Effect of cathode microstructure on cathode polarization in sintered strontium-doped lanthanum manganite/yttria stabilized zirconia solid oxide fuel cells.

摘要

Cathode polarization in strontium-doped lanthanum manganite (LSM)/yttria stabilized zirconia (YSZ) Solid Oxide Fuel Cells (SOFCs) was compared to cathode microstructure under 1h isochronal sintering between 950 and 1400°C, and under isothermal sintering at 1200°C for 2-25h. My study investigated comprehensively the effects of two-dimensional (metric), three-dimensional (topological) microstructure properties on cathode activation, ohmic, and concentration polarizations.;In the study of the activation polarization, the developed focused ion beam/scanning electron microscopy (FIB/SEM) serial-sectioning techniques were combined with the disector homogeneity analysis. Investigation of the topological homogeneity ensured unbiased quantification of metric properties by applying classical stereology. A new method of preparing transmission electron microscopy (TEM) cross-sectional sample of the LSM/YSZ interface using a FIB and a micromanipulator was applied to the TEM study of the initial stages of La2Zr 2O7 (LZO) formation at the A-site deficient LSM/YSZ interface. The effect of LZO formation on activation polarization was underlined with respect of previous works that attached no relevance to it. It was found that LZO phase modifies the metric properties and rapidly degrades the activation polarization, thus makes difference in the relationship between the metric properties and the activation polarization, suggested in previous SOFC models.;During the investigation of the ohmic polarization, Ohm's law was applied to relate LZO thickness (one of the geometric factors) with high-frequency impedance (ohmic resistance). It was found that LZO phase dominated ohmic polarization by modifying geometry factors and physics of the oxygen reduction mechanism.;During analysis of the concentration polarization, a new way of quantification of the geometric tortuosity of the porous cathode was performed using an elementary skeletonziation model. In conjunction with two pore-network models under different flux domains, the elementary skeletonization model was effective to study transport properties of the oxygen. It was found that the faster kinetics of the gas transport through the porous cathode, the less resistance to the gas transport, thus the smaller concentration polarization.