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

The sluggish kinetics of negative V²⁺/V³⁺ 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 V²⁺/V³⁺ reaction. Taking the advantages of excellent conductivity and catalytic activity of MXene (Ti₃C₂T_x, Nb₂CT_x, V₂CT_x) with different transition metals are used as catalysts to improve the kinetics of V²⁺/V³⁺ reaction. At the current density of 160 mA cm⁻², the battery equipped with Nb₂CT_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 Nb₂CT_x surface should overcome a higher energy barrier compared with Ti₃C₂T_x and V₂CT_x, implying the ability to inhibit side reaction occurrence for Nb₂CT_x. Ascribing to the enhanced kinetics of V²⁺/V³⁺ reaction and the effective inhibition of HER, the Nb₂CT_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.