Two‐Dimensional MXenes Derived from Medium/High‐Entropy MAX Phases M2GaC (M = Ti/V/Nb/Ta/Mo) and their Electrochemical Performance

Two-dimensional (2D) transition metal carbides and/or nitrides, MXenes, are prepared by selective etching of the A-site atomically thin metal layers from their MAX phase precursors. High entropy MXenes, the most recent subfamily of MXenes, are in their infancy and have attracted great interest recently. They are currently synthesized mainly through wet chemical etching of Al-containing MAX phases, while various MAX phases with A-sites elements other than Al have not been explored. It is important to embody non-Al MAX phases as precursors for the high entropy MXenes synthesis to allow for new compositions. In this work, it is reported on the design and synthesis of Ga-containing medium/high entropy MAX phases and then their corresponding medium/high entropy MXenes. Gallium atomic layer etching is carried out using a Lewis acid molten salt (CuCl2). The as-prepared (Ti_1/4 V_1/4 Nb_1/4 Ta_1/4 )₂ CT_x exhibits a Li⁺ specific capacity of ≈400 mAh g^-1 . For (Ti_1/5 V_1/5 Nb_1/5 Ta_1/5 Mo_1/5 )₂ CT_x a specific capacity of 302 mAh g^-1 is achieved after 300 cycles, and high cycling stability is observed at high current densities. This work is of great significance for expanding the family members of MXenes with tunable chemistries and structures.