Optimization of Segmented-in-series Tubular SOFCs with an (La, Sr)CoO₃ System Cathode and the Generation Characteristics under Pressurization

Abstract

We studied the application of LaCoO₃ system cathode to improve the performance of segmented-in-series tubular type solid oxide fuel cells (SOFCs) operating at high temperature (1173 K). (La_1−xSr_x)CoO₃ (LSC, x=0.2 or more) was chosen to take advantage of two of its properties: high electric conductivity and favorable behavior of element diffusion to a cathode interlayer (CIL) of (Sm_0.2Ce_0.8)O₂ (SDC20). The cell stack performances were compared using LSC and (La_0.5Sr_0.25Ca_0.25)MnO₃ (LSCM) to cathode current collection layer (CCCL). The modification of cell stack structure composed of effective generation part and interconnector part was also examined. The area specific resistance (ASR) of the overall cell stack resistance with LSC modifying a stack structure decreased 18% than that of the stack using LSCM with conventional structure at atmospheric pressure. In a pressurized test of the cell stack fabricated with LSC, an increase of pressure resulted in a decrease of the ASR. As a result of comparing the pressurized performances of LSCM CCCL/(LSCM-10YSZ) CIL, LSCM/SDC20 and LSC/SDC20, the effect of ASR decrease by pressurization fell as the cell stack performances improve. We also found, however, that the cell stack fabricated with LSC will require improvements in long-term durability and thermal cycle characteristics.