More solid than solid: A potential hydrogen-storag...( One of the key engineering challenge...)

One of the key engineering challenges to building a clean, efficient, hydrogen-powered car is how to design the fuel tank. Storing enough raw hydrogen for a reasonable driving range would require either impractically high pressures for gaseous hydrogen or extremely low temperatures for liquid hydrogen. In a new paper* researchers at the National Institute of Standards and Technologys Center for Neutron Research (NCNR) have demonstrated that a novel class of materials could enable a practical hydrogen fuel tank.

A research team from NIST, the University of Maryland and the California Institute of Technology studied metal-organic frameworks (MOFs). One of several classes of materials that can bind and release hydrogen under the right conditions, they have some distinct advantages over competitors. In principle they could be engineered so that refueling is as easy as pumping gas at a service station is today, and MOFs dont require the high temperatures (110 to 500 C) some other materials need to release hydrogen.

In particular, the team examined MOF-74, a porous crystalline powder developed at the University of California at Los Angeles. MOF-74 resembles a series of tightly packed straws comprised of mostly carbon atoms with columns of zinc ions running down the inside walls. A gram of the stuff has about the same surface area as two basketball courts.

The researchers used neutron scattering and gas adsorption techniques to determine that at 77 K (-196 C), MOF-74 can adsorb more hydrogen than any unpressurized framework structure studied to datepacking the molecules in more densely than they would be if frozen in a block.

NCNR scientist Craig Brown says that, though his team doesnt understand exactly what allows the hydrogen to bond in this fashion, they think the zinc center has some interesting properties.

When we started doing experiments, we realized the metal interaction doesnt just increase the temperatur
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