NTO laminated graphite felt as high-performance negative electrode for vanadium redox flow batteries

In recent years, vanadium redox flow batteries (VRFBs) have attracted global interests owing to their advantages of large scale, high safety and long-term cyclability. Nevertheless, the unsatisfactory kinetics of carbon-based anodes limits the commercial application of VRFBs. Especially, graphite felt (GF) as a representative anode material, has critical disadvantage of poor electrolyte wettability due to its hydrophobic surface. This limitation of interfacial properties between the electrode and electrolyte causes inefficient charge transportation, which leads to low electrochemical performance with poor cycle stability. To improve the surface properties of GF anodes for VRFB, we introduce a lamination layer of Nb-doped TiO2 (NTO) to a heat-treated graphite felt (HGF) via ultrasonic spray pyrolysis deposition. The NTO laminated HGF offers hydrophilic surface with several advantages of high catalytic activity, high electrical conductivity, and high specific surface area. As an anode material, the hybrid structure of the NTO lamination layer on the HGF demonstrates synergistic effects, thus enabling superior energy storage performance compared with other electrodes. Especially, the NTO-HGF anode shows an energy efficiency of 82.03%, which is 6.2% higher than that of pristine GF. We demonstrate that the introduction of an NTO lamination layer can be a prospective candidate for improving the VRFB anodes performance. •Highly conductive Nb-doped TiO2 (NTO) laminating layer on graphite felt for VRFBs.•Uniform lamination process using horizontal ultrasonic spray pyrolysis deposition process•Enhanced catalytic active sites and oxygen-related functional groups from NTO layer.•NTO-HGF as promising candidates of high-efficiency anode for VRFBs.