Roles of Metal Ions in MXene Synthesis, Processing and Applications: A Perspective

Abstract

With a decade of effort, significant progress has been achieved in the synthesis, processing, and applications of MXenes. Metal ions play many crucial roles, such as in MXene delamination, structure regulation, surface modification, MXene composite construction, and even some unique applications. The different roles of metal ions are attributed to their many interactions with MXenes and the unique nature of MXenes, including their layered structure, surface chemistry, and the existence of multi‐valent transition metals. Interactions with metal ions are crucial for the energy storage of MXene electrodes, especially in metal ion batteries and supercapacitors with neutral electrolytes. This review aims to provide a good understanding of the interactions between metal ions and MXenes, including the classification and fundamental chemistry of their interactions, in order to achieve their more effective utilization and rational design. It also provides new perspectives on MXene evolution and exfoliation, which may suggest optimized synthesis strategies. In this respect, the different effects of metal ions on MXene synthesis and processing are clarified, and the corresponding mechanisms are elaborated. Research progress on the roles metal ions have in MXene applications is also introduced.

Ultrastrong MXene films via the synergy of intercalating small flakes and interfacial bridging

“…Titanium carbide (Ti 3 C 2 T x ) MXene 1 is an emerging two-dimensional transition metal carbide with excellent mechanical properties 2,3 , high electrical conductivity 4 , and low infrared (IR) emissivity 5,6 . Interest in assembling MXene flakes into high-performance macroscopic films has recently grown due to promising applications in flexible electrodes [7][8][9][10][11][12][13][14][15][16] , electromagnetic interference (EMI) shielding [17][18][19][20][21][22][23] , and thermal camouflage 5,6 , among many others. Because of their higher aspect ratio, large MXene flakes have proven to be better than small ones for making high-performance MXene films 24 .…”

A Review on MXene Synthesis, Stability, and Photocatalytic Applications

“…It is worth noting that the interlayer spacing expansion is different for different metal cations and typically depends on the hydration state of the cation. , Metal ion with a larger hydrated radius causes a larger d -spacing . However, some of these intercalants remain on the surface of nanosheets after the delamination, despite thorough washing. , The existence of intercalant ions in-between MXene nanosheets significantly influence the stability, electronic structure, electrical/mechanical properties, and surface chemistry of MXenes. − The removal of intercalants through annealing or cation exchange in an acid solution result in significantly increased electrical conductivity of MXene films. , …”

Recent Advances on Heterojunction‐Type Anode Materials for Lithium‐/Sodium‐Ion Batteries

“…In the general formula, M, X, and T stand for transition metal elements, carbon/ nitrogen elements, and surface functional groups, respectively. [206] MXene has a wide range of applications as an anode in LIBs/SIBs due to its good electrical conductivity and controlled chemical structure. However, due to the restacking of MXene, the pure MXene material suffers from slow reaction kinetics and limited active centers when used as anode.…”