OBSERVATION OF INTERMEDIATE CUCL SPECIES DURING THE ANODIC-DISSOLUTION OF CU USING ATOMIC-FORCE MICROSCOPY

Electrochemical oxidation and reduction reactions of Cu were studied in chloride-containing media by observing changes to the surface morphology of graphite and Cu working electrodes using in-situ electrochemistry atomic force microscopy (ECAFM). AFM images combined with cyclic voltammograms identified three overpotential (eta) regions corresponding to the anodic dissolution of Cu in low-concentration (0.002 M HCl) chloride solutions. At low eta, ''the Tafel region'', AFM images showed the dissolution of Cu, which was accompanied by an exponential increase in current density. At higher eta, the current-limiting region, AFM images showed the growth of CuCl crystals, which was accompanied by an abrupt decrease in current density. As eta was increased in the current-limiting region, AFM images showed the simultaneous electrodissolution of both CuCl and exposed Cu, which suggested electrochemical mechanisms involving both the formation of (CuCl2)(-), which reacts to form Cu2+ and 2Cl(-), and the direct conversion reaction of Cu to CU2+.