Degradation factors in (La,Sr)(Co,Fe)O3-δ cathode/Sm2O3–CeO2 interlayer/Y2O3–ZrO2 electrolyte system during operation of solid oxide fuel cells

•The microstructural change of the LSCF/SDC/YSZ system was analyzed quantitatively.•The distribution profile of SrZrO3 in the LSCF/SDC/YSZ system was revealed.•The TPB length reduced significantly after discharge for 400 h at 1000 °C.•The agglomeration of SDC and LSCF phases was also confirmed.•The solid-state reaction between YSZ and SDC proceeded considerably.

In this study, the miscrostructural change of the LSCF/SDC/YSZ system upon discharge was analyzed quantitatively by the focused ion beam–scanning electron microscopy as well as the transmission electron microscopy. It is widely recognized that the formation of highly-resistive SrZrO3 phase degrades the cell performance in this system. In fact, the ohmic loss and cathodic overpotential increased in response to the six-fold increase in the volume of SrZrO3 phase after 400 h of discharge at 1000 °C. However, the microstructural change proceeded in the whole part of this system, indicating that various degradation factors need to be considered; e.g., 1) the agglomeration of SDC and LSCF phases, 2) the reduction in triple phase boundary length, and 3) the formation of ceria-zirconia solid solution.