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

Abstract

Surface terminations of two-dimensional MXene (Ti₃C₂T_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 Ti₃C₂Cl₂. Using electrons as reaction agents, cathode reduction and anode etching can be spatially isolated; thus, no metallics are present in the Ti₃C₂Cl₂ 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 Ti₃C₂T_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 Ti₃C₂T_x prepared by other etching methods.