Fluoride‐Free Molten Salt Hydrate‐Assisted Synthesis of MXene in Air Down to 150 °C

Abstract The conventional Lewis acid molten salt etching approach for synthesizing MXenes typically necessitates elevated temperatures exceeding 550 °C, in addition to the use of inert gas protection to prevent oxidation. Additionally, delamination of molten salt‐etched MXenes typically requires hazardous intercalating agents. Herein, a scalable and non‐toxic low‐temperature shielded salt (LSS) approach for synthesizing MXene in air is reported, with the use of only a small portion of salts and a low reaction temperature down to 150 °C. Especially, the synergistic effect of the increased diffusion rate by Li + ions and the phase change of magnesium chloride hexahydrate (MgCl 2 ·6H 2 O) enables a redox‐controlled A‐site etching of the parent MAX phase, which even facilitates the synthesis of hard‐to‐etch MXenes. As a proof‐of‐concept demonstration, several theoretically hard‐to‐synthesize MXenes including Cr 2 CT x and Nb 2 CT x are successfully prepared through the LSS technique, where Cr 2 CT x is not achieved by Lewis acidic molten salt yet. Compared to conventional techniques, this low‐temperature shielded salt etching method exhibits unconventional molten behavior while offering several advantages, including a non‐oxidizing environment, shorter processing time, and elimination of highly corrosive washing agents and organic intercalants. These advances render the LSS approach a promising route for synthesizing MXenes with applications toward diverse practical applications.