National Institute of Standards and Technology (NIST) scientists are predicting that carbon nanotubes “decorated” with titanium or other transition metals can latch on to hydrogen molecules in numbers sufficient for efficient hydrogen storage—a key enabler for long-term efforts to develop affordable hydrogen fuel cell vehicles.

In the model to the right, the carbon nanotubes are represented in light blue, the titanium atoms in dark blue, and the hydrogen molecules in red.

Using established quantum physics theory, theorist Taner Yildirim and physicist Salim Ciraci, both of Turkey’s Bilkent University, found that hydrogen can amass in amounts equivalent to 8% percent of the weight of “titanium-decorated” single-walled carbon nanotubes. That’s one-third better than the 6 wt.% minimum storage-capacity requirement set by DOE for 2010. (The target is 9 wt.% for 2015.)

Equally important, the four hydrogen molecules that dock to a titanium atom are relinquished readily when heated. Such reversible desorption is another requirement for practical hydrogen storage.

Carbon nanotubes are among the promising candidates for next-generation hydrogen storage (earlier post). Achieving 6 wt.% storage, though, has been problematic. Positioning a titanium atom above the center of the hexagonally arranged carbon atoms (the repeating geometric pattern characteristic of carbon nanotubes) appears to resolve the impasse.

Yildirim and Ciraci are reporting their findings in Physical Review Letters: T. Yildirim and S. Ciraci, “Titanium-Decorated Carbon Nanotubes as a Potential High-Capacity Hydrogen Storage Medium”, Phys. Rev. Lett. 94, p. 175501 (2005).

NIST suggests that more information such as animation of the reaction paths and MD simulations can be obtained at www.ncnr.nist.gov/staff/taner/h2, but that link was not live at the time of this writing.