The low voltage/energy efficiency and relatively high cost of the vanadium redox-flow battery (VRFB) severely deter its commercial deployment. In this work, a low-cost and powerful cerium-oxide nanowire (CeO₂NW) modified with graphite felt (GF) electrode was successfully prepared through a hydrothermal system. Next, hydrogen annealing was performed to create defective-hydrogen-annealed CeO₂NWs-modified GF (H−CeO₂NWs−GF) for use in VRFB. The obtained electrochemical results indicate that the H−CeO₂NWs−GF reveals marvelous electrocatalytic performances toward the VO²⁺/VO₂⁺ redox couple to facilitate the electrochemical kinetics of the VRFB. The VRFB using different electrode materials were compared with a VRFB using H−CeO₂NWs−GF. The results revealed that the VRFB using H−CeO₂NWs−GF demonstrates the highest voltage efficiency of 90.4% at a current density of 40 mA cm⁻², which is considerably higher than those using pristine GF (81.1%) and a CeO₂NW electrode-modified GF (88.4%). The substantial performance improvement of the H−CeO₂NWs−GF might be accredited to the defect-rich H−CeO₂NWs on the GF surface, which acts as active sites and reduces the electrochemical polarization of the redox reaction. Furthermore, the one-dimensional nature of H−CeO₂NWs is favorable for the charge-transfer process and enhances the electrolyte accessibility, thus improving the electrode performance.