Comparison on electro-reduction of Cu(II) using polypyrrole and stainless steel electrodes

Electro-reduction of Cu(II) on polypyrrole (ppy) and stainless steel (SS) electrodes were studied in the solutions with different concentrations of CuSO4 and H2SO4. The redox behavior was investigated by cyclic voltammetry. Copper deposition and dissolution peaks are featured in voltammograms for both electrodes, but an additional peak assigned to the reduction of H+ in all the adopted solutions and the peak assigned to the repulsion of H+ in the solutions with higher ratio of H+/Cu2+ during the reduction process of ppy were observed. The mechanisms for copper deposition on ppy and SS were also discussed in this connection. Cu(II) species were directly reduced on SS and the reduction was shown as two-step process. ppy was supposed to be a mediator and has played as an electrocatalyst during Cu(II) reduction. Cu(I) ions were suggested to have inserted in the polymer matrix in this process. Potentiostatic reductions at different potentials on ppy and SS electrodes were conducted in the solution with 0.2 M CuSO4 and 0.1 M H2SO4. Higher current efficiencies were obtained on ppy, because it reveals the inhibition effect of hydrogen release which is the competing side reaction during copper reduction process. Appling −0.5 V for electro-reduction, hydrogen evolution was avoided. As a result, current efficiencies of about 100% were achieved for both electrodes in all the adopted solutions, but higher amount of removal mass of Cu(II) was achieved on ppy relative to SS. In addition, on both electrodes it increases with the concentration of CuSO4, which indicates that the mass of copper recovery is mainly dependent on the concentration of Cu(II) in the solutions.