Holdups in Nitride MXene's Development and Limitations in Advancing the Field of MXene

Abstract

3D graphite exhibit very diverse properties. Among these, 2D graphene has gained the most popularity due to its unique properties and technological impact. [1] The discovery of fascinating properties in graphene has led to the exploration of other 2D materials, such as silicene, germanene, transition metal dichalcogenides, and, very recently, MXenes.MXenes, a 2D material based on carbides, carbonitrides, and nitrides, were first reported in 2011, and are typically synthesized from their parent 3D MAX phases through exfoliation in hydrofluoric acid (HF). [2] As one of the most novel and versatile members of the 2D material family, MXenes have been drawing significant interest from various fields due to their wide range of applicability. The general formula for MXenes is M n + 1 X n T x , in which M, X, and T x represent early d-block transition metals, C and/or N atoms, and the surface termination groups (F, OH, and/or O), respectively. Through a top-down synthesis approach, A-layer atoms (i.e., Al, Si, and Ga) can be selectively etched from the structure of the MAX phase, leaving behind loosely stacked 2D MX layers, which can then be further exfoliated into single-layer MXene flakes. [3] To date, the MXene family includes more than 30 stoichiometric compositions that have been experimentally synthesized, with many more theoretically possible, each with distinct electronic, physical, and (electro)chemical properties. [4] Currently, there are at least 28 nitride MAX and 17 nitride MXene phases that have been reported to exist and be thermodynamically stable, but these mostly exist only in the theoretical realm due to difficulty of MAX phase synthesis and etching (Scheme 1). In addition, about 20 kinds of solid solutions on both the M and X sides have also been reported. The compositional diversity as well as surface chemistry modifications have resulted in numerous new materials, which are being explored for multitudinous applications, including energy storage, optoelectronics, wireless communication, catalysis, sensing, and medicine, as well as being explored for in situ/operando spectroelectrochemistry (Scheme 1). [5][6][7][8][9][10] Carbide versusNitride: What's the Holdup in Nitride MXenes? While a vast majority of the MXene work focuses on carbides (with hundreds of publications presently), especially Ti 3 C 2 , As nanomaterials are becoming a key component in various electronics, 2D nanomaterials are emerging and attracting tremendous attention in the scientific community due to their unique physical, chemical, and structural properties. In recent years, a new family of 2D carbides and nitrides, known as MXenes, has become the center of attention for many electrochemical energy storage and conversion systems. While nitride MXenes have some publications centered around them, the overwhelming majority revolve around carbide and their direct application to systems without understanding the underlying mechanism behind their performance. The lack of publications in both of these fields, nitrides and mechanistic u...

Two-dimensional carbide/nitride (MXene) materials in thermal catalysis

“…[16][17][18] Due to their diverse elemental compositions and adjustable surface terminations, 17,19 MXenes possess various interesting chemical and physical properties like a tunable bandgap, 1,20 good electrical conductivity, [21][22][23][24] excellent photoelectronic properties, and ultra-low optical attenuation. 25 Based on these superior features, MXenes play a signicant role in many elds, such as energy storage and conversion, [26][27][28] sensors, 18,29 electromagnetic interference shielding, 30 absorption, 31 electrocatalysis, [32][33][34] and photocatalysis. 23,35,36 Recently, MXenes have also been sought-aer in thermal catalysis, due to their tunable surface terminations and high thermal stability.…”

2D non-carbide MXenes: an emerging material class for energy storage and conversion

“…According to the latest report, there are currently 28 nitride MAX phases and 17 nitride MXenes which are thermodynamically stable. 13 However, most do not exist physically and are only theoretically proved. The major holdback in the progress of non-carbide MXenes is the difficulty in synthesizing their parent MAX phases and etching them to obtain non-carbide MXenes.…”

“…3,4,6,[18][19][20][21] Although Johnson and his group recently published a review on the underlying energy storage mechanisms of nitride MXenes, there is no detailed review focusing on the synthesis and properties of non-carbide MXenes. 13 Thus, the current review aims to provide a comprehensive critical overview of the theoretical and experimental advances, mainly in carbonitride and nitride MXenes. Firstly, the structural features and challenges in synthesizing non-carbide MXenes are discussed.…”

“…3,4,6,18–21 Although Johnson and his group recently published a review on the underlying energy storage mechanisms of nitride MXenes, there is no detailed review focusing on the synthesis and properties of non-carbide MXenes. 13…”

A first-principles study of the ultra-high spin rectification effect based on nitride MXenes (Sc2NO2, Ti2NO2)

“…A recent density functional theory (DFT) study predicted that nitride MXenes have a high reactive specific surface area, strong magnetic moment, and good stability compared with carbonized MXenes, with unique metallic properties. 39,40 The superior magnetic and metallic properties ensure excellent electrical conductivity and offer possible spin injection. Yierpan et al discovered that MXenes with -O as a termination group have better stability.…”