The passivating films on nickel in alkaline solutions I. General aspects of the Ni (II) region

Passivating films at the Ni(II) potential region in alkaline solutions have been studied qualitatively by voltammetry. One anodic (a(1)) and two cathodic (c(1) and c(2)) peaks were observed. It is shown that the peak at the more negative potential (c(1)) corresponds to the reduction of a film formed previously during the preparation of the electrode. Its appearance depends on the experimental conditions and it can be dissolved at sufficiently negative potentials. Peaks a(1)/c(2) correspond to the same film, which is attributed to NiO. As a consequence, the presence of the passivating film increases the hydrogen overpotential. The total cathodic charge densities have always been found to be smaller than the anodic one. In order to explain this behaviour, the existence of a disruption process which is discussed in the paper, is proposed. (C) 1998 Elsevier Science S.A. All rights reserved.