Unbiased characterization of three-phase microstructure of porous lanthanum doped strontium manganite/yttria-stabilized zirconia composite cathodes for solid oxide fuel cells using atomic force microscopy and stereology

Microstructural characteristics of porous LSM/YSZ composite cathodes greatly influence the performance of solid oxide fuel cells. The triple phase boundaries, for example, account for a significant portion of the electrochemically active sites in these porous composite cathodes. Nonetheless, experimental characterization of the relevant microstructural attributes has been problematic due to lack of suitable microscopy techniques for simultaneous observations of all three phases (i.e., LSM, YSZ, and porosity) needed for identification and unbiased characterization of the triple phase boundaries. In this contribution it is shown that a combination of chemical etching and atomic force microscopy clearly reveals all three phases and the triple phase junctions in the microstructural sections. Further, stereological techniques based on the geometric probabilities of stochastic geometry enable unbiased statistical estimation of total triple phase boundary length per unit volume and other microstructural attributes from simple counting measurements performed on representative microstructural sections.