Copper deposition and dissolution in mixed chloride-sulphate acidic electrolytes: cyclic voltammetry at static disc electrode

The electrochemistry of copper deposition and dissolution in chloride-sulphate electrolytes has been investigated using cyclic voltammetry. A wide range of chloride ion concentration (0.02 to 2.0 mol dm(-3) NaCl) in 0.05 mol dm(-3) CuSO4 and 0.5 mol dm(-3) Na2SO4 was used to examine the electrodeposition of copper onto platinum from chloride containing solution at 295 K. Cyclic voltammetry indicated that the stable dichlorocuprous anion was involved in the deposition and dissolution of copper at a platinum disc electrode. The transition from a single, two-electron transfer in a sulphate solution to two, single electron transfers in a chloride-sulphate solution was observed and the effect of chloride ion concentration on the deposition and the stripping charge density were investigated. Cu(II)/Cu(I) was found to be a quasi-reversible couple; the degree of reversibility increased at higher chloride ion concentrations. The formal potential for the reaction Cu(II)-> Cu(I) steadily increased while its exchange current and Tafel slope gradually decreased at higher concentrations of chloride ion. The participation of an adsorbed cuprous chloride filmin the oxidation and reduction reactions is discussed. These findings indicate that the presence of high chloride ion levels in a dilute copper solution inhibits both the deposition and the dissolution of copper.