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Borane leads the way to alternative fuels
02 July 2008
New routes to hydrogen storage materials, which could offer alternative fuel for cars, have been developed by two teams of scientists in the US and Singapore.
Hydrogen is an important energy source as it reacts with oxygen to release energy with the only by-product being water. However, at atmospheric pressure it is gaseous, and therefore needs to be stored at high pressure to reduce the storage volume. By using a solid material with a high hydrogen content, the volume required for hydrogen storage is considerably reduced, and the need for high pressure eliminated.
Ammonia borane could provide a source of hydrogen for fuelling the cars of the future
Ammonia borane (NH3BH3) has a high hydrogen content and is stable at room temperature, but has, in the past, proven difficult to prepare in high yield. Now, Tom Autrey and co-workers at the Pacific Northwest National Laboratory, Richland, US, have developed a new one-pot synthetic method to this solid material.1
Autrey's method requires in situ production of ammonium borohydride (NH4BH4) by the addition of NH4X and MBH4 salts (X = Cl, F, M = Na, Li) in liquid ammonia, followed by removal of the majority of the ammonia, then addition of tetrahydrofuran (THF) which causes the NH4BH4 to decompose to ammonia borane in high yield.
- Tom Autrey
Another problem with ammonia borane is that its decomposition leads to the production of the volatile compound borazine as a by-product. Borazine can poison proton exchange membrane fuel cells. This issue has been addressed by another team, led by Ping Chen at the National University of Singapore.2
- Zhitao Xiong
Chen's wet-chemical method allows pure sodium aminoborane to be made. He proposes two routes, the faster of which involves adding sodium hydride (NaH) to a solution of ammonia borane (NH3BH3) in THF. The reaction occurs within 10 minutes at -3 °C, giving solid sodium aminoborane which can be filtered off.
Zhitao Xiong, a member of Chen's team, says the most important aspect of this work is that 'it opened the road to a new class of materials comprising alkali or alkaline earth metal cation and [NH2BH3]- anion for storing hydrogen'.
- Todd Marder
1. David J. Heldebrant, Abhi Karkamkar, John C. Linehan and Tom Autrey, Energy Environ. Sci., 2008, DOI: 10.1039/b808865a
2. Zhitao Xiong, Guotao Wu, Yong Shen Chua, Jianjiang Hu, Teng He, Weiliang Xu, Ping Chen, Energy Environ. Sci., 2008, DOI: 10.1039/b805649h
Link to journal article
Synthesis of ammonia borane for hydrogen storage applications
David J. Heldebrant, Abhi Karkamkar, John C. Linehan and Tom Autrey, Energy Environ. Sci., 2008, 1, 156
Synthesis of sodium amidoborane (NaNH2BH3) for hydrogen production
Zhitao Xiong, Guotao Wu, Yong Shen Chua, Jianjiang Hu, Teng He, Weiliang Xu and Ping Chen, Energy Environ. Sci., 2008, 1, 360
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