Point Defect Engineering of 2D MXenes at Ambient and Elevated Temperatures

MXenes are a large family of 2D transition metal carbides, nitrides, and carbonitrides with more than fifty compositions synthesized to date. In addition to the compositional and structural tunability of MXenes, defects, specifically basal plane point defects (vacancies and substitutions) provide us with opportunities to control MXene stability and properties. In this talk, I will present how MXene synthesis conditions control the basal plane metal vacancy concentrations, ranging from less than 1 at.% vacancy to above 16 at.%. The optimized Ti₃C₂T<i>_x</i> single flakes with &lt; 1 at.% vacancies show remarkable stability in air up to 600 ^○C before oxidation and stability in an inert environment up to 1000 ^○C before transformation to 3D bulk carbide. Additionally, by controlling the vacancy concentration, it is possible to control cation interactions with MXenes, either cation decorating the surface or occupying the metal vacancy sites. When metal vacancies are occupied by alkali cations, defective MXene flakes can be stabilized and approach the stability of pristine MXene flakes. The concentration of vacancies and cation substitution also control the electrical conductivity of MXenes at ambient and elevated temperatures. Understanding and controlling defects demonstrate an important way to tune MXenes’ and, in general, 2D materials’ behavior and properties.