Microstructural Characterization of SrZrO3 Formation and the Influence to SOFC Performance

Thursday, 30 July 2015
Hall 2 (Scottish Exhibition and Conference Centre)
S. Kanae, Y. Toyofuku, T. Kawabata (Kyushu University), Y. Inoue (Kyushu University, Fukuoka, Japan), T. Daio, J. Matsuda (Kyushu University), J. T. Chou (Next-Generation Fuel Cell Research Center (NEXT-FC)), Y. Shiratori (Department of Hydrogen Energy Systems, Kyushu University), S. Taniguchi, and K. Sasaki (Kyushu University)
One of the major phenomena to shorten SOFC durability is the formation of insulated phases, such as SrZrO3, between the cathode and the electrolyte. It is known that SrZrO3 is formed and grown during sintering processes as well as during long-term operation. A systematical study is therefore desired to clarify the SrZrO3formation mechanisms and their influence on electrochemical properties.

 In this study, four parameters are considered and systematically varied: sintering temperatures of cathode, electrolyte, and buffer layer, and buffer layer thickness. The cells tested consist of yttria stabilized zirconia (YSZ) as the electrolyte, Ni- yttria stabilized zirconia (Ni-YSZ) as the anode, La(Sr)Co(Fe)O3(LSCF)as the cathode, and Ce0.9Gd0.1O2 (GDC) as the buffer layer. The GDC layer was sintered at 1300oC with 5μm in thickness, while the YSZ electrolyte was sintered at 1400oC. Cathode sintering temperature was varied from (1) 1000oC to (2) 1100oC and (3) 1200oC. The electrochemical performance of the cells was tested at 800oC, 0.2A/cm2 for 100h by feeding humidified fuel: H2 (97 cc/min) and H2O (3 cc/min). Microstructure of the three types of model cells after sintering and testing for 100h was observed in details by FE-SEM (Field Emission Scanning Electron Microscope) and STEM (Scanning Transmission Electron Microscope).

 Microstructural observation has been revealed (1) no SrZrO3 formation during sintering LSCF at 1000oC, and (2) a partial formation of SrZrO3 between the cathode and the electrolyte after sintering LSCF at 1100oC. (3) After the sintering of the LSCF cathode at 1200oC, the interface was fully covered by the SrZrO3 layer, clarified by the microstructural observation with EDX elementary mapping. Such SrZrO3 formation led to a decrease in electrochemical performance. These results indicate the importance of the SrZrO3 formation controlling the SOFC performance.