Screening Surface Structure of MXenes by High-Throughput Computation and Vibrational Spectroscopic Confirmation

Abstract

Functionalized MXenes hold promises in a variety of applications in which the dispensable functional groups are mixed. The functionalization is spontaneously realized through competitive adsorption of active species on the MX matrix during the acid etching process of MAX phases. Nevertheless, the knowledge of proportion and distribution of functional groups on MXenes, i.e., surface structures, is still limited. By high-throughput computation screening, ground-state stable structures of four kinds of typical MXenesTi 2 CT x , Ti 3 C 2 T x , Nb 2 CT x , and Nb 4 C 3 T x (T = O, F, and OH)with mixed functional group compositions are figured out for the first time. The multicomponent functional group patterns definitely demonstrate an obvious feature of spatial mixing at a given component. However, the heterogeneous structure has a near linear dependence on the functional group components in terms of free energy. Most functionalized MXenes are dynamically stable except for Nb 2 CF 2 and Nb 2 C(OH) 2 due to their competing displacive counterparts. Last but not least, Raman spectra of the four kinds of MXenes confirm the predicted stable surface structures of MXenes. This study provides a clear fundamental basis for understanding the surface structures of MXenes.

Recent advances in MXenes: From fundamentals to applications

“…It is difficult to predict the electronic properties of MXenes using a model structure with the mixed adsorption of F, OH, and O on their surfaces. Hence, the majority of theoretical studies have been carried out using models with the uniform adsorption of one of the chemical groups on the surfaces [11] and very few using mixture of these groups [12,13]. Although such ideal structures might be unrealistic at present, they help with the in-depth understanding of the physics and chemistry of MXenes and may guide and motivate ones to perform new experiments.…”

“…ated crystal field, the 3d orbitals of surface Ti atoms split to form pseudogaps, whose values predict stability in order from highest to lowest of Ti 3 C 2 O 2 , Ti 3 C 2 F 2 , Ti 3 C 2 (OH) 2 , Ti 3 C 2 H 2 , and Ti 3 C 2 [55]. Moreover, the effect of mixture of F, OH, and O functionalization on the stability of Ti 2 CO x F y (OH) z , Ti 3 C 2 O x F y (OH) z , and Nb 4 C 3 O x F y (OH) z has also been examined [13]. As shown in Fig.…”

Understanding the Lithium Storage Mechanism of Ti3C2Tx MXene

“…These experimental results agree with the theoretical studies that O-terminated MXene is the most stable species. (48,49) Due to the two-dimensional nature, Ti 3 C 2 T x MXene is regarded as a combination of a central homoleptic Ti-centered octahedron and a surface heteroleptic Ti-centered octahedron. (48) Since the difference in the immediate environment of Ti atoms, referred to as central Ti and terminal Ti, the binding energies of electrons arising from Ti may be distinguished.…”

Local chemical bonding and structural properties in Ti3AlC2 MAX phase and Ti3C2Magnuson1, Näslund2 2020Phys. Rev. Research212161View full textAdd to dashboardCite

“…Despite vast interest in MXenes in general, and in Ti 3 C 2 T x in particular, there is little known experimentally about the bonding between the transition metals and the terminating species, T x . Previous work of MXenes' electronic structure has mainly been based on ground-state density functional theory (DFT) calculations at 0 K [14][15][16][17]19]. Many of the theoretical investigations find no obstacles regarding replacing the inherently formed termination species with others in the pursuit of tailoring the properties for specific applications.…”