Advantage of Larger Interlayer Spacing of a Mo 2 Ti 2 C 3 MXene Free-Standing Film Electrode toward an Excellent Performance Supercapacitor in a Binary Ionic Liquid-Organic Electrolyte.

MXenes show outstanding specific capacitance in aqueous electrolytes. However, the narrow potential window of aqueous electrolytes restrains the energy density. Ionic liquid electrolytes can provide a higher potential window and superior specific energy but are subject to slow ion transport and difficult intercalation for their larger ion size. It is desirable to explore larger interlayer-spaced ( d -spaced) MXenes that can facilitate the large ion intercalation-deintercalation process. This work reports the first-ever supercapacitor application of the Mo 2 Ti 2 C 3 MXene free-standing film electrode (f-Mo 2 Ti 2 C 3 ) using 1 M 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)-imide (EMIMTFSI) in acetonitrile electrolyte. Without any preintercalating agents, the authors achieved an interlayer spacing of ∼2.4 nm in the f-Mo 2 Ti 2 C 3 material through etching, followed by a vacuum-assisted filtration technique. The microstructure, electrochemical properties, and charge storage kinetics of the f-Mo 2 Ti 2 C 3 outperform the conventional f-Ti 3 C 2 T x . The f-Mo 2 Ti 2 C 3 -based symmetric two-electrode device exhibited remarkable specific energy and specific power of 188 Wh kg -1 and 22 kW kg -1 , respectively, along with a high specific capacitance of 152 F g -1 . This larger d -spaced f-Mo 2 Ti 2 C 3 can emerge as a better alternative to the conventional f-Ti 3 C 2 T x in ionic liquid electrolytes to design next-generation high-performance MXene supercapacitors.