Jaseung Koo

Although MAX exhibits excellent heat resistance, chemical resistance, and electrical conductivity due to its metallic and ceramic properties, the exfoliation of the MAX sheets with oxidation stability is a key issue in maximizing its advantages and improving its performance. In this study, the supercritical CO 2 (scCO 2 ) technique is employed to mechanically exfoliate MAX sheets without chemical etching. The supercritical fluid process is conducted in two continuous steps under different CO 2 conditions: supercritical drying and rapid exfoliation of the supercritical suspension (RESS). X‐ray diffraction and scanning electron microscopy results reveal that both supercritical drying (45 °C and 100 bar) and RESS (100 °C and 120 bar) processes are required for MAX sheet exfoliation. During these processes, scCO 2 molecules are deeply intercalated into the MAX sheet interlayers. The scCO 2 ‐treated MAX sheets and oxidized MXene exhibit electrical conductivities of 457, 303, and 46 S cm −1 at 100 bar based on the powder resistivity measurement system. Because the layer exfoliation of MAX sheets is closely correlated with the performance of MAX‐based materials, the technique employed in this study can provide a route for applications requiring expanded MAX, ranging from nanoelectronic devices to energy‐storage materials such as supercapacitors and battery anodes.