Electrochemical copper deposition from an ethaline-CuCl2·2H2O DES

• Long term copper deposition is feasible from an ethaline-CuCl2·2H2O melt at room temperature.
• Hydrated copper chloride can be mixed in the melt without purification.
• Choline chloride is co-reduced with the metal which makes the deposit less pure.
• Homogeneous copper deposits can be obtained from the pure ethaline-CuCl2·2H2O melt.

Cu electroplating was carried out using a pure ethaline melt, a 1:2 ratio of choline chloride and ethylene glycol, at room temperature by potentiostatic and galvanostatic methods. Hydrated cupric chloride was added to the pure ethaline melt. Polarisation data for cupric ion reduction to copper was collected using an RDE to determine where metal deposition was feasible. Smooth Cu deposits were obtained at − 4.7 × 10− 3 A/cm2 using 0.2 M CuCl2·2H2O at 25 °C at a current efficiency of (95 ± 5)% at a rotation speed of 700 rpm. XRD analysis of the deposit showed a polycrystalline face centred cubic structure with (111) texture. The crystalline size was 66 ± 10 nm with some internal strain. EDX analysis showed the presence of carbon and chlorine with copper in the deposit, which was due to the break-down of the DES. Several deposition processes were carried out from a single bath to examine bath stability. The bath was found to be stable when a soluble anode was employed, and became unstable when an insoluble anode was used due to other reactions proceeding at the cathode.