Electrical Properties of Alkali/Alkaline-Earth Borosilicate Glass Composite Sealants for Solid Oxide Fuel Cells

Development of a reliable sealant or sealing system remains one of the top priorities in planar solid oxide fuel cells (SOFCs) technology. Recently, a compliant glass seal such as an alkali silicate glass was proposed for SOFCs. In contrast to the conventional glass–ceramic sealant which develops a rigid or semi-rigid microstructure after sealing, the compliant glass shows so called “self-healing” behavior and will remain vitreous without substantial crystallization after sealing and during operation at elevated temperatures. The objective of this study was to investigate the relationship between sealant structure and high temperature electrical conductivities of glass composite sealants for SOFCs. Alkali/alkaline-earth borosilicate glass-based sealants, both with and without Al₂O₃ or ZrO₂  fillers, were heat treated at various temperatures for periods of up to 48 h. The effects of filler type, densification of glass and alkali/alkali-earth oxide content in sealants on the electrical conductivities of the sealants were investigated. The results showed that the electrical conductivity of a glass composite sealant containing ZrO₂ filler increased ten times after 48 hours of heat treatment. The electrical conductivity of a ZrO₂ filler-containing glass after heat treatment was similar to that of an Al₂O₃ filler-containing glass. This was attributed to the densification of sealing glass by heat treatment.