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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: urn:nbn:se:uu:diva-320733OAI: oai:DiVA.org:uu-320733DiVA, id: diva2:1090557
Available from: 2017-04-24 Created: 2017-04-24 Last updated: 2017-05-03
In thesis
1. Hydrogen in nano-sized metals: Diffusion and hysteresis effects
Open this publication in new window or tab >>Hydrogen in nano-sized metals: Diffusion and hysteresis effects
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
Hydrogen, diffusion, hysteresis, optical technique
National Category
Natural Sciences
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-320796 (URN)978-91-554-9928-0 (ISBN)
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

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