Constructing BiN and BiC on graphite felt for high- efficiency vanadium redox flow batteries

Tackle the problems of slow V 2+ /V 3+ reaction kinetics and severe hydrogen evolution side reactions of vanadium redox flow batteries (VRFB), this research proposes a strategy rooted in synergistic modification of graphite felt (GF) with Bi and N. Through high-temperature carbonization, bismuth atoms decomposed from bismuth nitrate react with the nitrogen formed from 2-methylimidazole to establish strong Bi N and Bi C coordination bonds at the GF interface. This process constructs a highly active bismuth-based composite electrode (1BiGF) that significantly Improves the activity of the V 2+ /V 3+ redox pair while simultaneously increasing the hydrogen evolution potential, effectively suppressing hydrogen evolution side reactions. Batteries incorporating 1BiGF as the negative electrode deliver an energy efficiency of 80.26 % at a current density of 220 mA cm −2 , outperforming the GF electrodes(74.32 %). The peak power density of the 1BiGF electrode increased by 6.7 % compared to the original GF (780.3 vs. 731.36 mW cm −2 ). Furthermore, after 600 cycles at a current density of 220 mA cm −2 , the 1BiGF electrode exhibited an energy efficiency retention rate of 98.2 %, demonstrating excellent long-term stability. This research focuses on developing high-performance VRFB negative electrodes by leveraging the synergistic action of N doping and Bi-based catalysis, thereby broadening the application scope of Bi-based composite electrodes in VRFBs.