A comprehensive study on the hydroxyl multiwalled carbon nanotubes (hydroxyl MWCNTs) as catalysts in a positive reaction was performed to improve the efficiency of the vanadium redox flow battery (VRFB). e physicochemical properties of the hydroxyl MWCNT-modified electrode were characterized by using a scanning electron microscope (SEM), conductivity measurement, Brunner-Emmet-Teller (BET) measurement, X-ray photoelectron spectroscopy (XPS) analysis, cyclic voltammetry (CV) tests, electrochemical impedance spectroscopy (EIS) analysis, and charge-discharge tests. e prepared composite electrode possesses a huge amount of oxygen-containing groups, high-specific surface area, high electrical conductivity, and high catalytic activity towards the VO 2 + /VO 2+ reaction based on physicochemical characterization. e hydroxyl MWCNT-modified graphite felt (hydroxyl MWCNTs/GF) shows the best cell performance with the energy efficiency of 79.74% and remains in high stability after 50 cycles. e improved cell performance is probably ascribed to the increase in active sites, fast charge transfer, and mass transfer rate of the introduced hydroxyl MWCNTs.