Effect of phase transformation of zirconia on the fracture behavior of electrolyte-supported solid oxide fuel cells

Zirconia solid electrolyte provides the functions of mechanical support, electronic insulation and oxygen ions conductivity for electrolyte-supported solid oxide fuel cell. Ferritic stainless steel is used as current collector to study the structural stability of the two cells during the cooling process. The sample using fully-stabilized zirconia is cracked after the cooling process, while the partially-stabilized zirconia sample has no obvious changes. Thermal expansion coefficient of the two samples is similar, which exhibits that TEC is not the main factor to result in the fracture. In-situ X-ray diffraction results indicated that the conflict between the compression state in cell due to TEC and the volume expansion of the fully-stabilized zirconia sample due to phase transformation can cause cracking. Partially-stabilized zirconia sample can be transformed from tetragonal to cubic phase during the temperature rising, while can be recovered to its initial state during cooling. Even much more cubic phase can be transformed to the tetragonal phase induced by pressure stress during cooling, which plays an important role on the anti-cracking performance.