Preparation Of Au-Pd Nanocrystals And The Study Of Their Electrocatalytic Performances

Nobel metal (such as gold, silver, platinum, palladium and so on) nanocrystals (NCs), especially the bimetallic or multimetallic nanocomposite, have been widely used in the field of catalysts, energy, biosensors, medical diagnostics and therapeutics and so on, due to their unique electronic, optical, magnetic and catalytic properties. Au/Ag nanocomposite exhibits surface plasmon resonance(SER) properties, which is highly dependent on their structures, sizes, and morphologies. Through tuning these factors, we could obtain Au/Ag nanocrystals with enhanced SER. Besides, nanostructured palladium, platinum, gold and their compostites are the key parts of the direct ethanol fuel cell (DEFC) because of their superior catalytic properties. Therefore, in order to enhance their catalatic activity, CO tolerance, and stability, it is valuable to fabricate Au/Pd nanocomposites with different structures to realize their potential application in the field of DEFC.This paper mainly contains two parts:(1) The synthesis of core-shell (CS) structured Au@Ag NCs. We synthesized CS Au@Ag NCs with distinct thickness of Ag shell through tuning the concentration of Ag+ions at room temperature, via employing quai-spherical Au NCs with different sizes (including12nm,24nm and30nm) as seeds, hydroquinone (HQ) as reducing agent, and citrate as capping agents. Then, we characterized their surface plasmon resonance properties and morphologies through their UV-vis spectra and TEM images. We obtained the controllable range of the Ag shell thickness under different size of Au NCs. Finally, we analysized the critical value of the Ag shell thickness, the ratio of Ag shell thickness to the radius of the whole NP, the ratio of Ag volume to the whole NP volume etc. when Ag plasmonic resonance dominated.(2) The fabrication of Au/Pd NCs of distinct morphologies and their catalytic properties of ethanol oxidation in alkaline media. We synthesized Au/Pd NCs of five kinds of morphologies including CS Au@Pd NCs, Half-encased CS(HECS) Au@Pd NCs, Open-mouthed, Yolk-Shell Structured (OMYS) Au@Pd NCs, Normal Yolk-Shell Structured (NYS) Au@Pd NCs, and Popcorn-like, Yolk-Shell Structured (PLYS) Au@Pd NCs through tuning the reaction kinetic using galvanic replacement method at room temperature. That is, we adjusted the concentration of Pd2+ions added into the as-prepared aqueous solution of CS Au@Ag NCs with30nm Au NCs as seeds.What’s important is that we obtained OMYS Au@Pd NCs and PLYS Au@Pd NCs for the first time. We characterized and identified their structures employing UV-vis spectra, TEM, HAADF-STEM, Three-Dimensional Rotation and Reconstruction technologies. So as to investigate the size impact, we synthesized the Au/Pd NCs with12nm Au NCs as seed via the same method.Concequently, we obtained OMYS Au@Pd NCs. Besides, we also synthesized the CS Au@Pd NCs via direct reduction. Furthermore, the catalytic performance of ethanol oxidation under the alkaline media was investigated with the three kinds of YSS Au@Pd NCs, CS Au@Pd NCs and commercial Pd/C catalysts. As a result, OMYS Au@Pd NCs shows superior catalytic activity and stablity due to its open-mouth structure. Because the curved outer and inner side of Pd shell enlargedthe active surface area and the exposed Au core enhanced the CO tolerance ability.