<p>Vanadium redox flow battery (VRFB) exhibits a great potential for application in large-scale and long-term energy storage systems due to its high safety, longevity, and environmental friendliness. However, the poor electrocatalytic activity of the pristine graphite felt electrode seriously hinders the energy density and efficiency of VRFB. To address the issue, in this work, the rich active site-NiMoO₄ nanorods were used to in situ modify graphite felt for high-performance VRFB. The rod-to-diameter ratio and deposition of NiMoO₄ were controlled by adjusting the ratio of water/ethanol and concentration of the precursor solution to obtain the optimal length of NiMoO₄ nanorods uniformly deposited on the graphite felt surface. This abundant micropores, dual active sites of Mo–O–Ni, and additional oxygen vacancies effectively increase the specific surface area, the number of active sites, and the hydrophilicity for graphite felt, which boosts the charge transfer and mass transfer for VO²⁺/VO₂⁺ and V³⁺/V²⁺ redox reactions. The modified battery exhibits an energy efficiency of 71.1% at 150&#xa0;mA·cm⁻², which is 19.8% higher than the blank battery. Furthermore, the modified battery shows excellent stability during 100 cycles. This work will promote the development and application of binary metal oxides with rich active sites in VRFB.</p> Graphical abstract <p></p>