| Because of the abandent fuel sources, easy storageand transport and high power density, direct methanol fuel cells (DMFCs) and direct formic acid fuel cells (DFAFCs) have been the focus of low-temperature fuel cells. Pt, which has superior catalytic activity, are generally used as of low-temperature fuel cells catalysts. However, the high cost and limited resource of Pt restrict the large scale commercialization of fuel cells. Additionally, CO as the intermediate in the methanol or formic acid oxidation can be adsorbed on Pt surface, which could result in the severe poisoning of Pt catalyst. In recent years, In order to reduce the cost of fuel cell catalysts, and improve the CO-tolerance and stability of catalysts, many efforts have been devoted to develop Pt-based alloy catalysts and novel support materials for catalysts.In this thesis, by modulating the structure of catalysts, preparing novel support material we attempt to improve catalytic activty and CO-tolerance. the structure and electrochemical properties of the as-prepared Pt-Pd/GR, Pt/TiO2-C, Pd/CeO2catalysts were studied. Their catalytic performance toward methanol oxidation or formic acid oxidation has been investigated. The research works are summarized as follows:(1) Pt-Pd bimetallic nanospheres supported on graphene (GR) nanosheets was prepared by a facile surfactant-free method. The pre-nucleated Pd seeds via the redox reaction between Na2PdC14and graphene oxide (GO) direct the growth of Pt nanoparticles (NPs), resulting in the bimetallic nanospheres. The presence of Pt-Pd nanospheres can effectively prevent the aggregation of graphene nanosheets. This structure is favorable to the electron and mass transport in electrocatalyst. The Pt-Pd/GR catalyst exhibits high catalytic activity and long-term stability towards the methanol oxidation reaction (MOR) with specific current density of51.8mA cm-2.(2) TiO2-C hybrid material was prepared by calcination of mixed precursor containing TiO2with urea, which was used as support material to prepare Pt/TiO2-C catalyst. The Pt-TiO2-C hetero interfaces can be achieved with Pt nanoparticles deposited on the boundaries of rutile TiO2and graphitic carbon of the TiO2-C substrate. The as-prepared Pt/TiO2-C catalyst possesses a large electrochemical surface area (ESA) and exhibited remarkably improved catalytic activity and stability toward methanol electrooxidation.(3) CeO2nanotubes were employed as support material to prepare the Pd/CeO2-NT catalyst. Pd nanoparticles are deposited both on the outer surfaces and inside interiors of CeO2nanotubes. The as-prepared Pd/CeO2-NT catalysts possess a large electrochemically active surface area (ESA) and exhibited improved electrocatalytic performance towards formic acid oxidation, in comparison with the Vulcan XC-72carbon black and the commercial CeO2nanopowder supported Pd catalysts. This work demonstrates that CeO2nanotubes are promising support materials in application of the direct liquid fuel cells anode electrocatalysts. |
