Inhibitory effects of NO2− on Ni deposition

The influence of NO2− on the first stages of Ni deposition onto vitreous carbon was studied by means of voltammetry, potentiostatic steps and AFM techniques in neutral sulphate solutions. At low overpotentials and NO2− concentrations lower than 5×10−4 M, the adsorption of NO2− on forming nuclei increases the energy of nucleation, diminishing the nucleation rate. At more negative potentials and/or in the presence of higher concentrations, the reduction of NO2− increases the local alkalisation to a great extent and Ni nucleates by reduction of the precipitated Ni(OH)2 particles which are adsorbed on the active sites of the substrate. Then, further growth is limited by the transport of Ni2+ through the adjacent precipitated hydroxide layer.