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Synthesis and Characterisation of Potential Hydrogen Storage Materials
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics, Physics III.
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The dissociative and non-dissociative hydrogen uptake in carbon nanostructures and metallic films were investigated by measurements and analysis of solubility isotherms. The total, non-dissociative, uptake for multi-walled nano-barrels and amorphous nanoporous carbon was determined to be 6.2 and 4.2 wt. % respectively at 77 K and the adsorption energies (at lowest coverage) -7.2 and -4.2 kJ/mol. At 298 K the H-uptake was negligible.

At low concentrations the H-uptake of Nb-films is strongly affected by the film thickness. For thicknesses less then about 31 nm, the absorption energy was found to be temperature dependent. Such changes have not been observed in Nb films before. The presence of multiple absorption energies was shown to limit the possibility to obtain relevant absorption and interaction energies by traditional Sievert's and van 't Hoff analysis.

The Mg1-xNix system (0<0.43) was investigated with respect to the hydrogen uptake. For Mg2Ni the hydrogen uptake, at an external hydrogen pressure of 1 bar, is close to 1.33 H/M (Mg2NiH4). The enthalpy of formation is smaller in the film as compared to bulk material. The changes in the absorption energy are caused by the adhesion to the substrate as well as the nanocrystallinity of the absorbing layers. The optical band gap of Mg2NiH4 was determined to be 2.4 eV.

In Mg1-xYx (0<0.17) it was found that the Y-concentration limits the hydrogen uptake at 1 bar. However, the kinetics of the uptake improves substantially with a minimum of 7 at.% of Y. For Mg-Y the optical band gap (3.6 eV) is independent of Y concentration within the concentration range investigated, while the transmittance decreases with increasing Y content.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis , 2004. , p. 74
Series
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 1005
Keywords [en]
Physics, Hydrogen, adsorption, absorption, thermodynamics, thin films, carbon nanostructures
Keywords [sv]
Fysik
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-4509ISBN: 91-554-6020-8 (print)OAI: oai:DiVA.org:uu-4509DiVA, id: diva2:164982
Public defence
2004-09-23, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Polacksbacken, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2004-09-01 Created: 2004-09-01 Last updated: 2009-04-30Bibliographically approved
List of papers
1. Hydrogen in carbon nanostructures
Open this publication in new window or tab >>Hydrogen in carbon nanostructures
2002 (English)In: Journal of Alloys and Compounds, ISSN 0925-8388, Vol. 330-332, p. 670-675Article in journal (Refereed) Published
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-92034 (URN)
Available from: 2004-09-01 Created: 2004-09-01 Last updated: 2012-03-07Bibliographically approved
2. Solubility of hydrogen at low concentrations in thin epitaxial Nb(110) films
Open this publication in new window or tab >>Solubility of hydrogen at low concentrations in thin epitaxial Nb(110) films
2004 (English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984, Vol. 16, p. 1165-1174Article in journal (Refereed) Published
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-92035 (URN)
Available from: 2004-09-01 Created: 2004-09-01 Last updated: 2012-03-07Bibliographically approved
3. Hydrogen uptake and optical properties of sputtered Mg-Ni thin films
Open this publication in new window or tab >>Hydrogen uptake and optical properties of sputtered Mg-Ni thin films
Show others...
(English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984Article in journal (Refereed) Submitted
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-92036 (URN)
Available from: 2004-09-01 Created: 2004-09-01 Last updated: 2012-03-07Bibliographically approved
4. Structural and optical properties of Mg2NiHx switchable mirrors upon hydrogen loading
Open this publication in new window or tab >>Structural and optical properties of Mg2NiHx switchable mirrors upon hydrogen loading
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2004 (English)In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 70, p. 165411-Article in journal (Refereed) Published
Abstract [en]

The structural, thermodynamic and optical properties of Mg2Ni thin films covered with Pd are investigatedupon exposure to hydrogen. Similar to bulk, thin films of metallic Mg2Ni take up 4 hydrogen per formula unitand semiconducting transparent Mg2NiH4−d is formed. The dielectric function e˜ of Mg2Ni and fully loadedMg2NiH4−d is determined from reflection and transmission measurements using a Drude-Lorentz parametrization.Besides the two “normal” optical states of a switchable mirror—metallic reflecting and semiconductingtransparent—Mg2NiHx exhibit a third “black” state at intermediate hydrogen concentrations with low reflectionand essentially zero transmission. This state originates from a subtle interplay of the optical properties of theconstituent materials and a self-organized double layering of the film during loading. Mg2NiH4−d preferentiallynucleates at the film/substrate interface and not—as intuitively expected—close to the catalytic Pd cappinglayer. Using e˜Mg2Ni and e˜Mg2NiH4and this loading sequence, the optical response at all hydrogen concentrationscan be described quantitatively. The uncommon hydrogen loading sequence is confirmed by x-ray diffractionand hydrogen profiling using the resonant nuclear reaction 1Hs15N,agd12C. Pressure-composition isothermssuggest that

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-92037 (URN)10.1103/PhysRevB.70.165411 (DOI)
Available from: 2004-09-01 Created: 2004-09-01 Last updated: 2017-12-14Bibliographically approved
5. Hydrogen solubility at low concentrations in sputtered Mg-Ni thin films
Open this publication in new window or tab >>Hydrogen solubility at low concentrations in sputtered Mg-Ni thin films
(English)Manuscript (Other (popular science, discussion, etc.))
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-92038 (URN)
Available from: 2004-09-01 Created: 2004-09-01 Last updated: 2012-03-07Bibliographically approved
6. Growth and hydrogen uptake of Mg-Y thin films
Open this publication in new window or tab >>Growth and hydrogen uptake of Mg-Y thin films
Show others...
(English)Manuscript (Other (popular science, discussion, etc.))
National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-92039 (URN)
Available from: 2004-09-01 Created: 2004-09-01 Last updated: 2012-01-27Bibliographically approved

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