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

摘要

Growth of the anodic AG2O film on a polycrystalline silver disk electrode in 1 mol/cu. dm KOH 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 AG2O film. In the case of thicker film, 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 Ag2O nucleation and growth peak has been observed in chronoampermetric transients above potential of + 240 mV(vs. Ag/AgCl). It has been observed that the nucleation and growth peak decreases as the convective diffusion is accelerated by the rotation speed of the RDE.