Ultrafast Synthesis of MXenes in Minutes via Low‐Temperature Molten Salt Etching

Developing green and efficient preparation strategies is a persistent pursuit in the field of 2D transition metal nitrides and/or carbides (MXenes). Traditional etching methods, such as HF-based or high-temperature Lewis-acid-molten-salt etching route, require harsher etching conditions and exhibit lower preparation efficiency with limited scalability, severely constraining their commercial production and practical application. Here, an ultrafast low-temperature molten salt (LTMS) etching method is presented for the large-scale synthesis of diverse MXenes within minutes by employing NH₄HF₂ as the etchant. The increased thermal motion and improved diffusion of molten NH₄HF₂ molecules significantly expedite the etching process of MAX phases, thus achieving the preparation of Ti₃C₂T_x MXene in just 5 minutes. The universality of the LTMS method renders it a valuable approach for the rapid synthesis of various MXenes, including V₄C₃T_x, Nb₄C₃T_x, Mo₂TiC₂T_x, and Mo₂CT_x. The LTMS method is easy to scale up and can yield more than 100 g Ti₃C₂T_x in a single reaction. The obtained LTMS-MXene exhibits excellent electrochemical performance for supercapacitors, evidently proving the effectiveness of the LTMS method. This work provides an ultrafast, universal, and scalable LTMS etching method for the large-scale commercial production of MXenes.