An electrochemical study of Au–Ni alloy electrodeposition from cyanide–citrate electrolytes

Abstract

Cyclic voltammetry, j– t transients and transient time measurements have been used to characterize the Au–Ni alloy deposition and to obtain the nucleation and growth mechanism. The electrodeposition of gold, nickel and gold–nickel alloys was studied in cyanide–citrate electrolytes. The analysis of the voltammograms and j– t transients clearly shows that deposition of the Au and hence, of Au–Ni alloys, is affected by adsorbed cyanide ligands mainly at low overpotentials and a direct reduction occurs at high overpotentials. In this case, the Au deposition is kinetically favored, while the Ni deposition is controlled by the cyanide–citrate adsorbed adlayer. In an alloy electrolyte, the Au and Ni deposit simultaneously in the whole negative potential region. In addition, the current transients revealed that the nucleation mechanism is progressive for Au–Ni alloy deposition at the lower potentials, and instantaneous at the higher overpotentials with a three-dimensional growth mechanism. The number of nucleation sites increases with overpotential, where the most nucleation sites are concerned with gold deposition. The composition of the alloys is markedly dependent on the potential and varies with polarization behavior. The microstructure of the Au–Ni alloy deposits was investigated by TEM, indicating a gold uniform texture with a single-phase fcc structure containing a few rectangular nuclei of nickel.