Fluorine‐Free Synthesis of High‐Purity Ti₃C₂T_<i>x</i> (T=OH, O) via Alkali Treatment

MXenes, 2D compounds generated from layered bulk materials, have attracted significant attention in energy-related fields. However, most syntheses involve HF, which is highly corrosive and harmful to lithium-ion battery and supercapacitor performance. Here an alkali-assisted hydrothermal method is used to prepare a MXene Ti₃ C₂ T_x (T=OH, O). This route is inspired from a Bayer process used in bauxite refining. The process is free of fluorine and yields multilayer Ti₃ C₂ T_x with ca. 92 wt % in purity (using 27.5 m NaOH, 270 °C). Without the F terminations, the resulting Ti₃ C₂ T_x film electrode (ca. 52 μm in thickness, ca. 1.63 g cm^-3 in density) is 314 F g^-1 via gravimetric capacitance at 2 mV s^-1 in 1 m H₂ SO₄ . This surpasses (by ca. 214 %) that of the multilayer Ti₃ C₂ T_x prepared via HF treatments. This fluorine-free method also provides an alkali-etching strategy for exploring new MXenes for which the interlayer amphoteric/acidic atoms from the pristine MAX phase must be removed.