SOFC cell development

The three components are cofired and a 5 layer LSM-based cathode, graded with respect to composition and structure is sprayed and sintered. A patent application has been filed. The cell is strong (150MPa) and flexible. Upscaling of production procedures has scaled the original 5x5 cm cell to 21x21 cm and the size of the tape casting equipment sems the only limiting size factor. Sulzer cells (120 mm OD, 20 mm center hole) have also been made. Current densities around 2A/cm2 have been achieved, corresponding to 0.3 OMEGAm2 and 1.1 W/cm2. The new 5-layer cathode was used to achieve this result. Furhter decrease of the internalk resistance is anticipated through reduction of diffusion problems through introduction of porosity added with pore formers. Test of the cell type in Sulze Hexis Balance of Plants has been agreed to occur spring 2000. Equipment for examining fundamental principles of ceramic contacts has been completed and is presently used in the project. The equipment allows measurement of contact resistance and change of total height of two pieces of ceramics, pressed against each other with controlled variation of contact pressure, current, temperature and oxygen partial pressure. Important results have been generated which show machining of ceramic surfaces to be detrimental to contact resistance. Machining leads to creation of an almost amorphous top layer (approx 1mum) on a layer with reduced grain size and highly porous. Subsequent heat treatment enhances surface resistance through formation of an easy spalling layer