| With the grobal economy growing, the fossil fuels powered energies are dramaticlly consumed, leading to a forthcoming energy and environment crisis. Proton exchange membrane fuel cell (PEMFC) has many advantages such as high efficiency, low emission, quiet, and wide source of H2fuel, and applied in stationary power station, electricity vehicles, protable power sources and aerospace. Hence, PEMFC has been greatly concerned by the governments. One of the key issues hindering the commericalization of PEMFC is catalyst-posioning. Trace amount of SO2/CO in the catalysts leads to deactivation or even shutdown of PEMFCs. Enhancing the catalyst activity towards SO2/CO oxidation is crucial to the stability of fuel cells. In addition, the preparation procedures of multi-metallic catalysts are complex, causing the high cost. Therefore, enhancing the catalyst SO2/CO oxidation resistance and simplizing preparation process are of importance to the commericalization of PEMFCs.In this thesis, low content of armphorous CeO2is first introduced to the20wt%Pt/C catalyst, revealing that the oxygen diffusion from CeO2to Pt assists the electrochemical oxidation towards SO2/CO. Then, the crystal CeO2having different morphologies are prepared by a hydrothermal process. The effect of oxygen vancancy on SO2/CO oxidation for the crystal CeO2supported Pt catalyst is studied. At last, the hybrid catalysts with different noble metals on carbon nanotube and carbon black are prepared, and the effect of electron transfer on CO oxidation of such ctalysts is studied. The main progress is summarized as follows.(1) Ce(NO3)3as a precursor is introduced when preparing the Pt/C catalyst. The prepared CeO2is in amphorous state, and uniform dispersion of CeO2and Pt nanoparticles with a particle size of around3nm are achieved. The decline of catalytic activity is mitigated because the activity sites on Pt surfaces are hardly covered by CeO2. Increasing the content of CeO2, the oxidation activity towards CO increases, and the maxium peak shift is60mV on catalysts containing6wt%CeO2. Moreover,2wt%CeO2gives the catalyst the best acitvity towards SO2oxidation where the peak shifts negatively by50mV, and the activity declines as the content of CeO2increases. The oxygen supplied by CeO2is proposed to be the reason for different catalytic activity of Pt catalysts.(2) Nano-cubic, nano-rod, and nano-octahedra CeO2are prepared by hydrothermal process and used to support different amount of Pt (5,10,20wt%). The catalytic acitivty towards CO and SO2oxidation is related to the concentration of oxygen vancacy, which varies in different CeO2due to their varied structure. The highest concentration of oxygen holes is258×1011mg-1in nano-cubic CeO2, which is almost three times of nano-rod CeO2and ninefold of nano-cubic CeO2. The cubic CeO2loading20wt%Pt is most active of all the catalysts, the peak potential towards SO2oxidation shifts negatively by100mV compared to20wt%Pt/C. CO oxidation is enhanced as well.(3)20wt%Pt,Pd, Ru, Au, and Ag are loaded on carbon nanotube and carbon black. The monometallic catalysts are hybridized and tested by CO stripping. The metals stay independent in the hybrid catalyst, identified by EDX and XPS, no alloy-was formed. The hybrid catalysts behave similarly to the alloy catalysts. The peak potentials of CO oxidation are between the coresponding monometallic catalysts. The inherent properties and ratio of different monometallic catalysts have great effect on the catalvtic activity towards CO electrochemical oxidation. |
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