Study of the Initial Stages of Anodic Oxidation of Polycrystalline Silver in KOH Solutions

Growth of the anodic film on a polycrystalline silver disk electrode in solution at ambient temperature has been examined using a variety of electrochemical techniques. On the basis of the experimental results, a solid‐state model of silver electrode covered by a thin semiconductor film with a finite ionic conductivity has been proposed. It has been found that under potentiostatic control, thickness of the oxide film adjusts very quickly to the hydrodynamic conditions by a deposition/dissolution process, and the steady‐state oxidation currents fulfill the Levich equation for RDE, despite the fact that the electrode is covered by a thin film. In the case of thicker films, after completion of nucleation and growth, changes in the hydrodynamic conditions do not influence the oxidation current, and adjustment of the thickness of the oxide film to new hydrodynamic conditions proceeds at slower rate because of the slowness of the solid‐state diffusion step. The nucleation and growth peak has been observed in chronoamperometric transients above potential of + 240 mV ( vs. ). It has been observed that the nucleation and growth peak decreases as the convective diffusion is accelerated by the rotation speed of the RDE. The dependence of the oxidation current upon the rotation speed vanishes gradually during the nucleation and growth process.