Quantitative Analysis of LSCF and LSM-YSZ Cathode Microstructure by FIB/SEM Tomography

摘要

The mixed ionic-electronic conducting cathode (La, Sr)(Co, Fe)O3-Δ (LSCF) is applied for solid oxide fuel cells (SOFCs) at intermediate temperatures [1] because of its high oxygen reduction reaction rate. Secondary phases and interdiffusion reactions at the interface LSCF cathode/zirconia-based electrolyte may counteract its advantages [2]. For higher temperatures (> 700°C) the composite cathode (La, Sr)MnO3 (LSM) – Y2O3 doped ZrO2 (YSZ) is an adequate alternative. Oxygen reduction reaction takes place at triple phase boundaries between LSM (electron conductor), YSZ (ion conductor) and pore. Quantitative information about microstructure characteristics at the micro- and nanoscale, which determine the cathode performance, is receivable by advanced imaging techniques such as focused ion beam/scanning electron microscopy (FIB/SEM) or X-ray tomography [3,4]. The composite cathode, in particular, comprises the challenge of overcoming the weak material contrast between LSM and YSZ using SEM. This contribution will give quantitative values on porosity, surface area, tortuosity and triple phase boundary length of high-performing LSM-YSZ and LSCF cathodes, and will show how FIB/SEM tomography using different detector configurations can help to identify these parameters. We will compare microstructure characteristics of both types of cathodes and enlighten challenges in image reconstruction, parameter acquisition and interpretation.