Electrochemical impedance spectroscopy and voltammetry of zinc in dilute alkaline solutions

Cyclic voltammograms and electrochemical impedance spectra of zinc electrodes in deaerated dilute KOH solutions have been studied. Under cathodic polarization from the equilibrium potential, cathodic current of hydrogen evolution is larger than the anodic current of zinc oxidation. The potential starting the anodic dissolution of zinc is about the same as in concentrated solutions. The passivation films start to be formed at the anodic dissolution potentials. Under anodic polarizations, the zinc electrode surfaces are partially covered with the precipitated Zn(OH)(2) and/or ZnO, where composition can be expressed as ZnyOx(OH)(2-2x), with y greater than or equal to 1 and 0 less than or equal to x less than or equal to 1. Thus, the passive film composition is dependant on the anodic potential applied. The resultant cathodic stripping peak potentials shift towards cathodic direction with more anodic polarization. Electrochemical impedance spectra have also been analyzed to characterize the interface.