Surface-modified graphite felt incorporating synergistic effects of TiO2 decoration, nitrogen doping, and porous structure for high-performance vanadium redox flow batteries

Construction of porous surface, decoration of metal oxide, and introduction of defects are three major strategies to improve the electrocatalytic capability of graphite felt (GF) for vanadium redox flow battery (VRFB). In this study, we have successfully achieved the urea-assisted deposition of TiO2 onto GF, resulting in a synergistic effect that realizes the three modifications mentioned above, through a facile one-pot approach. During the post-annealing process, the decorated TiO2 can further undergo carbon-thermal reduction to etch the GF surface, leading to a porous surface. Additionally, the defective structures such as oxygen defects and nitrogen doping also be can simultaneously incorporated in the modified GF. As a result, the modified GF shows a dramatically improved electrocatalytic capability towards the VO2+/VO2+ redox reactions due to better hydrophilicity, larger surface area, and numerous oxygen defects. The VRFB with the modified GF electrode can deliver the coulombic efficiency (CE), voltage efficiency (VE), and energy efficiency (EE) of 95.0, 81.8, and 77.8 %, respectively, at 160 mA/cm2, which are much better than those of VRFB based on untreated GF. •The modified GF electrodes with a synergistic effect of surface modification have been prepared.•The carbon-thermal reduction of TiO2 can form porous structure on the GF electrode.•The modified GF reveals higher surface area, improved hydrophilicity and electrochemical resistance.•The VRFB using the modified GF electrode shows a great energy efficiency of 83.3 % at 100 mA/cm2.