Electrodeposition of Nanocrystalline Nickel Coatings from a Deep Eutectic Solvent with Water Addition

The electrodeposition of nanocrystalline Ni coatings from electroplating baths containing deep eutectic solvents (analogues of room-temperature ionic liquids) is studied. To improve physicochemical properties of electrolytes and enhance mechanical properties and corrosion resistance of Ni films, we suggest introducing extra water into plating baths based on a deep eutectic solvent. The effect of water addition on the electrodeposition of nickel coatings is investigated using an electrolyte containing choline chloride, ethylene glycol, nickel chloride and water in the molar ratio of 1: 2: 1: x where x is equal to 6, 9, 12, 15 or 18 (i.e., Ethaline + NiCl2 + xH2O). The introduction of water into the liquid mixture results in an increase in conductivity and a decrease in viscosity. The addition of extra water leads to more uniform and finer grained deposits. The electrodeposited Ni coatings with an average crystallite size of about 5 to 7 nm have an fcc crystal nanostructure. An increase in water content in the plating bath results in an increase in the microhardness of deposits and the inverse Hall–Petch effect is observed. According to electrochemical impedance spectroscopy measurements, the coatings with higher corrosion resistance are deposited from Ni plating bath containing water addition.