Manipulating Thermal Transport of 2D MOFs by Hierarchical Structural Design.

Manipulating the thermal conductivity of 2D metal-organic frameworks (MOFs) via their pre-designable and well-defined structures plays a critical role in their broad applications. Nevertheless, the intricate vibrational structures and nontrivial phonon dynamics of these unconventional organic-inorganic hybrid solid-state materials challenge our understanding on the heat-transport mechanism. Here, by using multiscale simulations with data-driven deep neural-network potential, and taking nickel bis(dithiolene) and its derivatives as examples, we provide a unified understanding on how to modulate thermal conductivity of 2D MOFs by mapping the structure-function relationship. We find that hierarchical structural modifications endow them with both highly tunable thermal conductivities (spanning three orders of magnitude) and controllable anisotropy. Among them, atomic-scale coordination geometry modification, and molecular-level defect and disorder engineering enable a dramatic decline in thermal conductivity. The reason for the former is the strengthened vibrational anharmonicity, while the latter is attributed to the localized and softened vibrational structures. Furthermore, tailoring their phonon mean free path by nano-level size control markedly elevates thermal conductivity. We anticipate that these insights open up new opportunities for rationally designing MOF-based thermal functional materials.