Electrodeposition of copper on glassy carbon and palladium from choline chloride - ethylene glycol deep eutectic solvent

Abstract

Electrodeposition of copper from deep eutectic solvents (DES) based on a mixture of choline chloride and ethylene glycol containing CuCl2·2H2O at 50 °C and 80 °C was studied. Electrochemical reduction/oxidation of Cu(II)/Cu(0) on glassy carbon (GC) and palladium (Pd) electrodes was investigated by cyclic voltammetry (CV) and square wave voltammetry (SWV) emphasizing that this process takes place through two steps, Cu(II) ↔ Cu(I) and Cu(I) ↔ Cu(0). The CV results showed that in chloride-rich DES electrolytes, the increased presence of chloro ligands raises the overpotential required for Cu electrodeposition. The electrochemical impedance spectroscopy (EIS) results indicate simultaneous electrodeposition of Cu and electrosorption of large cations on electrodeposited Cu on both GC and Pd substrates. Scanning electron microscopy (SEM) results showed that Cu grains of approximately 1 μm were obtained by electrodeposition of Cu on both Pd and GC, whereby better coverage by electrodeposited Cu was obtained on Pd than on GC. Cu electrodeposited on Pd was relatively uniform and smooth, but porous, while Cu electrodeposited on GC was dispersed in small agglomerates. Energy-dispersive X-ray spectroscopy (EDS) of Cu electrodeposited on Pd detected the dominant presence of Cu with the possibility of the formation of CuPd alloy. The presence of CuPd alloy face-centred cubic structures is confirmed by X-ray diffraction (XRD) along with metallic Cu.