Understanding the Effect of Pore Size on Electrochemical Capacitive Performance of MXene Foams

Wearable electronics demand energy storage devices with high energy density and fast charging-discharging rates. Although various porous electrodes have been constructed, the effect of pore size on the capacitive performance of 2D nanomaterials has been rarely studied. Herein, flexible MXene foams with significantly different pore structures are fabricated using varying diameter polystyrene (PS) spheres (80, 310, and 570 nm), which shows uniform pores and interconnected pores providing enough active sites and a good electrical connection for electron transfer. Noteworthy, when MXene flakes and templates (310 nm) have a similar size, the foam delivers the highest gravimetric capacitance of 474 ± 12 F g^-1 at 2 mV s^-1 than others. Additionally, the mass ratio between MXene and PS controls the packing density of foams influencing the inner resistance of foam electrodes. A carbon nanotube is introduced to further improve the electrical conductivity of foams to achieve a capacitance of 462 ± 8 F g^-1 at 2 mV s^-1 and retains 205 ± 10 F g^-1 at 1000 mV s^-1 , demonstrating promises in energy storage applications and providing an insightful guidance for designing 2D nanomaterials-based porous electrodes for supercapacitors.