Molten-salt synthesized MXene for catalytic applications: A review

Abstract

Two-dimensional MXenes, characterized by their exceptional electrical conductivity, extensive specific surface area, and intricate surface chemistry, serve as both effective catalysts and ideal supports for various catalytic applications. However, the prevalent method of synthesizing MXenes involves the selective etching of A-layer atoms from MAX phases using hydrofluoric acid (HF), which, due to its hazardous nature, significantly restricts large-scale production. Recently, the molten salt method has emerged as a promising alternative. This method, renowned for its safety and versatility, eliminates the need for HF and exploits the diversity of molten salts to meticulously control the surface chemistry and structure of MXenes. By doing so, it facilitates the introduction of functional groups on the MXene surface terminations that are challenging to achieve with HF etching. Consequently, this leads to tailored electronic properties and enhanced chemical reactivity in the synthesized materials. This paper comprehensively reviews several techniques for synthesizing MXene in molten salt media, including the basic molten salt method, molten salt-shield synthesis, and molten-salt-assisted electrochemical etching. Moreover, it highlights that MAX phases, serving as precursors for MXenes, play a critical role in defining the properties of the resultant MXene. Efforts to synthesize MAX phases by molten salt method are also thoroughly examined. The review concludes with a discussion on the catalytic applications of MXene synthesized via molten salt etching method, particularly in the fields of electrocatalysis and photocatalysis, underscoring the extensive potential of this innovative material in cutting-edge catalytic applications.