Capacitance of Ti₃C₂T_x MXene in ionic liquid electrolyte

Ti₃C₂T_x MXene, a two-dimensional (2D) early transition metal carbide, has shown an extremely high volumetric capacitance in aqueous electrolytes, but in a narrow voltage window (less than 1.23 V). The utilization of MXene materials in ionic liquid electrolytes with a large voltage window has never been addressed. Here, we report the preparation of the Ti₃C₂T_x MXene ionogel film by vacuum filtration for use as supercapacitor electrodes operating in 1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMI-TFSI) neat ionic liquid electrolyte. Due to the disordered structure of the Ti₃C₂T_x hydrogel film and a stable spacing after vacuum drying, achieved through ionic liquid electrolyte immersion of the Ti₃C₂T_x hydrogel film, the Ti₃C₂T_x surface became accessible to EMI⁺ and TFSI⁻ ions. A capacitance of 70 F g⁻¹ together with a large voltage window of 3 V was obtained at a scan rate of 20 mV s⁻¹ in neat EMI-TFSI electrolyte. The electrochemical signature indicates a capacitive behavior even at a high scan rate (500 mV s⁻¹) and a high power performance. This work opens up the possibilities of using MXene materials with various ionic liquid electrolytes.