Electrochemical and mechanical performance degradation mechanisms of solid oxide fuel cell stacks under long-term operation

Solid oxide fuel cells (SOFC) are an efficient energy conversion technology that directly convert chemical energy in fuel into electricity. However, the instability of the electrochemical and mechanical performance of SOFC during long-term operation presents a significant challenge to their commercialization. To address this issue, we employ electrochemical impedance spectroscopy, small punching tests and nanoindentation techniques to investigate the evolution of voltage and mechanical performance of SOFC stacks over 5000 h. Our findings indicate an average cell voltage degradation rate of 6.23 %/kh at 300 mA/cm² after 5000 h. The contribution of each factor causing voltage degradation is quantitatively evaluated, revealing that ohmic resistance degradation predominates, followed by cathodic-side O₂ surface exchange kinetic and O²⁻ diffusion. Furthermore, the high-temperature flexural strength, elastic modulus, and hardness of the single cell exhibit noticeable declines within the initial 10 h, with a 67.72 % reduction in flexural strength after 5000 h. Severe deterioration of nickel particles is observed in the anode, while strontium segregation, chromium poisoning and silver contamination are identified in the cathode. Overall, the quantitative analysis of changes in the performance of the stack is crucial for enhancing the long-term durability of SOFCs and their commercial applications in renewable energy systems.