Gas Rattling Motions Drive Anomalous Thermal Conductivity in Hydrogen-Bonded Organic Frameworks

Hydrogen-bonded organic frameworks (HOFs) are porous materials known for gas adsorption, but their thermal transport behavior with gas adsorbates remains unexplored. This study investigates the thermal conductivity (k) of TCF-1, a three-dimensional HOF, with three gas adsorbates (Xe, CO2, and CH4) using atomic simulations. Anomalous trends are observed: along the pore channel direction, k in TCF-1/Xe and TCF-1/CH4 initially decreases, then peaks at a concentration of four gas molecules per unit cell, and subsequently decreases. Conversely, k in TCF-1/CO2 decreases monotonically. These behaviors are driven by competing factors: (1) gas-induced heat conduction channels, (2) solid–gas phonon scattering, and (3) volume expansion from flexible hydrogen bonds. The enhanced k in TCF-1/Xe is attributed to gas rattling motions, which reduce phonon scattering and restrict gas diffusion, enabling efficient heat conduction. These findings reveal fundamental insights into the thermal transport of host–guest systems and highlight the potential of HOFs in multifunctional material design.