Synthesis of facet-controlled platinum nanocrystals with enhanced activities toward oxygen reduction
Lee, Chi Ta
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Platinum (Pt) nanocrystals have been applied to a wide variety of applications due to their excellent catalytic properties. However, due to its scarcity, the high price of Pt has been prohibiting many technologies from being used on an industrial scale, such as proton-exchange membrane fuel cells (PEMFCs). It is estimated that the loading of Pt as the electrocatalyst in PEMFCs should be reduced by at least four-fold relative to that of state-of-art commercial Pt/C to make it profitable to commercialize PEMFCs. Therefore, it is appealing to develop new types of Pt catalysts to replace the state-of-art Pt/C catalyst. The surface structure of Pt nanocrystals has found to be critical to their interaction with reactant molecule, which directly relates to their catalytic activities. The surface structure can be directly impacted by the sizes, facets and surface strains of nanocrystals. By tuning one of the factors, the catalytic activity or selectivity could be significantly changed to many structure-sensitive reactions due to the change of the electronic structure of surface atom. In this work, I successfully developed a facile, aqueous-phase synthesis of Pt octahedra with an edge length of c.a. 8 nm. The Pt octahedra showed a specific activity of 1.5 mA cm−2, much greater than that of commercial Pt/C, which only has a specific activity of 0.38 mA cm−2. However, the mass activities are similar, which was attributed to its relative large particle size. Therefore, the future work will focus on reducing the size down below 5 nm to achieve closer specific electrochemical surface area (ECSA) of commercial Pt/C.