Au@Pd nanostructures with tunable morphologies and sizes and their enhanced electrocatalytic activityElectronic supplementary information (ESI) available: Additional TEM images of Au seed and Au@Pd nanostructures, XRD pattern of flower-like Au@Pd nanostructures, and table summarizing solution volume and concentration of Na2PdCl4 and CPC used for obtaining those samples in Fig. 2 and their average sizes. See DOI: 10.1039/c3ce40986d

We report a facile method for the synthesis of Au@Pd nanostructures with controlled sizes and morphologies from flower-like to cuboctahedral shape by seed-mediated growth using Au nanospheres as seeds and cetylpyridinium chloride (CPC) as a surfactant. The use of CPC as a surfactant and its molar ratio with respect to Na 2 PdCl 4 were critical factors to generate the Au@Pd nanostructures with flower-like morphology. In addition, the morphology of Au@Pd nanostructures could be easily controlled by changing the concentration of CPC in the reaction solution, where controlled reduction kinetics according to the concentration of CPC brought variety to the morphology of the Pd shell and eventually the Au@Pd nanostructures. The size of Au@Pd nanostructures could be also readily tuned in a controllable fashion by varying the concentration of Na 2 PdCl 4 . We also investigated the morphology-dependent electrocatalytic activities of Au@Pd nanostructures toward ethanol electrooxidation as a probe reaction. Thanks to their larger electroactive surface area and higher density of electroactive sites, the flower-like Au@Pd nanostructures exhibited 2.2 times enhanced electrocatalytic activity per Pd unit mass than cuboctahedral Au@Pd nanostructures. Morphology-controlled Au@Pd nanostructures were synthesized by using CPC as a surfactant and their electrocatalytic activities toward ethanol electrooxidation were investigated.