Simplified Synthesis of Fluoride-Free Ti₃C₂T_x via Electrochemical Etching toward High-Performance Electrochemical Capacitors

MXenes have been intensively studied for electrochemical energy storage and other applications. However, time-consuming multistep procedures involving hypertoxic HF or alike are utilized in conventional synthesis methods of MXenes. Besides, −F terminal functional groups inevitably exist in these MXenes, detrimental to supercapacitor and battery performances. Herein, we develop a facile and time-saving electrochemical etching method to synthesize F-free and Cl-containing Ti3C2Tx in a mixed LiOH and LiCl aqueous solution with an etching efficiency of 92.2%. During the synthesis, sonification alone is able to delaminate Ti3C2Tx without using any hazardous organic intercalant. The obtained delaminated Ti3C2Tx flakes are ∼3.8 μm in lateral size and ∼3.9 nm in thickness, and can be stable in an aqueous dispersion for at least 15 days. The filtrated Ti3C2Tx film is 20.5 MPa in tensile strength, 13.4 GPa in Young’s modulus, and 1663 S cm–1 in electrical conductivity, and exhibits specific capacitances of 323.7 F g–1, 1.39 F cm–2, and 1160 F cm–3 for supercapacitors. Also, a flexible zinc-ion hybrid capacitor with energy density values of 20.8 mWh cm–3 and 249.9 μWh cm–2 is assembled by using the Ti3C2Tx film as the cathode, and can maintain almost all its capacity under bending.