Thermo-Electro-Chemo-Mechanical Modeling of Solid Oxide Fuel Cell for Stress and Failure Evolution during Duty Cycle

A comprehensive three-dimensional model for an assembled button solid oxide fuel cell is developed by coupling thermal-electrochemical and mechanical models. Different mechanical effects including residual strain, thermal strain, accelerated and normal creep, mechanical properties change of anode, as well as chemical expansion are considered. The mechanical response of the button cell subjected to an idealized duty cycle from the as-fabricated state, heating-up stage, reduction stage, to three operation periods of 800 C, 700 C, and 600 C is numerically simulated. Simulations are based on and validated by the experimental polarization curves and residual stress curve. Results show that the sealant is susceptible to fracture at the as-fabricated state, while the cathode is likely to fail during heating-up stage. The accelerated creep effect during reduction significantly eliminates the tensile stress in the anode nevertheless leads to higher stress in the cathode and electrolyte. It indicates that the assumption of zero-stress temperature at the reduction point could cause an underestimation of stress in the cathode and electrolyte in the case of a constrained cell. The chemical expansion effect in the cathode is more prominent at higher operating temperatures. A minimum failure probability of the cell is found at 700 C with consideration of chemical expansion.