Copper electrodeposition in a deep eutectic solvent. First stages analysis considering Cu(I) stabilization in chloride media

Abstract

The aim of the present work is to study copper electrocrystallization in a Deep Eutectic Solvent (DES) (eutectic mixture of choline chloride and urea 1:2) as electrolyte, paying special attention to the influence of the liquid on the nucleation mechanism. Deposition process was studied from both Cu(II) and Cu(I) solutions. As the DES solvent is chloride rich, a parallel analysis was made in aqueous solution containing an excess of chloride to compare medium influence on nucleation mechanism. While copper (I) can be directly electrodeposited from chloride excess solutions, copper (II) electrodeposition takes place via a separate step in which Cu(II) is firstly reduced to Cu(I). A methodology is proposed for studying mechanistic aspects of the early stages of copper electrodeposition from the Cu(II) chloride solutions. For all solutions, cyclic voltammetry was used to establish the potential range at which copper electrodeposition occurred, while potentiostatic technique was used to study the nucleation mechanism. In all media, deposition follows a nucleation and three-dimensional growth controlled by diffusion. The diffusion coefficient of Cu(I) species present in the solution has been calculated from potentiostatic curves by logarithmic linear regression of j vs t−1/2 at long deposition times, whereas the same parameter for copper (II) was calculated from cyclic voltammetry, taking advantage from the process quasi -reversibility. The viability of the nucleation mechanism by Scharifker-Hills model was demonstrated by the analysis of the rising part of the j-t transients independently of the selected solution.