Fluorine- and Acid-Free Strategy toward Scalable Fabrication of Two-Dimensional MXenes for Sodium-Ion Batteries.

MXenes are emerging 2D materials that have gained great attention because of their unique physical-chemical properties. However, the wide application of MXenes is prohibited by their high cost and environmentally harmful synthesis process. Here a fluoride- and acid-free physical vacuum distillation strategy is proposed to directly synthesize a series of MXenes. Specifically, by introducing a low-boiling-point element into MAX and subsequently evaporating A elements via physical vacuum distillation, fluoride-free MXenes (Ti 3 C 2 T x , Nb 2 CT x , Nb 4 C 3 T x , Ta 2 CT x , Ti 2 NT x , Ti 3 CNT x , etc.) are fabricated. This is a green and one-step process without any acid/alkaline involved and with all reactions inside a vacuum tube furnace, avoiding any contamination to external environments. Besides, the synthetic temperature is controlled to regulate the layered structures and specific surface areas of MXenes. Accordingly, the synthesized Ti 3 C 2 T x MXene exhibits improved sodium storage performance. This method may provide an alternative for the scalable production of MXenes and other 2D materials.