Nb2CTx decorated graphite felt as high performance negative electrode for vanadium redox flow battery

The sluggish kinetics of negative V 2+ /V 3+ reaction is the key factor limiting the performance of vanadium redox flow battery (VRFB). To further enhance the competitiveness of VRFB in the fields of energy storage, it is urgent to develop anode material with high catalytic activity toward V 2+ /V 3+ reaction. Taking the advantages of excellent conductivity and catalytic activity of MXene (Ti 3 C 2 T x , Nb 2 CT x , V 2 CT x ) with different transition metals are used as catalysts to improve the kinetics of V 2+ /V 3+ reaction. At the current density of 160 mA cm −2 , the battery equipped with Nb 2 CT X modified composite electrode shows the highest energy efficiency of 83.1 %, which is 12.3 % higher than that with pristine graphite felt (GF). Furthermore, the effect of MXene with different transition metals on hydrogen evolution reaction (HER) is studied based on density functional theory (DFT). HER occurred on Nb 2 CT x surface should overcome a higher energy barrier compared with Ti 3 C 2 T x and V 2 CT x , implying the ability to inhibit side reaction occurrence for Nb 2 CT x . Ascribing to the enhanced kinetics of V 2+ /V 3+ reaction and the effective inhibition of HER, the Nb 2 CT x -modified electrode exhibits the highest catalytic activity, reversibility and cycle stability. This work promotes the development and application of Nb-based MXene as a catalyst in VRFB.