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News – What`s happening in energy research

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Stack of 40 cells with plates from new material
© elringklinger ag
Cost-effective metal alloy is ready for market
03.01.2012

With the help of an improved high-performance material for solid-oxide fuel cells, it is possible to produce a block of several fuel cells for use in vehicles.
© ThyssenKrupp AG

Fuel cells are becoming lighter

Small, decentralised power plants are on the increase: as fuel cells, they are enormously energy efficient, provide heat and electrical energy whilst giving off harmless emissions. Scientists from the Research Centre Jülich and the metal group ThyssenKrupp VDM are now making a contribution towards competitive production costs.

The solid-oxide or high-temperature fuel cell provides clean energy in the form of heat and electricity at high levels of efficiency and is therefore regarded as an energy source of the future (abbreviated: SOFC, Solid Oxide Fuel Cell). With this form of fuel cell technology, the required hydrogen-rich gas is obtained from fuels such as diesel, petrol or methanol at temperatures of up to 900 degrees Celsius. The conditions prevailing in the fuel cell call for particular materials: the new “Crofer 22 H” metal mixture has been designed especially for high-temperature fuel cells. It contains between 20 and 24 percent chromium as well as further alloy components such as tungsten, niobium, titanium and lanthanum. The new material distinguishes itself through high corrosion resistance at temperatures of up to 900 degrees, good electrical conductivity of the oxide layer and high mechanical strength at application temperature. It is also easy to process. The properties of the Crofer 22 H were optimised by ThyssenKrupp VDM within the scope of the “ZEUS III” research programme, carried out together with the Research Centre Jülich with funding from the German Federal Ministry of Economics and Technology.

During the project, which lasted several years and involved further industrial partners, Crofer 22 H was brought to market readiness. With the help of the new material, so-called lightweight stacks, i.e. blocks of several fuel cells, can be produced, for example for use in vehicles. “When developing Crofer 22 H, our aim was in particular to achieve industrial-scale production,” emphasises Dr. Jutta Klöwer, Head of Research and Development at ThyssenKrupp VDM. “As a result, a more cost-effective alloy with improved properties compared to steel is now available for inter-connector plates.” This applies for the field of industrial-scale energy supply, for small, decentralised household units as well as for the energy supply in automotive applications.

More favourable structure

In fuel cells, the high-performance material is used in the so-called inter-connectors. These intermediate steel plates connect the individual cells to an efficient fuel-cell “stack”. The list of requirements on the material for this component is long: Within the fuel cell, it must be electrically conductive, corrosion resistant, mechanically stable and mechanically durable, must be easy to process and have no negative effects on the cell. Crofer 22 H satisfies all of these very specific requirements. A further advantage is created by the expansion levels under the influence of heat which correspond to those of the ceramics used for the cells. This avoids mechanical tension between the two materials which could damage the ceramics. “Production of the material on an industrial scale enables favourably-priced manufacture of the fuel cells. Ultimately, it is not least a matter of reducing system costs,” explains Dr. Robert Steinberger-Wilckens from the Research Centre Jülich. “The fact that, with Crofer 22 H, we were able to dispense with steel production in vacuum induction ovens has enabled a significant reduction in manufacturing costs,” emphasises Dr. Jutta Klöwer. In addition to Crofer 22 H, further materials from ThyssenKrupp VDM are used in fuel cells. Thus, for example, high-temperature nickel alloys play a role in other SOFC components such as heat exchangers and reformers.

APU and power plant

The fuel cell can be used as “Auxiliary Power Unit”, i.e. as on-board electricity supply aggregate – in mobile form in cars, trucks, aircraft or on ships. It is also suitable for stationary use in building energy supply or in small and large CHP plants. Its use therefore enables more efficient obtaining of heat and electricity for private households as well as for vehicles. Given the high prices for fossil fuels, the development of the fuel cell is proving to be both sustainable and cost-favourable. It is on the way to blanket use.
In September 2011, BINE reported on “On-board power supply with fuel cells”.

(ph)

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