Modeling of cooperative defect transport and thermal mismatch in a planar solid oxide fuel cell

Mixed ionic-electronic conducting (MIEC) membranes are widely applied as cathode material in solid oxide fuel cells (SOFCs). Nonetheless, the chemical expansion of an MIEC membrane caused by point defects (oxygen vacancies and small polarons) during oxygen transport induces cell failure. In this study, a multilayer thermo-chemical-mechanical model was proposed to consider defect diffusion under sudden changes in the cathode atmosphere, thermal expansion mismatch, and mechanical bending deformation. Under the set boundary conditions, the overall structural curvature of the multilayer system was relieved when the cathode was subjected to a high tensile stress. The influences of relevant parameters on the transient stress field were also investigated, and the overall stress of the multilayer structure decreased significantly when the oxygen partial pressure in the inlet channel was constrained. Reducing the sintering temperature and chemical expansion coefficient could improve the reliability of the planar SOFC. In addition, the effect of constraints in different directions on the multilayer system stresses is also investigated. This study provides theoretical support for use in designing the stabilities and gas supply strategies of planar solid fuel cells.