Nitrogen (N) and phosphorous (P) co-doped carbon felt is proposed as a promising electrode for enhancing VO²⁺/VO₂⁺ redox reactions. Nitrogen and phosphorous can be simultaneously incorporated onto the carbon felt through straightforward synthesis method using aniline and triphenylphosphine as N and P source. The successful incorporation of nitrogen and phosphorous functional groups onto the carbon felt surface can be confirmed by X-ray photoelectron spectroscopy analysis. Compared to the carbon felt electrode doped solely with nitrogen or phosphorous functional groups on its surface, the electrochemical activity of the proposed carbon felt electrode towards slow redox reactions of VO²⁺/VO₂⁺ can be greatly enhanced owing to the synergistic effects of the nitrogen and phosphorous functional groups. Consequently, VRFB cell assembled with N, P co-doped carbon felt electrode exhibits much stable cycle performance accompanied by highly improved energy efficiencies of 84.94 and 84.33% in the 1^st and 50^th cycle, respectively.