Reaction mechanisms of copper electrodeposition from 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP) solution on glassy carbon

Abstract The specific forms of the coordination compounds were calculated and the specific process of copper reduction was investigated in non-cyanide alkaline baths with 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP, or H 4 L) complexing agent. The results indicate that Cu 2+ coordinated with HEDP molecules to form CuL 2 6− coordination compound, and OH − would coordinate with CuL 2 6− to form more stable Cu(OH) 2 L 2 8− complex as pH increased. The electrochemical reduction of Cu 2+ on glassy carbon electrode is composed of individual reduction processes of the above-mentioned two coordination complexes. The reduction processes are irreversible and controlled by diffusion. As the overpotential increased, the low-coordinate compound CuL 2 6− was reduced to copper first, following by the reduction of high-coordinate compound Cu(OH) 2 L 2 8− . The copper electrodeposition involves nucleation process, and the electrocrystallization is consistent with progressive nucleation in three dimensions.