(Invited) Towards a Fundamental Understanding of the Cathode Degradation Mechanisms

While impressive solid oxide fuel cell (SOFC) performance has been achieved, durability under “real world” conditions is still an issue for commercial deployment. In particular cathode exposure to H₂O and CO₂ results in long-term performance degradation issues. Therefore, we have embarked on a multi-faceted fundamental investigation of the effect of these contaminants on cathode degradation mechanisms in order to establish cathode composition/structures and operational conditions to enhance cathode durability Using a dual Focused Ion Beam (FIB)/SEM) we are quantifying in 3-D the microstructural changes of cathode before and after the onset of cathode performance degradation. This includes changes in TPB density, phase-connectivity, and tortuosity, as well as tertiary phase formation. This is linked to heterogeneous catalysis methods to elucidate the cathode oxygen reduction reaction (ORR) mechanism to determine how H₂O and CO₂ affect the ORR as a function of temperature, time, and composition. By use of in-situ ¹⁸O-isotope exchange of labeled contaminants we will determine whether oxygen incorporated in the lattice of LSM and LSCF, and their composites with YSZ, originated from ambient O₂ or the contaminant as well as intermediate adsorbed species and mechanisms that lead to degradation. The results will be used to develop a cohesive and overarching theory that explains the microstructural and compositional cathode performance degradation mechanisms.