Hydogen Storage
by Using Clathrate Hydrate
Block-copolymer self-assembly center
Seung-yun Yang
Contents
Introduction
-Hydrogen storage (Hydrogen property, storing method)
-Clathrate structure
Research paper
-Background and Previous study
-Results
Summary
Future Energy Source - Hydrogen Energy
• pyrolysis of methane
Production
• Electrolysis of water
• Photosynthesis by MO
• Pressrue
• Fuel cell
Utilization
Storage
• Temperature
• Metal alloy
Introduction – Hydrogen Storage
Goal of hydrogen storage
- packing hydrogen as close as possible
- Safely, cleanly
Difficulties in hydrogen storage
Very low density : 0.084 grams/liter
Tboiling : -253 ℃ (20K)
At ambient temp, atmospheric pressure,
Many efforts are requied
to increase hydrogen density
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.
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
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
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)
Research Paper
Tuning chathrate hydrates for Hydrogen storage
Huen Lee, John A. Ripmeester et al.
Nature 434, 743 (2005)
Background
Clathrate hydrate
- 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
Previous studies I
H ~ 0.27 nm
Hydrogen cluster can be
stored in hydrate clusters
up to 5wt%
51264
512
D ~ 0.67nm
D ~ 0.54nm
Problem : 2kbar needed to stabilize the hydrogen clusters
in clathrate hydrate
Wendy L. Mao et al
Science 297, 2247 (2002)
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
TH
F
Large cage are filled with THF and small
cage are available to H2 in SII structure
Louw J. Florusse et al
low storage
efficiency (~2wt%)
Science 306, 469 (2004)
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)
Results – 1HNMR spectra
2wt% H2 content
By controlling the
THF concentration,
H2 storage
capacity increase
4wt% H2 content
At 270K , 120bar
Results – H2 storage capacity
g of H2 /
g of hydrate
All of cavity : H2
Depend on THF
concentration,
Three regions exist
small cavity : H2
Large cavity : THF
Significance & Unsolved Problem
Significance
- 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%
Summary
- Hydrogen could be a future energy source due to
1) Abundance
2) Cleanness
3) 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.
Thank you !