Electrochemical Behavior of the Passive Films Formed on Copper in Aqueous KOH Solutions

The electrochemical behavior of the passive films formed on copper in the alkaline solutions was investigated by potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and Mott–Schottky analysis. In the Mott–Schottky analysis, no evidence for n-type behavior was obtained, indicating that the oxygen vacancies and the copper interstitials do not have any significant population density in the passive films. Also, this analysis revealed that with the decrease of solution concentration, the acceptor density of the passive films increased. The EIS plots indicated that the presence of two time constants, a high frequency incomplete semicircle and a low frequency rising arc. The EIS studies showed that the impedance value increased with decreases in solution concentration, which is consistent with the results of the polarization experiment.