Synthesis Of Pt, Rh-based Bi-metallic Nanocrystals And Their Catalytic And Electrocatalytic Applications

Pure hydrogen is an optimum fuel for proton exchange membrane fuel cells (PEMFCs). However, these issues associated with hydrogen storage, transportation, and safe use severialy limit the widespread commercialization of PEMFCs. As an alternative candicate, hydrazine hydrate in a liquid has a high hydrogen content as high as 7.9 wt%, which can achieve efficient decomposition in the presence of rhodium-based catalysts. Therefore, hydrazine hydrate has been considered to be one of the most efficient fuel for PEMFCs.As a kind of PEMFCs, direct methanol fuel cells have received much more attention as a clean and sustainable energy-conversion device for automobile and portable applications due to their easy storage and transportation, high energy conversion efficiency, high power density, and low pollutant emission. However, the successful commercialization still requires electrocatalysts should meet three major criteria including low cost, high activity and high durability. Bimetallic catalysts with unique components and structural advantages have been considered to be the ideal candidate for direct methanol fuel cells.In this dissertation, we have developed servral facile approaches to the synthesis of Pt- and Rh-based nanocrystals with excellent catalytic properties.The main innovative results are displayed as follows:(1) Au-Pt core-shell star-shaped decahedra has been prepared by the incorporation of amine group and Br- ions. The Au-Pt core-shell star-shaped decahedra with controlled shell thickness exhibits enhanced oxygen reduction reaction (ORR) properties in terms of activity and durability due to the synergetic effects arising from the ORR preferred{111} facet, twin structure and likely strong electron interaction.(2) Au-Pt core-shell decahedra with different compositions has been synthesized through an oil-phase method. The composition control was achieved by varying the molar ratios of the Au to Pt precursors. The incorporation of Au into Pt-based nanocrystals can substantially enhanced the specific activity and durability towards MOR relative to commercial Pt/C, while the Au62Pt38 decahedra being the best catalysts due to the possible synergistic effects between facet and composition.(3) High-quality Pt-Cu alloy octahedra have been synthesized by a facile hydrothermal approach. The composition of the octahedra was simply tuned by varying the molar ratios of the Au to Pt precursors. The use of Cl- ions arising from the reactants were found to greatly facilitate the underpotential deposition (UPD) of Cu on the{100} facets of Pt, and thus promote the formation of Pt-Cu alloy octahedra.The Pt-Cu alloy octahedra exhibited enhanced electrocatalytic activity and CO poison tolerance for methanol oxidation reaction (MOR) relative to the commercial Pt/C.(4) We have synthesized the surface-embedded Pt/CeO2 one-dimentional hybrid nanostructures through solid-solution (S-S) interfacial redox between Pt2+ and Ce3+ ions in the presence of cetyltrimethylammonium bromide (CTAB) as a selective capping agent. The In-situ transmission electron microscopy (TEM) with a heater analysis indicates that the surface-embedded Pt/CeO2 hybrid nanostructures show significantly improved thermal stability compared to the conventional loaded Pt/CeO2 hybrid catalyst. In addtion, the surface-embedded Pt/CeO2 hybrid nanostructures also exhibit the substantial enhanced catalytic properties relative to the conventional loaded catalysts for the reduction test of p-nitrophenol.(5) We have demonstrated a facile method based on seed-mediated growth for the synthesis of Au-Rh core-shell star-shaped decahedron and their conversion to Rh nanoframes by selective etching of the Au cores. In comparison with the Rh/C, the Au-Rh decahedra with 1 mg rhodium precursor exhibit a much higher H2 selectivity and efficiency toward the decomposition of hydrazine.