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Computational Studies of Hydrogen Storage Materials: Physisorbed and Chemisorbed  Systems
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. (Condensed Matter Theory)
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis deals with first-principles calculations based on density functional theory to investigate hydrogen storage related properties in various high-surface area materials and the ground state crystal structures in alkaline earth dicarbide systems.

High-surface area materials have been shown to be very promising for hydrogen storage applications owing to them containing numerous hydrogen adsorption sites and good kinetics for adsorption/desorption. However, one disadvantage of these materials is their very weak interaction with adsorbed hydrogen molecules. Hence, for any feasible applications, the hydrogen interaction energy of these materials must be enhanced.  In metal organic frameworks, approaches for improving the hydrogen interaction energy are opening the metal oxide cluster and decorating hydrogen attracting metals, e.g. Li, at the adsorption sites of the host.  In covalent organic framework-1, the effects of the H2-H2 interaction are also found to play a significant role for enhancing the hydrogen adsorption energy. Moreover, ab initio molecular dynamics simulations reveal that hydrogen molecules can be trapped in the host material due to the blockage from adjacent adsorbed hydrogen molecules.

In light metal hydride systems, hydrogen ions play two different roles, namely they can behave as "promoter" and "inhibitor" of Li diffusion in lithium imide and lithium amide, respectively.  By studying thermodynamics of Li+ and proton diffusions in the mixture between lithium amide and lithium hydride, it was found that Li+ and proton diffusions inside lithium amide are more favorable than those between lithium amide and lithium hydride.

Finally, our results show that the ground state configuration of BeC2 and MgC2 consists of five-membered carbon rings connected through a carbon atom forming an infinitely repeated chain surrounded by Be/Mg ions, whereas the stable crystal structure of the CaC2, SrC2 and BaC2 is the chain type structure, commonly found in the alkaline earth dicarbide systems.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis , 2010. , p. 90
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 782
Keyword [en]
Density functional theory, Ab initio molecular dynamics, Ab initio random structure searching, Hydrogen storage materials, Alkaline earth dicarbide
National Category
Condensed Matter Physics
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
URN: urn:nbn:se:uu:diva-132875ISBN: 978-91-554-7933-6 (print)OAI: oai:DiVA.org:uu-132875DiVA, id: diva2:359504
Public defence
2010-12-10, Å80101, Ångström Laboratory, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Note
Felaktigt tryckt som Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology 712Available from: 2010-11-19 Created: 2010-10-28 Last updated: 2011-03-21Bibliographically approved
List of papers
1. A comparative investigation of H-2 adsorption strength in Cd- and Zn-based metal organic framework-5
Open this publication in new window or tab >>A comparative investigation of H-2 adsorption strength in Cd- and Zn-based metal organic framework-5
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2008 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 129, no 16, p. 164104-164104-5Article in journal (Refereed) Published
Abstract [en]

Hydrogen binding energies for the primary and secondary adsorption sites in the Cd- and Zn-based metal organic framework-5 (MOF-5) were studied using density functional theory. Out of the three exchange-correlation functionals employed in our study, we find that the local density approximation yields a qualitatively correct description of the interaction strengths of H-2 in MOF-5 systems. The H-2 adsorption energies for all trapping sites in Zn- and Cd-based MOF-5 are seen to be of the same order of magnitude but with a generally stronger binding in Cd- based MOF-5 as compared to Zn- based MOF-5. In particular, the H-2 binding energy at the secondary adsorption sites in Cd- based MOF-5 is increased by around 25% compared to Zn-based MOF-5. This result suggests that Cd- based MOF-5 would be better suited to store hydrogen at higher temperatures than Zn-based MOF-5.

Keyword
Direct energy conversion and storage, Chemisorption/physisorption: adsorbates on surfaces, Density functional theory, local density approximation, gradient and other corrections
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-107093 (URN)10.1063/1.2997377 (DOI)000260572300007 ()
Available from: 2009-07-16 Created: 2009-07-16 Last updated: 2017-12-13Bibliographically approved
2. Ab Initio Study of Molecular Hydrogen Adsorption in Covalent Organic Framework-1
Open this publication in new window or tab >>Ab Initio Study of Molecular Hydrogen Adsorption in Covalent Organic Framework-1
Show others...
2009 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 113, no 19, p. 8498-8504Article in journal (Refereed) Published
Abstract [en]

The adsorption energies of hydrogen molecules at all possible adsorption sites of covalent organic framework-1 (COF-1) are studied by density functional theory (DFT) and second-order Moller-Plesset perturbation theory (MP2). The most favorable adsorption sites from our DFT results are on the top of an oxygen atom for the B3O3 ring and on the top of the center of the C-C bond for the benzene ring when a single H-2 is interacting with the COF-1. The adsorption energy trend obtained from the DFT calculations is found to be in good agreement with the MP2 binding energy trend. The binding preferences are slightly changed when high hydrogen loading is considered. H-2 molecules prefer to be trapped on the top of the carbon atoms of the benzene ring and also on the top of the oxygen atoms of the B3O3 ring. These findings are confirmed by hydrogen center-of-mass distribution results obtained using molecular dynamics simulations. Moreover, our DFT results reveal that the hydrogen adsorption energies are boosted when we increase the number of hydrogen loadings due to attractive H-2-H-2 interactions. In addition, the nonavailability of the remaining adsorption sites in the COF-1 leads to a reduction of the H-2 mobility.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-129067 (URN)10.1021/jp809167b (DOI)000265895500075 ()
Available from: 2010-08-06 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
3. Li-decorated metal-organic framework-5: A route to achieving a suitable hydrogen storage medium
Open this publication in new window or tab >>Li-decorated metal-organic framework-5: A route to achieving a suitable hydrogen storage medium
2007 (English)In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 104, no 51, p. 20173-Article in journal (Refereed) Published
Abstract [en]

A significant improvement in molecular hydrogen uptake properties is revealed by our ab initio calculations for Li-decorated metal-organic framework 5. We have found that two Li atoms are strongly adsorbed on the surfaces of the six-carbon rings, one on each side, carrying a charge of +0.9e per Li atom. Each Li can cluster three H-2 molecules around itself with a binding energy of 12 kJ (mol H-2)(-1). Furthermore, we show from ab initio molecular dynamics simulations with a hydrogen loading of 18 H2 per formula unit that a hydrogen uptake of 2.9 wt % at 200 K and 2.0 wt % at 300 K is achievable. To our knowledge, this is the highest hydrogen storage capacity reported for metal-organic framework 5 under such thermodynamic conditions.

Keyword
first-principles calculations, molecular adsorption, molecular dynamics, porous materials
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-96890 (URN)10.1073/pnas.0708603104 (DOI)000251885000006 ()
Available from: 2008-03-20 Created: 2008-03-20 Last updated: 2017-12-14Bibliographically approved
4. Hydrogen Binding in Alkali-decorated Iso-reticular Metal Organic Framework-16 based on Zn, Mg, and Ca
Open this publication in new window or tab >>Hydrogen Binding in Alkali-decorated Iso-reticular Metal Organic Framework-16 based on Zn, Mg, and Ca
Show others...
2011 (English)In: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 36, no 1, p. 555-562Article in journal (Refereed) Published
Abstract [en]

Hydrogen adsorption energies were investigated in three different types of iso-reticular Metal Organic Framework-16, Zn-/Mg-/Ca-MOF16, decorated with either Li, Na, or K. Concerning the binding strengths of the alkali metals, the density functional theory calculations reveal that Li is bound strongest to the host framework, followed by K and Na. Decoration with Li also results in the highest hydrogen adsorption energies among the studied alkali metals. Furthermore, Zn-MOF16 exhibits the highest hydrogen adsorption energies near the metal oxide cluster, while hydrogen binding strengths at organic linker sites do not differ substantially between Zn-/Mg-/Ca-MOF16. Based on these results, we conclude that for Metal Organic Framework-16, Li-decorated Zn-MOF16 appears to be the optimal choice for hydrogen storage among the nine combinations.

Keyword
Hydrogen Storage, Metal Organic Frameworks, Hydrogen adsorption energy
National Category
Condensed Matter Physics Other Materials Engineering
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-132780 (URN)10.1016/j.ijhydene.2010.10.035 (DOI)000288102700058 ()
Available from: 2010-10-26 Created: 2010-10-26 Last updated: 2017-12-12Bibliographically approved
5. Hydrogen as promoter and inhibitor of superionicity: A case study on Li-N-H systems
Open this publication in new window or tab >>Hydrogen as promoter and inhibitor of superionicity: A case study on Li-N-H systems
Show others...
2010 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 82, no 2, p. 024304-Article in journal (Refereed) Published
Abstract [en]

Materials which possess a high lithium ion conductivity are very attractive for battery and fuel cell applications. Hydrogenation of the fast-ion conductor lithium nitride (Li3N) leads to the formation of lithium imide (Li2NH) and subsequently of lithium amide (LiNH2). Using ab initio molecular dynamics simulations, we carried out a comparative study of the Li diffusion in these three systems. The results demonstrate that hydrogen can work as both promoter and inhibitor of Li mobility, with the lowest transition temperature to the superionic state occurring in Li2NH. Furthermore, we show that the creation of Li vacancies strongly affects Li diffusion in Li3N, but not so in Li2NH. Finally, we explain our findings with the help of a simple model.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-130225 (URN)10.1103/PhysRevB.82.024304 (DOI)000280293100001 ()
Available from: 2010-09-04 Created: 2010-09-04 Last updated: 2017-12-12Bibliographically approved
6. Li+ and H+ Diffusions in Lithium Amide and Hydride: A first-principles study
Open this publication in new window or tab >>Li+ and H+ Diffusions in Lithium Amide and Hydride: A first-principles study
(English)Manuscript (preprint) (Other academic)
Abstract [en]

In the present work, the reaction energies of Li+ and H+ migrations with two different situations, namely inside LiNH2 and between LiNH2 and LiH are determined by the density functional theory. Our results reveal that the Li+ migrations in both cases are rather easy. However, H+ diffusion from LiNH2 to LiH is found to be more difficult than that inside LiNH2. Consequently, diffusions of Li+ and H+ inside LiNH2 are more favorable than those between LiNH2 and LiH. Finally, the migration energies of Li+ and H+ migrations in LiNH2 are determined by the nudged elastic band method and we found that Li+ and H+ migration energy barriers in LiNH2 are 0.30 and 0.58 eV, respectively.

Keyword
Lithium-hydrogen-nitrogen system, reaction energy, migration energy
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-132781 (URN)
Available from: 2010-10-26 Created: 2010-10-26 Last updated: 2012-03-29
7. One-dimensional polymeric carbon structure based on five-membered rings in alkaline earth metal dicarbides BeC2 and MgC2
Open this publication in new window or tab >>One-dimensional polymeric carbon structure based on five-membered rings in alkaline earth metal dicarbides BeC2 and MgC2
Show others...
2010 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 82, no 12, p. 125439-Article in journal (Refereed) Published
Abstract [en]

We studied five alkaline earth dicarbide systems MAEC2 (where M-AE =   Be-Ba) by using ab initio random structure search. For BeC2 and MgC2,   the lowest energy and dynamically stable configuration consists of five-membered carbon rings connected to each other via an individual  arbon atom, stabilized through the donation of electrons from the   surrounding alkaline earth ions. For CaC2, SrC2, and BaC2, our study   shows that the chain crystal structure is more stable than the   predicted structure due to strains induced by the increasing size of   alkaline earth metal ions. The reaction energies of the typical synthesis pathway are comparable to those calculated for the experimental reaction of the known chain-type structure. Finally, the proposed structure should be optically distinguishable due to a   significantly narrower band gap.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-131049 (URN)10.1103/PhysRevB.82.125439 (DOI)000282009000006 ()
Available from: 2010-09-22 Created: 2010-09-22 Last updated: 2017-12-12Bibliographically approved

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