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Structural, electronic and thermodynamic properties of Al- and Si-doped alpha-, gamma-, and beta-MgH2: Density functional and hybrid density functional calculations
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
2012 (English)In: International journal of hydrogen energy, ISSN 0360-3199, Vol. 37, no 11, 9112-9122 p.Article in journal (Refereed) Published
Abstract [en]

In this work, we present a detailed study of Al- and Si-doped alpha-, gamma-, and beta-MgH2 phases using the gradient corrected density functional GGA-PBE and the hybrid Hartree-Fock density functionals PBE0 and HSE06 within the framework of generalized Kohn-Sham density functional theory (DFT) using a plane-wave basis set. We investigate the structural, electronic, and thermodynamical properties of these compounds with regard to their hydrogen storage effectiveness. PBE0 and HSE06 predict cell parameters and bond lengths that are in good agreement with the GGA-PBE calculations and previously known experimental results. As expected smaller band gaps (E(g)s) are predicted by GGA-PBE for the pure magnesium hydride phases. PBE0 overcomes the deficiencies of DFT in treating these materials better than HSE06 and yields E(g)s that compare even better with previous GW calculations. Both the hybrid functionals increase the E(g)s of the Al-doped magnesium hydrides by much less magnitudes than of the Si-doped phases. This difference is interpreted in terms of charge density distributions. Best H-2 adsorption energies (Delta H-ads) are computed by HSE06 while GGA-PBE significantly overestimates them. Si-doped alpha- and beta-MgH2 exhibited the least negative Delta H-ads in close proximity to the H-2 binding energy range of -0.21 to -0.41 eV ideal for practical H-2 storage transportation applications.

Place, publisher, year, edition, pages
2012. Vol. 37, no 11, 9112-9122 p.
Keyword [en]
Hybrid density functionals, Magnesium hydride, Hydrogen storage, Density of states
National Category
Natural Sciences
URN: urn:nbn:se:uu:diva-177237DOI: 10.1016/j.ijhydene.2012.03.038ISI: 000304976300021OAI: oai:DiVA.org:uu-177237DiVA: diva2:540270
Available from: 2012-07-09 Created: 2012-07-04 Last updated: 2014-01-23Bibliographically approved
In thesis
1. Computational Insights on Functional Materials for Clean Energy Storage: Modeling, Structure and Thermodynamics
Open this publication in new window or tab >>Computational Insights on Functional Materials for Clean Energy Storage: Modeling, Structure and Thermodynamics
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The exponential increase in the demands of world’s energy and the devastating effects of current fossil fuels based sources has forced us to reduce our dependence on the current sources as well as finding cleaner, cheaper and renewable alternates. Being abundant, efficient and renewable, hydrogen can be opted as the best possible replacement of the diminishing and harmful fossil fuels. But the transformation towards the hydrogen-based economy is hindered by the unavailability of suitable storage medium for hydrogen. First principles calculations based on density functional theory has been employed in this thesis to investigate the structures modelling and thermodynamics of various efficient materials capable of storing hydrogen under chemisorption and physisorption mechanisms.

Thanks to their high storage capacity, abundance and low cost, metal hydride (MgH2) has been considered as promising choice for hydrogen storage. However, the biggest drawback is their strong binding with the absorbed hydrogen under chemisorption, which make them inappropriate for operation at ambient conditions. Different strategies have been applied to improve the thermodynamics including doping with light and transitions metals in different phases of MgH2 in bulk form.  Application of mechanical strain along with Al, Si and Ti doping on MgH2 (001) and (100) surfaces has also been found very useful in lowering the dehydrogenation energies that ultimately improve adsorption/desorption temperatures.

Secondly, in this thesis, two-dimensional materials with high surface area have been studied for the adsorption of hydrogen in molecular form (H2) under physisorption. The main disadvantage of this kind of storage is that the adsorption of H2 with these nanostructures likes graphane, silicene, silicane, BN-sheets, BC3 sheets are low and demand operation at cryogenic conditions. To enhance the H2 binding and attain high storage capacity the above-mentioned nanostructures have been functionalized with light metals (alkali, alkaline) and polylithiated species  (OLi2, CLi3, CLi4). The stabilities of the designed functional materials for H2 storage have been verified by means of molecular dynamics simulations.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2013. 66 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1073
Density functional theory, Molecular dynamics, Hydrogen storage, Chemisorption, Physisorption, Functionalization
National Category
Condensed Matter Physics
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
urn:nbn:se:uu:diva-206938 (URN)978-91-554-8751-5 (ISBN)
Public defence
2013-10-28, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Available from: 2013-10-04 Created: 2013-09-07 Last updated: 2014-01-23

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Maark, Tuhina AditHussain, TanveerAhuja, Rajeev
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