Storing hydrogen into organic molecules
While it is possible to store hydrogen in metal containers to use as fuel in hydrogen-powered vehicles, it is not today a cost-effective solution. But now, researchers at the University of California at Riverside (UCR) have identified organic molecules that mimic metals. They've used carbenes, molecules which contain a carbon atom with only six electrons, to demonstrate that these organic molecules could be used for storing hydrogen.
This work on carbenes has been done at UCR by a team led by Guy Bertrand, professor of chemistry. Below is a figure showing one of the structures obtained during the experiments: "NH3 was bubbled for 4 hours at room temperature through a n-hexane solution (5 mL) of carbene (200 mg, 0.52 mmol). The solvent was removed in vacuo and [this particular structure] was obtained as a white solid." (Credit: UCR, via Science)
The molecules used, called cyclic alkyl amino carbenes or CAACs, "can split hydrogen under extremely mild conditions," but also ammonia.
"The mode of action of these organic molecules, however, is totally different from that of metals," said Guy Bertrand, a distinguished professor of chemistry who led the research. "Moreover, the CAACs are able to split ammonia as well – an extremely difficult task for metals." Bertrand explained that such a splitting of ammonia, under certain conditions, can pave the way for transforming abundant and inexpensive ammonia into useful amino compounds used to make pharmaceuticals and bulk industrial materials. "This is one of the top challenges for the 21st century," he said.
This research work has been published by Science under the name "Facile Splitting of Hydrogen and Ammonia by Nucleophilic Activation at a Single Carbon Center" (Volume 316, Issue 5823, Pages 439-441, April 20, 2007). Here are two links to the abstract of this technical paper and to some supporting online material from which the above figure has been extracted.
Finally, when will we use hydrogen tanks made of carbenes? Probably not before many years.
Sources: University of California at Riverside, April 19, 2007; and various websites
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