Impact of carbon dioxide loading on the thermal conductivity of metal organic frameworks

Owing to their unrivaled porosities and high surface areas, metal organic frameworks (MOFs) hold great promise for mitigating the global warming crisis through capturing and storing CO2 gas. However, the exothermic process of CO2 uptake can lead to temperature rises that can severely compromise the efficiency of these materials for such purposes. In this work, we employ reactive molecular dynamics simulations and anharmonic lattice dynamics calculations to investigate the influence of varying levels of CO2 uptake in dictating the heat transfer mechanisms in MOF-5. Compared to the empty framework, we find that the thermal conductivity of the gas loaded framework is highly dependent on the gas diffusivities and temperatures. At low temperatures, where the gases have low diffusivities and are predominantly adsorbed to the pore walls, vibrational scattering from the solid-gas interactions leads to drastically reduced thermal conductivities. At higher temperatures (above ∼200 K), however, we find that the CO2 molecules with increased diffusivities can lead to additional channels of heat conduction for high gas densities. Our spectral analyses show that the addition of gas adsorbates has a negligible influence on the heat carrying acoustic modes of the framework at such relatively higher temperatures. Contrastingly, at lower temperatures, gas infiltration leads to considerable scattering and reduced lifetimes of the acoustic vibrational modes of the framework. These findings provide critical insights into the mechanistic processes dictating heat conduction in guest-infiltrated MOFs and offer a pathway to tailor their thermal properties for advanced applications in gas storage, separation, catalysis, and thermoelectrics.