Decorating Graphite Felt Electrode With Uniformly M‐N x Functionalized Carbon Nanosheets for High‐Performance Vanadium Redox Flow Batteries

Vanadium redox flow batteries show considerable promise for energy storage, yet their overall performance is still hindered by the limited electrochemical activity of graphite felt (GF) electrodes. Herein, using folic acid and metal salts as precursors, M–N–C functionalized carbon nanosheets (M–NC, M=Co, Fe, and Ni) were prepared via a hydrothermal method to in situ decorate GF electrode (M–NC@GF). The M–NC catalysts exhibit a larger specific surface area, excellent hydrophilicity and highly dispersed M–N 4 active sites, thereby improving the reaction kinetics of VO 2+ /VO 2 + and V 3+ /V 2+ redox pairs. Notably, Co–NC@GF–M presents the most outstanding performance among them. Density functional theory calculations confirm that M–NC materials enhance adsorption and accelerate charge transfer processes. The battery employing the Co–NC@GF–M electrode remains stable even at a high current density of 350 mA cm −2 , maintaining an energy efficiency (EE) of 60.64%, whereas the blank battery ceases operation at 200 mA cm −2 . At 150 mA cm −2 , after 200 cycles, the modified battery exhibits an EE decay rate of merely 1.88%.