<p>Carbon nanotubes (CNTs) are promising electrocatalysts for vanadium redox flow batteries (VRFBs); however, their inherent hydrophobicity poses challenges for practical application. In this study, we introduce a straightforward and industrially feasible urea-assisted treatment that facilitates carbonyl-rich oxygen functionalization on CNT surfaces through mild oxidation, while maintaining the integrity of the graphitic framework. X-ray photoelectron spectroscopy confirms a significant enrichment of carbonyl (C = O) species, resulting in a marked enhancement in surface wettability, with only a moderate reduction in electrical conductivity. Electrochemical analyses demonstrate a substantial increase in catalytic activity towards both VO²⁺/VO₂⁺ and V²⁺/V³⁺ redox couples, with anodic peak current densities approximately 2.32 times greater than those of pristine CNTs and a decreased charge-transfer resistance (66.1% post-treatment). When applied to graphite felt electrodes, CNT/urea exhibits improved single-cell VRFB performance, achieving an energy efficiency of approximately 64.5% and a discharge capacity of 25.77 Ah L⁻¹ at 400&#xa0;mA cm⁻², along with stable operation over 1,000 cycles. This research highlights urea-assisted carbonyl functionalization as a cost-effective and scalable approach for developing hydrophilic, catalytically active CNT electrodes for practical VRFB applications.</p>