Overpotential Nucleation and Growth of Copper onto Polycrystalline and Single Crystal Gold Electrodes

The copper electrodeposition process was studied using cyclic voltammetry and through application of potential pulses within the so called OPD zone (E < E-eq), initiating the pulse with a jump to an anodic rest potential (E-ar) more positive than the equilibrium potential, E-eq, such that the gold surface was free from copper. The deposition was carried out onto gold electrodes having different cristallinity, namely Au single crystal, Au(111), and polycrystalline Au, from an aqueous CuSO4 1 mM dissolution in 0.1 M H2SO4 at pH 1.0. From the analysis of the transients obtained within the overpotential region, several mechanisms were proposed to explain the rate controlling steps underlying the overall shape of the experimental deposition transients. For the single crystal electrode three contributions to the current measured became evident, which correspond to: an adsorption process, a 2D nucleation process and a 3D diffusion-limited nucleation process. For the polycrystalline electrode the processes considered taking place during 3D multiple growths were: an adsorption process, a 3D diffusion-limited growth process and a proton reduction process occurring on the growing surface of the new copper nuclei.