Effect of water addition in ChCl-Urea-χH2O DES system on electrodeposition of Zn-Ni alloy

Purpose The purpose of this study is to investigate the effects of water addition on the electrochemical behavior, electrocrystallization mechanism and corrosion resistance of Zn-Ni alloy in choline chloride-urea deep eutectic solvent (ChCl-Urea DES). Design/methodology/approach This paper constructs the ChCl-Urea-χH2O system and characterizes the system properties through infrared spectroscopy, viscosity and conductance measurements. Combined with cyclic voltammetry (CV) and chronoamperometry (CA), it explores the influence of water addition amount on the electrochemical behavior and electrocrystallization mechanism of Zn-Ni alloy. The microscopic morphology and elemental composition of the coating have been analyzed by scanning electron microscopy (SEM), X-ray diffraction and X-ray photoelectron spectroscopy (XPS). Finally, the corrosion resistance of the deposited coating has been evaluated by Tafel polarization curves (Tafel) and electrochemical impedance spectroscopy (EIS). Findings CVs tests show increased ion diffusion with higher water addition. The CAs results show that as the deposition potential shifts negatively, the nucleation mode changes from continuous nucleation to instantaneous nucleation. The addition of water does not alter the nucleation mechanism. SEM/EDS tests show that the Zn-Ni alloy is normally co-deposited in the ChCl-Urea-χH2O system, and the coating quality is the best when the addition of water is 5 wt.%. XPS tests show that more Zn(OH)2 can be found in the deposited coating from ChCl-Urea-χH2O system; Tafel/EIS tests confirm that the deposited coating in 5 wt.% H2O content exhibits superior corrosion resistance. Originality/value The electrochemical window of the depositing system under different water addition was analyzed. The influence of water addition on the coating nucleation mechanism was studied. The effects of water addition on the morphology and corrosion resistance of deposited Zn-Ni coatings were investigated.