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Novel Approach to Strengthening Ceramic Cathode Contact and Validation in a Generic Stack Test Fixture

Tuesday, 25 July 2017
Grand Ballroom East (The Diplomat Beach Resort)
Y. S. Chou, J. F. Bonnett, and J. W. Stevenson (Pacific Northwest National Laboratory)
The mechanical integrity of cathode contact during routine thermal cycling plays an important role in the performance of solid oxide fuel cells. This is because the final stack firing is typically a few hundred degrees lower than normal sintering temperatures, which led leads to poor solid-state sintering and hence poor cathode contact strength. To improve the contact strength and thermal cycle stability, precious metal such as silver has been used and showed good thermal cycle stability. However, issues of cost as well as long-term volatility remain unacceptable for practical industrial application. In this work, we examined three approaches to strengthening cathode contact by (1) mechanical interlocking with engineered surface, (2) enhanced sintering with sintering aid CuO and Bi2O3, and (3) reinforcement with strong and inert YSZ short fibers. Density was measured and bulk strength was determined with diametral compression tests. Ceramic bilayer couples were joined at elevated temperatures of 850 and 950oC for 2h with candidate LSM20 contact using the three approaches. Uniaxial tensile strength measurements were conducted on joined couples at room temperature. Fracture surface analysis was applied to correlate with strength results. The results showed the largest improvement in contact strength with both engineered cathode surface and sintering aid of Bi2O3. The effect of YSZ short fibers alone resulted in very poor strength due to sintering with rigid inclusion. The strength contribution was minute when combining both sintering aid and YSZ fibers. Finally, candidate cathode contact compositions will be tested on a 2”x2” LSM-based cell in a generic stack fixture to assess its effect on thermal cycle stability as well as stability at 800oC for 500-1000h. Post-mortem optical and electron microscopy will be conducted to assess the microstructure and chemical compatibility of cathode and contact materials.