Phonon-Dominated In-Plane Thermal Conductivity of Single-Flake Metallic Ti3C2Tx MXene

MXenes are a promising class of 2D materials, with prospects in applications such as electromagnetic interference shielding, energy storage, catalysis, and thermal management. Despite the importance of understanding their thermal transport properties, it is not clear whether electrons or phonons dominate heat transport, and the experimentally obtained in-plane thermal conductivities vary substantially. Here, we address this by studying in-plane heat transport in single Ti3C2Tx MXene flakes using spatiotemporal microscopy, directly visualizing heat transport in space and time. We obtain a thermal diffusivity of 0.05 cm2 s-1, corresponding to an in-plane thermal conductivity of 13-16 W m-1 K-1. Using an upper limit for the electronic conductivity based on terahertz measurements, we find that electrons carry at most half of the heat. This shows that─despite their metallic nature─phonons play an important role in the heat transport of Ti3C2Tx MXene, providing an unconventional combination of heat and charge transport properties.