Potential-controlled electrodeposition of gold dendrites in the presence of cysteinew

Gold (Au) nanostructures have attracted much attention because their chemical and physical properties differ considerably from those of bulk Au. The flurry of research activity into nanosized Au has been stimulated by its diverse range of prospective applications. For example, the nano-structured Au electrodes exhibit a strong catalytic activity for the oxidation of CO and CH3OH and the reduction of O2. 1 Because the chemical and physical properties of Au nanostructures depend markedly on their sizes and shapes, these properties are tunable through control of morphology and structure. Various chemical methods have been developed for the manufacture of Au nanomaterials possessing various shapes and structures. Much attention has also been paid to the fabrication of the dendrites because of their importance in realizing and understanding the mechanism of growth and their potential applications in catalysis, molecular sensing and other technological fields. In particular, the synthesis of hierarchical architectures in an effective condition, which is an essential step towardmerging the nanoscale building blocks into complex functional devices, remains a challenge. Dendritic nanomaterials have been prepared by electrochemical deposition because of its ease of control, highly pure and uniform deposits, and simple operation, but the dendritic Au nanostructure formed from this electrochemical deposition has not been reported.We report here an electrochemical deposition of three-dimensional dendritic Au at 295 K, which is grown simply and rapidly in an aqueous solution; this method is superior to ionic liquidand surfactant-assisted growths. The SH groups of thiols adsorb covalently onto Au surfaces to form protecting or insulating layers stabilized through strong Au–S bonds. Such adsorbed thiols can be desorbed through electrochemical reactions at a potential depending on the crystallographic facet of the Au surface. Ohsaka et al. demonstrated that cysteine (HO2CCH(NH2)CH2SH) molecules adsorbed on a polycrystalline Au (poly-Au) electrode were removed selectively from domains presenting plane (111), but remained on domains presenting planes (110) and (100), during a potential-controlled reductive desorption. In this communication, we report the induction of anisotropic crystal growth of Au after an addition of cysteine to an electrochemical solution; controlling the potential of deposition resulted in the formation of Au dendrites on a glassy carbon (GC) surface. Reduction of Au ion resulted in deposition of the Au metal on GC from a HAuCl4 solution at a potential less than B+0.8 V (vs. SCE), according to a cyclic voltammetric (CV) scan (Fig. S1, ESIw). The cysteine adsorbed on the poly-Au was removable from Au(111) domains at a potential in a range between 0.7 and 0.9 V through reductive desorption but remained on Au(100) and (110) (Fig. S2, ESIw). The reduction of Au to form Au is thus expected to occur preferentially on Au(111) facets on a poly-Au surface in HAuCl4 solution containing cysteine at 0.8 V, because cysteine adsorbed on Au(100) and (110) acts as a blocking molecule. The presence of cysteine in the solution of HAuCl4 might induce anisotropic growth during electrodeposition. Fig. 1 displays SEM images of the Au structures electrodeposited onto a GC electrode in HAuCl4 solutions in the absence and presence of cysteine. In the absence of cysteine, the deposited Au possessed a structure of densely packed nanoparticles, as previously reported. The growth rate of