Construction of mesoporous MXenes by thermal shock-induced pore engineering for high-performance supercapacitors

As some of the latest additions to the two-dimensional (2D) family, transition metal carbides, carbonitrides and nitrides (MXenes) suffer from sluggish ion transport kinetics and insufficient active-site utilization, resulting from self-restacking for applications in electrochemical energy storage. The construction of in-plane pores will restrain the restacking and avoid redundant macropores; however, this remains hindered due to MXenes' unique etching preparation process and vulnerability to oxidation. Herein, by taking advantage of the confined interlayer spaces of Ti₃C₂T_x MXenes, combined with a rapid annealing process, a novel thermal shock-induced pore-engineering strategy is proposed to successfully construct in-plane mesoporous MXene nanosheets while preserving their hydrophilicity. Consequently, the optimized porous electrode structures significantly provide substantial redox-active sites and accelerate ion transportation, leading to a remarkable specific capacitance (494.8 F g^-1 at 5 mV s^-1), an unparalleled rate capability (91.5% capacitance retention at a low mass loading and 59.7% capacitance retention at a high mass loading of 7.89 mg cm^-2 at 2000 mV s^-1) and robust cycling stability. This work sheds new insights into the construction of in-plane pores in MXenes and provides an exciting opportunity for boosting their practical application for energy storage.