ICMMS-2: Metal−organic Frameworks for Hydrogen Storage: Theoretical Prospective (original) (raw)
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Density Functional Methods for Fast Screening of Metal-Organic Frameworks for Hydrogen Storage
Classical density functional theory (DFT) has been routinely used for the characterization of pore size distribution and specific surface area of porous materials by gas physisorption. However, its application to large-scale screening of materials for gas storage has been largely unexplored because it is commonly believed that the DFT calculations are applicable only to one-dimensional systems and highly sensitive to the approximations introduced in the free-energy functionals. In this work, we have investigated four representative versions of nonlocal density functionals for predicting H 2 adsorption using both the slit pore model and a large library of metal−organic frameworks (MOFs) under a broad range of temperatures and pressures. The four versions of DFT share a common functional from the modified fundamental measure theory to account for the molecular excluded volume effects while differing in their approximations to represent the intermolecular attractions, viz., meanfield approximation, two versions of weighted-density approximations (WDA), and the quadratic functional expansion method. We have tested these functionals by extensive comparison with Monte Carlo simulation data for H 2 adsorption at conditions of practical interest. Overall all four versions of DFT are reasonably accurate in comparison with the simulation results. While the density expansion method performs rather well at the DOE target condition for hydrogen storage, the WDA methods are found most accurate at low temperature, a condition typically used in materials characterization. In addition to rapid prediction of the adsorption isotherms, DFT is able to generate molecular density profiles revealing microscopic details such as favorable adsorption sites. From a computational perspective, the DFT calculation is at least 1 order of magnitude faster than conventional simulation methods, promising for large-scale screening of nanostructured materials for gas storage. 5374−5385 temperature and pressure of hydrogen gas in the bulk are fixed at T = 243 K and P = 100 bar, respectively. The DFT functionals are (a) WDA-Y, (b) WDA-L, (c) FMSA, (d) MFA, and (e) WDA-Y with FMSA EOS. Color code: Blue, top 300 from excess CH 4 adsorption in weight category; Red, top 300 from excess CH 4 adsorption in volume category; Purple, top 300 from void fraction category; Teal, top 300 from surface area category.
2014
Practical methods for hydrogen storage are still a prime challenge in the realization of an energy economy based on Hydrogen. Metal organic frameworks (MOFs) are crystalline ultra-porous materials with ability to trap and store voluminous amounts of gas molecules. MOFs represent an encouraging storage method relying on their enormous surface area. However, MOFs show reduced hydrogen uptake at room temperature due to low adsorption energy of hydrogen. To increase the adsorption uptake of MOFs at room temperature, the adsorption energy must be increased. In this contribution, materials exhibiting higher adsorption energy and enhanced hydrogen adsorption, namely MIL-53 (Al) and MOF-74, have been investigated using molecular dynamics (MD) simulation. MD simulations were performed within the density functional based tight binding method (DC-SCC-DFTB). Our results demonstrate that DC-SCC-DFTB method predicts structural parameters, adsorption sites, adsorption energies and diffusion factor...
A Simulation Study of Hydrogen in Metal-Organic Frameworks
Adsorption Science & …, 2010
Molecular simulations have been used to evaluate the effect exerted by metal centres on the adsorption and diffusion of hydrogen in metal-organic frameworks. Simulations were carried out for the MIL-53 (Cr and Al) structures and the isostructural vanadium analogue MIL-47 at room temperature. To validate the models and force fields used in this work, the adsorption isotherms, energies and entropies, and self-diffusivities in Cu-BTC and IRMOF-1 metal-organic frameworks were computed. Using the validated force fields and models, a detailed analysis of the preferential adsorption sites is reported, allowing the energetic contribution in the low-coverage regime (Henry constants and adsorption energies and entropies) to be determined as a function of loading (adsorption isotherms). The influence of each energetic contribution to the charged and uncharged models of hydrogen has also been analyzed.
Application of Metal-Organic Frameworks (MOFs) for Hydrogen Storage
CRC Press eBooks, 2017
Metal-organic frameworks (MOFs) based on lanthanum metal ions (La 3+) and 2,6naphthalenedicarboxylic ligand (La-MOFs) have been synthesized by solvothermal method at 120 0 C and 150 0 C for 24 h using dimethylformamide and water (5:1) as a solvent. Furthermore, the chemical bonding and vibration spectroscopy, crystallographic structure, band gap, particle size and microscopic, and redox potential studies of La-MOFs were also investigated as well. FTIR results shown that there were no wave numbers at 1690-1730 cm-1 , which affirmed that the La-MOFs had been formed. UV-VIS DRS characterization with solvent (DMF: Water) using (Ln 3+) metal was confirmed at 492 nm (2.53 eV). SEM/EDX results shown that La-MOFs have an ultrahigh skeleton and the EDS revealed the composition of La, O, and C atoms that reside within La-MOFs, cyclic voltammetry results shown that LUMO level was-2.5 V vs. H + /H2. Finally, the photocatalytic activity of La-MOFs was performed, which produced 24.99 µmol of H2 after being measured for 4 hours.
The Journal of Physical Chemistry C, 2010
The incorporation of coordinatively unsaturated metal sites in microporous metal-organic frameworks (MOFs) has emerged as an important synthetic strategy for the development of potential room-temperature hydrogen storage materials, because the relatively strong, localized interaction of hydrogen with the metal centers induces an increase of the isosteric heat of hydrogen adsorption. Previous modeling studies have shown that these interactions are not adequately modeled when literature force-field parameters are used. Typical results of grand-canonical Monte Carlo (GCMC) simulations exhibit a pronounced underestimation of the hydrogen uptake at low pressures and low temperatures. In this study, it is shown that this shortcoming can be resolved by deriving a new set of potential parameters to represent the metal-dihydrogen interaction from ab initio calculations for molecular model systems. The approach is computationally efficient and could be applied for any coordination environment of the metal center. The present work focuses on three MOFs with unsaturated copper centers. The newly derived Cu-H 2 potential model is combined with literature force-field parameters to model the dispersive interactions with other framework atoms. At cryogenic temperatures and pressures up to 1 bar, GCMC simulations using these parameters provide for a massively improved prediction of the hydrogen storage characteristics when compared to parameters from a literature force field. On the other hand, the unmodified literature parameters perform best in predicting the saturation uptake. At room temperature, the effect of the potential modification is much smaller, and the best agreement with experiment is obtained when the localized metal-dihydrogen interaction is not accounted for in the simulations. This indicates that the metal-dihydrogen interaction is too weak to permit a significant adsorption at the metal sites under these conditions. Calculations using an artificially enhanced potential model show that a drastic increase of the interaction strength could boost the hydrogen storage capacity at room temperature, although the attainable uptake remains limited by the number of available metal sites. The implications of these results for the synthesis of new MOFs are critically discussed.
2015
The MIL-100 metal organic framework was synthesized through solvothermal route, modified with Pt-loaded active carbon and H 2 adsorption capacity was evaluated. The maximum specific surface area of MIL-100 was obtained upto 1,960 m 2 g-1 with a type I adsorption isotherm confirmed from N 2 adsorption isotherms. The pristine MIL-100 was modified with 5 wt% Pt-loaded activated carbon and the carbonyl bridge was established to facilitate the hydrogen spillover effect. The hydrogen storage capacity of modified MIL-100 was 0.41 wt% measured at 31 bar and 298 K. This value is much higher than that of pristine MIL-100. XANES spectra indicated that the valency of central chromium metal ions of MIL-100 structure was Cr(III). EXAFS data also revealed that MIL-100 had a first shell of Cr-O bonding with bond distance of 1.965 Å and the coordination number of 4.8.
Chemical Society Reviews, 2009
This critical review covers the application of computer simulations, including quantum calculations (ab initio and DFT), grand canonical Monte-Carlo simulations, and molecular dynamics simulations, to the burgeoning area of the hydrogen storage by metal-organic frameworks and covalent-organic frameworks. This review begins with an overview of the theoretical methods obtained from previous studies. Then strategies for the improvement of hydrogen storage in the porous materials are discussed in detail. The strategies include appropriate pore size, impregnation, catenation, open metal sites in metal oxide parts and within organic linker parts, doping of alkali elements onto organic linkers, substitution of metal oxide with lighter metals, functionalized organic linkers, and hydrogen spillover (186 references).
Hydrogen Storage in New Metal–Organic Frameworks
The Journal of Physical Chemistry C, 2012
New five metal-organic frameworks (MOFs, 325, and 62) of either short linkers (pyrazolecarboxylate and pyrazaboledicarboxylate) or long and thin alkyne functionalities (ethynyldibenzoate and butadiynedibenzoate) were prepared to examine their impact on hydrogen storage in MOFs. These compounds were characterized by single crystal X-ray diffraction, and their low-pressure and high-pressure hydrogen uptake properties were investigated. In particular, volumetric excess H 2 uptake by MOF-324 and IRMOF-62 outperform MOF-177 up to 30 bar. Inelastic neutron scattering studies for MOF-324 also revealed strong interactions between the organic links and hydrogen, in contrast to MOF-5 where the interactions between the Zn 4 O unit and hydrogen are the strongest. These data are indicative that smaller pores and polarized linkers in MOFs are indeed advantageous for hydrogen storage.
Microporous metal−organic frameworks are a class of materials being vigorously investigated for mobile hydrogen storage applications. For high-pressure storage at ambient temperatures, the M 3 [(M 4 Cl) 3 (BTT) 8 ] 2 (M-BTT; BTT 3− = 1,3,5-benzenetristetrazolate) series of frameworks are of particular interest due to the high density of exposed metal cation sites on the pore surface. These sites give enhanced zero-coverage isosteric heats of adsorption (Q st ) approaching the optimal value for ambient storage applications. However, the Q st parameter provides only a limited insight into the thermodynamics of the individual adsorption sites, the tuning of which is paramount for optimizing the storage performance. Here, we begin by performing variable-temperature infrared spectroscopy studies of Mn-, Fe-, and Cu-BTT, allowing the thermodynamics of H 2 adsorption to be probed experimentally. This is complemented by a detailed DFT study, in which molecular fragments representing the metal clusters within the extended solid are simulated to obtain a more thorough description of the structural and thermodynamic aspects of H 2 adsorption at the strongest binding sites. Then, the effect of substitutions at the metal cluster (metal ion and anion within the tetranuclear cluster) is discussed, showing that the configuration of this unit indeed plays an important role in determining the affinity of the framework toward H 2 . Interestingly, the theoretical study has identified that the Zn-based analogs would be expected to facilitate enhanced adsorption profiles over the compounds synthesized experimentally, highlighting the importance of a combined experimental and theoretical approach to the design and synthesis of new frameworks for H 2 storage applications.
Synthesis and characterization of porous HKUST-1 metal organic frameworks for hydrogen storage
International Journal of Hydrogen Energy, 2012
Hydrogen storage XANES/EXAFS a b s t r a c t Hydrogen storage capacity has been investigated on a copper-based metal organic framework named HKUST-1 with fine structural analyses. The crystalline structure of HKUST-1 MOF has been confirmed from the powder X-ray diffraction and the average particle diameter has been found about 15e20 mm identified by FE-SEM. Nitrogen adsorption isotherms show that HKUST-1 MOF has approximately type-I isotherm with a BET specific surface area of 1055 m 2 g À1 . Hydrogen adsorption study shows that this material can store 0.47 wt.% of H 2 at 303 K and 35 bar. The existence of Cu (II) in crystalline framework of HKUST-1 MOF has been confirmed by pre-edge XANES spectra. The sharp feature at 8985.8 eV in XANES spectra represents the dipole-allowed electron transition from 1s to 4p xy . In addition, EXAFS spectra indicate that HKUST-1 MOF structure has the CueO bond distance of 1.95 Å with a coordination number of 4.2.