Excellent stability and electrochemical performance of the electrolyte with indium ion for iron–chromium flow battery

Iron–chromium flow battery (ICFB) is one of the most promising technologies for energy storage systems, while the parasitic hydrogen evolution reaction (HER) during the negative process remains a critical issue for the long-term operation. To solve this issue, In3+ is firstly used as the additive to improve the stability and performance of ICFB. The results suggest that In3+ not only effectively inhibits the HER but also accelerates the kinetics of Cr3+/Cr2+ and Fe3+/Fe2+ to some extent. More importantly, the ICFB using an optimal concentration of 0.01 M In3+ in the anolyte exhibits an energy efficiency of 77.0% at 200 mA cm−2, and a 36.3% higher capacity retention ratio than that of the pristine anolyte after 140 cycles at 160 mA cm−2. Furthermore, the capacity decay rate is low to 0.16% per cycle during the cycle test, which is much lower than that in the previous studies. Both the enhanced stability and electrochemical performance are attributed to the coupling effect of the inhibited HER and promoted kinetics of Cr3+/Cr2+ after In3+ is introduced. Therefore, In3+ as an anolyte additive can be a promising and cost-effective method to further improve the battery performance of ICFB and promote its engineering application.