Multiple-dimensioned defect engineering for graphite felt electrode of vanadium redox flow battery

The scarcity of wettability, insufficient active sites, and low surface area of graphite felt (GF) have long been suppressing the performance of vanadium redox flow batteries (VRFBs). Herein, an ultra-homogeneous multiple-dimensioned defect, including nano-scale etching and atomic-scale N, O co-doping, was used to modify GF by the molten salt system. NH4Cl and KClO3 were added simultaneously to the system to obtain porous N/O co-doped electrode (GF/ON), where KClO3 was used to ultra-homogeneously etch, and O-functionalize electrode, and NH4Cl was used as N dopant, respectively. GF/ON presents better electrochemical catalysis for VO2+/VO2+ and V3+/V2+ reactions than only O-functionalized electrodes (GF/O) and GF. The enhanced electrochemical properties are attributed to an increase in active sites, surface area, and wettability, as well as the synergistic effect of N and O, which is also supported by the density functional theory calculations. Further, the cell using GF/ON shows higher discharge capacity, energy efficiency, and stability for cycling performance than the pristine cell at 140 mA cm-2 for 200 cycles. Moreover, the energy efficiency of the modified cell is increased by 9.7% from 55.2% for the pristine cell at 260 mA cm-2. Such an ultra-homogeneous etching with N and O co-doping through "boiling" molten salt medium provides an effective and practical application potential way to prepare superior electrodes for VRFB. An ultra-homogeneous modification was used for multiple-dimensioned defect engineering of graphite felt electrodes for a vanadium redox flow battery. Graphite felt obtains nano-scale etching and atom-scale N/O co-doping. The electrode offers a larger surface area, more active sites, and better hydrophilicity for both VO2+/VO2+ and V3+/V2+ redox reactions. The cell using a modified electrode further shows lower polarization and higher energy efficiency. image