The future of the clean-fuel hydrogen economy lies in carrying the alternative energy substance in liquid state, argues Robert Crabtree of Yale University, New Haven.

This method would ensure that cars running on fuel cells, which run on hydrogen and oxygen, could fill-up at fuel stations using roughly the same liquid-fuel infastructure that already exists and is commonplace in our everyday lives. There would also be no need for totally new distribution networks and fuel delivery systems as a result.

Crabtree, who recently told of his work developing nitrogen-packed organic liquids that hold and release hydrogen, said briefly, $quot;By using a liquid, we simplify the engineering.$quot;

Most of the research into hydrogen storage to date has focused on materials called hydrides and metal-organic-frameworks (MOF's), incredibly porous materials that can be packed with gas. These are not without difficulties however, as getting enough hydrogen into these frameworks to make a fuel tank of reasonable size and weight is problematic and getting the fuel in and out would require innovative fueling systems.

Crabtree envisages a system using a standard petrol tank filled with an organic liquid, which would be passed through a heated module containing a catalyst to unlock hydrogen and release it a little at a time to be used as a fuel. The remaining dehydrogenated liquid would then be removed at a filling station and whisked away to be reprocessed. The liquid can be hydrogenated and re-hydrogenated repeatedly, making it reusable and incredibly versatile and economic. Meanwhile, the tank could be quickly refilled with fresh, hydrogenated liquid.

High-pressure gaseous hydrogen, which is potentially dangerous, could therefore be taken completely out of the public sphere.

Air Products and Chemicals is investing serious cash in developing a similar liquid-based system and says that public concern about the safety of high-pressure gas is one of the reasons for its interest in liquids.

Alan Cooper, a research chemist at Air Products, comments, $quot;In any future hydrogen economy you would expect it to be much easier to move liquids around rather than gas.$quot;

Gaseous hydrogen storage is seen as the future method of fueling a hydrogen economy and a number of breakthrough forms of storage have been discovered, but this doesn't mean liquid technologies should be dismissed altogether. Peter Edwards, a hydrogen storage expert at Oxford University, UK, wisely notes, $quot;All potential innovative chemical routes to effective hydrogen storage materials - solid or liquid - are highly important.$quot;