Hydrogen storage for green cars
Many people predict that one day we'll drive cars powered by hydrogen. These 'green' cars would only release water after combustion of the hydrogen, which would be good for our planet. But there is a big hurdle: we really don't know how to store safely this hydrogen. Now, researchers in the U.K. and Canada say they've discovered -- almost by accident -- a new material which could be used to safely store hydrogen at room temperature. This new material, a rhodium-hydrogen compound, can store and release hydrogen with a simple switch. And the researchers hope to have an hydrogen tank prototype ready within two to three years.
Here are some comments from Dr. Andrew Weller of the Department of Chemistry at the University of Bath.
Hydrogen has a low density and it only condenses into liquid form at -252°C so it is difficult to use conventional storage systems such as high-pressure gas containers which would need steel walls at least three inches thick, making them too heavy and too large for cars.
Our new material works at room temperature and at atmospheric pressure at the flick of a switch. Because it is made from a heavy metal (Rhodium), its weight to fuel ratio is low, 0.1 per cent, but it could certainly fill the time lag between a driver putting their foot on the accelerator and a metal hydride fuel tank getting up to temperature.
But it's fun to notice that the researchers discovered the properties of this material by a combination of luck and curiosity.
The University of Bath researchers made the discovery whilst investigating the effect that hydrogen has on metals. Having constructed an organo-metallic compound containing six rhodium (a type of metal that is also currently found in catalytic converters in cars) atoms and 12 hydrogen atoms, they began studying the chemical properties of the complex with researchers in Oxford (UK) and Victoria (Canada). They soon realised that the material would absorb two molecules of hydrogen at room temperature and atmospheric pressure – and would release the molecules when a small electric current was applied to the material.
Below is a diagram showing the calculated structure for one of these chemical compounds containing rhodium and hydrogen atoms. This particular one is known as [Rh6(PH3)6H14]+. (Credit: Andrew Weller et al.) And it might be used to build your future hydrogen tanks.
So what is the next step? The researchers want to build an hydrogen storage device "by printing the material onto sheets that could be stacked together and encased to form a storage tank." But it will take several years.
In the mean time, if you want more information, this research work has been published by the scientific journal Angewandte Chemie under the name "Storing and Releasing Hydrogen with a Redox Switch" (Volume 118, Issue 36, Pages 6151-6154, September 11, 2006, but published online on August 4, 2006). Here is a link to the article (no abstract available) and to some online additional information from which the above diagram has been extracted (PDF format, 15 pages, 351 KB). Finally, here is a link to the full paper via the international edition of Angewandte Chemie (PDF format, 4 pages, 220 KB).
Sources: University of Bath news release, December 4, 2006; and various websites
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