Hydrogen Storage in Molecular Compounds
Wendy L. Mao1, Kimberly Tait1, Yusheng Zhao1, Konstantin Lokshin2, Ho-kwang Mao3
1LANSCE-LC,
Los Alamos National Laboratory, 2Dept of Materials Science and Engineering, University of Tennessee, 3Geophysical Laboratory, Carnegie Institution of Washington
ƒClathrates
ƒCrystalline structures based on a hydrogen-bonded
water framework (‘host’ lattice) with cavities which
contain ‘guest’ molecules
ƒFilled Ice
ƒHydrates with structures related to known ice phase
ƒvan der Waals Compounds
ƒStoichiometric crystals of mixtures of atoms and
molecules held together by weak van der Waals forces
A
B
H2
HH-sII
110
H2+H2O
240
140
Relative In tensity
10 kPa, 144 K
10 kPa, 78 K
200 MPa, 99 K
Trifid Nebula
200 MPa, 234 K
4120
4140
4160
Absorbance
A b so rb an ce
100 kPa, 140 K
100 kPa, 126 K
100 kPa, 107 K
100 kPa, 80 K
4120
4140
4160
Wavenumber (cm -1)
4180
W. Mao et al, Science 2002
1.2 - 1.8
1.0 - 1.5
HH-C2
H2(H2O)
11.2
3.7
3.5
HM4
(H2)4(CH4)
33.4
11.1
~10
DOE target
2005
4.5
1.5
1.2
DOE target
2010
6
2
1.5
DOE target
2015
9
3
2.7
W. Mao et al, PNAS 2004
Acknowledgements
500 MPa, 80 K
4100
kWh/L
3.5 - 5.3
ƒ H4M holds the largest amount of hydrogen of any compound. How
does it do this? We need to solve its crystal structure and hydrogen
dynamics using neutron diffraction
ƒ Can we add other molecules to stabilize the hydrogen clathrate
structure while the additional molecules are also a useful fuel? Dual
fuels and ternary systems
ƒ Can we use more ionic, hydrogen-bonded molecules (such as
ammonia borane) to form clathrate-like cages to hold hydrogen above
room temperature?
4180
Raman Shift, cm-1
0.05
kWh/kg
H2(H2O)2
Future Work
• HH-sII in small, icy bodies?
Free H2, 200 MPa,
284 K
H2 wt.%
HH-sII
280
10 kPa, 150 K
512
W. Mao et al, CPL 2005
Hydrogen Storage
Raman and FTIR Spectroscopy
4100
1.0 GPa, 120 K
Somayazulu et al, Science 1996
0.2 GPa
10 kPa
77 K
51264
0.4 GPa, 86 K
ƒ But, the neutron fluxes are much lower than
synchrotron x-ray sources necessitating large samples.
ƒ Neutron interaction with the nucleus of an atom is
weak, making them a highly penetrating probe. This
feature allows the use of complex sample environments
(e.g. Al pressure cells) that would be opaque to x-rays.
~300 microns
t = 30 min
H4M
crystals
ƒ it is easier to sense light atoms, such as hydrogen, in the
presence of heavier ones.
ƒ the nuclear dependence of scattering allows isotopes of an
element to have substantially different scattering lengths.
Isotopic substitution can be used to label different parts of
the sample.
H2O
249 K
t=0
liquid
ƒ Neutrons scatter by interacting with the nucleus of an
atom rather than the electron cloud, so, unlike x-rays
and electrons, the scattering power (cross-section) of
an atom is independent of its atomic number. So:
H2-H2O System
300 MPa
250 K
H2-CH4 System
Neutron Study
Molecular Compounds
4200
Spectra from WL5, protostar in the
ρ Ophiuchus cloud complex
Sandford et al, Science 1993
Lokshin et al, PRL 2004
UNCLASSIFIED
This work has benefited from the use of the Lujan Neutron Scattering
Center at LANSCE, which is funded by the Department of Energy's Office of
Basic Energy Sciences. Los Alamos National Laboratory is operated by the
University of California under DOE Contract W-7405-ENG-36."