Abstract
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 SrZrO3 formation 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 and time were varied. The electrochemical performance of the cells was tested under various conditions of testing temperature, current density, and testing time by feeding humidified fuel: H2 (97 cc/min) and H2O (3 cc/min). Microstructure of model cells after sintering and testing 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. This shows that cathode sintering temperature depends on SrZrO3 formation. Microstructure of model cells after sintering for (a) 0.5h, (b) 1h, (c) 2h, (d) 16h was observed in details by STEM. Figure 1 shows that sintering time of cathode depends on SrZrO3 formation. Figure 1 indicates SrZrO3 formation mechanisms that SrZrO3 was partially formed between the YSZ and the GDC by grain boundary diffusion or surface diffusion along pore walls and covered fully the interface. Such SrZrO3 formation led to a decrease in electrochemical performance (Figure 2). These results indicate the importance of the SrZrO3 formation controlling the SOFC performance. Figure 1
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call