Surface Functionalization of 2D MXenes: Trends in Distribution, Composition, and Electronic Properties

Area of Science:

• Materials Science
• Surface Chemistry
• Computational Chemistry

Background:

• Two-dimensional (2D) transition metal carbides and nitrides (MXenes) are a class of materials with diverse applications.
• The surface chemistry of MXenes, particularly the distribution of functional groups (-O, -OH, -F), significantly influences their properties.
• Understanding these surface groups is crucial for tailoring MXene performance in various fields.

Purpose of the Study:

• To investigate the distribution and composition of surface functional groups on various MXenes.
• To explore how MXene chemistry and atomic layer structure affect surface functionalization.
• To determine the impact of surface composition on key MXene properties.

Main Methods:

• A multiscale computational scheme was employed.
• Methods included cluster expansion, Monte Carlo simulations, and density functional theory (DFT).
• Simulations were conducted under experimentally relevant conditions.

Main Results:

• Mixtures of functional groups (-O, -OH, -F) are thermodynamically favorable on all studied MXene surfaces.
• The distribution of these functional groups is largely independent of the specific metal, carbon, or nitrogen species and the number of atomic layers.
• Surface composition strongly influences properties like work function, but has a weaker effect on electric conductivity.

Conclusions:

• Surface functionalization of MXenes exhibits predictable patterns across different compositions and structures.
• While functional group distribution is robust, surface composition critically impacts specific material properties.
• This study provides fundamental insights for the rational design and application of MXenes.