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

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.