Effects of surface termination and tensile strain on the thermal conductivity of the Ti3C2Tx MXene

Abstract

This study investigates the effects of surface termination and tensile strain on the thermal conductivity of Ti₃C₂T_x MXene nanosheets using ReaxFF molecular dynamics (MD) simulations. The results demonstrate that the thermal conductivity of Ti₃C₂O₂ MXene is significantly higher than that of Ti₃C₂(OH)₂ MXene, primarily due to its higher phonon group velocity and longer phonon mean free path (MFP). The presence of OH functional groups in Ti₃C₂(OH)₂ MXene results in reduced thermal conductivity compared to the O groups in Ti₃C₂O₂. This reduction is attributed to high-frequency vibrations of hydrogen atoms, which enhance phonon scattering and suppress low-frequency phonon modes. Furthermore, the thermal conductivity of Ti₃C₂T_x MXenes exhibits a nonmonotonic dependence on the fraction of OH groups. Specifically, it decreases initially with increasing OH content up to a fraction of 0.8, followed by a slight increase at higher concentrations. This behavior is explained by the interplay between phonon scattering and the uniformity of OH group distribution. The application of tensile strain further reduces thermal conductivity by broadening the C-atom projected phonon spectrum and inducing phonon peak splitting, which enhances phonon scattering and shortens phonon lifetime. These findings offer critical insights into the tunability of thermal conductivity in MXenes, providing a foundation for optimizing their performance in applications such as electronics, energy conversion, and thermoelectric devices.