Voltammetric Study and Electrodeposition of Cu from CuO in Deep Eutectic Solvents

Abstract

The electrodeposition of copper (Cu) from copper oxide (CuO) in the eutectic mixtures of choline chloride (ChCl) with either ethylene glycol (EG) or urea has been investigated. CuO was dissolved in the both media (i.e., ChCl/EG and ChCl/urea based eutectics) to form different copper ion complexations and served as electrolytes for the electrodeposition process. Voltammetric measurements confirm that the electrodeposition of Cu in ChCl/EG and ChCl/urea systems takes place via two well-separated reaction steps. The reductions of Cu(II) to Cu(I) and Cu(I) to Cu in the both eutectic mixtures are determined to be diffusion-controlled reversible process and quasi-reversible process, respectively. The calculated diffusion coefficients of the Cu(I) species are much higher than those of the Cu(II) species in the both media, indicating that the diffusion process of Cu(II) species is the rate-determining step in the electroreduction processes. The surface morphology of the electrodeposited Cu can be significantly influenced by the type of eutectics and the electrodeposition potential. The morphology observations show that the Cu electrodeposits obtained in ChCl/urea system possess more homogenous microstructures than those produced in ChCl/EG system.