N-Butyllithium-Treated Ti3C2Tx MXene with Excellent Pseudocapacitor Performance

MXenes, a family of two-dimensional (2D) transition metal carbide and nitride materials, are supposed to be promising pseudocapacitive materials because of their high electronic conductivity and hydrophilic surfaces. MiXenes, prepared by removing the A elements of their corresponding MAX phases by hydrofluoric acid (HF) or LiF-HCl etching, possess abundant terminal groups like -F, -OH, and -O groups. It has been proven that the MXenes with fewer -F terminal groups and more -O groups showed a higher pseudocapacitor performance. In organic reactions, -OH and -X (X = halogen) groups could turn to ether groups in strong nucleophilic reagent. Inspired by that, herein, we report an n-butyllithium-treated method to turn the -F and -OH terminal groups to -O groups on the Ti3C2Tx MXenes. Two types of Ti3C2Tx MXenes prepared by either HF or LiF-HCl etching were systematically investigated, and a comparison with the traditional KOH/NaOH/LiOH-treated method was also carried out. It is found that most of the -F terminal groups on the Ti3C2Tx MXenes can be successfully removed by n-butyllithium, and abundant -O terminal groups were formed. The n-butyllithium-treated Ti3C2Tx MXenes show promising applications in high-performance pseudocapacitors. A record high capacitance of 523 F g(-1) at 2 mV s(-1) was obtained for the n-butyllithium-treated Ti3C2Tx MXenes, and 96% capacity can remain even after 10 000 cycles.