(Invited) 2D Mxenes for Energy Storage Applications

MXenes are a family of two-dimensional (2D) transition metal carbides and nitrides, with a general structure of M n+1 X n T x , where M is the transition metal, X is carbon and/or nitrogen, and T represents the surface terminations (F, O, OH). MXenes have attracted attention in a multitude of energy storage applications due to their high electronic conductivity, tunable interlayer spacing, redox-active transition metals, and hydrophilic surface groups. In this talk, we discuss the use of MXene electrodes in supercapacitor applications, including aqueous, non-aqueous, and water-in-salt electrolytes. The variability of MXenes is demonstrated with each electrolyte system showing unique electrochemical responses, not limited to redox and/or intercalation pseudocapacitance, and hydrated cation intercalation. Furthermore, the versatility of the hydrophilic, 2D morphology of MXenes is demonstrated through its use in multiple form factors, not limited to flexible free-standing films, multilayer powder electrodes, interdigitated microsupercapacitors, knitted textiles, and more. New directions and perspectives for MXenes in energy storage are discussed, including MXenes’ use as passive components (separators, current collectors, binders, scaffolds, conductive additives) in energy storage systems. Figure 1 (A) Schematic illustration showing MXenes’ electrochemical properties for ion storage applications. (B) Cyclic voltammetry (CV) data collected at scan rates from 10 to 100,000 mV·s −1 for a 90-nm-thick Ti 3 C 2 T x film. (C) Influence of an electrolyte’s solvent on the lithium-ion storage capacity of Ti 3 C 2 T x ; CV curves of microporous Ti 3 C 2 T x electrode in 1 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in DMSO, acetonitrile (ACN), or propylene carbonate (PC) electrolytes. (D) A digital photograph showing the wafer scale fabrication of an array of 143 MXene microsupercapacitors. (E) Photograph of a knitted textile with an interdigitated pattern made using Ti 3 C 2 T x MXene-coated cotton yarn to produce electrodes for wearable textile supercapacitor. Reference [1] A. VahidMohammadi, J. Rosen, Y. Gogotsi, Science, 2021 , 372 , eabf1581. Figure 1