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

Abstract

The effect of current collecting layer (CCL) and cathode functional layer (CFL) thicknesses on the catalytic activity of the La0.6Sr0.4Co0.2Fe0.8O3-δ-Ce0.8Sm0.2O1.9 (LSCF-SDC) composite cathode was investigated by electrochemical impedance spectroscopy at 600 °C for 100 h. 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 (25–5 μm) while the LSCF-SDC CFL thickness (5-25 μm) 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 (3.31 Ω cm2). When LSCF CCL (5 μm) 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 100 h 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 in 100 h thermal treatment.