# Progress in Electrodeposition of Zinc and Zinc Nickel Alloys Using Ionic Liquids
## 6 Recent Developments  
In general, cation plays an important role in controlling the physical properties of the salt and anion on the stability and chemical reactivity. While the cationic structure and size control the mass transport of metal ions to the electrode surface, anions will influence the co-ordination geometry around the metal ion, reduction potential, reduction current, and nucleation. In addition, anions will also affect the conductivity and viscosity of the ILs. The other important role that the cation probably plays in electrodeposition is in controlling the Helmholtz double layer thickness and structure. This area is practically unstudied for the zinc and zinc alloy deposition, although few reports have shown that the cation appears to control the morphology of zinc deposited from various triflamide-based ILs. A vast number of ILs (estimated to be more than \(10^{18}\)) [70] have been developed over the past 20 years, which is indicative of the possible future market. Further, it is also evident that new classes \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Iomic Liquid** & **Substrate** & **Zn/Zn-Ni** & **Reference** \\ \hline HEAl/ZnO\({}_{2}\) & ITO & Zn & [6] \\ ChCl/EG & Steel (AlSI 304) & Zn & [25] \\ [BMIMCI]/ZnCl\({}_{2}\) & Carbon steel sheet (S235 JR) & Zn & [31] \\ ChCl/urea & Cu & Zn-Ni & [40] \\ ChCl/EG & Cu & Zn-Ni & [43] \\ ChCl/urea & Carbon steel & Zn-Ni & [44] \\ ChCl/urea & Steel & Zn & [51] \\ ChCl/ZnCl\({}_{2}\) & Mg & Zn & [63] \\ ChCl/ZnCl\({}_{2}\) & Mg-alloy (A291, WE43,Q2E2,MgGd5 Sc1,MgY4 SCl) & Zn & [63] \\ ChCl/ZnCl\({}_{2}\) & Low carbon steel & Zn & [63] \\ ChCl/urea & Mg & Zn & [63] \\ ChCl/EG & Mg & Zn & [63] \\ ChCl/Gl & Mg & Zn & [63] \\ ChCl/Mal & Mg & Zn & [63] \\ [BMP-DCJ]/Z/CL\({}_{2}\) & Mg & Zn & [64] \\ ChCl/EG & Ti/TiO\({}_{2}\) & Zn & [65] \\ ChCl/EG & Alumina & Zn & [66] \\ ChCl/Lac & Low carbon steel & Zn & [67] \\ [BPyl]/ZnCl\({}_{2}\) & Cu & Zn & [68] \\ \hline \hline \end{tabular}  
* Lac: lactic acid; [BMP-DCA]: N-butyl-N-methyl-pyrrolidinium dicyanamide; HEAP: 2- hydroxyethyl ammonium propionate; [BMIMCI]: 1-butyl-3 methylimidazol chloride; [BPyl]: 1-butylpyrrolidine.  
\end{table} 
Table 4: The Zn deposition in different ionic liquids on different substrates. of ILs will be developed in the coming years. The choice of ionic liquid electrolyte for depositing Zn and Zn-Ni alloys depends on the reduction potential of the metals and the potential window of the liquid. However, it is worth noting that reduction potentials are significantly affected by the co-ordination of the anion to the Zn metal and its alloys. Alternative precursor salts to halides (chlorides, bromides, fluorides), with high solubility in ionic liquids, must be considered in order to have an inert environment with good conductivity (10 mS cm\({}^{-1}\)). [PERSON] group [71] demonstrated the possibility of obtaining a potentially high quality deposit by reducing the concentration of chloride in the ionic liquid-based plating system. Though the release of chlorine gas was controlled to an extent, they failed to maintain the conductivity. Attempts were made by the introduction of acetate precursor salts in organic solutions as the supporting electrolyte for the electrodeposition of zinc while eliminating the chloride source. [PERSON] et al. [6] studied the electrodeposition of zinc from chloride, acetate, and propionate-based ILs, and compared the results with coatings obtained using aqueous media. The results displayed a good efficiency and selectivity when Zn propionate was used as a zinc source in the 2-hydroxyethyl ammonium propionate (2-HEAP) ionic liquid-based system, while maintaining a smooth and homogeneous deposit. However, the conductivity and long-term stability of the ionic liquid-based system were not studied. [PERSON] et al. [72] developed a chloride-free ionic liquid electrolyte using ethylene glycol as the main supporting electrolyte and zinc acetate as the precursor salt and sodium acetate to increase conductivity.