MXenes: A Family of 2D Materials with Remarkable Chemical Diversity

Since their discovery in 2011, MXenes, a rapidly expanding family of 2D transitionmetal carbides, nitrides, and carbonitrides (more than 100 members), have emerged as versatilematerials for energy-related applications and beyond.1 Their unique combination of highelectronic conductivity, tunable chemistry, theoretical high specific surface area and clay-likeprocessability makes them ideal candidates for numerous applications.The synthesis of 2D MXenes involves the selective removal of the A layers from theirMAX phase precursors (Mn+1AXn), where M is an early transition metal (e.g., Ti, Mo, V, Cr),A is an element from groups 13–16 (e.g., Al, Si,…), X is carbon (C) and/or nitrogen (N) and n= 1, 2, 3 or 4 (Figure 1). The resulting MXene (Mn+1XnTx) retains the Mn+1Xn layered structurebut is terminated with Tx surface groups (mainly -OH, -O, -Cl and/or -F), introduced during theetching process. The nature of these groups can serve as a lever to control the surface properties.The synthesis parameters, including the choice of MAX phase precursor, etching conditions(e.g. HF, LiF/HCl or other etchants), temperature, duration and delamination process, plays apivotal role in defining the MXene’s properties and composition.This presentation has three main objectives: (i) to highlight the chemical diversity ofMXenes, (ii) to emphasize the scalability and industrial relevance of MXenes, thanks to theirsolution-processable nature and compatibility with existing manufacturing techniques and iii)to demonstrate the critical role of the synthesis route in determining their surface properties.