Synthesis of Bimetallic Au@Pt Nanoparticles with Au Core and Nanostructured Pt Shell toward Highly Active Electrocatalysts

Au@Pt nanocolloids with nanostructured dendritic Pt shells are successfully synthesized by chemically reducing both H2PtCl6 and HAuCl4 species in the presence of a low-concentration surfactant solution. By applying an ultrasonic treatment, the particle size of the Au@Pt nanocolloids is dramatically decreased and their size distribution becomes very narrow. The difference in reduction potentials of the two soluble metal salts (Au(III) and Pt(IV) species) plays a key role in the one-step synthesis of the core−shell structure. Because of the different reduction potentials, the reduction of Au ions preferentially occurs over a short time to form the Au seeds. It is followed by overgrowth of Pt nanodendritic nanowires on the Au seeds, which is confirmed by ultraviolet−visible light absorption spectroscopy and transmission electron microscopy. Interestingly, the Pt shell thicknesses on Au cores can be easily tuned by controlling the Pt/Au molar ratios in the starting precursor solutions. Through the optimization of the Pt shell thicknesses, the Au@Pt nanocolloids can exhibit enhanced activity as an electrocatalyst for a methanol oxidation reaction, which will be important to improve the utilization efficiency of Pt catalysts in the future.