Mechanistic Studies of Zinc Electrodeposition from Deep Eutectic Electrolytes

Deep eutectic electrolytes have been suggested as alternatives to classical room temperature ionic liquids and been used for the electrodeposition of metals. We have investigated the electrodeposition of zinc from a Lewis-basic choline chloride/ethylene glycol deep eutectic solvent containing ZnCl2. The system was examined by cyclic voltammetry at static and rotating glassy carbon disc electrodes. The formation of a dissolved, intermediate species Z during the cathodic sweep is proposed to account for the observed deposition behaviour in the deep eutectic electrolyte in agreement with the effect of rotation rate on the deposition current in RDE voltammetry. The zinc electrodeposition behaviour with sodium ethoxide added to the deep eutectic solvent supports the suggestion that Z is a complex of Zn2+ and deprotonated components of the solvent. The absence of a plateau current in RDE experiments points to the potential dependent blocking of the reduction of Z by an adsorbed layer.