Chemical keeps hydrogen on ice

One of the challenges in using pure hydrogen as fuel is finding ways to store the hydrogen that do not involve high pressures and low temperatures.

Researchers from Delft University of Technology in the Netherlands, the Colorado School of Mines, and the University of Canterbury in New Zealand have devised a new way to store hydrogen at low pressure and a temperature that is just above freezing. The work is a step toward practical hydrogen storage for vehicles.

The researchers have demonstrated that it's possible to store hydrogen clusters at low-pressure within a clathrate hydrate, or ice-like framework of water molecules that form large and small cages capable of trapping other molecules.

Key to the method is a promoter molecule, tetrahydrofuran, that occupies the large water cages while the small water cages are occupied by hydrogen. This allows hydrogen to be stored at much lower pressure within the clathrate hydrate than the pressure needed to store just hydrogen.

Without the promoter molecule, clathrate hydrate hydrogen storage requires 300 megapascals, which is 2,961 atmospheres of pressure, at 6.85 degrees Celsius. The promoter molecule enables storage at five megapascals, or 49 atmospheres, at about the same temperature.

The researchers are working to optimize the method by reducing the amount of tetrahydrofuran required and are exploring different clathrate hydrate structures.

The basic research for the hydrogen storage system will take three to five years, according to the researchers. The work appeared in the in October 15, 2004 issue of Science.