Defect-rich three-dimensionally ordered macroporous magnesium cobalt oxide spinel coupled with graphite felt for vanadium redox flow batteries

Developing electrodes that simultaneously enable rapid redox kinetics and efficient mass transport is critical for advancing high-performance vanadium redox flow batteries (VRFBs). Herein, a defect-rich three-dimensionally ordered macroporous MgCo 2 O 4 catalyst is integrated onto heat-treated graphite felt (3DOM MC@400-HGF) via colloidal-template-assisted impregnation. Although electrochemically inactive, Mg 2+ acts as an effective electronic modulator, inducing local lattice strain that promotes oxygen-vacancy formation and enriches octahedral Co 3+ active sites. DFT calculations reveal that oxygen vacancies introduce defect-derived states across the Fermi level, closing the near-surface semiconducting bandgap and driving a quasi-metallic transition that facilitates charge transport and vanadium-species adsorption. Concurrently, the interconnected 3DOM framework provides abundant accessible active sites and continuous pathways for electrolyte penetration and mass transport. This cooperative coupling of macroporous transport and Mg-induced electronic modulation establishes a pronounced structure-electronic synergy, simultaneously accelerating interfacial charge transfer and mitigating transport limitations. Consequently, 3DOM MC@400-HGF delivers an energy efficiency of 74.57% at 160 mA cm −2 and maintains stable operation over 500 charge-discharge cycles. These findings establish a rational strategy for integrating defect-mediated electronic regulation with ordered pore-architecture engineering to design efficient and durable VRFB electrodes.