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Hydrogen desorption studies of the Mg24Y5–H system: Formation of Mg tubes, kinetics and cycling effects
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Materials Chemistry, Inorganic Chemistry.
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2008 (English)In: Acta Materialia, ISSN 1359-6454, Vol. 56, no 11, 2421-2428 p.Article in journal (Refereed) Published
Abstract [en]

The current study focuses on the hydrogen desorption properties of hydrogenated Mg24Y5. Recently, we have reported the formation of unidirectional MgH2 structures by hydrogen absorption and induced disproportionation of Mg24Y5. During hydrogen desorption, a complex voiding phenomenon produces Mg tubes and carved particles with nano-sized walls. The selected area electron diffraction patterns demonstrate that the Mg tubes are single crystals. A harmonized picture of the unidirectional growth based on different Mg vapor models is proposed. The kinetic properties of hydrogen desorption are improved as compared with commercial MgH2. Hydrogenation/dehydrogenation cycling lowers the thermal stability of the hydrogen desorption at the expense of the total desorbed hydrogen capacity. Both whiskers and microparticles are depleted into clusters of nanoparticles after extensive cyclin

Place, publisher, year, edition, pages
2008. Vol. 56, no 11, 2421-2428 p.
Keyword [en]
Magnesium intermetallics, Hydrides, Microstructure, Hydrogen desorption
National Category
Inorganic Chemistry
URN: urn:nbn:se:uu:diva-17441DOI: 10.1016/j.actamat.2008.01.029ISI: 000257367800001OAI: oai:DiVA.org:uu-17441DiVA: diva2:45212
Available from: 2008-06-24 Created: 2008-06-24Bibliographically approved
In thesis
1. Light-Metal Hydrides for Hydrogen Storage
Open this publication in new window or tab >>Light-Metal Hydrides for Hydrogen Storage
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Demands for zero greenhouse-gas emission vehicles have sharpened with today’s increased focus on global warming. Hydrogen storage is a key technology for the implementation of hydrogen powered vehicles. Metal hydrides can claim higher energy densities than alternative hydrogen storage materials, but a remaining challenge is to find a metal hydride which satisfies all current demands on practical usability. Several metals store large amounts of hydrogen by forming a metal hydride, e.g., Mg, Ti and Al. The main problems are the weight of the material and the reaction energy between the metal and hydrogen.

Magnesium has a high storage capacity (7.6 wt.% hydrogen) in forming MgH2; this is a slow reaction, but can be accelerated either by minimizing the diffusion length within the hydride or by changing the diffusion properties. Light-metal hydrides have been studied in this thesis with the goal of finding new hydrogen storage compounds and of gaining a better understanding of the parameters which determine their storage properties. Various magnesium-containing compounds have been investigated. These systems represent different ways to address the problems which arise in exploiting magnesium based materials. The compounds were synthesized in sealed tantalum tubes, and investigated by in situ synchrotron radiation X-ray powder diffraction, neutron powder diffraction, isothermal measurements, thermal desorption spectroscopy and electron microscopy.

It is demonstrated that hydrogen storage properties can be improved by alloying magnesium with yttrium or scandium. Mg-Y-compounds decompose in hydrogen to form MgH2 nano-structures. Hydrogen desorption kinetics are improved compared to pure MgH2. The influence of adding a third element, gallium or zinc has also been studied; it is shown that gallium improves hydrogen desorption from YH2. ScAl1-xMgx is presented here for the first time as a hydrogen storage material. It absorbs hydrogen by forming ScH2 and Al(Mg) in a fully reversible reaction. It is shown that the hydrogen desorption temperature of ScH2 is reduced by more than 400 °C by alloying with aluminium and magnesium.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2009. 56 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 666
Metal-hydrogen compounds, hydrides, hydrogen storage, X-ray diffraction, neutron diffraction, thermal desorption spectroscopy
National Category
Chemical Sciences Inorganic Chemistry
Research subject
Inorganic Chemistry
urn:nbn:se:uu:diva-107380 (URN)978-91-554-7585-7 (ISBN)
Public defence
2009-09-25, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Available from: 2009-09-04 Created: 2009-08-10 Last updated: 2009-09-04Bibliographically approved

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Sahlberg, MartinAndersson, Yvonne
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