Tuning clathrate hydrates for hydrogen storage
TL;DR: Hydrogen storage capacities in THF-containing binary-clathrate hydrates can be increased to ∼4 wt% at modest pressures by tuning their composition to allow the hydrogen guests to enter both the larger and the smaller cages, while retaining low-pressure stability.
Abstract: The storage of large quantities of hydrogen at safe pressures is a key factor in establishing a hydrogen-based economy. Previous strategies--where hydrogen has been bound chemically, adsorbed in materials with permanent void space or stored in hybrid materials that combine these elements--have problems arising from either technical considerations or materials cost. A recently reported clathrate hydrate of hydrogen exhibiting two different-sized cages does seem to meet the necessary storage requirements; however, the extreme pressures (approximately 2 kbar) required to produce the material make it impractical. The synthesis pressure can be decreased by filling the larger cavity with tetrahydrofuran (THF) to stabilize the material, but the potential storage capacity of the material is compromised with this approach. Here we report that hydrogen storage capacities in THF-containing binary-clathrate hydrates can be increased to approximately 4 wt% at modest pressures by tuning their composition to allow the hydrogen guests to enter both the larger and the smaller cages, while retaining low-pressure stability. The tuning mechanism is quite general and convenient, using water-soluble hydrate promoters and various small gaseous guests.
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TL;DR: Findings place COFs among the most porous and the best adsorbents for hydrogen, methane, and carbon dioxide.
Abstract: Dihydrogen, methane, and carbon dioxide isotherm measurements were performed at 1−85 bar and 77−298 K on the evacuated forms of seven porous covalent organic frameworks (COFs). The uptake behavior and capacity of the COFs is best described by classifying them into three groups based on their structural dimensions and corresponding pore sizes. Group 1 consists of 2D structures with 1D small pores (9 A for each of COF-1 and COF-6), group 2 includes 2D structures with large 1D pores (27, 16, and 32 A for COF-5, COF-8, and COF-10, respectively), and group 3 is comprised of 3D structures with 3D medium-sized pores (12 A for each of COF-102 and COF-103). Group 3 COFs outperform group 1 and 2 COFs, and rival the best metal−organic frameworks and other porous materials in their uptake capacities. This is exemplified by the excess gas uptake of COF-102 at 35 bar (72 mg g−1 at 77 K for hydrogen, 187 mg g−1 at 298 K for methane, and 1180 mg g−1 at 298 K for carbon dioxide), which is similar to the performance of COF...
2,102 citations
TL;DR: Different methods for hydrogen storage are discussed, including high-pressure and cryogenic-liquid storage, adsorptive storage on high-surface-area adsorbents, chemical storage in metal hydride and complex hydrides, and storage in boranes.
Abstract: Hydrogen is a promising energy carrier in future energy systems. However, storage of hydrogen is a substantial challenge, especially for applications in vehicles with fuel cells that use proton-exchange membranes (PEMs). Different methods for hydrogen storage are discussed, including high-pressure and cryogenic-liquid storage, adsorptive storage on high-surface-area adsorbents, chemical storage in metal hydrides and complex hydrides, and storage in boranes. For the latter chemical solutions, reversible options and hydrolytic release of hydrogen with off-board regeneration are both possible. Reforming of liquid hydrogen-containing compounds is also a possible means of hydrogen generation. The advantages and disadvantages of the different systems are compared.
1,222 citations
TL;DR: It is demonstrated that for maximum delivery of the gas the optimum adsorbent must be homogeneous, and that introduction of heterogeneity, such as by ball milling, irradiation, and other means, can only provide small increases in physisorption-related delivery for hydrogen.
Abstract: The storage of gases in porous adsorbents, such as activated carbon and carbon nanotubes, is examined here thermodynamically from a systems viewpoint, considering the entire adsorption-desorption cycle. The results provide concrete objective criteria to guide the search for the "Holy Grail" adsorbent, for which the adsorptive delivery is maximized. It is shown that, for ambient temperature storage of hydrogen and delivery between 30 and 1.5 bar pressure, for the optimum adsorbent the adsorption enthalpy change is 15.1 kJ/mol. For carbons, for which the average enthalpy change is typically 5.8 kJ/mol, an optimum operating temperature of about 115 K is predicted. For methane, an optimum enthalpy change of 18.8 kJ/mol is found, with the optimum temperature for carbons being 254 K. It is also demonstrated that for maximum delivery of the gas the optimum adsorbent must be homogeneous, and that introduction of heterogeneity, such as by ball milling, irradiation, and other means, can only provide small increases in physisorption-related delivery for hydrogen. For methane, heterogeneity is always detrimental, at any value of average adsorption enthalpy change. These results are confirmed with the help of experimental data from the literature, as well as extensive Monte Carlo simulations conducted here using slit pore models of activated carbons as well as atomistic models of carbon nanotubes. The simulations also demonstrate that carbon nanotubes offer little or no advantage over activated carbons in terms of enhanced delivery, when used as storage media for either hydrogen or methane.
932 citations
TL;DR: Main research trends on hydrogen storage materials, including metal hydrides, porous adsorbents and hydrogen clathrates, are reviewed with a focus on recent developments and an appraisal of the challenges ahead.
613 citations
TL;DR: In this article, a review focusing on various hydrogen producing and storing methods that can be employed for creating a hydrogen economy is presented, where the latest advancements that have been made on different hydrogen storing materials and hydrogen storing technologies which have proven useful both on gravimetric and volumetric basis, have been highlighted.
Abstract: The review focuses on various hydrogen producing and storing methods that can be employed for creating a hydrogen economy. The latest advancements that have been made on different hydrogen storing materials and hydrogen storing technologies which have proven useful both on gravimetric and volumetric basis, have been highlighted. The encouraging and hopeful aspect of their developments is that the most of the materials are approaching the hydrogen storing capacity requirement that have been laid down by DOE. The classification of different systems has been done on basis of their storage mechanism, keeping in mind their advantages and disadvantages while they tend to store hydrogen both in the atomic and molecular form.
606 citations
References
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Book•
01 Jan 1978TL;DR: In this article, the normal modes of vibration are illustrated and corresponding vibrational frequencies are listed for each type, including diatomic, triatomic, fouratomic, five-atomic, six-atomic and seven-atomic types.
Abstract: Inorganic molecules (ions) and ligands are classified into diatomic, triatomic, four-atomic, five-atomic, six-atomic, and seven-atomic types, and their normal modes of vibration are illustrated and the corresponding vibrational frequencies are listed for each type. Molecules of other types are grouped into compounds of boron, carbon, silicon, nitrogen, phosphorus, and sulfur, and the structures and infrared (IR)/Raman spectra of select examples are shown for each group. Group frequency charts including band assignments are shown for phosphorus and sulfur compounds. Other group frequency charts include hydrogen stretching frequencies, halogen stretching frequencies, oxygen stretching and bending frequencies, inorganic ions, and metal complexes containing simple coordinating ligands.
Keywords:
inorganic compounds;
coordination compounds;
diatomic molecules (ligands);
triatomic molecules (ligands);
four-atomic molecules (ligands);
five-atomic molecules (ligands);
six-atomic molecules (ligands);
seven-atomic molecules (ligands);
boron compounds;
carbon compounds;
silicon compounds;
nitrogen compounds;
phosphorus compounds;
sulfur compounds;
group frequency charts
15,951 citations
TL;DR: Recent developments in the search for innovative materials with high hydrogen-storage capacity are presented.
Abstract: Mobility — the transport of people and goods — is a socioeconomic reality that will surely increase in the coming years. It should be safe, economic and reasonably clean. Little energy needs to be expended to overcome potential energy changes, but a great deal is lost through friction (for cars about 10 kWh per 100 km) and low-efficiency energy conversion. Vehicles can be run either by connecting them to a continuous supply of energy or by storing energy on board. Hydrogen would be ideal as a synthetic fuel because it is lightweight, highly abundant and its oxidation product (water) is environmentally benign, but storage remains a problem. Here we present recent developments in the search for innovative materials with high hydrogen-storage capacity.
7,414 citations
Additional excerpts
...Previous strategies—where hydrogen has been bound chemicall...
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TL;DR: Inelastic neutron scattering spectroscopy of the rotational transitions of the adsorbed hydrogen molecules indicates the presence of two well-defined binding sites (termed I and II), which are associated with hydrogen binding to zinc and the BDC linker, respectively.
Abstract: Metal-organic framework-5 (MOF-5) of composition Zn4O(BDC)3 (BDC = 1,4-benzenedicarboxylate) with a cubic three-dimensional extended porous structure adsorbed hydrogen up to 4.5 weight percent (17.2 hydrogen molecules per formula unit) at 78 kelvin and 1.0 weight percent at room temperature and pressure of 20 bar. Inelastic neutron scattering spectroscopy of the rotational transitions of the adsorbed hydrogen molecules indicates the presence of two well-defined binding sites (termed I and II), which we associate with hydrogen binding to zinc and the BDC linker, respectively. Preliminary studies on topologically similar isoreticular metal-organic framework-6 and -8 (IRMOF-6 and -8) having cyclobutylbenzene and naphthalene linkers, respectively, gave approximately double and quadruple (2.0 weight percent) the uptake found for MOF-5 at room temperature and 10 bar.
4,284 citations
"Tuning clathrate hydrates for hydro..." refers background in this paper
...—have problems arising from either technical considerations or materials cos...
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Book•
30 Jul 1996
TL;DR: The aim of this book is to provide a history of Supramolecular Chemistry from its inception in the 1920s to the present day, with a focus on the period between 1950 and 1983.
Abstract: Volume 1 - Molecular Recognition: Receptors for Cationic Guests. Volume 2 - Molecular Recognition: Receptors for Molecular Guests. Volume 3 - Cyclodextrins. Volume 4 - Supramolecular Reactivity and Transport: Bioorganic Systems. Volume 5 - Supramolecular Reactivity and Transport: Bioinorganic Systems. Volume 6 - Solid-State Supramolecular Chemistry: Crystal Engineering. Volume 7 - Solid-State Supramolecular Chemistry: Two- and Three-Dimensional Inorganic Networks. Volume 8 - Physical Methods in Supramolecular Chemistry. Volume 9 - Templating Self-Assembly and Self-Organization. Voulme 10 - Supramolecular Technology. Volume 11 - Cumulative Index.
3,905 citations
TL;DR: High-pressure Raman, infrared, x-ray, and neutron studies show that H2 and H2O mixtures crystallize into the sII clathrate structure with an approximate H2/H2Omolar ratio of 1:2.
Abstract: High-pressure Raman, infrared, x-ray, and neutron studies show that H2 and H2O mixtures crystallize into the sII clathrate structure with an approximate H2/H2O molar ratio of 1:2. The clathrate cages are multiply occupied, with a cluster of two H2 molecules in the small cage and four in the large cage. Substantial softening and splitting of hydrogen vibrons indicate increased intermolecular interactions. The quenched clathrate is stable up to 145 kelvin at ambient pressure. Retention of hydrogen at such high temperatures could help its condensation in planetary nebulae and may play a key role in the evolution of icy bodies.
790 citations