Optimization of Segmented-in-series Tubular SOFCs using an La0.5Sr0.5−xCaxMnO3 System Cathode and the Generation Characteristics Under Pressurization

In this research, we studied the optimization of a segmented-in-series tubular solid oxide fuel cell using La0.5Sr0.5−xCaxMnO3 system materials for the cathode. La0.5Sr0.25Ca0.25MnO3 (LSCM25) was chosen for the cathode to obtain high electric conductivity and prevent the formation of highly resistive second phases with Y2O3-stabilized ZrO2 (YSZ) electrolyte as a result of X-ray diffraction. To obtain lower resistance at the cathode/electrolyte interface, we studied the optimization of the cathode interlayer by changing the LSCM25-YSZ volume ratio and YSZ particle sizes. As a result, the lowest resistance was obtained at 50 vol.% LSCM25 (particle size: 3 µm)+50 vol.% YSZ (2 µm). The area-specific resistance of a tubular cell stack using the LSCM25 cathode and the LSCM25-YSZ interlayer decreased by 17% compared to a stack using only an LSCM25 cathode. We also conducted power-generation tests under pressurization to measure the cell stack performance integrated with micro gas turbines. Judging from the I-V characteristics, an increase of test pressure brought about not only an increase of open circuit voltage but also a decrease of internal resistances. According to our analysis of the internal resistances using the current interruption method, the electrode polarizations decreased as the operating pressure rose.