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Structural Basis for Hydrogen Interaction in Selected Metal Hydrides
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström. (Inorganic Chemistry)ORCID iD: 0000-0002-4752-5491
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Metal hydrides have existing and potential uses in many applications such as in batteries, for hydrogen storage and for heat storage. New metal hydrides and a better understanding of the behaviour of known metal hydrides may prove crucial in the realisation or further development of these applications. The aims of the work described in this thesis have been to characterise new metal hydrides, investigate how the properties of known metal hydrides can be improved and understand how their structure influences these properties. Metal hydrides, in most cases synthesised via high-temperature techniques, were structurally characterised using X-ray powder diffraction, X-ray single crystal diffraction and neutron powder diffraction and their thermodynamic and kinetic properties by in-situ X-ray powder diffraction, thermal desorption spectroscopy and pressure-composition-temperature measurements.

The investigations showed that: the storage capacity of the hexagonal Laves phase Sc(Al1-xNix)2 decreases with increasing Al content. There is a significant decrease in the stability of the hydrides and faster reaction kinetics when Zr content is increased in the cubic Laves phase Sc1-xZrx(Co1-xNix)2. Nb4M0.9Si1.1 (M=Co, Ni) form very stable interstitial hydrides which have very slow sorption kinetics. MgH2 mixed with 10 mol% ScH2 reaches full activation after only one cycle at 673 K while it takes at least four cycles at 593 K. LnGa (Ln=Nd, Gd) absorb hydrogen in two steps, it is very likely that the first step is interstitial solution of hydride ions into Ln4 tetrahedra and the second step places hydrogen atoms in Ln3Ga tetrahedra. The nature of the Ga-H bond is still unclear.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2015. , 74 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1234
National Category
Metallurgy and Metallic Materials Materials Chemistry Inorganic Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-245046ISBN: 978-91-554-9187-1 (print)OAI: oai:DiVA.org:uu-245046DiVA: diva2:793013
Public defence
2015-04-24, Häggsalen, Ångströmlaboratoriet Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Funder
Swedish Research Council
Available from: 2015-04-01 Created: 2015-02-24 Last updated: 2015-09-07
List of papers
1. Hydrogen absorption and desorption properties of a novel ScNiAl alloy
Open this publication in new window or tab >>Hydrogen absorption and desorption properties of a novel ScNiAl alloy
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2011 (English)In: Applied Physics A: Materials Science & Processing, ISSN 0947-8396, E-ISSN 1432-0630, Vol. 104, no 1, 235-238 p.Article in journal (Refereed) Published
Abstract [en]

A new hydrogen absorbing material has been discovered, ScNiAl, which can store 1.5 wt.% hydrogen reversibly. In this compound, hydrogen absorption is a two-step process; solid solution of hydrogen at temperatures below 180A degrees C and decomposition into ScH2 and NiAl at higher temperatures. Detailed analysis of the hydrogen absorption/desorption has been performed using in situ synchrotron radiation powder X-ray diffraction and thermal desorption spectroscopy. The apparent activation energy for hydrogen desorption was determined to be 182 kJ/mol and the material is stable during cycling.

National Category
Natural Sciences Inorganic Chemistry
Research subject
Chemistry with specialization in Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-156009 (URN)10.1007/s00339-010-6116-z (DOI)000291652600034 ()
Available from: 2011-07-05 Created: 2011-07-05 Last updated: 2017-12-11Bibliographically approved
2. Structure and hydrogen storage properties of the hexagonal Laves phase Sc(Al1-xNix)2
Open this publication in new window or tab >>Structure and hydrogen storage properties of the hexagonal Laves phase Sc(Al1-xNix)2
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2012 (English)In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 196, 132-137 p.Article in journal (Refereed) Published
Abstract [en]

The crystal structures of hydrogenated and unhydrogenated Sc(Al 1-xNi x) 2 Laves phases have been studied by combining several diffraction techniques and it is shown that hydrogen is situated interstitially in the A 2B 2-sites, which have the maximum number of scandium neighbours. The hydrogen absorption/desorption behaviour has also been investigated. It is shown that a solid solution of hydrogen forms in the mother compound. The hydrogen storage capacity exceeds 1.7 H/f.u. at 374 K, and the activation energy of hydrogen desorption was determined to 4.6 kJ/mol H 2. It is shown that these compounds share the same local coordination as Frank-Kasper-type approximants and quasicrystals, which opens up the possibility of finding many new hydride phases with these types of crystal structures.

Keyword
Hydrogen storage, Metal hydrides, X-ray diffraction, Approximants, Diffraction techniques, Hydrogen absorption, Hydrogen desorption, Hydrogen forms, Hydrogen storage capacities, Hydrogen storage properties, Laves phasis, Laves-phase, Local coordination, Mother compounds, New hydrides, Activation energy, Desorption, Hydrides, Hydrogen, X ray diffraction, Scandium
National Category
Chemical Sciences
Identifiers
urn:nbn:se:uu:diva-184879 (URN)10.1016/j.jssc.2012.06.002 (DOI)000310394500019 ()
Available from: 2012-11-21 Created: 2012-11-15 Last updated: 2017-12-07
3. Hydrogen storage properties of the pseudo binary Laves phase (Sc1-xZrx)(Co1-yNiy)2 system
Open this publication in new window or tab >>Hydrogen storage properties of the pseudo binary Laves phase (Sc1-xZrx)(Co1-yNiy)2 system
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2013 (English)In: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 38, no 23, 9772-9778 p.Article in journal (Refereed) Published
Abstract [en]

The (Sc1-xZrx)(Co1-yNiy)(2)-H-z system has been studied using both experimental techniques and ab initio calculations. The material was synthesised through high temperature synthesis and characterised using powder XRD. Hydrogen absorption and desorption was studied in-situ using synchrotron radiation. Maximal storage capacity increased when Co replaced Ni and substitution of Sc for Zr increased the equilibrium pressure. Density functional based calculations reproduce the experimental trends in terms of cell parameters both for the non-hydrogenated systems as well as for the hydrogenated systems, and helped to quantitatively understand the observed hydrogen uptake properties. 

Keyword
Laves phase, Metal hydride, Hydrogen storage, In-situ diffraction, Ab initio
National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-206981 (URN)10.1016/j.ijhydene.2013.05.053 (DOI)000322500800018 ()
Available from: 2013-09-09 Created: 2013-09-09 Last updated: 2017-12-06
4. Activation effects during hydrogen release and uptake of MgH2
Open this publication in new window or tab >>Activation effects during hydrogen release and uptake of MgH2
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2014 (English)In: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 39, no 18, 9888-9892 p.Article in journal (Refereed) Published
Abstract [en]

Scandium(II)hydride, ScH2, and scandium(III)chloride, ScCl3, are explored as additives to facilitate hydrogen release and uptake for magnesium hydride. These additives are expected to form more homogeneous composites with Mg/MgH2 as compared to metallic scandium. However, scandium(III)chloride, reacts with MgH2 during mechano-chemical treatment and form ScH2 and MgCl2 (that later crystallise during heat treatment). The composite MgH2-ScH2 was investigated using in-situ synchrotron radiation powder X-ray diffraction during up to five cycles of continuous release and uptake of hydrogen at isothermal conditions at 320, 400 and 450 degrees C and p(H-2) = 100-150 or 10(-2) bar. The data were analysed by Rietveld refinement and no reaction is observed between either MgH2/ScH2 or Mg/ScH2 during cycling. The extracted sigmoidal shaped curves for formation or decomposition of Mg/MgH2 suggest that a nucleation process is preceding the crystal growth. The reaction rate increases with increasing number of cycles of hydrogen release and uptake at isothermal conditions possibly due to activation effects. This kinetic enhancement is strongest between the first cycles and may be denoted an activation effect. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Keyword
Hydrogen storage, Magnesium hydride, Scandium(II)hydride, Scandium(III)chloride, In situ synchrotron powder X-ray diffraction
National Category
Chemical Sciences
Identifiers
urn:nbn:se:uu:diva-229295 (URN)10.1016/j.ijhydene.2014.02.112 (DOI)000337859700039 ()
Available from: 2014-08-06 Created: 2014-08-05 Last updated: 2017-12-05
5. Hydrogen-sorption properties of Nb4M0.9Si1.1 (M = Co,Ni) hydrides
Open this publication in new window or tab >>Hydrogen-sorption properties of Nb4M0.9Si1.1 (M = Co,Ni) hydrides
2015 (English)In: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 40, no 6, 2692-2697 p.Article in journal (Refereed) Published
Keyword
PCT, TDS, phase analysis, metal hydride, x-ray diffraction
National Category
Inorganic Chemistry
Research subject
Chemistry
Identifiers
urn:nbn:se:uu:diva-245041 (URN)10.1016/j.ijhydene.2014.12.031 (DOI)000349738300025 ()
Funder
Swedish Research Council
Available from: 2015-02-24 Created: 2015-02-24 Last updated: 2017-12-04Bibliographically approved
6. Hydrogen Absorption in Rare-Earth-Gallide Zintl-Phases LnGa (Ln=Nd, Gd)
Open this publication in new window or tab >>Hydrogen Absorption in Rare-Earth-Gallide Zintl-Phases LnGa (Ln=Nd, Gd)
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(English)Manuscript (preprint) (Other academic)
Keyword
Zintl phase, Metal Hydride, Neutron Diffraction, in-situ diffraction, structure determination
National Category
Inorganic Chemistry
Research subject
Chemistry
Identifiers
urn:nbn:se:uu:diva-245042 (URN)
Funder
Swedish Research Council
Available from: 2015-02-24 Created: 2015-02-24 Last updated: 2015-09-07

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