Two-dimensional MXenes

Abstract

The family of two-dimensional (2D) transition-metal carbides, carbonitrides, and nitrides, known as MXenes, has grown from a single composition in 2011 to a ~50-composition family. With a large number of possible transition metals and their combinations, four possible 2D thickness ranges for a single 2D flake, tunable surface chemistry and the capability for hosting species between their 2D flakes, MXenes can be considered one of the most amendable families of materials in the 2D space. MXenes have a unique combination of properties complementary to other 2D materials, such as high electrical conductivity (up to 24,000 S/ cm), high Young's modulus (reaching ~380 GPa), combined with 2D flexibility, and tunable and hydrophilic surfaces. These set of properties as well as their simple and scalable synthesis qualified MXenes to be studied in a variety of different areas, including energy storage and conversion, electrocatalysis, sensing, electromagnetic interference shielding and wireless communications, structural materials, tribology, environmental remediation, and biomedical fields. This issue covers the various MXene synthesis routes and some of MXenes emerging areas in sensing, environmental, and biomedical applications. Additionally, the structure, stability, and properties of MXenes are discussed from the computational studies perspective.

Thermally Conductive MXene

“…The outer M layers in MXenes are terminated, providing additional adjustability and customization to MXenes. Reprinted with permission from ref . Copyright 2023 Springer Nature.…”

Two‐Dimensional MXenes Derived from Medium/High‐Entropy MAX Phases M2GaC (M = Ti/V/Nb/Ta/Mo) and their Electrochemical Performance

“…[ 12 ] Afterward, other novel HE‐MXenes have been reported; and their electrochemical behaviors were explored. [ 13 ] For example, Yang's group reported the synthesis of (Ti 1/5 V 1/5 Zr 1/5 Nb 1/5 Ta 1/5 ) 2 CT x [ 14 ] that is capable of guiding the nucleation and growth of lithium without dendrites. In another study, Du et al, expanded the HE‐MXenes compositional space to carbonitride, viz., (Ti 1/3 V 1/6 Zr 1/6 Nb 1/6 Ta 1/6 ) 2 C y N 1–y T x , which exhibited outstanding adsorption and catalytic abilities towards lithium polysulfides.…”

M5X4: A Family of MXenes

“…MXenes are a large family of 2D materials, with more than 50 stoichiometric MXenes experimentally synthesized, hundreds of computationally predicted compositions, and an infinite number of solid-solution MXenes (Figure ). , The general formula of MXenes can be expressed as M n +1 X n T x where M is an early transition metal (Ti, Nb, Ta, Mo, V, etc. ), X is carbon and/or nitrogen, and n is an integer 1–4.…”

“…While MXenes have the general formula M n +1 X n T x , the metallic component (M) can include two or more metals. Generally, these MXenes can be divided into ordered MXenes or solid-solution MXenes . The ordered MXenes exhibit ordering in one of two ways: in-plane ( i -MXene) or out-of-plane ordering ( o -MXene).…”

“…Generally, these MXenes can be divided into ordered MXenes or solid-solution MXenes. 2 The ordered MXenes exhibit ordering in one of two ways: in-plane (i-MXene) or out-ofplane ordering (o-MXene). In-plane ordering is only found in (M′ 4/3 M″ 2/3 )CT x structures (M′ = Mo, W, V, Cr; M″ = Sc, Zr, Y, or some lanthanides) 39 and has alternating rows of the Mmetals within the planes.…”