Impedance Behavior of a Sulfuric Acid‐Cupric Sulfate/Copper Cathode Interface

Abstract

The impedance characteristics of a copper disk electrode/sulfuric acid‐cupric sulfate interface were investigated and interpreted in terms of equivalent circuit models. A single reaction mechanism, proposed to correspond to the charge transfer, limited deposition rates over a wide current density range at a well‐agitated interface. A rate constant of, a transfer coefficient of 0.5, and a double layer capacitance of 25 μF/cm2 were determined from impedance data corresponding to the rate‐limiting step. Arrhenius plots yielded an activation energy of 66 kJ/M and a pre‐exponential term of approximately 105 cm/s. The involvement of a freely diffusing cupric ion in the rate‐limiting step was consistent with the observed data, but the possibility of adsorbed species involvement cannot be eliminated. A minor impedance feature, believed to correspond to a relatively fast surface diffusion limited charge transfer, was observed at low ac frequencies. In quiescent solutions, the observation of a significant Warburg impedance demonstrated that deposition rates became limited by diffusion of cupric ion to the interface.