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 courtesy of NIST

New research by the National Institute of Standards and Technology (NIST, www.nist.gov) shows that ethylene might be a good fit for storing hydrogen, which is being touted by many as the transportation fuel of the future. Findings reported by scientists from NIST and Turkey’s Bilkent University (www.bilkent.edu.tr) predicts that “ethylene, a well-known inexpensive molecule, can be an important basis in developing frameworks for efficient and safe hydrogen-storage media.”

The research 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, according to a report by NIST. 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, NIST says the engineered material will 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 — approximately double the Department of Energy’s (www.doe.gov) minimum target of 6.5 percent for economically practical storage of hydrogen in a solid-state material. While NIST acknowledges that significant challenges remain to be overcome before this process is ready for real-world applications, it believes solid-state storage is preferred to storing hydrogen as a liquid or compressed gas, both of which require large-volume tanks. The research 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.