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In this work, a 3D multi-physics coupled model was developed to analyze the temperature and thermal stress distribution in a planar solid oxide fuel cell (SOFC) stack, and then the effects of different flow channels (co-flow, counter-flow and cross-flow) and electrolyte thickness were investigated. The simulation results indicate that the generated power is higher while the thermal stress is lower in the co-flow mode than those in the cross-flow mode. In the cross-flow mode, a gas inlet and outlet arrangement is proposed to increase current density by about 10%. The generated power of the stack increases with a thin electrolyte layer, but the temperature and its gradient of the stack also increase with increase of heat generation. The thermal stress for two typical sealing materials is also studied. The predicted results can be used for design and optimization of the stack structure to achieve lower stress and longer life.

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Solid oxide fuel cell (SOFC) is one of the new energy conversion technologies producing electricity and heat from fuel and oxidant through an electrochemical reaction. The high operating temperature has many advantages including high efficiency, flexible fuel adaptability and low emissions. However, it has also some drawbacks, e.g., thermal expansion mismatches among the involved materials, particularly when the temperature reaches around 1400 oC during the sintering process, which may cause non-uniform distribution of thermal stress and even further deformation and warpage observed in the cell manufacturing steps. A three-dimensional CFD (computational fluid dynamics) simulation model is developed to study the thermal stress distributed in the sintered function layers of the anode-supported planar SOFC unit cells (10×10 cm2) using a finite element method. Five layers are included, i.e., cathode and its separation layer (GDC/LSCF, 70 µm), anode support and active layers (Ni/YSZ, 550µm), and electrolyte layer (YSZ, 30 µm) between them. In terms of the thermal stress and deformation, the predicted results are presented and discussed for the sintered unit cells with different angels located around the four cornels. It is found that the maximum thermal stress occurs at the interface between the electrode and electrolyte; the magnitude and distribution of thermal stress at the interfaces are closely related to the material thermal properties; the maximum deformation about 13 mm in the thickness direction is predicted for the 90-angel shaped cornels at the sintering temperature 1400 oC, which is bigger than that for the case with the circular shaped cornels; the deformation magnitude depends not only on the maximum thermal stress, but also the difference between the maximum and minimum thermal stress. The findings and predicted results may be applied for optimization of design and sintering conditions for SOFC unit cells. Acknowledgements This work is supported by the National Key Research and Development Project of China (2018YFB1502204, 2018YFB1502203, 2018YFB1502205), the Ningbo major special projects of the Plan “Science and Technology Innovation 2025” (2018B10048). Figure 1

Typical operating temperature for a solid oxide fuel cell (SOFC) ranges from 700°C to 800°C. A large temperature gradient and thermal stress are induced by internal losses and electro-chemical reactions, resulting in significant structural damage and performance degradation of a SOFC stack, which has become a hindrance to its applications. In this study, a three-dimensional multi-physics CFD model is developed and employed to study the temperature and thermal stress distribution of a planar SOFC stack, then effects of the structure design parameters are investigated, including the flow channel arrangement (i.e., co- and cross-flow) and thickness of the electrolyte layer. The stack modeled is composed of three-unit cells, metallic interconnect layers, sealing components, and anode/cathode current collectors. The simulation results show that the temperature difference in the co-flow case is smaller and the thermal stress is lower than those predicted in the cross-flow. The overall performance of the stack improves as the thickness of the electrolyte layer decreases, but the temperature and its gradient inside the stack become higher. In addition, a large temperature gradient is observed inside the thin electrolyte layer, which leads to a significant increase of the thermal stress. The findings and the research methods in this study can be applied to design and optimize the stack structures by considering the temperature and the thermal stress distribution.