Identifying the surface properties of Ti3C2Tx MXene through transmission electron microscopy

Abstract

The titanium carbide Ti 3 C 2 T x (T x = surface functional groups) MXene exhibits promising physical properties and chemical activity as one of the most commonly and extensively investigated materials, but the participating surface structures and properties have yet to be clarified. Here, we reveal the superficial nature of etching-processed Ti 3 C 2 T x using transmission electron microscopy/spectroscopy, first-principles calculation, and molecular dynamics simulation. An O-rich, but C-deficient, diffusion layer (approximately 3 nm) with an inverse gradient distribution is identified. Associated with the superficial substitution of O for C, an amorphous overlayer (approximately 2 nm) containing oxyfluoride of Ti, Al, and C is also revealed. The stable diffusion layer has a high density of states at the Fermi level and a low shear modulus to bulk modulus ratio, implying that the formation of the diffusion layer is not detrimental to Ti 3 C 2 T x ’s conductivity and ductility. These findings are significant for improving oxidation strategies and understanding the structural properties of this material. • O-rich, but C-deficient, diffusion layer and oxyfluoride overlayer are identified • Diffusion layer preserves layered structure, and oxyfluoride overlayer is amorphous • Electron transfer is found between Ti and C and between Ti and O in diffusion layer • Stable diffusion layer is no harm to conductivity and ductility of Ti 3 C 2 T x Wang et al. reveal the atomic configurations and electrical and mechanical properties of superficial Ti 3 C 2 T x MXene using transmission electron microscopy, first-principles calculation, and molecular dynamics simulation. The discovery of the diffusion layer and oxyfluoride overlayer is critical for improving oxidation strategies and understanding the structural properties of this material.