Using probe beam deflection (PBD) to investigate the electrochemical oxidation of silver in perchlorate media in the presence and absence of chloride ions

The electrochemical oxidation of silver in 0.1 M KClO4 solutions containing KCl were investigated by cyclic voltammetry (CV) and electrochemical probe beam deflection (PBD). Ag+(aq) ions were the main product of the silver oxidation in the absence of the halide. The formation of Ag+(aq) provoked a beam deflection towards the electrode surface. A beam deflection away from the electrode surface was then observed during the reduction of the Ag+(aq) ions. A convolution analysis yielded a diffusion coefficient of 1.2x10-9 m2 s-1 for Ag+(aq) in this medium. An anodic peak due to the formation of AgCl(s) film was observed for the oxidation of silver in solutions containing Cl-(aq). As the applied potentials were made more positive in media containing chloride (after the peak due to the AgCl(s) formation), a flux of ions away from the electrode surface was clearly detected by PBD. This was assigned to the formation of Ag+(aq) ions through the porous AgCl(s) film structure. Oscillations on the position of the laser beam were present during the oxidation at high chloride concentrations, due to the precipitation of AgCl(s) from the solution phase. The electrochemical and PBD data were consistent with a dissolution-precipitation mechanism for the AgCl(s) film formation