Microstructural Characterization Using Orientational Imaging Microscopy of SOFC Cathodes Subjected to Thermal and Electrochemical Loads

Cathodes in SOFCs consist of interconnecting and contacting two-phase interfaces and three-phase lines in a complex three-phase microstructure. Furthermore, the interfacial crystallography is dynamic and changes in response to thermal loads and to interfacial electrochemical polarizations. Owing to this inherent complexity, a complete and fundamental understanding of both the basic mechanisms of cathodic processes and their performance degradation has not been achieved. We have carried out quantitative orientational imaging microscopy (OIM) on button-cell geometry SOFCs containing porous cathodes of yttria-stabilized zirconia and lanthanum strontium manganese oxide. A series of cathodes, taken from cells subjected to both open-circuit and current-loaded fuel-cell conditions, were characterized with OIM to determine their microstructural and crystallographic properties as a function of thermal and electrochemical history. In this presentation we will discuss the results of these studies, focusing on the crystallographic nature of the statistically important two-phase interfaces and three-phase lines