Copper ion reduction catalyzed by chloride ions

The cathodic reduction of copper(II) is studied in the absence and in the presence of chloride ions (1 x 10(-3) less than or equal to c(Cl) less than or equal to 8 X 10(-3) M) in an electrolyte that is comparable to galvanic copper baths (2.2 M H2SO4 + 0.3 M CuSO4). Experiments conducted with the electrochemical quartz-microbalance, largely under conditions of cyclic voltammetry, demonstrate the formation and reduction of CuCl on the copper surface. A mechanism of Cu(II) reduction with intermediate formation of CuCl is postulated. Its rate is comparable to that of chloride-free Cu(II) reduction. The enhancement of the reduction current observed in the presence of chloride is proposed to result from the fact that the mechanism involving CuCl mediation proceeds in parallel with the chloride-free path