Influence of temperature on copper bromide formation and dissolution

The influence of temperature on copper bromide formation and dissolution has been investigated in deaerated aqueous solutions of 0.2 M NaBr at pH 4. The morphology of CuBr accumulated on the copper anode supports the idea that CuBr precipitates in the vicinity of the electrode. Under a constant potential of −70 mV sec very large flat platelets of CuBr are observed at 71 °C compared to grains at 22 °C. In addition, irregular current variations are noted on the current time curves at 71 °C when large cracks are present in the film. It is deduced that the irregular current variations are due to the formation and repair of the cracks in the film. The current of the anode eventually reaches a steady value equal to the dissolution rate of the copper bromide precipitate formed on the electrode.The influence of the temperature on the dissolution rate of CuBr may be entirely predicted assuming that the rate-determining step for the dissolution of this compound is the mass transfer of intermediates, e.g., CuBr 2 − from the electrode surface to the bulk electrolyte.