Etude de la dissolution du bromure cuivreux formé sur le cuivre

Abstract

The dissolution of cuprous bromide, formed by the electrochemical oxidation of copper immersed in aqueous NaBr, has been studied. NaBr concentration was varied between 0.1 and 1.2 M at pH 4. The corrosion product accumulating on the electrode is crystalline γ-CuBr. The presence of this material contributes to the local enrichment of dissolved copper close to the electrode. This enrichment leads to a characteristic electrode voltage in open circuit, which is about −149 mV (ECS) at a stationary electrode immersed in a solution of 0.2 M NaBr. The complete dissolution of CuBr coincides with a rapid fall in voltage which permits the definition of the transition time τ from which the speed of CuBr dissolution has been calculated. For example, the speed of dissolution is 0.074 ± 0.003 mA cm−2 in a current equivalent for a stationary electrode in the presence of a non-stirred solution of 0.2 M NaBr. This is constant until the complete disappearance of the CuBr. On the other hand, use of a rotating disc electrode demonstrates that the dissolution is entirely dominated by the diffusion of ions in the liquid phase. The experimental results are compatible with the simultaneous presence of [Formula: see text] and [Formula: see text] as diffusing species. Finally, the potentiodynamic polarization curves show two oxidation waves. A non-negligible portion of the dissolution current, if not almost all, is associated with the formation of CuBr as the sole corrosion product on the electrode. [Journal translation]