Electrodeposition of Ni from Choline Chloride/Ethylene Glycol Deep Eutectic Solvent and Pure Ethylene Glycol

The electrochemical behavior of Ni(II) ions at a glassy carbon electrode was studied using choline chloride–ethylene glycol (ChCl-EG) and ethylene glycol (EG) as solvents. The deposition behavior of Ni(II) was investigated by cyclic voltammetry (CV) tests. The results showed that the reduction of Ni(II) in both non-aqueous solvents was an irreversible process controlled by diffusion, and that the cathodic efficiency and the diffusion coefficient of Ni(II) in EG were higher. The nucleation process of Ni was investigated in detail by chronoamperometry (CA) experiments, and the results showed that the reactions of Ni in EG and ChCl-EG conformed to the three-dimensional transient nucleation mechanism and continuous nucleation mechanism. Scanning electron microscopy (SEM) and x-ray diffraction (XRD) were used to study the microscopic morphology and phase composition of the \nickel plating, and it was verified that different species of complex anions [NiCl3(EG)3]− and [NiCl4]2− affected the morphology and density of \nickel metal, and that the nickel plating in EG had small "needle-like" nuclei. The corrosion resistance of the nickel plating was investigated by polarization curves and AC impedance tests, and the results showed that the nickel plating obtained by electrodeposition in EG and EG-NaCl had the best corrosion resistance.