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Transition-Metal-Ethylene Complex
Suggested for Hydrogen Storage
08 Dec 2006
Transition-Metal-Ethylene complex might have an exciting future in
storing hydrogen. New research reported by scientists from the National
Institute of Standards and Technology and Turkey’s Bilkent University makes
the surprising prediction that “ethylene, a well-known inexpensive molecule,
can be an important basis in developing frameworks for efficient and safe
hydrogen-storage media.”
 Results
of modeling studies indicate that attaching titanium atoms (blue) to the
ends of an ethylene molecule (yellow-green) will result in a capsule-shaped
complex that absorbs 10 hydrogen molecules (red). The results open a new
avenue in the pursuit of materials that will enable efficient solid-state
storage of hydrogen. Credit: NIST
The team’s calculations
show that attaching titanium atoms at opposite ends of an ethylene molecule
(four hydrogen atoms bound to a pair of carbon atoms) will result in a very
attractive “two for” deal. The addition of the two metal atoms results in a
net gain of up to 10 hydrogen molecules that can absorb onto the
ethylene-titanium complex, for a total of 20 hydrogen atoms. As important,
the engineered material is predicted to release the hydrogen with only a
modest amount of heating.
The absorbed hydrogen molecules account for about 14 percent of the weight
of the titanium-ethylene complex. That’s about double the Department of
Energy’s minimum target of 6.5 percent for economically practical storage of
hydrogen in a solid state material. Although significant challenges stand in
the way, solid state storage is preferred to storing hydrogen as a liquid or
compressed gas, both of which require large-volume tanks.
“The success of future hydrogen and fuel-cell technologies is critically
dependent upon the discovery of new materials that can store large amounts
of hydrogen at ambient conditions,” explains Taner Yildirim, a theorist at
the NIST Center for Neutron Research.
Yildirim
and collaborators have been searching for routes to develop these needed
materials. Their earlier research has pointed to several candidates,
including carbon nanotubes coated with titanium atoms. Difficulties in
securing bulk amounts of small-diameter nanotubes and other challenges have
foiled efforts to create these materials in the laboratory.
The team anticipates that ethylene-based complexes, made with titanium or
other so-called transition metals, will prove easier to synthesize and,
then, to evaluate for their potential for high-capacity hydrogen storage.
Citation:
E.
Durgun, S. Ciraci, W. Zhou, and T. Yildirim. Transition-metal-ethylene
complexes as high-capacity hydrogen-storage media. Physical Review
Letters. 97, 226102 (2006)
Source: NIST |
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