# Progress in Electrodeposition of Zinc and Zinc Nickel Alloys Using Ionic Liquids
## Zinc Deposition in Ionic Liquids  
Few investigations on zinc electrodeposition in the past decade have been carried out in traditional ILs, and demonstrated the possibility to obtain high purity films. [PERSON] et al. [18] investigated the electrochemical potential windows and thermal stability of 33 ILs and 23 DESs. The study comprised of five traditional cations, namely, imidazolium, pyridinium, pyrrolidinium, piperidinium, and ammonium, and 13 types of anions. In addition, electrochemical potential windows of choline with different halides such as chloride (Cl-), bromide (Br-), and iodide (I-) were also studied in combination with methyl urea as DESs. Among the selected combinations, deep eutectic solvents composed of choline chloride (ChCl) and methyl urea resulted in the largest potential window with good stability. Besides, ChCl can be synthesized via a one-pot, solvent-less process, making the process scale up simple. Furthermore, ChCl-based ILs are considered closest to commercialisation in the metal finishing industry. The presence of a high concentration of OH groups in ChCl-based ILs favors the metal ion adsorption, even in the presence of significant amount of moisture, and does not affect the electrodeposition of metals such as Zn. [PERSON] et al. [21] studied the deposition of Zn in ChCl/ZnCl\({}_{2}\) system (1:2 molar ratio) and observed the formation of clear homogeneous colourless liquid on mixing the constituent components at room temperature. Hull cell results displayed a smooth thick grey/white deposit at a current density of 0.29-0.47 mA cm\({}^{-2}\), while a thinner white deposit in the range between 0.21 mA cm\({}^{-2}\) and 0.29 mA cm\({}^{-2}\) and a non-homogeneous deposit was observed, when deposited at current densities below 0.21 mA cm\({}^{-2}\). The cathodic current efficiency (CCE) with respect to metal (Zn) deposition represents the quantity of the metal (Zn) deposited at the cathode under normal electroplating conditions and was reported to be \(>\)99%. The Zn deposits obtained on mild steel were non-porous, indicating that the Zn deposit could act as a barrier and mitigate corrosion. However, the potential of the systems needs to be controlled as chlorine evolution reaction (CER) becomes a \begin{table}
\begin{tabular}{c c c} \hline \hline
**Type \#** & **Name** & **Preparation Method** \\ \hline Type I & Halometallic & Mixing an organic chloride with a metal halide such as Cl- (ZnCl\({}_{2}\)) \\ Type II & Air and water stable & Generally composed of organic cations and discrete anions such as [BF\({}_{4}\)]– [PF\({}_{6}\)]\({}^{-}\) \\ Type III & Deep eutectic solvents & Simple eutectic mixtures of organic halides with hydrogen bond donors (HBDs) such as urea and ethylene glycol (EG) \\ Type IV & ILs with metal containing cations & Mixing an ionic liquid with cationic metal complex \\ Type V & Protic ILs & Mixing a bronsted acid to a bronsted base (formed through the transfer of proton) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Types of ionic liquids (ILs) employed for the deposition of zinc and zinc-based alloys [9]. problem at higher potentials, such as 2V, owing to the oxidation of chlorozincate complexes at the anode. Electrodeposition of Zn and Zn-Ni alloys from ILs based on eutectic mixtures of ChCl such as ethylene glycol (EG) urea have gained significant interest in the past decade. These liquid systems consist of large choline cation, which has an unsymmetrical structure and a complex anion formed between Cl\({}^{-}\) ion and a hydrogen bond donor (urea, EG). Moreover, they represent a different physical environment in terms of relative viscosity (328 cp for ChCl/2 urea vs. 20 cp for ChCl/2 EG) and co-ordination ability [22]. [PERSON] and [PERSON] group [23; 24] and [PERSON] group [25] studied on the electrodeposition of Zn from ILs using ChCl-based combinations such as urea, EG, and ChCl-based DESs.