Electrodeposition of gold at glassy carbon electrodes in room-temperature ionic liquids

The cyclic voltammetric behavior of [AuCl4](-) on glassy carbon (GC) and gold electrodes in room-temperature ionic liquids, i.e., 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF4) and 1-n-butyl-3-methylimidazolium tetrafluoroborate (BMIBF4) has been examined. A series of two-electron (2e-) and one-electron (1e-) reductions of the [AuCl4](-)-[AuCl2](-)-Au redox system could be observed at GC electrode. For example, the cathodic and anodic peaks corresponding to the [AuCl4](-)/[AuCl2](-) redox couple were observed at ca. 0.2 and 1.2 V vs a Ag wire quasi-reference electrode, respectively, in EMIBF4, while those observed at -0.5 and 0.5 V were found to correspond to the [AuCl2](-)/Au redox couple. The disproportionation reaction of the 2e-reduction product of [AuCl4](-), i.e., [AuCl2](-) to [AuCl4](-) and Au metal, was also found to occur significantly. A single reduction peak corresponding to the three-electron (3e-) reduction of [AuCl4](-) to Au metal was observed at Au electrode. The electrodeposition of Au nanoparticles was carried out on GC electrode in these ionic liquids containing [AuCl4](-) by applying potential-step electrolysis in a different potential range, i.e., the potential was stepped from 0.4 V to 0 and -1.0 V, at which the reduction of [AuCl4](-) to [AuCl2](-) and Au, respectively, takes place. The results obtained demonstrate that the electrodeposition of gold may occur via a disproportionation reaction of [AuCl4](-) to [AuCl2](-) and Au as well as via a series of the reductions of [AuCl4](-) to [AuCl2](-) and further, [AuCl2](-) to Au. The size and morphology of the prepared Au nanoparticles as well as the relative ratio of the Au(111), Au(110), and Au(100) crystalline orientation domains constituting the polycrystalline Au nanoparticles electrodeposited were found to largely depend on the stepped potential (i.e., 0 and -1.0 V). Interestingly, the Au nanoparticles prepared by a potential-step electrolysis from 0.4 to 0 V are enriched in the Au(110) single-crystalline domain. (c) 2007 The Electrochemical Society.