A powder made from carbon and zinc could be the key to making a hydrogen-powered car that’s as easy to refuel as filling up at a petrol station is today.

Designing a fuel tank that’s as convenient as one that stores petrol is one of the key engineering challenges to building a clean, efficient, hydrogen-powered vehicle. Researchers at the US National Institute of Standards and Technology believe a novel class of materials known as metal organic frameworks, or MOFs, might be the answer.

Staff from NIST’s Center for Neutron Research collaborated with scientists from the University of Maryland and the California Institute of Technology on a study reported in a paper published this month by the American Chemical Society.

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

The researchers used neutron scattering and gas adsorption techniques to determine that at a temperature of 77K, MOF-74 can adsorb more hydrogen than any unpressurised framework structure studied to date. Exactly what allows the hydrogen to bond in this fashion isn’t clear, admits NIST scientist Craig Brown, but it’s probably connected to the properties of the zinc component.

“When we started doing experiments, we realised 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,” Brown says. “This is absolutely the first time this has been encountered without having to use pressure.”

Fully understanding the physics of the interaction might allow scientists to develop the need for refrigeration or insulation in hydrogen fuel tanks, Brown added.

Image: Hydrogen molecules, shown in green, pack into the tubes of MOF-74 more densely than they would in solid form [NIST]