11 January 2007

Fuel cell future eyes ethylene

Results of modeling studies indicate 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. Source: NIST

Ethylene, a material used in the most common plastic, might have a big future in storing hydrogen, the fuel of the future.

A well-known inexpensive molecule, ethylene can be an important basis in developing frameworks for efficient and safe hydrogen-storage media, according to research from scientists from the National Institute of Standards and Technology (NIST) and Turkey’s Bilkent University.

The team’s calculations show attaching titanium atoms at opposite ends of an ethylene molecule (four hydrogen atoms bound to a pair of carbon atoms) will result in a “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, totalling 20 hydrogen atoms. One other important aspect is the engineered material should release the hydrogen with only a slight amount of heating.

The absorbed hydrogen molecules account for about 14% of the weight of the titanium-ethylene complex. That’s about double the Department of Energy’s minimum target of 6.5% for economically practical storage of hydrogen in a solid state material. Although significant challenges stand in the way, solid-state storage remains the preferred method to storing hydrogen as a liquid or compressed gas. The problem is both 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,” said Taner Yildirim, a theorist at the NIST Center for Neutron Research.

Yildirim and collaborators continue to search 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 transition metals, will prove easier to synthesize and, then, to evaluate for their potential for high-capacity hydrogen storage.

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