Designing glass sealants for intermediate- and low-temperature solid oxide fuel cells: challenges and prospects

Glass sealants are indispensable for commercialising the energy-efficient and environmentally friendly planar design of solid oxide fuel/electrolyser cells (SOFC/SOECs). Mostly, alkaline-earth-modified aluminosilicate and aluminoborosilicate glass systems are standard and state-of-the-art glass sealants for high-temperature (HT) SOFCs (700-1000 °C). For intermediate-temperature (IT) and low-temperature (LT) SOFC operation, glass systems such as silicate-, borosilicate-, and phosphate-based glasses have been explored. Borosilicate-based sealants exhibit tunable thermal expansion and a lower characteristic temperature with poor stability in reducing oxygen partial pressure than silicate-based glasses. On the other hand, phosphate-based glasses offer lower sealing temperatures but often exhibit limited chemical durability and thermal stability. Thus, an appropriate glass sealant is still required for IT/LT-SOFCs, which should be compatible with the new set of materials to lower SOFC operating temperatures. Thus, designing suitable glass compositions for IT/LT-SOFCs poses several challenges, owing to the simultaneous requirements of compatibility with various SOFC components, fundamental constraints in optimising glass properties, and stability issues during long-term thermochemical cycles during operation. This perspective presents challenges and prospects for developing new sealant materials for IT/LT-SOFC, along with the background and required properties for glass sealants.