Copper‐Regulated Electron‐Deficiency of Oxide‐Derived Bismuth Electrocatalysts for Enhanced V 2+ /V 3+ Redox Kinetics in Vanadium Redox Flow Batteries

ABSTRACT Vanadium redox flow battery (VRFB) is attractive for grid‐scale energy storage, yet its high‐power‐density operation is limited by the sluggish V 2+ /V 3+ redox kinetics at the negative electrode. Herein, a Cu‐doped oxide‐derived Bi electrocatalyst (Cu‐OD‐Bi) is fabricated from in situ reconstruction of pre‐electrodeposited Cu‐doped Bi 2 O 3 on graphite felt (GF) during the first charge process of VRFB, in which the electronic structures of the Bi atoms could be controllably regulated by the doping level of Cu. Electrochemical analyses show that the Cu‐OD‐Bi possesses stronger electron‐deficiency and exhibits a higher intrinsic catalytic activity toward the V 2+ /V 3+ redox reactions compared to oxide‐derived Bi and directly electrodeposited metallic Bi. Density functional calculations further reveal strengthened adsorption of V 2+ /V 3+ ions on the electron‐deficient Bi‐sites of Cu‐OD‐Bi, which accelerates the charge‐transfer processes. Consequently, the VRFB assembled with the Cu‐OD‐Bi@GF electrode achieves an energy efficiency of 80.38% at 200 mA cm −2 and an ultrahigh peak power density of 1126 mW cm −2 . Moreover, after operation for 1000 cycles at 300 mA cm −2 , this VRFB still renders an energy efficiency of 73.41%, with 0.165‱ decay per cycle. This work provides a feasible strategy and valuable insights for rational design and regulation of the electronic structures of Bi‐based electrocatalysts toward different applications.