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 hydrophilicity 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 capacity 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 electrocatalytic property.