Electrochemical impedance spectroscopic studies of the passive layer on the surface of copper as a function of potential

Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were used to investigate the oxide layer formed on a copper disc electrode and the changes that took place when treated potentiostatically in the range of -0.3 V to 0.9 V in buffer of pH 8.5. The response of an electrode using EIS, initially at equilibrium, to an applied potential was then modeled with equivalent circuits, proposed for different potential regions that completely illustrated the Cu/oxide/electrolyte systems and their properties in terms of 2 interfaces. Criterion for the applicability of equivalent circuit models was discussed. Changes in the film/metal interface as a function of potential were also probed at 30 mHz using Nyquist plots. Diffusion coefficient and concentration of mobile ions in the film calculated from the EIS data came out of the order of 10(-6) cm(2) s(-1) and 10(-6) mmol mL(-1), respectively.