Abstract: Numerous compounds, ranging from clays to boron nitride (BN) and transition metal dichalcogenides, have been produced as 2-D sheets. Although many of these materials remain the subject of purely academic interest, others have jumped into the limelight because of their attractive properties, which have led to practical applications.

Among the latter are carbides and nitrides of transition metals known as MXenes (pronounced ​“maxenes”), a fast-growing family of 2-D materials. This family of 2-D transition metal carbides and nitrides has been expanding rapidly since the discovery of Ti₃C₂ at Drexel University in 2011. More than 30 different MXenes have been reported, and the structure and properties of numerous other MXenes have been predicted by using density functional theory (DFT) calculations. Moreover, the availability of solid solutions on M and X sites, control of surface terminations, and discovery of ordered double-M MXenes, such as out-of-plane ordered o-MXenes (e.g., Mo₂TiC₂) and in-plane ordered i-MXenes (e.g., Mo_1.33C), offer the potential for producing dozens of new distinct structures.

This presentation will describe the state of the art in the field. The manufacturing of MXenes, their delamination into single-layer 2-D flakes, and assembly into films, fibers, and 3-D structures will be briefly covered. Synthesis-structure-properties relations of MXenes will be addressed on the example of Ti₃C₂. The use of MXenes in ceramic-, metal-, and polymer-matrix composites, smart fibers, and textiles will also be discussed.

The versatile chemistry of the MXene family renders their properties tunable for a large variety of applications. Oxygen or hydroxyl-terminated MXenes, such as Ti₃C₂O₂, have been shown to have redox-capable transition metals layers on the surface and offer a combination of high electronic conductivity with hydrophilicity, as well as fast ionic transport. This, among many other advantageous properties, makes the MXene family promising for energy storage and related electrochemical applications, but applications in plasmonics, electrocatalysis, biosensors, electronics, water purification or desalination, and other fields are equally exciting.

Bio: Yury Gogotsi is Distinguished University Professor and Charles T. and Ruth M. Bach Professor of Materials Science and Engineering at Drexel University. He received his M.S. in metallurgy and Ph.D. in physical chemistry from Kiev Polytechnic and a D.Sc. from the Ukrainian Academy of Sciences.