# Progress in Electrodeposition of Zinc and Zinc Nickel Alloys Using Ionic Liquids
## Influence of Additives
### Zinc-Nickel  
Additives play an important role in the Zn-Ni electroplating bath in improving the physical and mechanical properties of the coating such as brightness, roughness, thickness, and hardness, and making the Zn-Ni alloy deposits suitable for corrosion mitigation applications [54]. Additives, when introduced into the electroplating bath, improve the operating performance in terms of cathodic current efficiency, throwing power. Moreover, they control the Zn/Ni alloy ratio, grain size, and crystal orientation, and improve the morphology of the coatings. Thus, with proper selection of additives during Zn-Ni electrodeposition, it is possible to tailor the composition and morphology by selective reduction of either Ni(II) ions or Zn(II) ions. [PERSON] et al. [55] studied the influence of ethylene diamine tetra acetic acid (EDTA) and ammonium chloride (NH4 Cl) additives on electrodeposition behavior of Zn-Ni alloys from ChCl-based ionic liquid and investigated the composition, morphology, and corrosion performance. The authors found that the addition of ammonium chloride (NH4 Cl) to the ChCl-based ionic liquid refined the grain size of the electrodeposited Zn-Ni films, reduced the Zn content, and increased the cathodic current efficiency of the Zn-Ni deposits and corrosion resistance. In addition, increasing the EDTA concentration resulted in the Zn content of Zn-Ni film, reduced the grain size of the deposits. However, the conductivities and current efficiency of the Zn-Ni ionic liquid electrolytes decrease with the increase in EDTA concentration. Amines are often added as additives owing to their ability to improve the surface coverage of the deposit. [PERSON] et al. [56] described the effect of adding ethylamine and ethylenediamine to the ChCl/EG eutectic-based ionic liquid on the electrochemical profile of Zn-Ni and deposit morphology. The surface coverage was shown to  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**System**} & \multirow{2}{*}{**Additive**} & **Onset Reduction Potential** & **Difference in Potential** \\  & & **(V vs. Ag wire)** & **(mV vs. Ag wire)** \\ \hline \multirow{3}{*}{ChCl/urea (1:2 molar ratio)} & NiI & \(-\)1.080 & – \\  & Acetonitrile & \(-\)1.080 & 0 \\ \cline{1-1}  & Ethylene diamine & \(-\)1.120 & \(-\)40 1 \\ \cline{1-1}  & Ammonia & \(-\)1.020 & 60 \\ \hline \multirow{3}{*}{ChCl/EG (1:2 molar ratio)} & NiI & \(-\)1.080 & – \\ \cline{1-1}  & Acetonitrile & \(-\)1.080 & 0 \\ \cline{1-1}  & Ethylene diamine & \(-\)1.034 & 46 \\ \cline{1-1}  & Ammonia & \(-\)0.991 & 92 \\ \hline \hline \end{tabular}  
* Negative values indicate an increase in shift in reduction potential.  
\end{table}
Table 2: The onset in reduction potential for the Zn deposition in deep eutectic solvents using different additives [50].  
be significantly improved after the addition of amines to the plating bath containing the ionic liquid system. The results showed that Zn-Ni alloy obtained with ethylenediamine when added as an additive has the higher corrosion resistance, owing to better grain refinement increase of corrosion potential. [PERSON] [48] studied the effect of additives--boric acid and sodium bromide--on the Zn-Ni deposit in ChCl/2 EG, demonstrating that boric acid worked as a brightening agent in refining the crystal size in the Zn-Ni deposit, while sodium bromide contributed towards increasing the conductivity and cohesion of the Zn-Ni deposit. However, the Ni content of the Zn-Ni deposited from the ChCl/2 EG-based IL containing the additives reported an increase up to 71.5%, and the alloy became electrochemically more noble and less sacrificial to the steel substrate.