The electrochemical behaviour of polycrystalline silver electrodes in Na2CO3 solution and the effect of ClO4- ions

The electrochemical behaviour of polycrystalline silver electrodes in Na2CO 3 solutions was studied under potentiodynamic and potentiostatic conditions and complemented with X-my diffraction analysis. Potentiodynamic E/i anodi c curves exhibit active passive transition prior to an oxygen evolution rea ction. The active region involves a small peak BI followed by a major peak All before the passive region. Peak AI is assigned to the formation of an A g2O layer while peak All is due to the formation of an Ag2CO3 layer. The he ight of the anodic peaks increases with increasing Na3CO3 concentration, sc an rate: and temperature. The effect of increasing additions of NaClO4 on t he electrochemical behaviour of Ag in Na2CO3 solutions was investigated. Th e perchlorate ions stimulate the active dissolution of Ag, presumably as a result of the formation of soluble AgClO4 salt. In the passive region, ClO4 - ions tend to break down the dual passive film, leading to pitting corrosi on at a certain critical pitting potential. The pitting potential decreases with ClO4- concentration. Potentiostatic current/time transients showed th at the formation of Ag2O and Ag2CO3 layers involves a nucleation and growth mechanism under diffusion control, However, in the presence of ClO4 ions, the incubation time for pit initiation decreases on increasing the anodic p otential step.