Synthesis And Performances Investigation Of Pd-based Anode Electrocatalysts For Alkaline Direct Alcohols Fuel Cell

Nowadays, alkaline direct alcohol fuel cell (ADAFC) has attracted wide attention by the researchers due to its high energy density, environment friendly. The traditional ADAFC faced some serious problems, such as inferior activity and stability of the catalyst. Therefore, the design of catalysts with low cost, high catalytic activity and high stability of the catalyst became a hot topic in the ADAFC research. In allusion to the problems mentioned above, the high catalytic activity and high stability of the Pd-based catalysts have been designed and prepared, and mechanism of the oxidation reaction of alcohols on the Pd catalyst surface have also been implemented in this thesis.In this paper, the nano core-shell structure Au@Pd catalyst has been prepared by three-phase transfer method. Specifically, method of three-phase transfer process has been optimized, and the key parameters which could influence on core-shell morphology, such as intermediate phase and reducing agent was also analyzed, the activity of the Au@Pd catalyst has been tested, and the mechanism of the activity improvement also be researched; In addition, the dosage of Pd precursor, the kinds and ratio of alloy also have been optimized for higher catalysis activity. The results show that the intermediate phase and reducing agent can affect morphology and the activity of the Au@Pd catalyst by controlling the reduction rate of Pd precursor. The core shell structure Au@Pd catalyst shows much higher activity and stability in the alkaline medium for methanol electrooxidaiton, and the enhanced performance attribute to the intense electronic interaction between the Au core and Pd shell.In order to further reduce the cost of the Pd-based catalysts, the monodispersed nano-scale CeO2particles have been prepared by thermal decomposion method. And the Pd-around-CeO2nanostructure composite catalyst has also been prepared with the three-phase transfer method with the CeO2core. The results of the performance test show that: the Pd-around-CeO2catalyst shows much higher activity than the traditional Pd/CeO2/C and Pd/C catalysts in the alkaline medium for ethanol electrooxidaiton. The results of acetaldehyde stripping voltammetry and XPS indicated the elevated of the performance of the Pd-around-CeO2attribute to the intense interaction between the Pd and CeO2naonparticles, and the “dual improvement mechanism” has been proposed for the first time in this thesis.In order to further enhance the interaction between Pd and the oxide, the Ni-doped CeO2nanoparticles hve been prepared with the ceric ammonium nitrate and acetylacetone nickel as the precursor via the thermal decomposion method. And the Pd/Ni-CeO2/C catalyst has also been prepared with the microwave-assisted ethylene glycol reduction method, and the activity of the Pd/Ni-CeO2/C catalyst has been tested in the alkaline medium for ethanol electroxidation respectively. The results indicated that the Ni-doped CeO2nanoparticles show positive effect of the ethanol electrooxidation as a promoter. The Pd/Ni-CeO2/C shows enhanced activity for ethanol electroxoidaiton than traditional Pd/C and Pd/CeO2/C catalysts. The enhanced active oxygen species release ability of the Ni-doped CeO2nanoparticles and the interaction between metal and oxide is the mainly reasons for the improved performance of Pd/Ni-CeO2/C catalyst.In order to further improve the ability of promoter and stability of catalysts, the Pd-doped CeO2nanowires have been prepared with the solvothermal method, and the Pd/C@Pd-CeO2NWs catalysts have also been prepared with the carbon coated Pd-doped CeO2nanowires support. Some critical parameter which could affect the1-D nanowire morphology have been analyzed and optimized, such as the content of Pd doping, the reaction time, and dosage of the nitric acid. The formation mechanism of the Pd-doped CeO2nanowires in the solvothermal environment have been explored, and the activity of the Pd/C@Pd-CeO2NWs catalysts for ethanol electroxidaiton has been tested in the alkaline medium, and the catalyst shows much higher activity and stability than the traditional catalysts. According to results of XPS, the active oxygen species releasing ability of CeO2have been remarkable enhanced by Pd doping, and this is the mainly reason for its high activity. The excellent corrosion resistance of the CeO2nanowires is the main reason for the catalyst splendid stability.