Defect-Mediated Oxygen Vacancy Engineering of CeO2 Unlocks Fast V2+/V3+ Kinetics for Vanadium Redox Flow Batteries

Abstract Vanadium redox flow batteries (VRFBs) are promising for large-scale energy storage, yet their high-power capability is hindered by sluggish V2+/V3+ redox kinetics at the negative electrode. While CeO2-decorated graphite felts are widely investigated, most lack precise oxygen vacancy tuning and atomic-level mechanistic insights. Here, we fabricate a defect-engineered CeO2/graphite felt electrode with precisely regulated oxygen vacancies via citric acid chelation-mediated in situ growth. Structural characterizations verify maximized active sites and preserved efficient mass transport. Combined experiments and DFT calculations reveal that moderate oxygen vacancies narrow the d–p band center gap and optimize V–O adsorption to accelerate reaction kinetics. The optimized electrode achieves 79.1% energy efficiency at 300 mA cm–2, 66.4% at 500 mA cm–2, and 1500-cycle stability with 0.003% decay per cycle. This work provides a scalable strategy and fundamental insights for high-performance VRFB electrodes.