Engineering FEA Sintering Model Development for Metal Supported SOFCs

Chatzimichail, Rallou and Dawson, Richard (2021) Engineering FEA Sintering Model Development for Metal Supported SOFCs. PhD thesis, Lancaster University.

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Abstract

Sustainable energy and robust environmentally friendly methods of energy production are a few of the most discussed and researched topics in the past few decades. Now, more than ever, science and technology have contributed significantly to greener energy. Part of this effort is the constant evolution of the solid oxide fuel cells (SOFCs), and more specifically, metal supported SOFCs, which consists of thin ceramic layers on a thick metal substrate. This unique design and technology produces power and heat at low operating temperatures, which makes it accessible for a wide range of applications, such as residential homes, business centres, data centres and transportation applications. The aim of this work was to develop an engineering FEA model to understand the role of thermal stresses in the manufacturing processes of a specific metal supported SOFC, SteelCell®, produced by Ceres Power in the UK. In such a model, material properties, such as the thermal expansion coefficient, Young’s modulus, layer densification rates and creep, are very important. These properties, when interacting with the applied thermal processes, give rise to stresses within the fuel cell layers, resulting in permanent deformation and residual stresses at room temperature at the end of the processing steps. For this predictive tool, the input data was gathered by experiments and literature reviews. To ensure that they were representative of the actual cell, the input data was validated. Similarly, the simulation was setup to best reflect the manufacturing process of the cell, by mimicking the sintering processes and boundary conditions. The produced results showed the evolution of the thermally induced stresses on the ceramic layers and steel during the sintering process, as well as the residual stresses distribution and permanent deformation. The developed stresses were compressive stresses on the dense electrolyte layer, with the highest values being in the middle of the cell’s active area, where the highest deformation was also observed. To further understand the impact of the various design and manufacturing process variables, sensitivity studies were performed. The results showed that the electrolyte’s thickness and the sintering temperature had the highest effect on the cell’s maximum stresses, which was expected, due to material thermal properties and the fact that this layer was fully dense after the simulated process. In addition, different cell footprints were also simulated, that also resulted in compressive stresses on the electrolyte, with similar factorial effects. To further increase the confidence in the simulation results, validation of the cell deformation, by laser measurements, and ceramic layers’ stresses by means of synchrotron X-ray diffraction, was conducted. Both the simulation and experimental results were in satisfactory agreement, which increased significantly the confidence in the results. The FEA engineering sintering model presented in this work, established a good basis for further development of further simulations that could be used towards the future cell generations as it is a unique combination of experimental and modelling techniques, leading to a robust and powerful tool.