Identifying the bottlenecks for heat transport in metal-organic frameworks

Metal-organic frameworks (MOFs) represent a highly porous type of materials formed by metal nodes connected by organic linkers. Their modular nature enables an almost limitless pool of possible materials leading to a wide range of different applications like gas storage, gas separation or catalysis. Many of the processes occurring during these applications rely on the dissipation of heat. Therefore, it is crucial to understand the mechanism of heat transport processes in order to design MOFs tailored for specific applications. We employ non-equilibrium molecular dynamics simulations to determine the thermal conductivity for a selection of different MOFs and to spatially resolve barriers for heat transport. We identify the interface between node and linker, specifically the bond between the metal and oxygen atoms, as the major bottleneck for the flow of thermal energy. This bottleneck can be tuned by utilizing metals with different masses or by changing metal-linker bonding strengths. This strategy is demonstrated by investigating a series of modified isoreticular MOFs. Additional insight is gained by identifying the phonons most relevant for thermal transport and by analyzing their harmonic and anharmonic properties.