Electrodeposition Studies of Zinc in Choline Chloride-Urea Deep Eutectic Solvents

The work aims to study the electrochemical behavior, electrocrystallization mechanism, electrodeposition process of zinc and corrosion resistance in the Choline Chloride-Urea deep eutectic solvent (ChCl-Urea DES). The electrochemical behavior and electrocrystallization mechanism of zinc on glass-carbon electrode were studied by Cyclic Voltammetry (CV) and chronoamperometry (CA). The micro-morphology and phase composition of zinc coatings were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Comparative study of the corrosion resistance and electrochemical impedance spectroscopy of zinc plating in ChCl-Urea DES and aqueous solutions using dynamic potential polarization curves. The CV test shows that only one pair of redox peaks appears in the whole redox process, which indicates that Zn(II) is a one-step reduction and oxidation in ChCl-Urea DES, and the reduction peak potential (vs. Ag) is ‒1.207 V. The CV curves at different scan rates show that the peak potentials of both the reduction and oxidation peaks are regular with the scan rate v. The positive shift, and the regular decrease of both peak currents Ip with increasing scan rate v, are consistent with the irreversible electrode reaction. The relationship between Ip and v1/2 was fitted linearly, and the relationship between Ip and v1/2 was found to be good, so the reduction reaction of Zn(II) in ChCl-Urea DES could be considered to be controlled by diffusion, and the diffusion coefficient DZn(II) was further calculated to be 6.67×10‒8 cm2/s. The nucleation mode of Zn(II) in ChCl-Urea DES is neither three-dimensional instantaneous nucleation nor three-dimensional continuous nucleation, but a hybrid nucleation with two nucleation modes. The microscopic morphology of zinc coatings varies considerably depending on the deposition time. The XRD shows that the coating is composed of polycrystalline zinc with hexagonal crystalline phase. Potentiodynamic polarization curve test and electrochemical impedance spectroscopy showed that without any additives, the corrosion resistance of zinc coating in CHCl urea DES was equivalent to that in aqueous solution, and the formation rate of zinc coating in CHCl urea DES was slightly higher than that in aqueous solution. The electrodeposition of Zn(II) in ChCl-Urea DES is a diffusion-controlled irreversible electrode process with a nucleation mode that is neither three-dimensional instantaneous nor three-dimensional continuous, but rather a hybrid nucleation mode characterized by two nucleation modes. The zinc coating is composed of polycrystalline zinc with a hexagonal crystal phase. Comparable corrosion resistance can be obtained in ChCl-Urea DES as in aqueous solutions. © 2022, Chongqing Wujiu Periodicals Press. All rights reserved.