Copper deposition via galvanic replacement in a CuCl solution in ethaline

Abstract

Copper deposition via galvanic replacement from aqueous sulfate electrolytes does not allow direct copper electroplating on metals and alloys more electronegative than copper (for example, iron and steel), since it prevents good adhesion of the coating to the matrix. An effective solution to this problem is the binding of copper ions in an electrolyte solution into stable complexes. The cathodic reduction of such complexes occurs at potentials more negative as compared to hydrated copper ions, which reduces the electromotive force of the galvanic replacement process. It is known that copper ions form chloride complexes in deep eutectic solvents based on choline chloride. In this work, for the first time, the contact deposition of copper on iron and steel substrates is investigated in a copper(I)-containing solution in the deep eutectic solvent – ethaline. Deposits are characterized by atomic force and electron microscopies and energy-dispersive X-ray spectroscopy. It has been established that copper deposition via galvanic replacement in a CuCl-containing ethaline takes place, however, the rate of this process is low and strongly depends on the substrate material (iron, grade-U8 steel, grade-20 steel). Furthermore, we show that galvanic replacement in the ethaline-based solution does not have any noticeable effect on morphology of the galvanic copper coating and its adhesion to the substrate.