Zinc Oxidation in Dilute Alkaline Solutions Studied by Real-Time Electrochemical Impedance Spectroscopy

Abstract

Electrochemical oxidation of zinc has been studied in dilute alkaline solutions, 0.010 and 0.10 M KOH, employing cyclic voltammetric and real-time Fourier transform electrochemical impedance spectroscopy (FTEIS) experiments. Thermodynamic analysis of cyclic voltammetric data indicates that Zn(OH)42– is produced as a major product in both 0.10 and 0.010 M KOH although ZnO/Zn(OH)2 may also be produced as a minor product in 0.010 M. A large body of impedance data was obtained as a function of swept potential by running combined staircase cyclic voltammetry and FTEIS (SCV-FTEIS) experiments at every 10 mV and 200 ms interval, which allowed a systematic and complete analysis to be made on the interface. Analysis of the extensive impedance data demonstrates that electron transfer takes place across the thin oxide/hydroxide film, whose electrical state undergoes drastic changes at the potential where charge transfer occurs. The capacitance of the film covering the surface was shown to undergo a large change during the charge transfer indicating that the electrode/electrolyte interface is strongly electrified during the charge transfer across it. Various electrode reaction kinetic parameters for oxidation of zinc are also reported by treating the impedance data and the reaction mechanism is discussed based on the data.