Ionic Liquid Mxene-Based Pseudocapacitors

Pseudocapacitors are types of electrochemical capacitors in which energy is stored via surface redox reactions rather than ion adsorption mechanisms as in electric double layer capacitors. Among two dimensional (2D) materials, MXenes are a newly discovered family of transitional metal carbides and/or carbonitrides with ≈ 20 synthesized members and over 30 members predicted to exist, making it not only the fastest growing but potentially the largest family ever known 2D materials[1-3]. In contrast to other well known 2D materials, the unique combination of a metal carbide and surface termination groups of MXenes make them exceptionally hydrophilic and highly conductive. Titanium carbide MXene (Ti 3 C 2 ), in particular, has shown outstanding capacitive performance in aqueous electrolytes due to its superior metallic conductivity[4, 5]. Here, we pre-intercalated Ti 3 C 2 binder free electrodes with ionic liquids (ILs) to enhance the interlayer spacing of the electrode material, which shows excellent capacitive performance up to 200 F/g and energy density of 100 W.h/kg. We also report on using two of the newly discovered molybdenum and chromium containing MXenes, Mo 2 TiC 2 , and Cr 2 TiC 2 free-standing films as pseudocapacitor electrodes in ILs electrolytes. The use of ILs enables us to increase the operating voltage window of MXene based electrodes and results in high energy density in comparison to aqueous electrolytes. This study opens new window for MXene based electrodes in applications that requires high energy density. References: 1. Naguib, M., et al., Two ‐ Dimensional Nanocrystals Produced by Exfoliation of Ti 3 AlC 2 . Advanced Materials, 2011. 23 (37): p. 4248-4253. 2. Anasori, B., et al., Two-Dimensional, Ordered, Double Transition Metals Carbides (MXenes). ACS Nano, 2015. 3. Naguib, M. and Y. Gogotsi, Synthesis of two-dimensional materials by selective extraction. Acc Chem Res, 2015. 48 (1): p. 128-35. 4. Lukatskaya, M.R., et al., Cation intercalation and high volumetric capacitance of two-dimensional titanium carbide. Science, 2013. 341 (6153): p. 1502-5. 5. Ghidiu, M., et al., Conductive two-dimensional titanium carbide/clay/'with high volumetric capacitance. Nature, 2014. 516 (7529): p. 78-81.