Low-pressure material holds hydrogen

One key to using hydrogen as a fuel is finding practical ways to store it. The challenge is storing useful amounts of hydrogen under manageable conditions.

Researchers from the University of Newcastle upon Tyne and the University of Liverpool have discovered a kinetic trapping effect that allows hydrogen to be adsorbed, or taking into a material that has pores that are so small that hydrogen molecules, which consist of a pair of linked hydrogen atoms, cannot pass through.

The material has a cage-like structure consisting of metal atoms linked by organic molecules. The cross-linking molecules are flexible; they hold hydrogen molecules in at ordinary pressures, but allow them through at low-pressure.

The researchers filled between 57 and 71 percent of the material's pore volume with hydrogen. The material stored the fuel at -196 degrees Celsius at one bar, or 14.5 pounds per square inch. One bar is slightly less than one atmosphere of pressure.

One version of the material retained the hydrogen until the pressure was reduced to 49 thousandths of a bar; another version retained hydrogen until the pressure was reduced to 300 thousandths of a bar.

Department of Energy guidelines for storing hydrogen for use in vehicles calls for materials that store at least six percent of their weight in hydrogen. The researchers' prototype stores one percent hydrogen by weight.

The prototype is a proof of principle that paves the way for further research into this type of effect, according to the researchers. The next step is to develop new materials along the same lines that have higher hydrogen capacity and show the kinetic trapping effect at higher temperatures.

It will be 10 to 20 years before the material could be used in practical applications, according to the researchers. The work appeared in the October 14, 2004 issue of Sciencexpress.