Two-Dimensional, Ordered, Double Transition Metals Carbides (MXenes)

Abstract

The higher the chemical diversity and structural complexity of two-dimensional (2D) materials, the higher the likelihood they possess unique and useful properties. Herein, density functional theory (DFT) is used to predict the existence of two new families of 2D ordered, carbides (MXenes), M′₂M″C₂ and M′₂M″₂C₃, where M′ and M″ are two different early transition metals. In these solids, M′ layers sandwich M″ carbide layers. By synthesizing Mo₂TiC₂T_x, Mo₂Ti₂C₃T_x, and Cr₂TiC₂T_x (where T is a surface termination), we validated the DFT predictions. Since the Mo and Cr atoms are on the outside, they control the 2D flakes’ chemical and electrochemical properties. The latter was proven by showing quite different electrochemical behavior of Mo₂TiC₂T_x and Ti₃C₂T_x. This work further expands the family of 2D materials, offering additional choices of structures, chemistries, and ultimately useful properties.