Catalyzing anode Cr2+/Cr3+ redox chemistry with bimetallic electrocatalyst for high-performance iron–chromium flow batteries

Renewable energy integration requires a safe and efficient solution to effectively store and release electrical energy in a vast scale. Cost-effective iron-chromium redox flow battery is a reviving alternative for long-duration grid-scale energy storage applications. However, sluggish kinetics of Cr2+/Cr3+ redox reaction along with parasitic hydrogen evolution at anode still significantly limits high-performance operation of iron-chromium flow batteries. Herein, a bimetallic Pb/Bi electrocatalyst is delicately designed and fabricated on carbon felt electrode, which synergistically boosts Cr2+/Cr3+ kinetics and alleviates hydrogen evolution. Combined experimental characterization and theoretical calculation prove that metallic Bi substantially enhances Cr2+/Cr3+ reversibility owing to strong adsorption and intensified Cr-3d and Bi-6p orbitals hybridization, while Pb endowed with a high activation energy barrier effectively alleviates hydrogen evolution. Benefitting from the bimetallic Pb/Bi electrocatalyst with optimized Pb/Bi ratio, the iron-chromium flow battery demonstrates low polarizations and substantially enhanced rate performance as compared to the flow cell using pristine carbon felt, with an energy efficiency of 77% readily achieved at 125 mA cm−2, which offers a deep insight into development of high-efficiency electrocatalyst for high-performance operation of iron-chromium flow batteries.