Silver electrocrystallization on vitreous carbon from ammonium hydroxide solutions

The early stages of the electrolytic deposition of silver onto vitreous carbon electrodes from ammonium hydroxide solutions have been investigated by the potential step technique. The analysis of the experimental current transients according to existing theories indicates that this process occurs by multiple three-dimensional nucleation, followed by diffusion controlled growth of nuclei. It is shown that treatments that involve classifying the process as either instantaneous or progressive nucleation are not always adequate for the quantitative analysis of electrochemical nucleation phenomena. The nucleation kinetics parameters A (nucleation rate constant per site) and No (number density of active sites on the substrate surface) were estimated separately from the current transient maxima by two different approaches. Both quantities were found to vary with the potential and with the concentration of silver ions, except at very high overpotentials for silver deposition. The potential dependence of the nucleation rate A was interpreted according to the atomistic theory and in all cases it was found that the number of atoms in the critical nucleus (n sub k ) was one over the entire potential range analyzed.