1. by Using Clathrate Hydrate
Hydogen Storage
by Using Clathrate Hydrate
Block-copolymer self-assembly center
Seung-yun Yang

2. Contents Introduction Research paper Summary
Hydrogen storage (Hydrogen property, storing method)
Clathrate structure
Research paper
-Background and Previous study
-Results
Summary

3. Future Energy Source - Hydrogen Energy
pyrolysis of methane
Electrolysis of water
Photosynthesis by MO
Production
Pressrue
Temperature
Metal alloy
Utilization
Storage
Fuel cell

4. Introduction – Hydrogen Storage
Goal of hydrogen storage
- packing hydrogen as close as possible
- Safely, cleanly
Difficulties in hydrogen storage
Very low density : grams/liter
Tboiling : ℃ (20K)
At ambient temp, atmospheric pressure,
Many efforts are requied
to increase hydrogen density

5. Introduction – Hydrogen Storage Method
Compressed hydrogen
200 and 250 bar is required
expensive, explosive
Liquid hydrogen
At -253°C, hydrogen can be liquefied
Reducing volume, most dense fuel (space program)
expensive, large insulated tanks are required
Bonded hydrogen
Metal and liquid hydrides and adsorbed carbon compounds
safest methods (no hydrogen release in accident)
bulky and heavy.

6. Increase the density of hydrogen by using metal
Introduction - Hydrogen metal alloy
Hydrogen bond with metal by absorption process
metallic hydrides working at RT are fully reversible
Material
H-atoms per cm3
(x 1022)
H2 gas, 200 bar (2850 psi)
0.99
H2 liquid, 20 K (-253 C)
4.2
H2 solid, 4.2 K (-269 C)
5.3
MgH2
6.5
Mg2NiH4
5.9
FeTiH2
6.0
LaNi5H6
5.5
Increase the density of hydrogen by using metal

7. Clathrate structure Clathrate (cage compound, host-guest molecule )
- Chemical substance consisting of frame molecule and containing molecule ( “locked” in Greek )
Ex. Clathrate hydrate
water(ice) molecules enclosing a trapped gas(CH4 , N2 , O2 etc)
Clathate complex are various depend on interaction with guest
and change the geometrical space of host molecule through
strong interaction via chemical bond, non-covalent bond

8. Clathrate structure Common hydrate structure
structure-I (sI) : a 12 Å cube consisting of 46 water molecules
2 small cavities (pentagonal dodecahedra (512) six large cavities tetradecanhedra (51262)
512 occupied by gas molecule
structure-II (sII) : 17.3 Å cube with 136 water containing 6 small cavities(512)and 8 large cavities(51264)
Stackelberg and Müller (1954)

9. Tuning chathrate hydrates for Hydrogen storage
Research Paper
Tuning chathrate hydrates for Hydrogen storage
Huen Lee, John A. Ripmeester et al.
Nature 434, 743 (2005)

10. Background Clathrate hydrate Can hydrogen be stored in clathrate ?
- Hydrogen-bonded water molecules(cage) ocuupied by low molecular weight gases molecues (O2, N2, CO2, CH4, H2S, Ar, Kr etc.)
- "cages" are unstable when empty, collapsing into conventional ice crystal structure(bcc, fcc)
Can hydrogen be stored in clathrate ?
Methane clathrate – burning ice

11. Previous studies I
H ~ 0.27 nm
Hydrogen cluster can be stored in hydrate clusters up to 5wt%
51264
D ~ 0.67nm
512
D ~ 0.54nm
Problem : 2kbar needed to stabilize the hydrogen clusters in clathrate hydrate
Wendy L. Mao et al Science 297, 2247 (2002)

12. THF (tetrahydrofuran)
Previous studies II
Clusters of hydrogen can be stabilized in presence of second guest component (THF) at relatively low pressure.
500bar (THF) vs 2 kbar at 280 K (pure H2)
THF (tetrahydrofuran) H2
THF
low storage
efficiency (~2wt%)
Large cage are filled with THF and small cage are available to H2 in SII structure
Louw J. Florusse et al Science 306, 469 (2004)

13. In order to Increase hydrogen content of the hydrate
Motivation
In order to Increase hydrogen content of the hydrate
H2 guest molecule must enter the large cavity as well as small cavity
They try to find optimum condition by tuning hydrate compositions(THF, H2) at modest pressure.
Huen Lee et al Nature 434, 743 (2005)

14. By controlling the THF concentration, H2 storage capacity increase
Results – 1HNMR spectra
2wt% H2 content
By controlling the THF concentration, H2 storage capacity increase
4wt% H2 content
At 270K , 120bar

15. Depend on THF concentration,
Results – H2 storage capacity
Depend on THF concentration,
Three regions exist
g of H2 /
g of hydrate
All of cavity : H2
small cavity : H2
Large cavity : THF

16. Significance & Unsolved Problem
Increase the hydrogen capacity up to 4wt%
non-explosive decomposition
cheap storage material (water, THF)
Unsolved Problem
100bar needed
increase storage capacity at least 6wt%

17. Summary - Hydrogen could be a future energy source due to Abundance
Cleanness
Cheapness
- Clathrate hydrate could be a useful method for hydrogen storage
Cavity in clathrate structure can trap the hydrogen molecule.
Second guest molecule can adjust the stabilization condition of clathrate.
By controlling the composition, hydrogen storage could be increase.

18. Thank you !