Heteroatom co-doped biomass carbon modified electrodes for all-vanadium redox flow batteries with ultra-low decay rate of energy efficiency

The intermittent nature of renewable energy calls for advanced energy storage systems, of which all-vanadium redox flow batteries (VRFBs) are recognized as the most promising long-duration energy storage devices. The most common electrode for VRFBs is graphite felt (GF), however with poor hydrophilicity and weak electrochemical activity, making it difficult to be a perfect electrode. In this work, we report a nitrogen-phosphorus codoped biomass carbon modified GF (NP-GF), in which the introduction of cross-linking agents enhances the linkage between the carbon material and the GF. With excellent electrolyte wettability and electrochemical catalytic activity, the NP-GF electrode exhibits enhanced electrochemical activity and reversibility for VO2+/VO2+ and V2+/V3+ in electrochemical tests. The coulombic efficiency (CE), voltage efficiency (VE), and energy efficiency (EE) are all boosted at current densities of 80-280 mA cm-2 in VRFB single cell tests assembled with NPGF. The power density of the VRFB reaches a peak of 757.0 mW cm-2. Furthermore, the VRFB has an extremely low EE decay rate per cycle (0.0018 %), demonstrating superior electrochemical performance stability.