Dimensional Behaviour of Ni-YSZ Anode Supports for SOFC Under RedOx Cycling Conditions

Previous studies on Ni-YSZ anode supported SOFC have shown severe mechanical failures upon re-oxidation of the nickel. Ni-YSZ anode support cermets with technologically relevant microstructures were prepared by ceramic slurry processing, tape casting and sintering. The bulk behaviour of the anode supports under reduction-oxidation cycles was studied in dilatometry in temperature range 850 to 1200 degrees C. The expansion on the first reoxidation was measured at 0.68 to 0.93%, depending on temperature, and on subsequent redox cycles the high temperature case became strongly irreversible. In tests where humidity was introduced and the pO(2) was varied, the effect of steam on redox expansion behaviour was found to be detrimental. Parameters describing the reversibility of cyclic redox behaviour are defined and compared in different cases. The processes leading to the observed irreversibility are discussed.