Hydrogen Evolution Inhibition via Dual Functional Electrolyte Additive to Achieve Highly Stable Aqueous Fe Ion Battery

Abstract Iron‐ion battery (FeIB) is a promising energy storage system for future grid applications due to the low cost and abundance of iron. However, owing to the serious hydrogen evolution reaction (HER) during cycling, the Coulombic efficiency (CE) of iron‐ion batteries is relatively low. Herein, ascorbic acid (VC) is employed as an electrolyte additive to suppress HER and enhance CE and long‐term stability of FeIB. Theoretical calculations and experimental results indicate that VC can regulate the d‐band center of Fe substrate, fix active H + , and thus inhibit HER. Meanwhile, it can also fine‐tune the solvation structure of Fe ions by enhancing the electrostatic potential. Therefore, the Fe||Fe symmetric cell with modified electrolyte exhibits an ultralong stable cycling performance of up to 1300 h with an average CE of 94%. The Fe|| Prussian Blue full cell exhibits excellent rate performance and cycle stability. This study provides a new perspective for achieving high reversibility of iron‐ion batteries.