Copper electrodeposition from a chloride free deep eutectic solvent

• The substitution of choline chloride with choline dihydrogencitrate in the ethaline deep eutectic solvent was studied
• The deep eutectic solvent obtained was characterized in terms of physical properties
• Copper electroreduction from the electrolyte was studied using voltammetric techniques
• Good quality layers of copper were electrodeposited from choline dihydrogencitrate/ethylene glycol in 1:4 molar ratio

The possibility of substituting choline chloride in the well-known choline chloride/ethylene glycol deep eutectic solvent is studied in the article. The substitution with choline dihydrogencitrate gives the possibility to maintain the choline moiety and to obtain an electrolyte free of chloride ions. Different ratios between choline dihydrogencitrate and ethylene glycol are tested to analyze the effect of this parameter on the behavior of the solution. Physical characterization and electrochemical investigation of the pure and the copper supplemented electrolytes are provided to properly link the chemistry of the electrolytes with their physical properties and their influence on metal electroreduction. From this point of view viscosity and conductivity of the new solutions are analyzed, highlighting a strong influence of the first on the possibility of good quality metal plating. Copper deposition is successfully attempted on nickel and the resulting coatings are analyzed by mean of SEM, hardness measurements, XRD and microprofilometry. Good quality coatings can be easily obtained from a choline dihydrogencitrate/ethylene glycol deep eutectic solvent presenting the ratio 1:4 between the two chemicals. The coatings produced are compared as well with their homologues obtained from the well characterized choline chloride/ethylene glycol system, showing equivalent quality.