MXene derivatives: synthesis and applications in energy convention and storage.

Transition metal carbides or nitrides (MXene) have shown promising applications in energy convention and storage (ECS), owing to their high conductivity and adjustable surface functional groups. In the past several years, many MXene derivatives with different structures have been successfully prepared and their impressive performance demonstrated in ECS. This review summarizes the progress in the synthesis of MXene and typical Ti3C2T x MXene derivatives with different morphologies, including 0D quantum dots, 1D nanoribbons, 2D nanosheets and 3D nanoflowers. The mechanisms involved and their performance in photocatalysis, electrocatalysis and rechargeable batteries are also discussed. Furthermore, the challenges of MXene derivatives in ECS are also proposed.

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. MXenes, 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.