Ionic liquid etched and microwave-assisted delaminated MXene as an excellent electrocatalyst for the hysteretic negative reaction of vanadium redox flow batteries

The reaction kinetics of V3+/V2+ redox couple in VRFBs are relatively lagging behind, thus developing excellent electrocatalyst to enhance the negative reaction kinetics is more efficient to improve the battery performance. In this work, a novel IL-MW-MXene with unique 2D structure and abundant active functional groups is prepared easily and effectively by ionic liquid etching and microwave-assisted stripping, which is proposed as a promising electrocatalyst for the V3+/V2+ redox reactions. The morphology, structure and surface element composition are systematically investigated. Carbon fibers felt covered with this novel 2D-MXene flake exhibits improved hy-drophilicity and electrocatalytic activity towards the V3+/V2+ redox reactions. And the single VRFB with IL-MW-MXene/CF composites as the negative electrode exhibits the higher energy efficiency of 83.56 % at 200 mA cm-2, which are 7.53 % higher than that with pristine CF as the negative electrode. More importantly, the energy efficiency shows no obvious attenuation over 200 continuous charge-discharge cycles, and the discharging ca-pacity decay rate is only 0.12 % per cycle. The IL-MW-MXene exhibits good application potential in VRFBs and other electrochemical devices due to the green and highly effective preparation process and excellent electro-catalytic property.