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Title: High-throughput screening of hypothetical metal-organic frameworks for thermal conductivity
Abstract Thermal energy management in metal-organic frameworks (MOFs) is an important, yet often neglected, challenge for many adsorption-based applications such as gas storage and separations. Despite its importance, there is insufficient understanding of the structure-property relationships governing thermal transport in MOFs. To provide a data-driven perspective into these relationships, here we perform large-scale computational screening of thermal conductivity k in MOFs, leveraging classical molecular dynamics simulations and 10,194 hypothetical MOFs created using the ToBaCCo 3.0 code. We found that high thermal conductivity in MOFs is favored by high densities (> 1.0 g cm −3 ), small pores (< 10 Å), and four-connected metal nodes. We also found that 36 MOFs exhibit ultra-low thermal conductivity (< 0.02 W m −1 K −1 ), which is primarily due to having extremely large pores (~65 Å). Furthermore, we discovered six hypothetical MOFs with very high thermal conductivity (> 10 W m −1 K −1 ), the structures of which we describe in additional detail. more »« less
In this work, we report a high thermal conductivity ( k ) of 162 W m −1 K −1 and 52 W m −1 K −1 at room temperature, along the directions perpendicular and parallel to the c -axis, respectively, of bulk hexagonal BC 2 P (h-BC 2 P), using first-principles calculations. We systematically investigate elastic constants, phonon group velocities, phonon linewidths and mode thermal conductivity contributions of transverse acoustic (TA), longitudinal acoustic (LA) and optical phonons. Interestingly, optical phonons are found to make a large contribution of 30.1% to the overall k along a direction perpendicular to the c -axis at 300 K. BC 2 P is also found to exhibit high thermal conductivity at nanometer length scales. At 300 K, a high k value of ∼47 W m −1 K −1 is computed for h-BC 2 P at a nanometer length scale of 50 nm, providing avenues for achieving efficient nanoscale heat transfer.
Abstract Tailor‐made materials featuring large tunability in their thermal transport properties are highly sought‐after for diverse applications. However, achieving `user‐defined’ thermal transport in a single class of material system with tunability across a wide range of thermal conductivity values requires a thorough understanding of the structure‐property relationships, which has proven to be challenging. Herein, large‐scale computational screening of covalent organic frameworks (COFs) for thermal conductivity is performed, providing a comprehensive understanding of their structure‐property relationships by leveraging systematic atomistic simulations of 10,750 COFs with 651 distinct organic linkers. Through the data‐driven approach, it is shown that by strategic modulation of their chemical and structural features, the thermal conductivity can be tuned from ultralow (≈0.02 W m−1K−1) to exceptionally high (≈50 W m−1K−1) values. It is revealed that achieving high thermal conductivity in COFs requires their assembly through carbon–carbon linkages with densities greater than 500 kg m−3, nominal void fractions (in the range of ≈0.6–0.9) and highly aligned polymeric chains along the heat flow direction. Following these criteria, it is shown that these flexible polymeric materials can possess exceptionally high thermal conductivities, on par with several fully dense inorganic materials. As such, the work reveals that COFs mark a new regime of materials design that combines high thermal conductivities with low densities.
Utilizing metal nanoparticles (NPs) in Additive Manufacturing (AM) enables fabricating parts with submicrometer resolution. The thermal properties of metal NPs are drastically different from their bulk and micronsize counterparts due to nanoscale thermal transport effects, e.g. ballistic phonon/electron transport instead of diffusive transport described by Fourier’s Law. Rough estimation of metal NPs’ thermal properties with bulk values will inevitably cause large errors for AM applications, because thermal properties evolve along with the sintering process. In this study, thermal properties of 100 nm Cu NPs are examined at different sintering stages. Effective density is measured between 3500 and 5300 kg/m 3 at a sintering temperature range of 100 and 400 °C, and the sintering of Cu NPs is determined to be around 300 °C using Thermogravimetry analysis (TGA) with Differential Scanning Calorimeter (DSC). A picosecond Transient Thermoreflectance (ps-TTR) technique is employed to measure the effective thermal conductivity of Cu NPs, which jumps from 18.5 ± 0.8 W/m ∙K to 26.8 ± 2.1 W/m ⋅K onset of sintering around 300 °C. These values are less than 1/10 of the bulk value (398 W/m ⋅K). The effective thermal conductivity is almost independent on porosity except in the temperature range close to 300 °C, which comes from two factors related with nanoscale thermal transport: (i) ballistic electron transport is important in particles with size comparable with electron mean free path; (ii) effective thermal conductivity is dominated by interface scattering on particles surfaces. Our results provide insights about the importance on accurate characterization of thermal properties in metal nanoparticles due to the nanoscale phenomena.
Achieving a molecular-level understanding of how the structures and compositions of metal–organic frameworks (MOFs) influence their charge carrier concentration and charge transport mechanism—the two key parameters of electrical conductivity—is essential for the successful development of electrically conducting MOFs, which have recently emerged as one of the most coveted functional materials due to their diverse potential applications in advanced electronics and energy technologies. Herein, we have constructed four new alkali metal (Na, K, Rb, and Cs) frameworks based on an electron-rich tetrathiafulvalene tetracarboxylate (TTFTC) ligand, which formed continuous π-stacks, albeit with different π–π-stacking and S⋯S distances ( d π–π and d S⋯S ). These MOFs also contained different amounts of aerobically oxidized TTFTC˙ + radical cations that were quantified by electron spin resonance (ESR) spectroscopy. Density functional theory calculations and diffuse reflectance spectroscopy demonstrated that depending on the π–π-interaction and TTFTC˙ + population, these MOFs enjoyed varying degrees of TTFTC/TTFTC˙ + intervalence charge transfer (IVCT) interactions, which commensurately affected their electronic and optical band gaps and electrical conductivity. Having the shortest d π–π (3.39 Å) and the largest initial TTFTC˙ + population (∼23%), the oxidized Na-MOF 1-ox displayed the narrowest band gap (1.33 eV) and the highest room temperature electrical conductivity (3.6 × 10 −5 S cm −1 ), whereas owing to its longest d π–π (3.68 Å) and a negligible TTFTC˙ + population, neutral Cs-MOF 4 exhibited the widest band gap (2.15 eV) and the lowest electrical conductivity (1.8 × 10 −7 S cm −1 ). The freshly prepared but not optimally oxidized K-MOF 2 and Rb-MOF 3 initially displayed intermediate band gaps and conductivity, however, upon prolonged aerobic oxidation, which raised the TTFTC˙ + population to saturation levels (∼25 and 10%, respectively), the resulting 2-ox and 3-ox displayed much narrower band gaps (∼1.35 eV) and higher electrical conductivity (6.6 × 10 −5 and 4.7 × 10 −5 S cm −1 , respectively). The computational studies indicated that charge movement in these MOFs occurred predominantly through the π-stacked ligands, while the experimental results displayed the combined effects of π–π-interactions, TTFTC˙ + population, and TTFTC/TTFTC˙ + IVCT interaction on their electronic and optical properties, demonstrating that IVCT interactions between the mixed-valent ligands could be exploited as an effective design strategy to develop electrically conducting MOFs.
In this study, we report the length dependence of thermal conductivity ( k ) of zinc blende-structured Zinc Selenide (ZnSe) and Zinc Telluride (ZnTe) for length scales between 10 nm and 10 μm using first-principles computations, based on density-functional theory. The k value of ZnSe is computed to decrease significantly from 22.9 W m −1 K −1 to 1.8 W m −1 K −1 as the length scale is diminished from 10 μm to 10 nm. The k value of ZnTe is also observed to decrease from 12.6 W m −1 K −1 to 1.2 W m −1 K −1 for the same decrease in length. We also measured the k of bulk ZnSe and ZnTe using the Frequency Domain Thermoreflectance (FDTR) technique and observed a good agreement between the FDTR measurements and first principles calculations for bulk ZnSe and ZnTe. Understanding the thermal conductivity reduction at the nanometer length scale provides an avenue to incorporate nanostructured ZnSe and ZnTe for thermoelectric applications.
Islamov, Meiirbek, Babaei, Hasan, Anderson, Ryther, Sezginel, Kutay B., Long, Jeffrey R., McGaughey, Alan J., Gomez-Gualdron, Diego A., and Wilmer, Christopher E. High-throughput screening of hypothetical metal-organic frameworks for thermal conductivity. Retrieved from https://par.nsf.gov/biblio/10401780. npj Computational Materials 9.1 Web. doi:10.1038/s41524-022-00961-x.
Islamov, Meiirbek, Babaei, Hasan, Anderson, Ryther, Sezginel, Kutay B., Long, Jeffrey R., McGaughey, Alan J., Gomez-Gualdron, Diego A., & Wilmer, Christopher E. High-throughput screening of hypothetical metal-organic frameworks for thermal conductivity. npj Computational Materials, 9 (1). Retrieved from https://par.nsf.gov/biblio/10401780. https://doi.org/10.1038/s41524-022-00961-x
Islamov, Meiirbek, Babaei, Hasan, Anderson, Ryther, Sezginel, Kutay B., Long, Jeffrey R., McGaughey, Alan J., Gomez-Gualdron, Diego A., and Wilmer, Christopher E.
"High-throughput screening of hypothetical metal-organic frameworks for thermal conductivity". npj Computational Materials 9 (1). Country unknown/Code not available. https://doi.org/10.1038/s41524-022-00961-x.https://par.nsf.gov/biblio/10401780.
@article{osti_10401780,
place = {Country unknown/Code not available},
title = {High-throughput screening of hypothetical metal-organic frameworks for thermal conductivity},
url = {https://par.nsf.gov/biblio/10401780},
DOI = {10.1038/s41524-022-00961-x},
abstractNote = {Abstract Thermal energy management in metal-organic frameworks (MOFs) is an important, yet often neglected, challenge for many adsorption-based applications such as gas storage and separations. Despite its importance, there is insufficient understanding of the structure-property relationships governing thermal transport in MOFs. To provide a data-driven perspective into these relationships, here we perform large-scale computational screening of thermal conductivity k in MOFs, leveraging classical molecular dynamics simulations and 10,194 hypothetical MOFs created using the ToBaCCo 3.0 code. We found that high thermal conductivity in MOFs is favored by high densities (> 1.0 g cm −3 ), small pores (< 10 Å), and four-connected metal nodes. We also found that 36 MOFs exhibit ultra-low thermal conductivity (< 0.02 W m −1 K −1 ), which is primarily due to having extremely large pores (~65 Å). Furthermore, we discovered six hypothetical MOFs with very high thermal conductivity (> 10 W m −1 K −1 ), the structures of which we describe in additional detail.},
journal = {npj Computational Materials},
volume = {9},
number = {1},
author = {Islamov, Meiirbek and Babaei, Hasan and Anderson, Ryther and Sezginel, Kutay B. and Long, Jeffrey R. and McGaughey, Alan J. and Gomez-Gualdron, Diego A. and Wilmer, Christopher E.},
}
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