Spectroelectrochemical studies on dissolution and passivation of zinc electrodes in alkaline solutions

Electrochemical oxidation of zinc electrodes has been studied in 1.0 M KOH solutions employing cyclic voltammetric and in situ spectroelectrochemical techniques. The results indicate that three different processes, i.e., dissolution, prepassivation, and passivation, take place in different potential regions. Two optically different solution species absorbing at 250 and 290 nm, which are assigned to Zn(OH)(4)(2-) and Zn(OH)(3)(-), respectively, are produced initially during anodic oxidation of zinc at different potentials to different extents with different respective ratios. These species undergo a series of consecutive chemical reactions to eventually lead to passive films on the surface. The film compositions were identified to be ZnO1-x(OH)(2x)OH--doped ZnO, and Zn-doped ZnO depending on the potential regime and aging. Details of the electrochemistry and chemistry taking place during electrolysis in these three regions are discussed based on the cyclic voltammetric and spectroelectrochemical data.