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 (TiCT, NbCT, NbCT, TaCT, TiNT, TiCNT, 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 TiCT MXene exhibits improved sodium storage performance. This method may provide an alternative for the scalable production of MXenes and other 2D materials.