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The illustration shows the compressed metal hydride composite material in pellet form.
© Fraunhofer IFAM
Metal hydrides

Hydrogen – storing energy in metals

Metal hydrides store hydrogen and heat. Their use in thermochemical storage systems is hampered, however, by the material's poor heat conductivity. To increase the charging and discharging performance, researchers are pelletising the material together with graphite, which has a high thermal conductivity. With different metal hydrides they can cover the temperature range from room temperature up to 400 degrees Celsius.

Hydrogen can play an important role in the transformation of the energy supply. It stores renewable energy, drives internal combustion engines with low-emissions and – when used in fuel cells – extends the range of electric cars. Depending on the use, it is stored as a gas in pressure accumulators or as a liquid. Another storage option is provided by metal hydrides. They contain more hydrogen than the same volume of the gas in liquid form and provide considerable safety benefits. Hydrogen, however, is only slowly absorbed and released in metal hydrides. This limits the application possibilities.

Researchers from the Fraunhofer Institute for Manufacturing Technology and Advanced Materials IFAM in Dresden and from the German Aerospace Centre (DLR) in Stuttgart are combining the hydrides with graphite to form a composite material which they are pressing into cylindrical pellets. They are therefore killing two birds with one stone. Not only does this improve the heat conduction and thus the absorption and release of hydrogen, the compression also increases the storage density.

Using various metal hydrides the researchers managed to cover a wide temperature range from room temperature up to 400 degrees Celsius. The hydrides for the low temperature range showed particularly promising results. The researchers succeeded in developing reliable and cost-effective production methods under ambient conditions. The composite material proved its long-term stability and robustness in tests with over 1000 charging and discharging cycles. It is particularly suitable for fuel cells or hydrogen combustion engines.

The project forms part of the Energy Storage research initiative – further information on the project can be found at the following link.


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