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Forschungszentrum Jülich - Annual Report 2012

Special connecting plates are needed to join solid oxide fuel cells together in a system that produces electricity in an efficient and climate-smart manner. In cooperation with the company Outokumpu VDM, Jülich scientists have developed a material that fulfils all of the requirements these interconnects must meet. The partners were awarded the 2012 Steel Innovation Prize for their work. Innovative Material for Fuel Cells S olid oxide fuel cells (SOFCs) have a high efficiency: they convert more than half of the energy contained in natural gas or hydrogen into electricity. Research- ers at Jülich are advancing the practical application of this resource-conserving and climate-smart energy technology. For example, they developed a demon- stration system for SOFC combined heat and power units, which they put into operation in 2012. Combined heat and power units can be used for the decentralized and efficient generation of heat and electricity for residential and industrial buildings. SOFCs are promis- ing candidates for supplying power in trucks, cars and ships. To ensure that such systems achieve sufficiently high voltages, the SOFCs within them are electrically connected in series. Conducting interconnect plates join the individual cells and give the system the necessary mechanical stability. In 2001, Prof. Willem Quadak- kers from Jülich’s Institute of Energy and Climate Research began to cooperate with Outokumpu VDM, aiming to identify a material for the interconnects capable of withstanding operating temperatures between 700 °C and 900 °C for periods of thousands of operating hours and more. The research partners quickly succeeded in developing a steel alloy that expands in a similar manner to the SOFC electrolyte when heated and also forms an electrically conductive protec- tive layer. Outokumpu VDM markets the steel under the trade name of Crofer® 22 APU. A significant disadvantage of this material, however, is that producing it requires expensive vacuum technology because it can only contain very small amounts of silicon. “In order to overcome this drawback, we used a metallurgic trick,” explains Quadakkers. The researchers increased the fraction of silicon in the steel alloy and simultaneously added small amounts of niobium and tungsten. Together, the three elements form a special compound that disperses very finely in the steel as precipitation. “This has two direct positive effects,” says Quadakkers. Firstly, the precipitates improve the stability of the steel at high temperatures even further. Secondly, the harmful internal oxidation of the silicon is suppressed. This means that the steel can contain enough silicon to be produced using a conventional melting process. Crofer® 22 H has also been launched on the market. Researchers analyse the surfaces of the new steel alloy for fuel cells (SOFCs) to determine whether chemical changes occur. Forschungszentrum Jülich | Annual Report 2012 Interconnects join individual planar solid oxide fuel cells (SOFCs) together to form a stack. The stack in this picture has a power output of 5 kW. 20 Institute