Deutsche Version  ACT
Thermal Storage
Thermochemical storage 21.4.2016

The figure shows the demonstrator of the metal hydride storage with a standard format of 19 inches.
© DLR Stuttgart

Metal hydrides store faster with graphite

Many metal alloys can reversibly bind large amounts of hydrogen, forming metal hydrides. The chemical reaction releases large amounts of heat. Metal hydrides are therefore suitable not only for hydrogen storage but also as thermochemical heat storage. Metal hydride storages achieve extremely high charging and discharging

performances by a combination of metal hydrides with thermally

conductive graphite in a composite material.

Project status Project completed
Typical system size Energy [MWh] 0.1
Typical system size Output [MW] 1
Volumetric energy density [Wh/l] 2,145
Gravimetric energy density [Wh/kg] 600 to 1,800
Storage loss [1/d] none
Efficiency AC/VNH2 80 %
Cycle durability (80% discharge level) > 1,000
Typical discharge time few minutes
Typical period between storage and withdrawal few minutes
Example application areas thermo-booster, hydrogen storage
Type of storage Reversible chemical reactions, Hydrogenation of metal alloys, storage material, storage construction (stainless steel tank), Components for charching and discharching (integrated heat exchanger), auxiliary equipment (valves, sensor technology)
Project duration July 2012 until December 2015

Future high dynamic hydrogen storage technologies, which allow a fast loading and unloading within a few minutes, rely on the ongoing improvement of the currently available storage materials. The targeted property improvements are not only beneficial towards reducing charging times of a hydrogen tank, but also facilitate the usage of suchlike materials for high dynamic thermo-chemical energy storage applications, such as high-temperatur process heat storage, thermo-booster or vibration-free and noiseless hydrogen compressor units.

  • Schematic hydride formation © Fraunhofer IFAM Dresden
  • Hydride-forming alloys are suitable for storing both hydrogen and heat. © Fraunhofer IFAM Dresden
  • Hydride composite material for thermochemical energy storage © Fraunhofer IFAM Dresden
  • Test rig for cycle test © DLR Stuttgart

Graphite increases thermal conductivity and hydrogen absorption

In order to achieve a suitable technical performance of the hydride-based hydrogen storage, it is enevitable to ensure sufficient long-term stable heat and gas transfer through the hydride bed. Hence, the project focuses the promising approach to prepare hydride-graphite composite materials. Their improved property portfolio is demonstrated in a technical realistic lab environment. In this respect graphite offers the possibility to control the hydrogen permeation as well as to increase the effective thermal conductivity from about 1 W/mK of pure hydrides up to 80 W/mK of the hydride-graphite composites. The project is divided into the sub-projects "Material synthesis and charecterization" and "Testing and Storage Tank".

Supported by: The Federal Government on the basis of a decision by the German Bundestag


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