Bidirectionally Enhanced Reaction Kinetics in Vanadium Redox Flow Battery via Regulating Mixed-Valence States in Perovskite Electrodes

Various metal oxide catalysts have been utilized to enhance the electrode reaction kinetics in vanadium redox flow battery (VRFB). However, the determining factor governing their catalysis is still insufficiently understood. Herein, selectively doping of Sr and Ce at La site of LaMnO₃ perovskite (LSMO and LCMO) was used to modulate chemical environments of Mn ion activity donors, thereby boosting vanadium redox reaction processes. Sr doping increases the valence state of Mn ions, making it easier for Mn ions to take an electron from the electrode and transfer it to V³⁺ ions, which lowers the reaction energy barrier of V³⁺/V²⁺ redox processes. Conversely, Ce doping decreases the Mn valence and increases the oxygen vacancies, boosting the charge transfer and mass transfer of VO²⁺/VO₂⁺ redox processes. Theoretical calculation further demonstrates that doping Sr and Ce enhances the vanadium ion's ability for charge transfer and adsorption. Compared with pristine VRFB, the VRFB with LSMO- and LCMO-modified anode and cathode, respectively, exhibits an excellent energy efficiency (EE) of 67% at a high current density of 300 mA cm^-2 and an increased EE of 15% at 150 mA cm^-2. This study is critical for promoting fundamental understanding and offering a design strategy for achieving superior-performance metal-based electrocatalysts in VRFB.