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 CaxMnO3 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 mu m) + 50 vol. % YSZ (2 mu m). 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, all 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 current interruption method, the electrode polarizations decreased as the operating pressure rose.