ELECTRODISSOLUTION KINETICS OF COPPER IN ACIDIC CHLORIDE SOLUTIONS

The anodic dissolution of copper in acidic chloride media was studied at a rotating disk electrode by the linear potential sweep method. The potential range from the rest potential to +400 mV vs. SCE, including a limiting current region, was investigated. Twenty different solutions of various chloride ion concentrations from 0.2 to 4M and various [K+] to [H+] ratios were tested. The observed anodic limiting current density was proportional to the square root of the rotation rate. A model, which assumes the formation of a CuCl film on the copper surface and diffusion of the chloride ions to the electrode as the rate-determining step, has been developed to interpret the experimental data. Complexation constants, K2 and K3 are calculated as 6.67 × 104 and 1.81 × 105, respectively, and K3/K2 = 2.67. These results lead to the conclusion that in solutions with [Cl-] < 0.7M the complex, CuCl2-, is dominant, while at more concentrated chloride solutions, CuC132- is the main complex formed. For [Cl-] < 0.05M, a considerable amount of the dissolved copper is in the form of Cu2 +. This restricts the proposed mechanism for anodic dissolution of copper to solutions of higher chloride concentrations. The calculations do not preclude the validity of a previously proposed mechanism which suggests that diffusion of the cuprous chloride complex to the bulk of the solution is the rate-determining step. © 1979, The Electrochemical Society, Inc. All rights reserved.