Effect of coordinated water of hexahydrate on nickel platings from choline-urea ionic liquid

Impacts of coordinated water of nickel chloride hexahydrate (NiCl 2 ·6H 2 O) on the properties of choline-urea (ChCl-2Urea) ionic liquid (IL), including viscosity and electrical conductivity, and electrodeposition behavior of Ni coatings were investigated. Results reveal that the coordinated water exhibited a profound influence on reducing viscosity, improved electrical conductivity and promoted the formation of a nanocrystalline Ni coating, while the Ni nucleation mechanism was not altered by the presence of coordinated water, proceeding via that from the progressive three-dimensional nucleation to instantaneous nucleation with hemispherical diffusion-controlled growth when the deposition potential shifts to the negative direction. When water content was maintained no more than ~ 8 wt%, a compact nanocrystalline Ni coating, with a current efficiency of almost 100%, was prepared from ChCl-2Urea-NiCl 2 ·6H 2 O with an aid of 400 mg/L nicotinic acid (NA) at 318 K. These results indicate hydrated Ni salts can be used to replace anhydrous counterparts in preparation of Ni coating from choline-urea IL, which could reduce the impact on environment and product cost. Such a strategy may be extended to other hydrated metal salts in IL electrolyte electrodeposition for high-quality coating preparation.