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Impact of the confinement on the intra-cage dynamics of molecular hydrogen in clathrate hydrates

Russina, Margarita; Kemner, Evout and Mezei, Ferenc LU (2017) 9th International Conference on Processing and Manufacturing of Advanced Materials, THERMEC 2016 In Materials Science Forum 879. p.1294-1299
Abstract

We have studied the diffusive mobility of hydrogen molecules confined in different size cages in clathrate hydrates. In clathrate hydrate H2 molecules are effectively stored by confinement in two different size cages of the nano-porous host structure with accessible volumes of about 0.50 and 0.67 nm diameters, respectively. For the processes of sorption and desorption of the stored hydrogen the diffusive mobility of the molecules plays a fundamental role. In the present study we have focused on the dynamics of the H2 molecules inside the cages as one aspect of global guest molecule mobility across the crystalline host structure. We have found that for the two cage sizes different in diameter by only 34% and in... (More)

We have studied the diffusive mobility of hydrogen molecules confined in different size cages in clathrate hydrates. In clathrate hydrate H2 molecules are effectively stored by confinement in two different size cages of the nano-porous host structure with accessible volumes of about 0.50 and 0.67 nm diameters, respectively. For the processes of sorption and desorption of the stored hydrogen the diffusive mobility of the molecules plays a fundamental role. In the present study we have focused on the dynamics of the H2 molecules inside the cages as one aspect of global guest molecule mobility across the crystalline host structure. We have found that for the two cage sizes different in diameter by only 34% and in volume by about a factor of 2.4, the dimension can modify the diffusive mobility of confined hydrogen in both directions, i.e. reducing and surprisingly enhancing mobility compared to the bulk at the same temperature. In the smaller cages of clathrate hydrates hydrogen molecules are localized in the center of the cages even at temperatures >100 K. Confinement in the large cages leads to the onset already at T=10 K of jump diffusion between sorption sites separated from each other by about 2.9 Å at the 4 corners of a tetrahedron. At this temperature bulk hydrogen is frozen at ambient pressure and shows no molecular mobility on the same time scale. A particular feature of this diffusive mobility is the pronounced dynamic heterogeneity: only a temperature dependent fraction of the H2 molecules was found mobile on the time scale covered by the neutron spectrometer used. The differences in microscopic dynamics inside the cages of two different sizes can help to explain the differences in the parameters of macroscopic mobility: trapping of hydrogen molecules in smaller pores matching the molecule size can to play a role in the higher desorption temperature for the small cages.

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Please use this url to cite or link to this publication:
author
organization
publishing date
type
Chapter in Book/Report/Conference proceeding
publication status
published
subject
keywords
Clathrates, Confinement, Diffusive mobility, Hydrogen storage, Neutron spectroscopy
in
Materials Science Forum
volume
879
pages
6 pages
publisher
Trans Tech Publications Ltd
conference name
9th International Conference on Processing and Manufacturing of Advanced Materials, THERMEC 2016
external identifiers
  • scopus:85000480316
ISSN
02555476
ISBN
9783035711295
DOI
10.4028/www.scientific.net/MSF.879.1294
language
English
LU publication?
yes
id
97b41700-55ee-48a4-b8b2-ce618b087702
date added to LUP
2017-02-27 09:39:34
date last changed
2018-01-07 11:52:54
@inproceedings{97b41700-55ee-48a4-b8b2-ce618b087702,
  abstract     = {<p>We have studied the diffusive mobility of hydrogen molecules confined in different size cages in clathrate hydrates. In clathrate hydrate H<sub>2</sub> molecules are effectively stored by confinement in two different size cages of the nano-porous host structure with accessible volumes of about 0.50 and 0.67 nm diameters, respectively. For the processes of sorption and desorption of the stored hydrogen the diffusive mobility of the molecules plays a fundamental role. In the present study we have focused on the dynamics of the H<sub>2</sub> molecules inside the cages as one aspect of global guest molecule mobility across the crystalline host structure. We have found that for the two cage sizes different in diameter by only 34% and in volume by about a factor of 2.4, the dimension can modify the diffusive mobility of confined hydrogen in both directions, i.e. reducing and surprisingly enhancing mobility compared to the bulk at the same temperature. In the smaller cages of clathrate hydrates hydrogen molecules are localized in the center of the cages even at temperatures &gt;100 K. Confinement in the large cages leads to the onset already at T=10 K of jump diffusion between sorption sites separated from each other by about 2.9 Å at the 4 corners of a tetrahedron. At this temperature bulk hydrogen is frozen at ambient pressure and shows no molecular mobility on the same time scale. A particular feature of this diffusive mobility is the pronounced dynamic heterogeneity: only a temperature dependent fraction of the H<sub>2</sub> molecules was found mobile on the time scale covered by the neutron spectrometer used. The differences in microscopic dynamics inside the cages of two different sizes can help to explain the differences in the parameters of macroscopic mobility: trapping of hydrogen molecules in smaller pores matching the molecule size can to play a role in the higher desorption temperature for the small cages.</p>},
  author       = {Russina, Margarita and Kemner, Evout and Mezei, Ferenc},
  booktitle    = {Materials Science Forum},
  isbn         = {9783035711295},
  issn         = {02555476},
  keyword      = {Clathrates,Confinement,Diffusive mobility,Hydrogen storage,Neutron spectroscopy},
  language     = {eng},
  pages        = {1294--1299},
  publisher    = {Trans Tech Publications Ltd},
  title        = {Impact of the confinement on the intra-cage dynamics of molecular hydrogen in clathrate hydrates},
  url          = {http://dx.doi.org/10.4028/www.scientific.net/MSF.879.1294},
  volume       = {879},
  year         = {2017},
}