In-Situ Atomic Force Microscopy Studies of Ti₃C₂: A Promising New Material for Electrochemical Capacitors

MXenes are a newly discovered class of two-dimensional materials prepared through extraction of metals such as Al from MAX phases, whose general formula is M n+1 AX n , where M is an early transition metal, A an A-group element, and X is carbon and/or nitrogen.[1-3] Ti 3 C 2 is one member of this MXene family which is capable of capacitances of up to 350 F cm -3 , making this an attractive material for electrochemical capacitors.[4] The high storage capacity of this material is attributed to rapid intercalation of electrolyte ions within the layered structure [Figure 1a]. In this work we use in-situ atomic force microscopy (AFM) to probe the macroscopic expansion of Ti 3 C 2 during electrochemical cycling. The in-situ electrochemical AFM cell used for this study as well as the relative height change of a Ti 3 C 2 electrode in 1 M KOH electrolyte are shown in Figures 1b and c. During negative polarization of the material K + ions are incorporated into the Ti 3 C 2 structure associated with a macroscopic expansion of the electrode. Studies are performed on various Ti 3 C 2 electrodes in several electrolytes to determine the effect of different ions and electrode structure on the electrochemical behavior and observed strain response. References: Naguib, M.;Come, J.;Dyatkin, B.;Presser, V.;Taberna, P.-L.;Simon, P.;Barsoum, M. W.; Gogotsi, Y. MXene: a promising transition metal carbide anode for lithium-ion batteries. Electrochemistry Communications 2012, 16 , 61-64. Naguib, M.;Kurtoglu, M.;Presser, V.;Lu, J.;Niu, J.;Heon, M.;Hultman, L.;Gogotsi, Y.; Barsoum, M. W. Two-Dimensional Nanocrystals Produced by Exfoliation of Ti3AlC2. Advanced Materials 2011, 23 , 4248-4253. Naguib, M.;Mashtalir, O.;Carle, J.;Presser, V.;Lu, J.;Hultman, L.;Gogotsi, Y.; Barsoum, M. W. Two-Dimensional Transition Metal Carbides. ACS Nano 2012, 6 , 1322-1331. Lukatskaya, M. R.;Mashtalir, O.;Ren, C. E.;Dall’Agnese, Y.;Rozier, P.;Taberna, P. L.;Naguib, M.;Simon, P.;Barsoum, M. W.; Gogotsi, Y. Cation Intercalation and High Volumetric Capacitance of Two-Dimensional Titanium Carbide. Science 2013, 341 , 1502-1505. Figure 1: a) SEM image of Ti 3 C 2 working electrode. b) Photograph of in-situ electrochemical AFM cell. c) Cyclic voltammogram of Ti 3 C 2 working electrode in 1 M KOH electrolyte and corresponding relative height change measured using in-situ AFM.