Self-propagating fabrication of 3D porous MXene-rGO film electrode for high-performance supercapacitors

2D MXene nanosheets with metallic conductivity and high pseudo-capacitance are promising electrode materials for supercapacitors.Especially,MXene films can be directly used as electrodes for flexible supercapacitors.However,they suffer from sluggish ion transport due to self-restacking,causing limited electrochemical performance.Herein,a flexible 3D porous MXene film is fabricated by incorporating graphene oxide(GO) into MXene film followed by self-propagating reduction.The self-propagating process is facile and effective,which can be accomplished in 1.25 s and result in 3D porous framework by releasing substantial gas instantaneously.As the 3D porous structure provides massive ion-accessible active sites and promotes fast ion transport,the MXene-rGO films exhibit superior capacitance and rate performance.With the rGO content of 20%,the MXene-rGO-20 film delivers a high capacitance of 329.9 F g^(-1) at 5 mV s^(-1) in 3 M H2 SO4 electrolyte and remains 260.1 F g^(-1) at 1,000 mV s^(-1) as well as good flexibility.Furthermore,the initial capacitance is retained above 90% after 40,000 cycles at 100 A g^(-1),revealing good cycle stability.This work not only provides a high-performance flexible electrode for supercapacitors,but also proposes an efficient and time-saving strategy for constructing 3D structure from 2D materials.

3D crumbled MXene for high-performance supercapacitors

MXene materials have recently attracted considerable attention in energy storage application owing to their metallic conductivity,2D structure and tunable surface terminations.However,the restacking of 2D MXene nanosheets hinders the ion transport and accessibility to the surface,resulting in adverse effect on their electrochemical performances.Here,with the assistance of hexamethylenetetramine(C6H12N4),2DTi3C2Tx MXene nanosheets were fabricated into a 3D architecture with crumbled and porous structure through an electrostatic self-assembly followed by annealing.The resultant 3D structure can expose massive active sites and facilitates the ion transport,which is beneficial for sufficient utilization of the outstanding superiorities of the MXene.Therefore,as a pseudocapacitive material,the 3D crumpled and porous Ti3C2Tx MXene shows a gravimetric capacitance of 333 F/g at 1 A/g,and maintains 261 F/g and 132 F/g at ultrahigh current densities of 100 A/g and 1000 A/g,respectively,revealing promising potential for application in supercapacitors.