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Hydrogen in nano-sized metals: Diffusion and hysteresis effects
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Physics.
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Metal hydrides can be used as hydrogen storage materials for fuel cells and batteries, and as sensors for detecting hydrogen gas. The use of metal hydrides for hydrogen storage can be hindered by poor kinetics and low capacity. Moreover, poor sensitivity, long recovery and response time, limit the applications of metal hydrides as hydrogen sensors. Diffusion is an important factor affecting the hydrogen kinetics and response time. Hysteresis effects accompany the phase transition of hydrogen in metals and can influence the properties of metal hydrides as well. These need to be considered in their applications as storage materials or sensors.

This thesis concerns the possibility of tuning hydrogen diffusion and studies the mechanism of hysteresis effects of hydrogen absorption in metals. In these experiments, nano-sized vanadium is used as the model system for these studies. Hydrogen concentration is determined by the light transmission. By measuring the concentration profiles and isotherms of hydrogen, it is possible to determine the diffusion coefficients and hysteresis effects.

A profound decrease of hydrogen diffusion in Fe/V(001) superlattice has been found, as compared to that in bulk vanadium. This result is interpreted as lower zero-point energy in octahedral site than that in tetrahedral site. Profound isotope effect on diffusion has also been found. Influence of clamping of the substrate on the diffusion of hydrogen with concentration in vanadium thin film is discovered. The diffusion coefficient below c = 0.1 [H/V] is close to that in bulk vanadium and decreases substantially when c > 0.1 [H/V] compared with that in bulk vanadium. This finding is interpreted as the site change from tetrahedral to octahedral occupancy when the hydrogen concentration increases. Large finite size effect on deuterium chemical diffusion is observed, which is concluded to be caused by D-D interaction change that will influence the deuterium chemical diffusion at different thickness of vanadium layers. However, finite size has no effect on hydrogen transport at extremely low hydrogen concentrations in Fe/V (001) superlattices, this illustrates that the interface can not influence the mean free path of hydrogen in any way. This is completely different from electron transport condition in nano-sized metals. Hysteresis effect is observed below critical temperature in Fe/V(001) superlattices; this occurrence confirms the hypothesis that hysteresis effect is caused by coherency strain in coherent  transformation.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. , p. 61
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1523
Keywords [en]
Hydrogen, diffusion, hysteresis, optical technique
National Category
Natural Sciences
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
URN: urn:nbn:se:uu:diva-320796ISBN: 978-91-554-9928-0 (print)OAI: oai:DiVA.org:uu-320796DiVA, id: diva2:1090959
Public defence
2017-06-13, Ång/4001, Lägerhyddsvägen 1, Uppsala, 13:30 (English)
Opponent
Supervisors
Available from: 2017-05-22 Created: 2017-04-25 Last updated: 2017-06-08
List of papers
1. The influence of site occupancy on diffusion of hydrogen in vanadium
Open this publication in new window or tab >>The influence of site occupancy on diffusion of hydrogen in vanadium
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2017 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 95, no 6, article id 064310Article, review/survey (Refereed) Published
Abstract [en]

We investigate the effect of site occupancy on the chemical diffusion of hydrogen in strained vanadium. The diffusion rate is found to decrease substantially, when hydrogen is occupying octahedral sites as compared to tetrahedral sites. Profound isotope effects are observed when comparing the diffusion rate of H and D. The changes in the diffusion rate are found to be strongly influenced by the changes in the potential energy landscape, as deduced from first-principles molecular dynamics calculations.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-275058 (URN)10.1103/PhysRevB.95.064310 (DOI)000395988800002 ()
Note

The manuscript version of this article is part of two PhD theses: http://uu.diva-portal.org/smash/record.jsf?pid=diva2:900624

http://uu.diva-portal.org/smash/record.jsf?pid=diva2:950756

Available from: 2016-01-28 Created: 2016-01-28 Last updated: 2018-05-14Bibliographically approved
2. Concentration dependence of hydrogen diffusion in clamped vanadium (001) films
Open this publication in new window or tab >>Concentration dependence of hydrogen diffusion in clamped vanadium (001) films
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2017 (English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 29, no 4, article id 045402Article in journal (Refereed) Published
Abstract [en]

The chemical diffusion coefficient of hydrogen in a 50 nm thin film of vanadium (0 0 1) is measured as a function of concentration and temperature, well above the known phase boundaries. Arrhenius analysis of the tracer diffusion constants reveal large changes in the activation energy with concentration: from 0.10 at 0.05 in II V-1 to 0.5 eV at 0.2 in II V-1. The results are consistent with a change from tetrahedral to octahedral site occupancy, in that concentration range. The change in site occupancy is argued to be caused by the uniaxial expansion of the film originating from the combined hydrogen induced expansion and the clamping of the film to the substrate.

Keywords
diffusion, hydrogen, single crystal
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-312024 (URN)10.1088/1361-648X/29/4/045402 (DOI)000389233200001 ()
Funder
Swedish Energy AgencySwedish Research Council
Available from: 2017-01-05 Created: 2017-01-04 Last updated: 2018-05-14Bibliographically approved
3. Diffusion of hydrogen in ultra-thin V(001) layers
Open this publication in new window or tab >>Diffusion of hydrogen in ultra-thin V(001) layers
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(English)Article in journal (Other academic) Submitted
National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-320733 (URN)
Available from: 2017-04-24 Created: 2017-04-24 Last updated: 2017-05-03
4. Finite size effects as a tool to accelerate diffusion of light interstitials
Open this publication in new window or tab >>Finite size effects as a tool to accelerate diffusion of light interstitials
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(English)Article in journal (Other academic) Submitted
National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-320562 (URN)
Available from: 2017-04-21 Created: 2017-04-21 Last updated: 2017-05-03
5. Experimental realization of hysteresis in a coherent phase transition
Open this publication in new window or tab >>Experimental realization of hysteresis in a coherent phase transition
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(English)Manuscript (preprint) (Other academic)
National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-320734 (URN)
Available from: 2017-04-24 Created: 2017-04-24 Last updated: 2017-05-03

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