Ionic liquids (ILs) have been extensively researched for electrochemical applications due to their exceptional properties including high thermal stability, non-flammability, and wide electrochemical windows.1 Water is often a contaminant in ILs and the addition of water can be used to customise its physical and electrochemical properties.2 Depending upon the nature of the IL ions, aqueous mixtures of ILs can mimic salt-in-water and water-in-salt systems, and are thus promising solvents for different electrochemical applications.3 In IL-aqueous mixtures, water molecules are generally dispersed into polar regions of the IL network at low water content. In contrast, high water content favours self-organization and aggregation of ILs, i.e. they appear “micelle-like” dispersed in aqueous media.2
In this work, we use the unique chemistry of IL-aqueous mixtures for the electrodeposition of copper nanostructures. Electrodeposition is a versatile and cost-effective material synthesis technique.4 Nanostructured Cu has been extensively employed in electrocatalysis and electroanalysis due to its abundance and good electrochemical stability.4 In this work, 1-butyl-3-methylimidazolium [BMIM]X (X= HSO4–,BF4–, Cl–, OTf–) hydrophilic ILs are used for this prototype study due to their miscibility with water. Cyclic voltammetry, chronoamperometry and SEM are used to study the effects of varying the nature and concentration of the IL in IL-aqueous mixtures on Cu electrodeposition. Imidazolium cations are readily adsorbed on the electrode surface under an electric field, thus impacting the morphology and crystallinity of Cu deposits. Varying the anion impacts the metal reduction potential and reaction mechanism by changing the coordination environment of the Cu2+ ions because of differences in electronegativity, polarizability, and the ability to donate electron pair to Cu2+ ions. The effects of electrolyte microheterogeneities on metal ion speciation and electroreduction are investigated, allowing tailoring of the electrolyte composition to produce specific metal nanoarchitectures.