High Gravimetric Capacitance MXene Supercapacitor Electrode Based on Etched Ti₃C₂T_x by Chemical Etching

Ti₃C₂T _x MXene is one of the most promising electrode materials for supercapacitors, but it often suffers in poor experiment gravimetric capacitance, which limits practical applications in industry needs. Herein, etched Ti₃C₂T _x MXene with high gravimetric capacitance is prepared by chemical etching of MXene with concentrated alkaline solution. The intercalation of K⁺ and the scissor role of OH⁻ can simultaneously enlarge the interlayer spacing and cut the size of sheets, which lead to the high active‐site concentration and cation diffusion. As a result, the etched Ti₃C₂T _x MXene displays high gravimetric capacitance of 368.1 F g⁻¹ at 2 A g⁻¹ and outstanding cycling stability without capacitance loss over 5000 cycles at 6 A g⁻¹,and the surface capacitance contribution in etched Ti₃C₂T _x MXene occurs to a greater extent compared with the pristine MXene. Moreover, the effect of chemical etching on the supercapacitor performance and energy‐storage mechanism indicates that the active‐size concentration and cation diffusion could be maximized when the chemical etching conditions are appropriate, leading to the highest performance of etched Ti₃C₂T _x MXene. Herein, it is demonstrated that the chemical etching approach is applicable to design MXenes with high gravimetric capacitance to maximize their potential applications in energy‐storage applications and other fields.