Thermal stresses in planar solid oxide fuel cells due to thermal expansion differences

Thermal stresses are a critical factor in the development of reliable, fuel efficient, planar solid oxide fuel cells (SOFCs). In the literature, broad recommendations have been made on the importance of minimising differences in thermal expansion coefficients (TECs) of materials used to fabricate SOFCs. The stresses due to temperature gradients, material property changes, material reliability, and differences in TECs in simple component configurations are reviewed. The purpose of the present paper is to examine the effect of size and to establish the minimum difference necessary in thermal expansion coefficients for a reliable SOFC. Two planar SOFC models with closed form solutions are used to investigate thermal tensile and shear stresses resulting from the fabrication process. For an acceptable probability of failure of less than 10^-6 in the zirconia electrolyte, the differences in the component TECs must be less than 1% of the zirconia electrolyte TEC.