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

MXenes are emerging 2D materials that have gained greatattentionbecause of their unique physical-chemical properties. However,the wide application of MXenes is prohibited by their high cost andenvironmentally harmful synthesis process. Here a fluoride- and acid-freephysical vacuum distillation strategy is proposed to directly synthesizea series of MXenes. Specifically, by introducing a low-boiling-pointelement into MAX and subsequently evaporating A elements via physicalvacuum distillation, fluoride-free MXenes (Ti3C2T x , Nb2CT x , Nb4C3T x , Ta2CT x , Ti2NT x , Ti3CNT x , etc.) are fabricated. This is a green and one-step processwithout any acid/alkaline involved and with all reactions inside avacuum tube furnace, avoiding any contamination to external environments.Besides, the synthetic temperature is controlled to regulate the layeredstructures and specific surface areas of MXenes. Accordingly, thesynthesized Ti3C2T x MXene exhibits improved sodium storage performance. This methodmay provide an alternative for the scalable production of MXenes andother 2D materials.