Electrochemical Behavior of Cr2+ in NaCl-CaCl2 Molten Salt and Electrodeposition of Chromium Coatings

The NaCl-CaCl2 molten salt system presents a cost-effective and stable medium for the electrodeposition of metallic chromium. However, the electrochemical behavior of Cr2+ and the deposition process for dense chromium coatings within this system remain unexplored. Using CrCl2 as a precursor, this study investigated the electrochemical behavior of Cr2+ in NaCl-CaCl2 molten salt at 620°C through cyclic voltammetry and square wave voltammetry. The results revealed that the reduction of Cr2+ involved a one-step, two-electron exchanged reaction (Cr2++ 2e-→ Cr), exhibiting quasi-reversible behavior controlled by diffusion, with a diffusion coefficient of 0.5× 10-5 cm2s-1. Electrodeposition on a molybdenum substrate demonstrated that current density significantly influenced coating morphology. An optimal condition of 30 mA cm-2 yielded a dense and uniform chromium coating, whereas current densities of 50-70 mA cm-2 resulted in significant degradation in coating planarity due to concentration polarization. Deposition time exhibited a linear positive correlation with coating thickness. Extending deposition time eliminated initial island growth and enhanced coating continuity. X-ray diffraction confirmed the coating consisted of pure chromium phase with a strong (200) preferred orientation. This research provided a theoretical and experimental foundation for electrodepositing chromium metal coatings in the NaCl-CaCl2 molten salt system.