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. Raman spectroscopy confirmed the presence of the [ZnCl4]2− ion in the electrolyte that was examined by cyclic voltammetry at static and rotating glassy carbon disk electrodes. The formation of a dissolved, intermediate reducible zinc species Z during the cathodic sweep is proposed to account for the unusual zinc electrodeposition behavior observed in the deep eutectic electrolyte in agreement with the effect of rotation rate, cathodic switching potential and potential sweep rate on the deposition current in RDE voltammetry. The zinc electrodeposition behavior 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 current plateau in RDE experiments with ethoxide containing electrolyte is thought to be the result of a potential dependent blocking of the reduction of Z by a layer adsorbed on the electrode.