Elucidation of the Charging Mechanisms and the Coupled Structural–Mechanical Behavior of Ti₃C₂T_x (MXenes) Electrodes by In Situ Techniques

Abstract

The discovery of the Ti3C2Tx compounds (MXenes) a decade ago opened new research directions and valuable opportunities for high‐rate energy storage applications. The unique ability of the MXenes to host various mono‐ and multivalent cations and their high stability in different electrolyte environments including aqueous, organic, and ionic liquid solutions, promoted the rapid development of advanced MXene‐based electrodes for a large variety of applications. Unlike the vast majority of typical intercalation compounds, the electrochemical performance of MXene electrodes is strongly influenced by the presence of co‐inserted solvent molecules, which cannot be detected by conventional current/potential electrochemical measurements. Furthermore, the electrochemical insertion of ions into MXene interspaces results in strong coupling with the intercalation‐induced structural, dimensional, and viscoelastic changes in the polarized MXene electrodes. To shed light on the charging mechanisms of MXene systems and their associated phenomena, the use of a large variety of real‐time monitoring techniques has been proposed in recent years. This review summarizes the most essential findings related to the charging mechanism of Ti3C2Tx electrodes and their potential induced structural and mechanical phenomena obtained by in situ investigations.

Recent Advances of Flexible MXene and its Composites for Supercapacitors

“…[65] Upon cation insertion either by potential application or by spontaneous ions exchange, the interlayer distance between the adjacent layers varies depending on the size and the valence of the intercalated ions. [57] It is reported that among twelve of the metal ion intercalants, the nanopillar effect of Be 2 + greatly enhanced the charge-transfer process of the obtained Be 2 + -MXene electrode with minimal decrease in the electrolyte diffusion rates. [66] More recently, Water-in-salt (WIS) electrolytes have been explored to increase the operating potential windows of MXene electrodes.…”

“…Additionally, Ti 3 C 2 T x films in acidic environments (1 M H 2 SO 4 ) reveal a potentially dependent gravimetric response, attributed to the varied hydration state of the inserted protons [64] . Based on DFT calculations it was found that the presence of water between the MXene layers facilitates its charging kinetics by providing a hydrogen‐bonded water network for fast proton diffusion [57] …”

“…[64] Based on DFT calculations it was found that the presence of water between the MXene layers facilitates its charging kinetics by providing a hydrogen-bonded water network for fast proton diffusion. [57]…”

“…Figure 2. Typical schematic CV and GCD plots of Ti 3 C 2 T x electrodes in a) neutral aqueous standard 1 M (dashed lines) and concentrated electrolytes b) acidic aqueous electrolytes andc) non-aqueous electrolyte solutions [57]. Reproduced with permission from ref [57]…”

Functional MXenes: Progress and Perspectives on Synthetic Strategies and Structure–Property Interplay for Next‐Generation Technologies

“…However, the widespread implementation of in situ techniques in MXenes research is still underway, and techniques such as in situ SEM and in situ TEM remain underutilized for studying MXenes. [ 163 ] Furthermore, certain novel MXenes (e.g., V‐based, Nb‐based, and Mo‐based MXenes) have received limited attention in terms of their applications and underlying mechanisms, with insufficient documentation. Therefore, it is crucial for future scientific research to integrate in situ techniques more extensively and accurately with traditional ex situ techniques.…”