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Hydrogen fuel goes liquid (Nature news article)
Published online: 24 August 2007; | doi:10.1038/news070820-14
Nitrogen unlocks the possibility of convenient clean fuels.
Katharine Sanderson
Forget trying to shove gaseous hydrogen into porous materials for safe storage: the future of the clean-fuel economy lies in carrying hydrogen in a liquid, argues Robert Crabtree of Yale University, New Haven.
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Most research on hydrogen storage and transport has focused on materials called metal hydrides and, recently, on metal-organic-frameworks (MOFs) — incredibly porous materials that can be stuffed full of gas. But getting enough hydrogen into these frameworks to make a fuel tank of reasonable size and weight is problematic1, and getting the fuel in and out would require novel fuelling systems.
Instead, Crabtree envisages a system that uses a standard petrol tank containing an organic liquid. This liquid would be passed through a heated module containing a catalyst, which would unlock hydrogen and release it a little at a time to be used as 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 rehydrogenated repeatedly, making it re-usable. Meanwhile the tank would be quickly refilled with fresh, hydrogenated liquid.
The main problem with such liquids is that it usually requires high temperatures (an increase of about 600 degrees Celsius) to unlock the hydrogen — not very practical in a car. Crabtree proposes getting around this by incorporating nitrogen into his organic liquids.
Nitrogen binds to hydrogen less strongly than carbon does, and the presence of nitrogen within a carbon-based ring weakens the remaining C-H bonds. These weakened bonds make it easier to get hydrogen out as the liquid passes over a catalyst, and lower operating temperatures would be needed — the material only needs to be raised by 50 degrees Celsius.
Not hard to handle
The world's largest hydrogen producer, Air Products and Chemicals, based in Allentown, Pennsylvania, is investing serious cash in a similar liquid-based system. "In any future hydrogen economy you would expect it to be much easier to move liquids around rather than gas," says Alan Cooper, a research chemist at Air Products. With the work that's going on now, he says, "consumers of the future will never have to handle hydrogen gas." He is confident that their liquids are close to meeting the US Department of Energy target of creating a fuel tank holding 6% hydrogen by weight by 2010.
......
Nitrogen unlocks the possibility of convenient clean fuels.
Katharine Sanderson
Forget trying to shove gaseous hydrogen into porous materials for safe storage: the future of the clean-fuel economy lies in carrying hydrogen in a liquid, argues Robert Crabtree of Yale University, New Haven.
.......
Most research on hydrogen storage and transport has focused on materials called metal hydrides and, recently, on metal-organic-frameworks (MOFs) — incredibly porous materials that can be stuffed full of gas. But getting enough hydrogen into these frameworks to make a fuel tank of reasonable size and weight is problematic1, and getting the fuel in and out would require novel fuelling systems.
Instead, Crabtree envisages a system that uses a standard petrol tank containing an organic liquid. This liquid would be passed through a heated module containing a catalyst, which would unlock hydrogen and release it a little at a time to be used as 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 rehydrogenated repeatedly, making it re-usable. Meanwhile the tank would be quickly refilled with fresh, hydrogenated liquid.
The main problem with such liquids is that it usually requires high temperatures (an increase of about 600 degrees Celsius) to unlock the hydrogen — not very practical in a car. Crabtree proposes getting around this by incorporating nitrogen into his organic liquids.
Nitrogen binds to hydrogen less strongly than carbon does, and the presence of nitrogen within a carbon-based ring weakens the remaining C-H bonds. These weakened bonds make it easier to get hydrogen out as the liquid passes over a catalyst, and lower operating temperatures would be needed — the material only needs to be raised by 50 degrees Celsius.
Not hard to handle
The world's largest hydrogen producer, Air Products and Chemicals, based in Allentown, Pennsylvania, is investing serious cash in a similar liquid-based system. "In any future hydrogen economy you would expect it to be much easier to move liquids around rather than gas," says Alan Cooper, a research chemist at Air Products. With the work that's going on now, he says, "consumers of the future will never have to handle hydrogen gas." He is confident that their liquids are close to meeting the US Department of Energy target of creating a fuel tank holding 6% hydrogen by weight by 2010.
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