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 H4L) complexing agent. The results indicate that Cu2+ coordinated with HEDP molecules to form CuL26− coordination compound, and OH− would coordinate with CuL26− to form more stable Cu(OH)2L28− complex as pH increased. The electrochemical reduction of Cu2+ 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 CuL26− was reduced to copper first, following by the reduction of high-coordinate compound Cu(OH)2L28−. The copper electrodeposition involves nucleation process, and the electrocrystallization is consistent with progressive nucleation in three dimensions.