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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.
Image: NIST
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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. |
