Violation of the Wiedemann-Franz law and ultra-low thermal conductivity of Ti$_3$C$_2$T$_x$ MXene

TL;DR

This study reveals that Ti$_3$C$_2$T$_x$ MXene exhibits ultra-low thermal conductivity and violates the Wiedemann-Franz law, indicating unique heat transport properties with potential for thermal insulation and thermoelectric applications.

Contribution

It provides the first detailed measurement of thermal conductivity in Ti$_3$C$_2$T$_x$ MXene and demonstrates significant deviation from classical laws, highlighting novel heat transport mechanisms.

Findings

Thermal conductivity of 0.78 W/m·K in Ti$_3$C$_2$T$_x$ MXene

Lorenz number is only 0.25 of the classical value

Heat loss is two orders of magnitude lower than metals

Abstract

The high electrical conductivity and good chemical stability of MXenes offer hopes for their use in many applications, such as wearable electronics, energy storage, or electromagnetic interference shielding. While their optical, electronic and electrochemical properties have been widely studied, the information on thermal properties of MXenes is scarce. In this study, we investigate the heat transport properties of Ti$_3$C$_2$T$_x$ MXene single flakes using scanning thermal microscopy and find exceptionally low anisotropic thermal conductivities within the Ti$_3$C$_2$T$_x$ flakes, leading to an effective thermal conductivity of 0.78$\pm$0.21 W m$^{-1}$ K$^{-1}$. This observation is in stark contrast to the predictions of the Wiedemann-Franz law, as the estimated Lorenz number is only 0.25 of the classical value. Due to the combination of low thermal conductivity and low emissivity of Ti$_3$C$_2$T$_x$, the heat loss from it is two orders of magnitude smaller than that from common metals. Our study explores the heat transport mechanisms of MXenes and highlights a promising approach for developing thermal insulation, two-dimensional thermoelectric, or infrared stealth materials.