One-Pot Green Process to Synthesize MXene with Controllable Surface Terminations using Molten Salts

Surface terminations of two-dimensional MXene (Ti₃ C₂ T_x ) considerably impact its physicochemical properties. Commonly used etching methods usually introduce -F surface terminations or metallic impurities in MXene. We present a new molten-salt-assisted electrochemical etching method to synthesize fluorine-free Ti₃ C₂ Cl₂ . Using electrons as reaction agents, cathode reduction and anode etching can be spatially isolated; thus, no metallics are present in the Ti₃ C₂ Cl₂ product. The surface terminations can be in situ modified from -Cl to -O and/or -S, which considerably shortens the modification steps and enriches the variety of surface terminations. The obtained -O-terminated Ti₃ C₂ T_x are excellent electrode materials for supercapacitors, exhibiting capacitances of 225 F g^-1 at 1.0 Ag^-1 , good rate performance (91.1 % at 10 Ag^-1 ), and excellent capacitance retention (100 % after 10000 charge/discharge cycles at 10 Ag^-1 ), which is superior to multi-layered Ti₃ C₂ T_x prepared by other etching methods.