Vanadium flow batteries (VFBs) are a promising candidate for large-scale energy storage systems. However, their commercialization is hindered by the sluggish redox kinetics of vanadium ions and high overpotentials occurring at high current densities. In this study, to enhance the electrochemical reactivity of vanadium ions, glucosamine chemically grafted onto carboxylic acid-functionalized carbon nanotubes (CACNTs) (GACNT) is developed as a catalyst for electrodes. Electrochemical analyses reveal that GACNT exhibits improved reversibility and significantly reduced charge transfer resistance for redox reactions of vanadium ions compared to CACNT. This improvement is attributed to the newly introduced functional groups, which provide active sites for vanadium ions and enhance wettability with the electrolyte. In VFB single-cell tests, the GACNT electrode demonstrates excellent voltage and energy efficiencies even at a high current density of 300 mA cm−2 . Notably, during a long-term cycling test over 1,000 cycles performed at 300 mA cm−2

, the VFB single-cells show exceptional durability by stably maintaining coulombic and voltage efficiencies of 97.7 and 74.6%. Taken together, this study proposes an eco-friendly and effective catalyst modification strategy utilizing biomass-derived materials, suggesting new possibilities for the exploration of high-power VFBs.