Effect of cysteine on the anodic dissolution of copper in sulfuric acid medium

The effect of cysteine (cys) on the anodic dissolution of copper in sulfuric acid media has been studied at room temperature using electrochemical methods. The anodic polarization curves showed two different regions: in the low overpotential range, the inhibitory effect of cys on the anodic dissolution was verified and in the high overpotential range this amino acid does not influence the copper anodic dissolution. Moreover, a limiting current was observed for cys concentrations higher than 10(-3) mol l(-1) which was attributed to the formation of a film on the copper surface. The electrochemical impedance diagrams obtained at the current plateau showed a typical diffusion process. These results suggest that the mass transport through this film is the rate determining step for copper oxidation in this medium. According to the copper electrodissolution mechanism proposed for sulfate media, in the absence of cys, the main species present on the copper surface at low anodic polarization is the intermediate Cu(I)(ads). This statement shows that the cys inhibitory effect is over this intermediate and suggests that the film formed at higher cys concentrations (10(-3) and 10(-2) mol l(-1)) is a Cu(I)-cys complex. The cys effect is not significant at high overpotentials, where the Cu(II)(ads) is the main species present at the copper surface. (C) 2004 Elsevier B.V. All rights reserved.