Near-Atomic Scale Perspective on the Oxidation of Ti$_3$C$_2$T$_x$ MXenes: Insights from Atom Probe Tomography

TL;DR

This study uses atom probe tomography to analyze the near-atomic scale oxidation behavior of Ti₃C₂Tₓ MXenes, revealing elemental distributions and impurities that influence their stability and catalytic activity.

Contribution

It provides the first detailed 3D atomic-scale analysis of MXene oxidation and impurity incorporation, enhancing understanding of their degradation mechanisms.

Findings

Presence of alkali and halogen elements in as-synthesized MXenes

Enrichment of alkali elements in TiO₂ nanowires after oxidation

Impurities influence MXene activity and degradation

Abstract

MXenes are a family of 2D transition metal carbides and nitrides with remarkable properties and great potential for energy storage and catalysis applications. However, their oxidation behavior is not yet fully understood, and there are still open questions regarding the spatial distribution and precise quantification of surface terminations, intercalated ions, and possible uncontrolled impurities incorporated during synthesis and processing. Here, atom probe tomography analysis of as-synthesized Ti$_3$C$_2$T$_x$ MXenes reveals the presence of alkali (Li, Na) and halogen (Cl, F) elements as well as unetched Al. Following oxidation of the colloidal solution of MXenes, it is observed that the alkalies enriched in TiO$_2$ nanowires. Although these elements are tolerated through the incorporation by wet chemical synthesis, they are often overlooked when the activity of these materials is considered, particularly during catalytic testing. This work demonstrates how the capability of atom probe tomography to image these elements in 3D at the near-atomic scale can help to better understand the activity and degradation of MXenes, in order to guide their synthesis for superior functional properties.