Nitrogen-Doped Bismuth Oxide-Modified Carbon Cloth as a Bifunctional Electrocatalyst for Iron–Chromium Redox Flow Batteries

As a large-scale electrochemical energy storage technology, iron–chromium redox flow batteries (ICRFBs) have the advantages of intrinsic safety, environmental friendliness, low raw material cost, long cycle life, etc. However, there is currently a problem of poor reaction activity of Cr3+/Cr2+. Herein, a composite electrode [PDA–Bi–treated carbon cloth (TCC)] modified with polydopamine (PDA)-assisted immobilization of the bismuth oxide (Bi2O3) catalyst is prepared. Bi2O3 as a catalyst can enhance the activity of the redox reactions. The self-assembly process of PDA not only serves to immobilize bismuth oxide catalysts and bind them to the surface of CC electrode but also serves as a nitrogen-doping agent, providing more active sites for electrodes. The benefits of the excellent physical and electrochemical performance of the PDA–Bi–TCC electrode are that the energy efficiency of the ICRFBs remains at 81.78% at a current density of 140 mA/cm2, far higher than that of the original TCC electrode. At 80 mA/cm2, it even achieved an energy efficiency of 86.23%. In addition, ICRFBs with the PDA–Bi–TCC electrode also have excellent long-term stability and are capable of stably conducting 300 charge–discharge cycles at 140 mA/cm2. These results demonstrate the potential of electrodes to improve the performance of ICRFBs and provide possibilities for the engineering application of ICRFBs.