Chemical Degradation of SOFCs: External Impurity Poisoning and Internal Diffusion-Related Phenomena

Durability of SOFCs is one of the most important requirements for commercialization. In this paper, we analyze chemical degradation phenomena caused by both extrinsic and intrinsic origins besides by thermal/redox cycling. As external degradation, impurity (sulfur,phosphorus etc.) poisoning has been systematically analyzed and classified based on both thermochemical and kinetic consideration. We present typical intrinsic chemical degradation phenomena observed, mainly diffusion-related processes (interdiffusion, grainboundary diffusion, dopant dissolution, phase transformation etc.) around interfaces between the electrolyte and the electrode, which has been revealed through high-resolution STEM-EDX analysis of cells after long-term operation. Degradation mechanisms have been classified.