Ambient oxidation of Ti₃C₂ MXene initialized by atomic defects

Area of Science:

• Materials Science
• Nanotechnology
• Surface Chemistry

Background:

• MXenes, 2D transition metal carbides/nitrides, show promise in energy storage, catalysis, and sensors.
• The ambient stability of MXenes is a critical limitation for large-scale applications.
• Detailed MXene degradation mechanisms under ambient conditions are not fully understood.

Purpose of the Study:

• To elucidate the atomic-level oxidation mechanism of MXene flakes under ambient conditions.
• To identify the role of defects and edges in MXene degradation.
• To provide insights for designing more stable MXenes and novel hybrid materials.

Main Methods:

• Aberration-corrected scanning transmission electron microscopy (STEM) was employed.
• High-resolution imaging and analysis of MXene flake oxidation.
• Identification of atomic defects, oxidation sites, and resulting structures.

Main Results:

• Heterogeneous growth of titanium oxide observed near atomic defects and on MXene edges.
• Carbon atoms at Ti-vacancies oxidized to form amorphous carbon aggregates.
• Titanium cations oxidized, with Ti-ion diffusion driven by an internal electric field.
• Anatase TiO2 nanoparticles preferentially grew along the {101} lattice plane.
• A loose orientation relationship was found between TiO2 and MXene, with TiO2 {101} perpendicular to MXene {0001}.

Conclusions:

• The study reveals the atomic-scale oxidation mechanism of MXenes in ambient conditions.
• Findings highlight the role of defects and ion diffusion in MXene degradation.
• Insights gained can guide the synthesis of more stable MXenes and carbon-supported TiO2 nanoparticle hybrids for advanced applications.