Monte Carlo simulations were performed modeling hydrogen sorption in a recently synthesized metal-organic framework material (MOF) that exhibits large molecular hydrogen uptake capacity. The MOF is remarkable because at 78 K and 1.0 atm it sorbs hydrogen at a density near that of liquid hydrogen (at 20 K and 1.0 atm) when considering H2 density in the pores. Unlike most other MOFs that have been investigated for hydrogen storage, it has a highly ionic framework and many relatively small channels. The simulations demonstrate that it is both of these physical characteristics that lead to relatively strong hydrogen interactions in the MOF and ultimately large hydrogen uptake. Microscopically, hydrogen interacts with the MOF via three principle attractive potential energy contributions: Van der Waals, charge-quadrupole, and induction. Previous simulations of hydrogen storage in MOFs and other materials have not focused on the role of polarization effects, but they are demonstrated here to be the dominant contribution to hydrogen physisorption. Indeed, polarization interactions in the MOF lead to two distinct populations of dipolar hydrogen that are identified from the simulations that should be experimentally discernible using, for example, Raman spectroscopy. Since polarization interactions are significantly enhanced by the presence of a charged framework with narrow pores, MOFs are excellent hydrogen storage candidates.
"However, significant hydrogen adsorptive storage capacities in physisorption need to be reached at liquid-nitrogen temperatures (77 K) and pressures of several MPa. This is attributed to weak binding energy between molecular hydrogen and the surface of sorbents in the range of 2–5 kJ mol À 1 H 2     . Generally, the hydrogen storage properties of physisorption appear to be limited by specific surface area (SSA), pore structures and pore size distributions, surface functionality and the bulk density of the adsorbents. "
[Show abstract][Hide abstract] ABSTRACT: Hydrogen storage is now the “bottle neck” to realize application of hydrogen as the renewable energy. The breakthrough in hydrogen storage is quite urgent. Magnesium is a promising candidate for hydrogen storage that attracts tremendous interest in last a few decades and significant progress has been made in recent years. Accordingly, in this article, we comprehensively reviewed different strategies to overcome the key barriers of high desorption temperature and low kinetics, especially on the recent approaches of nanosizing and interfacial confinement. We also try to give our own point of view on the future perspectives of research in Mg for hydrogen storage.
Renewable and Sustainable Energy Reviews 04/2015; 44. DOI:10.1016/j.rser.2014.12.032 · 5.90 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The capabilities and limitations of the application of molecular simulation techniques to the adsorption of hydrogen in metal-organic frameworks (MOFs) are explored for selected case studies. Force field based grand-canonical Monte Carlo simulations are employed to investigate the adsorption characteristics of three different isoreticular MOFs, resulting in good agreement with experimental findings. The predictive potential of the method is demonstrated for Zn4O(mip)3, a novel system which has not yet been fully characterized experimentally. Further calculations for MOFs with unsaturated metal sites reveal a shortcoming of the simulation technique, as the interaction of hydrogen with these sites is not adequately represented by the potential model. Density functional theory calculations are employed to study the metal–dihydrogen interaction in more detail, making use of a non-periodic model system which is representative for many copper-containing MOFs.
Colloids and Surfaces A Physicochemical and Engineering Aspects 03/2010; 357(1-3-1-3):35 - 42. DOI:10.1016/j.colsurfa.2009.11.025 · 2.75 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Six borazine-linked polymers (BLPs) have been synthesized through the thermolysis reaction of p-phenylenediamine, 1,3,5-tris-(4-aminophenyl)benzene, benzidine, or tetra-(4-aminophenyl)methane with boron tribromide or boron trichloride. Each product exists as an amorphous polymer whose chemical connectivity was confirmed by FT-IR and elemental analysis while thermogravimetric analysis revealed moderate thermal stabilities up to about 200 °C under nitrogen atmosphere. All BLPs possess high surface areas with chlorinated BLPs exhibiting higher values than brominated BLPs (1,174–1,569 vs. 503–849 m2/g, respectively). Gas storage capabilities were investigated as well. BLPs possess good hydrogen uptakes (0.68–1.75 wt% at 77 K) and zero-coverage isosteric heat of adsorption, Q
st, (7.06–7.65 kJ/mol) as calculated by the virial method. The uptakes and heat of adsorption for carbon dioxide (51–141 mg/g at 273 K with Q
st: 22.2–31.7 kJ/mol) are also attractive. BLPs do not, however, appear to exhibit significant methane storage capacities (1.9–15.2 mg/g at 273 K with Q
st: 17.1–21.7 kJ/mol). Accordingly, CO2/CH4 selectivity studies were performed using the ideal adsorbed solution theory and further supported by initial slope calculations. The results indicate that BLP-1(Br) and BLP-2(Br) exhibit very high CO2/CH4 selectivities 23 and 26, respectively, which make them attractive for small gas separation applications.
Journal of Nanoparticle Research 01/2013; 15(1). DOI:10.1007/s11051-012-1368-5 · 2.18 Impact Factor
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