REACTION BETWEEN SOLID OXIDE FUEL-CELL MATERIALS

In fabrication processes of solid oxide fuel cells, high-temperature heat treatments cannot be avoided. It will give rise to mutual reaction and interdiffusion of the cell component materials: yttria-stabilized zirconia (YSZ, electrolyte), (La, Sr)MnO3 (cathode), Ni-YSZ cermet (anode) and (La, Ca)CrO3 (separator). Reactivity of LaMnO3 and YSZ was estimated by thermodynamic calculations, and it was found that the nonstoichiometry at La site in LaMnO3 plays an important role on the reaction. Diffusion of Mn into YSZ leads to increase of La activity at the interface and promotes the reaction. Electrical conductivity of YSZ decreases when Mn dissolves in the cubic phase of YSZ. Oxidation state of the dissolving Mn varies with partial pressure of oxygen and affects the electrical properties of YSZ. Migration of Ca from (La, Ca)CrO3 separator to other cell components is one of the largest problems in the co-firing cell fabrication process because it prohibits the sintering of the separator.