Washington, April 3 : Scientists have come a step closer in designing a clean and efficient hydrogen-powered car, by demonstrating a novel class of materials, which could enable a practical hydrogen 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.
Now, researchers at the National Institute of Standards and Technology's Center for Neutron Research (NCNR) in US have demonstrated that a novel class of materials could enable a practical hydrogen fuel tank.
For the research, a 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, MOFs 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.
Also, they don't 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.
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 date-packing the molecules in more densely than they would be if frozen in a block.
According to NCNR scientist Craig Brown, "When we started doing experiments, we realized the metal interaction doesn't just increase the temperature at which hydrogen can be stored, but it also increases the density above that in solid hydrogen."
"This is absolutely the first time this has been encountered without having to use pressure," he added.
Although the liquid-nitrogen temperature of MOF-74 is not exactly temperate, it's easier to reach than the temperature of solid hydrogen (-269 C), and one of the goals of this research is to achieve energy densities great enough to be as economical as gasoline at ambient, and thus less costly, temperatures.