Capacitive Behavior Study of Free Standing Titanium Carbide (Mxene) Film Under External Pressure

Abstract

Titanium carbide (Ti3C2Tx, also called Mxene), uniquely combining metallic conductivity with hydrophilicity, has attracted burgeoning attention in batteries and supercapacitors application since reported in 2013. No matter with aqueous electrolytes or organic electrolytes, cation intercalation and pseudocapacitance contributes to the majority of the energy stored in Mxene-based electrochemical capacitors1-3, therefore, it is critical to understand its charge transport behavior within those negatively charged and electrically conductive Ti3C2X layers, especially the ionic diffusion process during charging/discharging.Pressure can cause peculiar and interesting structural changes in Ti3C2X Mxene as compared to other 2D materials such as graphene. Barsoum, et al. 6 have reported the phenomenon of interlayer expansion of Ti3C2X Mxene with external pressure up to 300MPa applied on in the presence of water, and they attribute the expansion to the shear-induced insertion of water molecules. To study its capacitive behavior under pressure will be of significant impact, because as a film of mechanical durability and flexibility, Ti3C2X free-standing films hold great potential in the field of wearable and portable electronics4,5, while in which, structure deformation caused by external pressure or temperature induced internal pressure is inevitable.In this work, the electrochemical performance under pressure of Ti3C2X Mxene free-standing film in various aqueous electrolytes (such as LiOH(aq), NaOH(aq), KOH(aq)) has been systematically investigated. Interestingly, different from other reported carbon-based electrode materials, Ti3C2X Mxene does not simply reach a capacitance saturation state as pressure increases. Further analysis on the structural changes and ionic diffusion under pressure suggests that complex mechanism occurs when charging/discharging under pressure. These findings should contribute to a more comprehensive understanding of the charge transport process within Mxene, and to future work of designing Mxene-based flexible electrodes for more advanced performance.Reference[1] M.R. Lukatskaya, O. Mashtalir, C.E. Ren, Y. Dall’Agnese, P. Rozier, P.L. Taberna, M. Naguib, P. Simon, M.W. Barsoum, Y. Gogotsi, Science, 2013, 341(6153), 1502-1505.[2] X. Wang, X. Chen, Y. Gao, Z. Wang, R. Yu, L. Chen, J. Am. Chem. Soc., 2015, 137, 7, 2715-2721.[3] H. Shao, Z. Lin, K. Xu, P.-L. Taberna, P. Simon, Energy Storage Materials, 2019, 18, 456-461.[4] J. Yan, C.E. Ren, K. Maleski, C.B. Hatter, B. Anasori, P. Urbankowski, A. Sarycheva, Y. Gogotsi, Adv. Funct. Mater., 2017, 27, 1701264.[5] C. Yang, Y. Tang, Y. Tian, Y. Luo, Y. He, X. Yin, W. Que, Adv. Funct. Mater., 2018, 1705487.[6] M. Ghidiu, S. Kota, V. Drozd, M.W. Barsoum, Sci. Adv., 2018, 4, 6850.