Improved Sofc Cathodes and Cathode Contact Layers

Abstract

SOFC development at Forschungszentrum Jülich is aiming at high power density and high durability to achieve cost reduction in manufacturing and installation. For higher power density the work on materials development has been focused on improving the cathode performance by modification of the component thickness, the microstructure and the choice of materials. All investigations were first carried out with 5×5 cm 2 cells and, if appropriate, scaled up to cells having a size of 10 × 10 and 20 × 20 cm 2 . In the case of (La,Sr)MnO 3 -based cathodes the power output was nearly doubled reproducibly from 0.56 to 1.0 W/cm 2 at 800°C and 0.7 V by varying the (La,Sr)Mn03/YSZ ratio in the composite layer as well as the grain size in and the thickness of both the composite layer and the overlaid pure (La,Sr)MnO 3 layer. In addition, SOFCs with cathodes based on (La,Sr)(Fe,Co)O 3 have successfully been developed giving a power output of 1.2 W/cm 2 at the same experimental conditions. Similar performance was achieved by depositing the cathode using either wet powder spraying or screen printing. A prerequisite for comparing different cathodes is the reliable and quality-assured fabrication of all other cell components. For improved durability the development of cathodic contact materials was directed towards a reduced interaction between the ceramic materials and the ferritic steel used as interconnect material. Several materials solutions are available in which the contact resistance remains constant below 70 mΩ cm 2 within the first 1500 h of testing. Currently, contact materials are under development that do not only show a reliable and low contact resistance but simultaneously act as a diffusion barrier for the chromium that is released from the interconnect.