Effect of Water on Zn Electrodeposition from a Deep Eutectic Solvent

Abstract

The electrodeposition of Zn films from a deep eutectic solvent (DES) of ZnCl2 and formamide and its mixture with water was studied. From spectroscopic analyses it was observed that water up to 30 v/v% does not change the Zn coordination in the electrolyte after which significant change in the coordination was observed. Electrochemical studies showed that with increase in water concentration in the DES, higher deposition/stripping current was achieved which was related to lowering of viscosity. The Zn deposit morphology changed significantly with water concentration. At low concentrations of water (up to 20 v/v%), porous Zn nanoplates formed whereas the morphology changed to a dense hexagonal structure on increasing the water concentration. X-ray diffraction results confirmed that at low water concentrations (up to 20 v/v%) Zn-Cu alloy formed. Above 20 v/v% water concentration in the DES, Zn peaks evolved with Zn-Cu alloy forming a shoulder. Based on the electrochemical and spectroscopic studies, it appears that 20–30 v/v% water is the critical region wherein significant changes occur from a DES rich region to a water-rich region.