A study of simultaneous electrodeposition of Cu and S in choline chloride-ethylene glycol deep eutectic solvents: a pathway to the synthesis of copper sulfide hexagons

Abstract

Copper sulfides, with their tunable semiconductor properties, are promising materials for electronic and optoelectronic devices. Among the various synthesis techniques, electrodeposition stands out as a particularly effective method, offering precise control over the structure and composition of these compounds. In this study, we demonstrate the feasibility of co-electrodeposition of copper and sulfur on a carbon substrate using deep eutectic solvents (DESs) based on choline chloride and ethylene glycol. The effects of electrodeposition potential and electrochemical bath composition on the electroreduction process of CuCl₂·2H₂O and Na₂S₂O₃ mixtures in DESs were investigated. By controlling the electrochemical deposition parameters, we successfully obtained various structures, including Cu clusters, S-doped Cu clusters, and copper sulfide (Cu_xS) hexagons. The morphology and composition of the obtained materials were characterized using scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS) techniques. Our findings indicate that co-electrodeposition of Cu and S requires potentials more negative than −0.84 V vs. Pt. Furthermore, the formation of Cu_xS hexagons was achieved by acidifying electrochemical baths with H₂SO₄. Interestingly, the electrodeposition of Cu from DESs was favored under all investigated synthesis conditions. Consequently, the average atomic percentage of S in the obtained Cu–S materials was a maximum of 9.36 at%, while EDS point analyses revealed that individual copper sulfide hexagons contained 22.7 to 23.8 at% of S. These results provide valuable insights into the co-electrodeposition of Cu and S from choline chloride-ethylene glycol DESs and pave the way for the future development of novel copper sulfide-based materials.