Synergistic effect of electrode defect regulation and Bi catalyst deposition on the performance of iron–chromium redox flow battery

Iron-chromium redox flow batteries (ICRFBs) possess advantages of high safety, long cycle time, and low-cost. Increasing Cr3+/Cr2+ reaction activity is suggested as one of the most promising strategies to improve the performance and prolong the lifetime of ICRFBs. To improve the slow reaction kinetics of the negative electrode, a type of defected carbon cloth with Bismuth (Bi) catalyst introduction is prepared by defect engineering method and electrochemical deposition, which provided defect sites and active sites to catalyze the redox couple's reaction of ICRFBs. Furthermore, this modified carbon cloth adsorbs Cr(III) hydrate more easily, which has a more stable structure and can significantly improve the performance of ICRFBs. Both experimental analysis and theoretical calculation indicated that the modified electrode has excellent electrocatalytic ability, which can enhance the reaction rate of Cr3+/Cr2+, improve capacity retention and stabilize cycling performance. The capacity degradation rate of an ICRFB single cell with the modified electrodes is just 0.23% per cycle at a current density of 140 mA/cm2. Additionally, the energy efficiency (EE) remains around 83%, which is 8.45% higher than that of the pristine electrode assembled battery under 60 cycles. This work supplies a simple method to obtain a high-performance electrode material for ICRFBs and makes it a practical solution to promote ICFRBs large-scale commercialization process.