Electrodeposition of copper from mixed sulphate-chloride acidic electrolytes at a rotating disc electrode

The effect of chloride ion on the deposition of copper from low metal concentrations in aqueous, acid sulphate solutions was investigated. The electrolytes contained 0.05 mol dm(-3) CuSO4 and 0.5 mol dm(-3) Na2SO4 at pH 2 and 296 K. The chloride ion concentration was varied in a wide range from 0.03 to 2.0 mol dm(-3). Linear sweep voltammetry was carried out under well defined flow conditions at a smooth platinum rotating disc electrode. The progressive transition from a single, two-electron reaction for the reduction of Cu(II)-> Cu(0) to two, single-electron reactions for the reduction sequence: Cu(II)-> Cu(I)-> Cu(0) was clearly evident as the chloride ion concentration increased. The charge transfer and mass transport characteristics of these reactions were evaluated. The formal potential for the Cu(II) reduction to Cu(I), the shift in the potential region for complete mass transport controlled reduction of Cu(I) to Cu(0) and the potential for hydrogen evolution at the deposited copper were also studied. A semi-logarithmic relationship between exchange current density and half-wave potential for Cu(II)-> Cu(I) with chloride ion was achieved when the Cl-/Cu(II) ratio in the electrolytes exceeded 2, due to the presence of the Cu(I) dichlorocuprous anion, CuCl2-.