Alkali Effect on the Electrical Stability of a Solid Oxide Fuel Cell Sealing Glass

An alkaline-earth silicate (Sr-Ca-Y-B-Si) sealing glass with varying K2O content (2-5 mol %) was developed and evaluated for solid oxide fuel cell (SOFC) sealing applications. Two metallic interconnect plates were sealed with the glass and tested for electrical stability in a dual environment at elevated temperatures under a dc loading of 0.7 V. The metallic interconnect material, a ferritic stainless steel, was tested in the as-received state and after surface aluminization. The isothermal aging results showed stable electrical resistivity at 850 degrees C for similar to 600 to 800 h for all the sealing glasses, with or without K2O. The electrical resistivities at 850 degrees C were several orders of magnitude higher than the typical SOFC stack components. However, the glass with high alkali content (5%) showed excessive interfacial reaction, which resulted in debonding from both the as-received and the aluminized steel. Interfacial microstructures were characterized and possible reactions were discussed.