Microstructure in SOFC: electrochemical simulations and experiments

Sammanfattning: Solid oxide fuel cells (SOFCs) are highly efficient and environmentally friendly power sources that convert chemical energy directly into electricity and heat, without the need for combustion. Despite their many benefits, the performance and durability of SOFCs heavily depend on the quality of their porous anode and cathode components. There are significant challenges with regard to their commercialization due to the potential failure and degradation of their anode and cathode components. Optimizing SOFC electrodes requires obtaining critical microstructure parameters and understanding their impact on the overall performance. This can be achieved through advanced tomography techniques and fully coupled Multiphysics simulations, which provide insights into the quality of the electrode and the complex electrochemical processes that occur within it. In this thesis, experiments were conducted to investigate different anode microstructure impacts on SOFC performance through electrochemical analysis. Besides, 2D microstructure tomography was obtained to construct real 3D volumes. Based on the tomography information, the porosity and tortuosity of the porous electrode were calculated and compared. Different tortuosity calculation methods were compared to obtain values used for Multiphysics simulations. A fully coupled Multiphysics model was constructed step by step. Firstly, the electrochemical kinetic models are compared based on the Butler-Volmer equations. Secondly, different diffusion models are compared with and without Knudsen diffusion. Based on the 3D Multiphysics CFD model, the microstructure parameters' impact on the SOFC performance was studied. Meanwhile, a SOFC model based on different sealant materials was constructed to investigate the overall thermal stress distribution. Thermal stress at an electrode/electrolyte interface was also modelled and analyzed. The results showed that the interface contact mode and the geometry size of the SOFC component significantly impacted the thermal stress distribution and its values.In summary, the experiment analysis findings emphasize optimizing the microstructure design to balance gas diffusion, charge transport, and electrochemical reactions. The fully coupled Multiphysics models can be used for further SOFC design, regarding internal transport processes and mechanical stability. In general, this thesis has made contributions to the field of SOFCs.