The electrochemical behaviour of polycrystalline silver electrodes in Na2CO3 solution and the effect of ClOÿ 4 ions

Abstract

The electrochemical behaviour of polycrystalline silver electrodes in Na2CO3 solutions was studied under potentiodynamic and potentiostatic conditions and complemented with X-ray diffraction analysis. Potentiodynamic E/i anodic curves exhibit active passive transition prior to an oxygen evolution reaction. The active region involves a small peak AI followed by a major peak AII before the passive region. Peak AI is assigned to the formation of an Ag2O layer while peak AII is due to the formation of an Ag2CO3 layer. The height of the anodic peaks increases with increasing Na2CO3 concentration, scan rate and temperature. The e ect of increasing additions of NaClO4 on the electrochemical behaviour of Ag in Na2CO3 solutions was investigated. The perchlorate ions stimulate the active dissolution of Ag, presumably as a result of the forma- tion of soluble AgClO4 salt. In the passive region, ClOÿ4 ions tend to break down the dual passive ®lm, leading to pitting corrosion at a certain critical pitting potential. The pitting potential decreases with ClOÿ4 concentration. Potentiostatic current/time transients showed that the formation of Ag2O and Ag2CO3 layers involves a nucleation and growth mechanism under dissusion control. However, in the presence of ClO4- ions, the incubation time for pit initiation decreases on increasing the anodic potential step.