Sustainable CuIn Electrodeposition from Deep Eutectic Solvents: Influence of Ethylene Glycol and Urea

The electrodeposition of CuIn coatings on platinum was investigated using CuCl₂.2H₂O and InCl₃ in the deep eutectic solvents (DES) 1ChCl:2EG (1 choline chloride: 2 ethylene glycol) and 1ChCl:2U (1 choline chloride: 2 urea). The cyclic voltammograms of the CuIn solution showed three reduction processes: the first two associated with Cu²⁺/Cu⁺ and Cu⁺/Cu and the third with In³⁺/In. Physicochemical properties, such as viscosity and specific mass, were measured at different temperatures for Cu²⁺ and In³⁺ cations. Increasing the temperature reduced viscosity and increased diffusion coefficient (D) values for the species studied in both solvents. The solvadynamic radius values decreased with increasing temperature for both species in 1ChCl:2EG, whereas the opposite was observed in 1ChCl:2U. Scanning electron microscopy (SEM) analysis of the coatings was performed potentiostatically at different temperatures and cation ratios. For 1ChCl:2EG, granular morphologies were observed, and the grain size increased with increasing temperature. By altering the In³⁺ concentration in the solution, an increase of approximately 20 wt % in the coatings was achieved. This was followed in relation to the result obtained from the equimolar solution. 1ChCl:2U coatings exhibited a granular morphology with Cu at 100 wt % at 296 K, whereas at 343 K, at more negative potentials, they exhibited 45 wt %. By altering the cation ratio, the cation with a higher concentration in the electrolytic solution predominated. The results show that examining CuIn electrodeposition in different media is essential to producing high-quality coatings.