Improved hydrogen storage for cars

An autocatalytic reaction mechanism releases cooler hydrogen faster.

As hydrogen is a gas that cannot be pumped into a tank like petrol, good storage is key to using the gas as an effective fuel. Now a team of scientists from the University of California and the Ford Motor Company in the US have developed a hydride (hydrogen amalgamated with other elements) that could be a useful starting point for the development of future automotive hydrogen-storage materials.
 
Published in the journal Angewandte Chemie, project leader Jun Yang and team describe their work as an “autocatalytic” reaction mechanism that causes the composite made of three different hydrides to rapidly release hydrogen at lower temperatures and without any dangerous by-products.
 
For example, to use lithium borohydride (LiBH4 ) and magnesium hydride (MgH2) for automotive applications, the hydrogen compounds need temperatures that are too high to release hydrogen. Alternatively, a combination of two different hydrides has previously been shown to improve the process. These compounds partly release hydrogen at lower temperatures than either of the individual components working separately.
 
However, the team 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 triplet has substantially better properties than previous binary materials.
 
A complex sequence of reactions holds the key as to why this has proved to be a successful method. 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.
 
This results in the temperature lowering as it begins at 150 °C. Additionally, the resulting hydrogen is very pure as neither ammonia nor any other volatile decomposition products are formed. Recharging the ternary hydride with hydrogen can also be accomplished.

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