One MAX phase, different MXenes: a guideline to understand the crucial role of etching conditions on Ti$_3$C$_2$T$_x$ surface chemistry

TL;DR

This paper investigates how different etching conditions affect the surface chemistry and properties of Ti₃C₂Tₓ MXenes, emphasizing the importance of synthesis parameters on material characteristics and potential applications.

Contribution

It provides a comprehensive analysis of how various etching agents influence the surface chemistry, defect structure, and properties of Ti₃C₂Tₓ MXenes, guiding tailored synthesis.

Findings

Etching agents significantly alter surface terminal groups (F, OH, O).

Different etching conditions affect oxidation sensitivity and delamination.

Surface chemistry impacts MXene's suitability for specific applications.

Abstract

MXenes are a new, and growing, family of 2D materials with very promising properties for a wide variety of applications. Obtained from the etching of MAX phases, numerous properties can be targeted thanks to the chemical richness of the precursors. Herein, we highlight how etching agents govern surface chemistries of Ti$_3$C$_2$T$_x$, the most widely studied MXene to date. By combining characterization tools such as X-ray diffraction, X-ray photoelectron, Raman and electron energy loss spectroscopies, scanning and transmission electron microscopies and a surface sensitive electrochemical reaction-the hydrogen evolution reaction, HER-we clearly demonstrate that the etching agent (HF, LiF/HCl or FeF$_3$/HCl) strongly modifies the nature of surface terminal groups (F, OH and/or O), oxidation sensitivity, delamination ability, nature of the inserted species, interstratification, concentration of defects and size of flakes. Beyond showing how using these different characterization tools to analyze MXenes, this work highlights that the MXene synthesis routes can influence targeted applications.