Coupled degradation mechanism of electrochemical and mechanical performance of solid oxide fuel cells under thermal cycling

Solid oxide fuel cells (SOFCs) are efficient energy conversion devices that directly convert chemical energy from fuel into electrical energy. Despite their potential, the commercialization of SOFCs faces significant challenges due to thermal cycling instability, which affects both electrochemical and mechanical performance. To address this issue, we employ electrochemical impedance spectroscopy, small punch testing, and nanoindentation techniques to investigate the changes in electrochemical and mechanical performance of SOFC stacks under 1 to 10 thermal cycles. The degradation mechanisms of SOFC performance are analyzed based on microstructure changes. The findings reveal a voltage degradation rate of 12.75 % after 10 thermal cycles at a current of 40 A. The significance of each degradation mechanism in voltage degradation is quantitatively determined. Ohmic resistance degradation is the dominant factor, followed by the degradation of the anode charge transfer reaction. The high-temperature flexural strength of the PEN decreases by 54.22 % after 10 thermal cycles, with the most significant deterioration occurring during the initial cycle. Additionally, after 10 thermal cycles, cathodic Sr segregation and substantial anodic deterioration are observed, including Ni particle coarsening, migration, and agglomeration. Based on the impact of anode Ni particle deterioration on both electrochemical and mechanical performance, a theoretical model of voltage and mechanical performance degradation is established. This model is significant for enhancing the thermal shock resistance of the SOFC stack.