Electrochemical behaviour of silver in borate buffer solutions

Abstract The electrochemical behaviour of Ag in aqueous 0.15 M borax and 0.15 M boric acid buffer solution was studied under various conditions using cyclic voltammetry and potentiostatic techniques. It was found that the anodic polarization curve of Ag in borate buffer solution was characterized by the appearance of two potential regions, active and passive, prior to the oxygen evolution reaction. The active potential region was characterized by the appearance of three anodic peaks, the first two peaks A1 and A2 correspond to the oxidation of Ag and formation of [Ag(OH)2]− soluble compound and a passive film of Ag2O on the electrode surface. The third anodic peak corresponds to the conversion of both [Ag(OH)2]− and Ag2O to Ag2O2. X-ray diffraction patterns confirmed the existence of Ag2O and Ag2O2 passive layers on the electrode surface potentiodynamically polarized up to 800 mV. Potentiostatic current transient measurements showed that the formation of Ag2O and Ag2O2 involves a nucleation and growth mechanism under diffusion control.