Enhanced electrocatalytic performance of nitrogen‐ and phosphorous‐functionalized carbon felt electrode for VO2+/VO2+ redox reaction

Summary Carbon felt co‐doped with nitrogen and phosphorus is suggested as an electrode for catalytically enhancing the redox reaction of the VO2+/VO2+ redox couple. N and P can be simultaneously incorporated with the carbon felt via a one‐step facile synthesis method using aniline and triphenylphosphine as the N and P sources. Successful co‐doping is confirmed using energy‐dispersive spectroscopy and X‐ray photoelectron spectroscopy analyses. The electrochemical activity of the proposed carbon felt electrode toward the VO2+/VO2+ redox reaction is significantly enhanced when compared to those of carbon felt electrodes doped with only nitrogen or phosphorus, owing to the synergetic effect of the N, P co‐doping. The all‐vanadium redox flow battery (VRFB) assembled with the N, P co‐doped carbon felt (NPCF) electrode exhibits a highly stable cyclic performance accompanied by considerably improved energy efficiencies of 84.94% and 84.33% in the 1st and 50th cycles, respectively. In addition, the cell employing the NPCF electrode exhibits an energy efficiency of 79.1%, approximately 11% higher than that of bare carbon felt (BCF: 68.1%), at a high current density of 100 mA cm−2. This improvement is mainly attributed to abundant electrochemical active sites for the oxidation and reduction of vanadium ions provided by the N and P functional groups formed on the carbon felt via our proposed treatment. These mitigate electrochemical polarization and accelerate the redox reaction. Carbon felt co‐doped with nitrogen and phosphorus is suggested as an electrode for catalytically enhancing the redox reaction of the VO2+/VO2+ redox couple. The all‐vanadium redox flow battery assembled with the N, P co‐doped carbon felt electrode exhibits a highly stable cyclic performance accompanied by considerably improved energy efficiencies. This improvement is mainly attributed to abundant electrochemical active sites for the oxidation and reduction of vanadium ions provided by the N and P functional groups formed on the carbon felt via our proposed treatment.