Current oscillations during electrodissolution of a cobalt electrode induced by the presence of nitrate ions in sulphuric acid solutions

Abstract

The anodic polarization behaviour and the current oscillations under potentiostatic conditions of a cobalt electrode were investigated in the electrolytic system 1.58 M sulphuric acid + x M nitrate ions. Oscillations were not observed in sulphuric acid solutions in the absence of NO − 3 ions. The anodic polarization curve for a cobalt rotating disc electrode in a solution of 1.58 M H 2SO 4 + x M NO − 3 ions displays a limiting current plateau. When the potential is fixed within a certain range on the limiting current plateau region, sustained current oscillations are observed. The width of the potential range for oscillatory behaviour depends on the experimental conditions, mainly on the disc rotation rate, nitrate ion and sulphuric acid concentration, as well as on the solution temperature. The onset potential for current oscillations varies linearly with the logarithm of NO − 3 ion concentration. Both the frequency of the oscillations and the current amplitude depend on the potential and the rotation rate. A mechanism is suggested for the appearance of current oscillations during the anodic dissolution of a cobalt electrode in the system 1.58 M H 2SO 4 + x M NO 3 − which is based on the oxidizing action of the nitrate ions.