Vanadium redox flow batteries using new mesoporous nitrogen-doped carbon coated graphite felt electrode

New and economical mesoporous nitrogen (N)-doped carbon structure is prepared using sodium citrate (SC) and urea precursors and then doped onto graphite felt (GF) electrode (SC/U-GF). The catalytic properties of SC/U-GF electrode are compared with those of pristine GF and SC-GF electrodes. When a large amount of mesoporous N-doped carbon is doped onto GF, the catalytic activity of SC/U-GF for improving the reactivity and reversibility of VO²⁺/VO₂⁺ and V²⁺/V³⁺ redox reactions is excellent, and its proper mesoporous structure promotes the mass transfer of vanadium ions. This is proved by measuring its low charge transfer resistance and high active area. When VRFB single cell using SC/U-GF is tested, its energy efficiency (EE) is 80.2 % at 120 mA cm⁻², which is 7.8 and 3.1 % better than VRFBs using pristine GF (72.4 %) and SC-GF (77.1 %). Even in a high current density (200 mA cm⁻²), its EE (71.6 %) is better than VRFBs using pristine GF (59.9 %) and SC-GF (66.4 %). Additionally, EE of VRFBs using SC-GF and SC/U-GF is well maintained (95.6 and 99.6 % preservation after 300 cycles). Based on that, it is obvious that SC/U-GF electrode strongly affects the enhancements in performance and stability of VRFB.