Hydrogen storage breakthrough paves way for green vehicles

A powder made from carbon and zinc could be the key to making a hydrogen-powered car that̵7;s as easy to refuel as filling up at a petrol station is today.

Designing a fuel tank that̵7;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 NIST̵7;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 isn̵7;t clear, admits NIST scientist Craig Brown, but it̵7;s probably connected to the properties of the zinc component.

̶0;When we started doing experiments, we realised the metal interaction doesn̵7;t just increase the temperature at which hydrogen can be stored, but it also increases the density above that in solid hydrogen,̶1; Brown says. ̶0;This is absolutely the first time this has been encountered without having to use pressure.̶1;

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]

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