Zinc Oxidation and Redeposition Processes in Aqueous Alkali and Carbonate Solutions: I . pH and Carbonate Ion Effects in Film Formation and Dissolution

The effects of carbonate ions on the electrolytic oxidation and reduction processes that take place at zinc electrodes in aqueous alkaline solutions have been studied by cyclic voltammetry; the behavior is compared with that in sulfate and chloride solutions at the same p H. A reaction which corresponds in the first anodic peak of the cyclic voltammograms for zinc in carbonate solutions is found to be first order with respect to hydroxide ions in the p H range 12.0–13.5. It has a diffusion‐controlled current component. A second anodic peak is only observed in carbonate solutions, but the diffusing species associated with the processes at peaks and is found to be the same, as indicated by the identity of slopes of vs. plots in rotating disk electrode experiments. It is suggested that this behavior can be explained in terms of a residual current passing through a porous oxide/hydroxide film that is already formed in the process. The breakdown of the passive films in Cl − or solutions, and the resistivity of the passive film formed in solutions, is examined and discussed.