Supplementary Information

Metal hydride storage systems, investigated in the BOR4STORE project HZG HyTech Laboratory FCH JU

Metal hydride storage systems, investigated in the BOR4STORE project

Certain metals and alloys have the ability to absorb and bind gaseous hydrogen. In the materials investigated in Bor4Store, a chemical bonding of the hydrogen with the boron metal compounds occurs in the form of a fine granulate or powder, similar to combustion with oxygen - only in this case with hydrogen and generally with generation of heat.

As these reactions are reversible, the hydrogen can be retrieved by means of an input of the heat energy previously released. No additional energy is required if there is an optimum adjustment between the metal hydride tank and fuel cell, as the fuel cell then generates sufficient heat for the hydrogen release. Solid state storage minimises the high energy costs, which are otherwise necessary, by storing at moderate pressures of less than 100 bar without the necessity of hydrogen liquefaction. With an operating life of over 1,000 filling and emptying cycles, this becomes competitive in comparison with other storage methods if the total life cycle costs are taken into account.

The storage of hydrogen in metal hydrides allows practically loss-free storage over a long period of time without additional energy input, as the gas is chemically bonded and cannot escape. Metal hydride storage is also much more suitable than pressurized gas or liquid hydrogen storage for safety reasons, as the hydrogen cannot escape explosively. However, it is problematic for vehicle construction that the metal hydride storage systems currently available only have a low mass specific storage density and are, therefore, very heavy. A metal hydride tank, equivalent to a conventional tank holding 50 litres of petrol, would weigh more than a quarter of a ton if metal hydrides were utilized such as those, for example, in German fuel cell submarines.

An additional problem is that, depending on the alloy, medium to very high temperatures of more than 100°C are necessary for the release of the hydrogen. Therefore, new kinds of hydrides are being investigated in Bor4Store, with up to nine times higher weight-related capacity and possibilities for the lowering of the hydrogen release temperatures. At present, these still lie at temperatures of over 250°C or, in the case of the hydrides with highest capacity, at up to 450°C.

Therefore, one focus in Bor4Store is the integration with a SOFC whose operating temperature of 650 to 1000°C will definitely provide sufficient heat for the hydrogen release.

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HZG HyTech Laboratory

Technicians at the Helmholtz Centre have established a new test laboratory, the HyTech-Laboratory, especially for the characterisation of hydrogen tanks. Particular attention has been given, hereby, to explosion and fire protection, with the support of DEKRA. Certification is being sought. In this laboratory, prototype and serial production hydrogen tanks can be filled and emptied in an especially protected laboratory room, at tank temperatures between room temperature and 180°C, hydrogen flows of up to 2500 standard litres/min and pressures from vacuum to 160 bar. The thermal management of the tanks is hereby controlled by means of thermal oil which flows around the tank. In a further, smaller test station, tanks can be tested – with special heating sleeves – at up to 400°C.

In these tank testing facilities, tests have already been carried out, for example, on ambient temperature hydride tanks for the FORTIS Saxonia experimental vehicles SAX3 and NIOS, a tank constructed in the scope of the European STORHY project with a capacity of 8 kg of sodium alanate, a sodium alanate tank module (4.5 kg storage material) optimised in the scope of the NESSHY project and on a smaller tank with 250 g boron- based reactive hydride composite as a storage material.

FCH JU

The Fuel Cells and Hydrogen Joint Undertaking (FCH JU) joint venture, which has emerged from the European Technology Platform, is a public private partnership for the support of research and the technological development and application of fuel cell and hydrogen technology in Europe. The objective is to advance the introduction of these technologies onto the market.

The FCH JU is the result of long-standing cooperation between representatives of business, science, public authorities, commercial enterprises, end users and the general public, in the scope of the European Hydrogen and Fuel Cell Technology Platform. This platform came into being within the 6th Framework Programme for Research (RP6, until 2007). The FCH JU was officially founded on 30.5.2008. At present the continuation of FCH JU within "Horizon 2020"; the next Framework Programme for Research of the EU, is being discussed by all parties concerned.

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