Current status of ferro-/ferricyanide for redox flow batteries

The ferro-/ferricyanide couple has been extensively investigated as a redox species in various redox flow batteries (RFBs) due to its advantageous electrochemical properties, user-friendliness, and affordable cost. However, the high concentration and stability of ferro-/ferricyanide are important for developing high-energy density and long-cycle life RFBs. Different methods have been explored to increase its concentration through diverse ion effects and cation modification while also exploring the effects of pH, light, and air sensitivity on its stability. This review will provide an overview of recent research on the concentration enhancement of ferro-/ferricyanide and its stability for RFBs. •Fe(CN)64−/3− is one of the most widely used redox couple in redox flow batteries.•Diverse ion effects and cation modifications increase Fe(CN)64−/3− concentration.•pH, air, and light affect Fe(CN)64−/3− stability, requires effective mitigation approaches.•High concentration Fe(CN)64−/3− needs for high energy redox flow batteries.•Stability of Fe(CN)64−/3− crucial for longevity operation of redox flow batteries.