Electrochemical behavior of copper in alkaline-sulfide solutions

Cyclic voltammograms and galvanostatic polarization curves were traced for the copper electrode in alkaline and alkaline sulfide solutions. In sulfide-free sodium hydroxide (NaOH) solutions, the anodic polarization curves are characterized by regions for the formation of cuprous oxide (Cu2O), cupric oxide (CuO), and soluble CuO22- before O-2 evolution. The cathodic branches indicate the reduction of the first two oxides before H-2 evolution commences. In the presence of increasing sulfide contents, the polarization curves are characterized by the presence of several anodic and cathodic regions corresponding to the formation, oxidation, and reduction of the different Cu sulfide species. A mechanism is proposed for the formation and reduction of copper sulfide (Cu2S) and cupric sulfide (CuS).