Pt catalyst has low electrocatalytic activity for the methanol oxidation and the intermediates of the methanol oxidation, such as linearly adsorbed CO species would poison the Pt catalyst. Usually, Pt based alloy catalysts are used to increase the electrocatalytic activity of Pt and to reduce the poison extent of the catalysts. In addition, the effect of some factors, such as the particle size and the particle size distribution etc. of the catalysts prepared with different methods on the electrocatalytic activity is expoited. Therfore, in this thesis, the carbon-supported Pt (Pt/C) and bimetallic Pt-Os (Pt-Os/C) catalysts were prepared via the carbonyl complex route. Their electrocatalytic behaviors for the methanol oxidation were evaluated and compared with that of the commercial E-Tek catalysts. The results obtained are as follows:The Pt/C catalysts with different Pt loading were prepared via a Pt carbonyl cluster route. X-ray diffraction (XRD) and transmission electron microscopy (TEM) results indicated that the average particle size of Pt in the Pt/C catalysts prepared with the different Pt loading is ca. 2-4 nm with a narrow size distribution and a good dispersion. The average particle size of Pt in the Pt/C catalysts prepared is very close to that of the commercial E-Tek catalyst. The cyclic voltammetric and chronoamperometric measurements demonstrated that the prepared Pt/C catalyst with 40% Pt showed the best electrocatalytic activities for methanol oxidation. It is ascribed to the suitable particle size and low inner resistance of the catalytic layer.Pt-Os/C catalysts with different Pt:Os atomic ratios were prepared via the carbonyl complex route. XRD data showed that the Pt-Os/C catalysts prepared are basically with the single-phase disordered structure (solid solution). The inductively coupled plasma (ICP) analysis confirmed that atomic compositions are nearly thesame as those anticipated from the relative concentrations of the initial reactants. It was observed from TEM images that the Pt-Os particles in the Pt-Os/C catalysts possess the good dispersity, narrow distribution of the particle size and small mean particle size of ca. 2.2 run. The electrocatalytic activity of the Pt-Os/C catalysts for methanol oxidation is higher than that of the Pt/C and Pt-Ru/C catalysts. The Pt-Os/C catalyst with Pt/Os atomic ratio of 3:1 showed the highest electrocatalytic activity for methanol oxidation. The enhanced catalytic activity of Pt-Os catalysts for methanol oxidation can be rationalized by a bifunctional mechanism in which Pt is responsible for dehydrogenation of methanol and metallic Os, rather than Os oxide, for the dehydrogenation of water. It was also found that an electronic effect in the electrocatalysis is associated with the amount of Os atoms in the catalysts.