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July 27, 2005

Titanium and Nanotubes Improve Fuel Cell Storage Capacity

Source: Small Times


July 26, 2005 – Researchers at the U.S. National Institute of Standards and Technology (NIST) and Turkey's Bilkent University discovered that titanium-crusted carbon nanotubes could meet two key requirements for efficient hydrogen storage: the abilities to latch on to hydrogen molecules in adequate numbers and to relinquish the hydrogen readily when heated.

The U.S. FreedomCar Research Partnership, which features participation from the U.S. Department of Energy and U.S. automakers, requires a 6 percent minimum storage capacity. The researchers' single-walled carbon nanotubes, which are decorated with titanium or other transition metals, can amass a predicted 8 percent of the nanotubes' weight worth of hydrogen.

Single-walled carbon nanotubes have been considered a candidate material for hydrogen storage by others in the past, but the 6 percent target has been an obstacle. According to calculations and models by the researchers, positioning a titanium atom above the center of hexagonally arranged carbon atoms appears to resolve this problem. The researchers discovered that interactions among carbon, titanium, and hydrogen give rise to unusual attractive forces.

As a result, four hydrogen molecules can dock on a titanium atom by means of a unique chemical bond of modest strength, it appears. The four hydrogen molecules that link to the titanium atom are then relinquished readily when heated. Taner Yildirim, a NIST theorist, says that several forces at work within the geometric arrangement appear to play a role in the reversible tethering of hydrogen.

As technology related to fuel cells continues to be refined, automakers are already sending fuel-cell vehicles onto the roads for testing.

Automaker DaimlerChrysler has announced that its first hydrogen-powered fuel cell cars will enter the commercialization phase by 2010. The company currently has a fleet of 30 fuel cell buses running in daily service in ten European cities and is testing a fleet of 60 Mercedes-Benz fuel cell powered cars in Germany, Japan, Singapore, and the United States.

"Everyday operation will help to optimize the essential features and bring the vehicles closer to market maturity," said Herbert Kohler, vice president of Body and Powertrain Research at DaimlerChrysler.