Chemical Stability Challenges and Mechanistic Insights of SOFC Cathodes

The cathode of solid oxide fuel cells (SOFCs) plays a critical role in the kinetics of the oxygen reduction reaction (ORR) and the overall device performance. Still, its long-term stability faces severe challenges from chemical degradation in high-temperature operating environments. This review focuses on the chemical poisoning mechanisms induced by thermodynamically driven surface and interfacial reactions, including alkaline earth metal segregation, Cr vapor poisoning, and the adsorption of acidic gases (CO2 or SO2), as well as the impact of chemical reactions caused by water vapor on the cathode. Alkaline earth metals (such as Sr2+ and Ba2+) in perovskite cathodes migrate to the surface, forming low-activity carbonates/sulfates with ambient CO2 or SO2, which block active sites and disrupt ion transport. Cr species volatilized from the Fe–Cr interconnects deposit on the cathode surface in the form of SrCrO4 or Cr2O3, accelerating the segregation of Ba/Sr and increasing the polarization resistance. Cathode degradation caused by these substances has attracted the attention of researchers, who have done a great deal of work on material development to address these issues. In the future, when developing SOFC cathode materials, these factors need to be considered, and appropriate strategies and methods should be adopted to minimize the resulting degradation as much as possible.