Advancing Non-Aqueous Etching Strategy for Swift and High-Yield Synthesis of 2D Molybdenum Carbides (MXenes).

Aqueous hydrofluoric acid (HF)-based solutions are widely used for etching MAX phases to synthesize high-purity 2D molybdenum carbides (MXenes). However, their applicability is limited to selected MAX phases, and the production of certain MXenes, such as Mo-based MXenes, remains challenging owing to low quality, low yield, and the time-intensive process, often requiring several days to weeks. In this study, a non-aqueous etchant for faster and more efficient synthesis of high-purity Mo-based MXenes is introduced. This etchant, containing Cl and F ions, is adequately effective to etch the MAX phase using the F ions of moderate concentration regenerated from GaF byproducts but only mildly caustic to prevent damage to the resulting MXene. Using this approach, the rapid production of MoCT is demonstrated within 24 h at 100 °C, achieving up to 90% multilayer and 45% monolayer yields. Furthermore, the resulting monolayer MoCT flake exhibits larger sizes and fewer defects, with an electrical conductivity of 5.9 S cm, 6.5 times higher than that (0.9 S cm) of aqueous HF-MoCT. This enhancement results in improved electrocatalytic activity of high-purity MoCT for hydrogen evolution reactions. These findings highlight the potential of non-aqueous etching solutions to address the limitations of HF-based MXene synthesis.