Influence of current collecting and functional layer thickness on the performance stability of La0.6Sr0.4Co0.2Fe0.8O3--Ce0.8Sm0.2O1.9 composite cathode

The effect of current collecting layer (CCL) and cathode functional layer (CFL) thicknesses on the catalytic activity of the La0.6Sr0.4Co0.2Fe0.8O3--Ce0.8Sm0.2O1.9 (LSCF-SDC) composite cathode was investigated by electrochemical impedance spectroscopy at 600 degrees C for 100h. Results revealed that the charge transfer process associated with the incorporation of O2- ions and the surface oxygen reduction reaction rate are dependent on CFL and CCL thicknesses, respectively. Area-specific resistance is dependent on CCL thickness in high-frequency arcs and on CFL thickness in low-frequency arcs. No significant change was observed in area-specific resistance value as the thickness of LSCF CCL decreased (25-5m) while the LSCF-SDC CFL thickness (5-25m) was gradually increased. However, the LSCF-SDC composite cathode (without CCL) showed poor catalytic activity toward the oxygen reduction reaction and had a high area-specific resistance value (3.31cm(2)). When LSCF CCL (5m) was used, the area-specific resistance value decreased by 16 times relative to the ASR of a sample without CCL. The field emission scanning electron microscopy results indicated that these cathodes exhibited a clear change in microstructure on the surface of the LSCF CCL after 100h of thermal treatment in oxygen. The particle agglomeration and Sr surface segregation affected the surface catalytic activity toward oxygen reduction reaction at the LSCF CCL. As a result, the ASR value increased gradually in100 h thermal treatment.