| Summary: | 碩士 === 元智大學 === 化學工程學系 === 93 === Support plays a vital role in the performance of a catalyst. This issue is more profound in proton exchange membrane fuel cell (PEMFC) applications in which electrocatalysts with very high loading of expensive precious metals are used. Platinum supported on carbon is currently the state-of-the-art cathode catalyst for PEMFC. Carbon black is the choice of catalyst support despite its physical and chemical properties are still not adequate for the demand of PEMFC electrocatalyst. Surface oxidation was employed in this study to enhance the amount of oxygen functional groups on the surface. Commercial carbon black (Cabot XC-72) was used as the carbon and hydrogen peroxide (H2O2) was used as the oxidizing agent in this study. Pt/C catalysts were prepared using carbons with variable amount of oxygen functional groups prepared. Relationship between surface functionality of carbon support and catalyst activity in the oxygen reduction reaction (ORR) was developed.
XPS, TPD and DRIFT results revealed that H2O2 treatment of XC-72 resulted in the formation of oxygen containing functional groups on the surface. The amount of oxygen functional group on carbon surface depends on the concentration of H2O2 employed; the temperature and time of treatment also affect the amount of oxygen on the carbon support. Furthermore, weak acidic surface sites are formed predominantly when H2O2 was used as the oxidizing agent. More active catalysts for the ORR are formed in using carbons with larger amount of weak acid sites, in conjunction with impregnation preparation method. Catalysts with Pt particle size (TEM) of Pt ranged from 1.9~5.8 nm were prepared depending on the type of carbon, preparation method and precursor used. Catalysts with Pt particle sizes around 3.0~3.5 nm showed the best activity towards ORR activity test.
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