Fracture process of nonstoichiometric oxide based solid oxide fuel cell under oxidizing/reducing gradient conditions

The influence of chemically induced expansion on the fracture damage of a nonstoichiometric oxide (ceria) based solid oxide fuel cell (SOFC) single cell laminate was investigated by using numerical stress analyses under oxidizing/reducing gradient condition. The single cell examined in this study was composed of electrolyte (Ce_0.8Sm_0.2O_2-δ), anode (Cermets of Ni-Ce_0.8Sm_0.2O_2-δ), and cathode (La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ), respectively. The finite element method (FEM) was employed to calculate the residual stress, thermal stresses, and chemically induced expansion stresses for the single cell. The residual and thermal stresses were calculated much smaller than the fracture strength of the individual components of the single cell. On the other hand, the chemically induced expansion stresses were shown to remarkably increase for the temperature range greater than 973 K and accounted their magnitude for primary part of the induced stress. It was shown from the FEM that the maximum circumferential stress induced in the single cell exceeded the fracture strength of the individual components at the onset of the fracture damage detect by acoustic emission (AE) method.