A Zippy Triple: Ternary hydride with autocatalytic reaction mechanism
gives off hydrogen faster and at lower temperature.
Hydrogen is the fuel of the future. Unfortunately, one problem remains:
Hydrogen is a gas and cannot easily be pumped into a tank like gasoline.
Storage in the form of solid hydrides, chemical compounds of hydrogen
and a metal or semimetal, are good storage materials in principle, but
have not been well suited to automotive applications. An American
research team at the Ford Motor Company in Dearborn and the University
of California, Los Angeles, has now developed a novel hydride that could
be a useful starting point for the development of future automotive
hydrogen-storage materials. As Jun Yang and his team report in the
journal Angewandte Chemie, an �autocatalytic� reaction mechanism causes
the composite made of three different hydrides to rapidly release
hydrogen at lower temperatures and without dangerous by-products.
Certain hydrogen compounds, such as lithium borohydride (LiBH4) and magnesium hydride (MgH2), can release hydrogen and then take it up
again. However, for automotive applications, they require temperatures
that are too high to release hydrogen, the hydrogen release and uptake
are far too slow, and decomposition reactions release undesirable
by-products such as ammonia. In addition, these compounds can only be
�recharged� under very high pressure and temperature conditions. The
combination of two different hydrides (binary hydride) has previously
been shown to improve things, as these compounds partly release
hydrogen at lower temperatures than either of the individual
components.
The researchers led by Yang went a step further and combined three
hydrogen-containing compounds - lithium amide
(LiNH2), lithium borohydride, and magnesium hydride -
in a 2:1:1 ratio to form a ternary hydride. This trio has
substantially better properties than previous binary materials.
The reason for this improvement is a complex sequence of reactions
between the various components. The first reactions begin as soon as
the starting components are ground together. Heating starts off more
reactions, releasing the hydrogen. The mixture is �autocatalytic�,
which means that one of the reactions produces the product cores for
the following reaction, which speeds up the entire reaction sequence.
The result is a lower desorption temperature; the release of hydrogen
begins at 150 �C. In addition the hydrogen is very pure because
neither ammonia nor any other volatile decomposition products are
formed. Recharging the ternary hydride with hydrogen can be
accomplished under moderate conditions.
Further Information and Source:
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Jun Yang, Dr., Andrea Sudik, Dr., Donald J. Siegel, Dr., Devin
Halliday, Andrew Drews, Dr., Roscoe O. Carter III, Dr., Christopher
Wolverton, Dr., Gregory J. Lewis, Dr., J. W. Adriaan Sachtler, Dr.,
John J. Low, Dr., Syed A. Faheem, David A. Lesch, Dr., Vidvuds
Ozolin, Dr. A Self-Catalyzing Hydrogen-Storage Material.
In: Angewandte Chemie International Edition 2008, 47,
doi: 10.1002/anie.200703756.
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Source: Angewandte Chemie
International Edition, press release 51/2007