Interfacial co-polymerization derived nitrogen-doped carbon enables high-performance carbon felt for vanadium flow batteries

Nitrogen-doped carbon felt has exhibited great promise in enhancing the cycling performance and lifespan of vanadium flow batteries (VFBs). However, the fabrication of stable and high-performance nitrogen-doped carbon felt is still to a certain extent hindered by existing preparation processes. Herein, a two-step novel in situ interfacial co-polymerization strategy is proposed to construct microvillus-like nitrogen-doped carbon on carbon felt, which features excellent homogeneity, high doping content and controllable nitrogen type conversion. By adding polyethyleneimine into the polymerization reaction, the aggregation effect of polydopamine is corrected and more strongly bonded nitrogen atoms are introduced via covalent interactions, yielding a hierarchical electrode interface with a greatly enhanced pyridinic-N content. Electrochemical characterization studies show that the prepared electrode possesses superior reaction kinetics towards both VO2+/VO2+ and V2+/V3+ redox couples, which can also realize a facile mass-transfer process. First principles calculations at the atomic level further ascribe the promoted V2+/V3+ kinetics to the enhanced vanadium adsorption on pyridinic-N, while attributing the promoted VO2+/VO2+ kinetics to a remarkably reduced activation energy barrier associated with doped N atoms. Adopting the prepared electrodes, the VFB demonstrates a superior energy efficiency of 73.6% at 300 mA cm−2, and achieves an excellent and long-term cycling stability over 600 cycles at 200 mA cm−2 with an extremely low energy efficiency decay of 0.006% per cycle.