An environment-friendly chromium electrodeposition process using additive-laden deep eutectic solvent

Abstract

The development of safer and more sustainable electrochemical processes has been one of the promising applications of deep eutectic solvents. In this study, a trivalent chromium-ethaline deep eutectic solvent electrolyte with the incorporation of significant plating additives such as water, boric acid, and lithium chloride was developed for chromium electroplating application. The effect of the selected plating additives on the morphology of the chromium deposits was mainly investigated. The effects on the properties of the plating solution were characterized by their viscosity, conductivity, and electrochemical behaviour via the linear sweep voltammetry (LSV) technique. The standard hull cell electroplating method was employed to obtain the effective plating current density range for chromium electroplating. A two-electrode cell composed of a brass cathode and SS304 anode with a DC power supply was used to deposit chromium from the prepared electrolytes at 40 °C. X-ray diffraction (XRD) analysis, field emission scanning electron microscopy (FESEM) and hardness measurement were performed on the obtained chromium deposits. The addition of water obtained the best result in terms of the improvement of the bath’s properties. This resulted in the formation of large grain structures, which were identified to be Cr, Cr2O3 and Cr3C2. With the addition of boric acid and LiCl, grain refinement and levelling characteristics were mainly observed. Nanocrystalline chromium was produced from these additives; however, relatively low hardness was achieved. Overall, the study confirms the improvements in chromium deposition using a safer and more sustainable trivalent Cr(III)-ethaline deep eutectic solvent.