3D hollow V2CTx MXene spheres on carbon felt enabling high-performance negative electrodes for vanadium redox flow batteries

The performance of vanadium redox flow batteries (VRFBs) is largely limited by the scarce active sites and low specific surface area of carbon felt (CF) electrodes. Herein, we transform sheet-like V 2 CT x MXene into three-dimensional hollow spherical architectures with a high specific surface area using a sacrificial template method. By loading the as-prepared hollow spheres onto carbon felt fibers, a composite electrode with high catalytic activity suitable for the negative electrode of vanadium flow batteries was fabricated, which effectively increased the number of reaction active sites of the composite electrode. Specific surface area measurements indicate that the hollow spherical structure increases the specific surface area of the carbon felt electrode by approximately twofold. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) tests on the CF decorated with these V 2 CT x hollow spheres confirmed their superior electrochemical activity and low impedance characteristics. Galvanostatic charge-discharge tests demonstrated that the modified electrode achieved a high energy efficiency (EE) of 82.9% at a current density of 200 mA cm −2 , which is 6.1% higher than that of pristine CF. Moreover, the EE remained highly stable over 500 cycles. This work provides a new structural design strategy for solving MXene stacking and enhancing the V 3+ /V 2+ redox kinetics simultaneously, and offers a promising strategy for designing high-performance negative electrode materials for VRFBs.