Recent Advances on Electrolytes for Iron-Chromium Redox Flow Batteries

The iron-chromium redox flow battery (Fe-Cr RFB) is considered the first RFB and utilizes low-cost, abundant iron and chromium chlorides as redox-active materials, making it one of the most cost-effective energy storage systems. This review first introduces the basic principles of Fe-Cr RFB and their advantages in energy storage systems, followed by an analysis of the key technical challenges they face, including low electrochemical activity of chromium ions, hydrogen evolution reaction (HER), and capacity degradation during long-term cycling. Based on these findings, the paper systematically summarizes the latest research progress on Fe-Cr RFB electrolytes, primarily including: (1) optimization of electrolyte composition; (2) application of functional additives; (3) Development of chelating electrolytes. Finally, this paper outlines future development directions for Fe–Cr RFBs aimed at enabling scalable and cost-effective energy storage.