Session: 08-01: Micro/Nanoscale Heat Conduction

Paper Number: 105783

105783 - Thermal Transport in Metal-Organic Frameworks: The Influence of Water Adsorbents and Mechanical Strain 

Abstract: 

  Metal-organic frameworks (MOFs) have gained tremendous attention due to their potential in energy areas, such as carbon capture, catalysis, chemical sensing, electrodes, and gas separation and storage. Their thermal transport properties which determine their performance must be known while are rarely studied. Using both atomistic simulations and experimental measurements, we systematically investigate the thermal transport properties of a typical MOF (i.e., HKUST-1) considering the adsorbed water molecules and external mechanical deformation.

  We experimentally and numerically find that the thermal conductivity of HKUST-1 is largely reduced by the adsorbed water molecules. Using the spectral analysis method, we show that the mean free path of these small wavevector vibrations can be as large as ~120 nm which is attributed to the good crystallinity of HKUST-1. By adsorbing water molecules in HKUST-1, these long mean path vibrations are strongly scattered by the adsorbed water molecules. Therefore, the thermal conductivity of HKUST-1 with adsorbed water molecules is decreased compared to that of the original HKUST-1. Meanwhile, the water molecules can transport thermal energy via their diffusion. Two pathways for the thermal energy exchange, e.g., the phonons and the water molecules, are then existing in the HKUST-1 with water molecules. The thermal conductivity of the adsorbed HKUST-1 is found to decrease and then increase with the quantity of the adsorbates owing to the competition between the two thermal pathways.

  Furthermore, we find that the thermal conductivity of HKUST-1 shows a negative mechanical strain dependence, which contradicts the conventional Liebfried and Schlömann theory [Math.-Phys. Kl., Math.-Phys.-Chem. Abt. 4, 71 (1954)]. Our results show that the thermal conductivity will increase and decrease with tension and compression, respectively. The thermal conductivity of HKUST-1 can be modulated largely (i.e., 2.5 times) using external mechanical strain. We further find that compression will significantly enhance the anharmonicity of HKUST-1, which leads to extremely strong scatterings among the heat carriers in HKUST-1. The thermal conductivity of HKUST-1 will therefore decrease with compression. When HKUST-1 is under tension, the interactions between the organic group and the metal atom become weaker, and the organic groups may be treated as lattice sites. The HKUST-1 under tension may then be treated as a perfect crystal of which all the organic groups can be represented by lattice sites, and the corresponding thermal conductivity is higher than that of the original HKUST-1.

  Our results demonstrate that the thermal transport properties of MOFs can be modulated largely by water adsorbents and mechanical strain, which can benefit the thermal management design of MOFs’ thermal-related applications.

Presenting Author: Yanguang Zhou The Hong Kong University of Science and Technology

Presenting Author Biography: Prof. Yanguang Zhou received his Ph.D. degree with “Ausgezeichnet” in the Mechanical Engineering Department at RWTH-Aachen University, as well as his M.Eng. degree and B.Eng. degree in Mechanical Engineering Department at Beihang University and China University of Geoscience, respectively. After graduation from Aachen, he worked as a postdoc research associate and an assistant visiting project scientist at the University of California, Los Angeles (UCLA) before joining HKUST as an assistant professor.

Prof. Zhou’s group designs advanced materials & structures, i.e., thermoelectric materials, magnetic materials and nanocomposites, via using nanotechnologies (both experimental and theoretical methods), with applications in energy, thermal management in solid-state batteries and soft electronics.

Authors:

Yanguang Zhou The Hong Kong University of Science and Technology