Morphology-induced vacancy engineering of Co3O4 nanoarrays on carbon felt enables high-performance vanadium flow batteries

Vanadium flow batteries (VFBs) face critical challenges in power density due to sluggish redox kinetics and inefficient mass transport. Herein, we propose a dual-functional strategy that synergistically addresses both limitations through precursor morphology engineering. By precisely regulating hydrothermal crystallization kinetics, cobalt carbonate hydroxide (CCH) precursors evolve from 1D nanorods to 2D nanosheets, which transform into Co₃O₄ nanoarrays after annealing while retaining structural features. The resulting 1D rod-like architectures create open mesoporous channels for rapid ion diffusion, while defective Co₃O₄ surfaces enriched with oxygen vacancies enhance redox kinetics. DFT calculations reveal that oxygen vacancies upshift the Co d-band center in Co₃O₄, strengthening vanadium ion adsorption and accelerating redox reactions. Finite element analysis demonstrates that the rod-like microstructure enhances mass transport and reduces concentration polarization, while its uniform potential distribution suppresses parasitic side reactions. As a result, the VFB with Co₃O₄@CF-90 achieves a high energy efficiency of 74.4 % at 300 mA cm⁻², outperforming conventional carbon felt by 9.7 %, and maintains 80.2 % efficiency at 200 mA cm⁻² over 400 cycles. This work establishes a scalable morphology-induced vacancy engineering paradigm for high-performance flow battery electrodes, decoupling catalytic and transport optimization through precursor design.