Microstructural Characterization of Solid Oxide Fuel Cell Cathode Materials

The microstructure of solid oxide fuel cell cathodes has been previously studied with respect to parameters such as grain size, pore distribution, and triple phase boundary distribution. However, little is known about the crystallographic nature of grain boundaries and pore interfaces in SOFC cathodes even though it has been demonstrated that crystallography can lead to anisotropies in surface reaction rates.;For dense YSZ and dense LSM, the steady state GBPDs exhibited weak anisotropies that reflected the thermodynamically preferred distribution. For the remaining systems, the steady state thermodynamically preferred GBPDs and the PBDs are affected by the constraints imposed by the presence of multiple phases. For dense YSZ, the GBED is inversely related to the GBPD and will be shown to not be predictable by known computed surface energies.;The benchmark material for SOFC cathodes is composed of strontium-doped lanthanum manganese oxide (LSM), yttria-stabilized zirconia (YSZ), and pores. This work investigates the crystallographic nature of interfaces in porous LSM/YSZ and the following constituent systems: dense YSZ, dense LSM, dense LSM/YSZ, porous YSZ, and porous LSM. Samples were prepared using standard SOFC preparation methods, where annealing temperature and time were varied, and orientation imaging microscopy was used to obtain crystallographic data. The results on the grain size distributions, pore size distributions, grain boundary plane distributions (GBPDs), pore boundary distributions (PBDs), and misorientation angle distributions of the six systems will be discussed as a function of temperatures and times. In addition, the results on the grain boundary energy distribution (GBED) in dense YSZ will be presented.