The effect of concentration on the electrocrystallization mechanism for copper on platinum ultramicroelectrodes

The mechanism of copper electrocrystallization on Pt ultramicroelectrode surfaces has been studied by cyclic voltammetry, chronoamperometry and ex situ atomic force microscopy in acid solutions containing different Cu2+ concentrations. To analyze the potentiostatic transients a new model developed in our laboratories that takes into account spherical diffusion towards a disc-shaped ultramicroelectrode was used. A mechanistic change from progressive to instantaneous nucleation was observed when the Cu2+ concentration was increased from 0.01 to 0.1 mol dm-3. The shape and distribution of the nuclei formed on the surface were investigated by AFM. The dependence of the nucleation rate with potential was analyzed in terms of the atomistic theory of electrocrystallization and the results suggest the presence of only one copper atom in the critical nucleus.