Effect of water content on physicochemical properties and electrochemical behavior of ionic liquids containing choline chloride, ethylene glycol and hydrated nickel chloride

We investigated the effect of water addition on some physicochemical properties of liquid mixtures containing choline chloride, ethylene glycol, nickel chloride and extra water in the molar ratio of 1:2:1:x (i.e. ethaline + NiCl2 + xH2O) where x was equal to 6, 9, 12 or 18. The influence of water upon density, viscosity, conductivity, and surface tension of ionic liquids is established for temperatures between 25 and 80 °C. An increase in the water content leads to decreasing density, viscosity and surface tension and to increasing conductivity. All these results are rationalized in terms of hole theory. The conductivity and viscosity of the liquid mixtures are controlled by the ionic mobility and the availability of voids of suitable dimensions. With increasing water content the average hole sizes increases which makes ionic motion considerably easier. There is a strong linear correlation between activation energies for conductivity and viscosity. Cyclic voltammograms recorded on Ni substrate in ionic liquids under consideration show that the electrochemical process of metal deposition is irreversible. An increase in water content in ethaline + NiCl2 + xH2O mixtures leads to the deceleration of Ni electrodeposition reaction.