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

Electrochemical oxidation and reduction reactions of Cu were studied i n chloride-containing media by observing changes to the surface morpho logy of graphite and Cu working electrodes using in-situ electrochemis try atomic force microscopy (ECAFM). AFM images combined with cyclic v oltammograms identified three overpotential (eta) regions correspondin g to the anodic dissolution of Cu in low-concentration (0.002 M HCl) c hloride solutions. At low eta, ''the Tafel region'', AFM images showed the dissolution of Cu, which was accompanied by an exponential increa se in current density. At higher eta, the current-limiting region, AFM images showed the growth of CuCl crystals, which was accompanied by a n abrupt decrease in current density. As eta was increased in the curr ent-limiting region, AFM images showed the simultaneous electrodissolu tion of both CuCl and exposed Cu, which suggested electrochemical mech anisms involving both the formation of (CuCl2)(-), which reacts to for m Cu2+ and 2Cl(-), and the direct conversion reaction of Cu to CU2+.