Zinc Oxidation and Redeposition Processes in Aqueous Alkali and Carbonate Solutions: II . Distinction Between Dissolution and Oxide Film Formation Processes

Abstract

The early stages of the process of anodic zinc oxidation in , , and Cl− solutions around pH 11.5, were studied by cyclic voltammetry, as in part I. Unusual peak current dependence on sweep rate is observed at the first anodic peak. This behavior is explained in terms of a mixed process involving coupled diffusion and film formation. By correlating the shapes of peaks and peak potentials for different Zn surface preparations, and the relation of the peak current to sweep rate and to electrode rotation rate, , the roles of film formation and diffusion of solution species are distinguished. A new method of plotting out cyclic voltammetry peak currents, , as a function of sweep rate, , is proposed that treats the anodic currents in terms of parallel components for dissolution into solution, with diffusion (proportional to ), and for film formation or reduction (proportional to ). This allows a separation of diffusion‐controlled and film formation currents to be made. The RDE experiments yield and sweep rate experiments showed relations apply to the for the peak. Two processes therefore take place: diffusion‐controlled dissolution and direct film formation. The importance of studies at single‐crystal surfaces is stressed where resolution of the various processes involved is much clearer. Thus, it is shown that only the direct oxide film formation process is predominant at the single‐crystal Zn(0001) face. This compact film is responsible for passivation. The results enable a model for dissolution and coupled‐film formation, associated with passivation, at the Zn electrode, to be suggested. The participation of these two types of process depends on pH and the types of ions present.