Abstract
<jats:p>Molten chloride salt is a widely studied high-temperature electrolyte, with established use in pyrochemical reprocessing and electrorefining, and frequent use as a model system for concentrated solar power and molten salt reactor applications. Chromium (Cr) is a key element in high-temperature structural alloys. However, the temperature-dependent evolution and stability of Cr species in this environment remain insufficiently understood. Cr-redox chemistry in molten chloride salts governs the dissolution, oxidation and transformation of Cr-containing species, with direct implications for corrosion and dealloying of structural alloys as well as broader molten-salt processing applications. In the present study, the chemical stability of CrCl2, CrCl3, and Cr2O3 in LiCl-KCl eutectic molten salt at elevated temperatures was systematically investigated using in-situ X-ray absorption spectroscopy. The results revealed that CrCl3 and Cr2O3 remained chemically stable under the tested conditions, whereas CrCl2 underwent oxidation by impurities to form Cr2O3 at 500 °C, but partially converted back to Cr2+ species upon cooling to room temperature. Additionally, the interaction between chromium and NiCl2 in molten salt was examined, indicating that chromium likely reduced Ni2+ to metallic Ni0, while being oxidized to Cr2+, which subsequently underwent a similar chemical evolution as CrCl2 in the molten salt. These findings unravel a temperature-dependent, impurity-mediated redox cycle of Cr species in molten chloride salt, providing a foundation for understanding and controlling Cr the dissolution, oxidation and transformation, and for developing effective corrosion-mitigation strategies to enhance the stability of high-temperature structural alloys in molten-salt systems.</jats:p>