Electrochemical impedance spectroscopy investigation of spinel type cobalt oxide thin film electrodes in alkaline medium

Spinel type Co₃O₄ thin films, for the oxygen evolution reaction (OER) in 1 M KOH, have been prepared, on stainless steel supports, using the thermal decomposition method at 400 °C. The electrochemical behaviour of the oxide film/1 M KOH interface was investigated by cyclic voltammetry and impedance techniques. The impedance measurements were carried out at different positive potentials, from the open circuit potential to a potential in the OER region and the electrical equivalent circuit, L (R₁Q₁) (R₂Q₂) (R₃Q₃) was used to fit the experimental results. At each potential, a good correlation between experimental and simulated data is found, thereby validating the proposed equivalent circuit model. The roughness factor value determined in the potential region where the charge transfer reaction is negligible is similar to that obtained by cyclic voltammetry, with a value of 70 ± 2.