Effect of Al2O3/SiO2 ratio on the properties of glass-ceramic sealants for solid oxide electrolysis cells

Reliable sealing is essential for planar solid oxide electrolysis cells (P-SOECs), particularly under high-temperature and steam-containing conditions. In this study, two processable CaO-MgO-Al 2 O 3 -SiO 2 -based glass-ceramics compositions were comparatively evaluated to examine how the Al 2 O 3 /SiO 2 ratio affects phase assemblage, network-related spectroscopic features, thermal expansion, hot-stage deformation, interfacial contact, and OCV response. Increasing the Al 2 O 3 /SiO 2 ratio from 0.09 to 0.25 decrease the average coefficient of thermal expansion (CTE) from 12.3 × 10 −6 to 11.35 × 10 −6 K −1 and increased Tg from 642 to 654 °C. In single-cell screening at 750 °C, the 3.14Al cell joined at 850 °C for 30 min gave the highest measured OCV among the tested conditions. During long-term operation at 750 °C, stable OCV values of 1.08 V in 3% H 2 O-H 2 and 0.95 V in 50% H 2 O-H 2 were maintained for 210 h without detectable degradation. Post-test analysis confirmed crack-free interfaces between the 3.14Al sealant and adjacent SUS430, NiO-YSZ, and YSZ components after prolonged exposure to a humid-reducing atmosphere. These results demonstrate that the optimized 3.14Al glass-ceramic combines good interfacial compatibility, long-term stability, and steam corrosion resistance, positioning it as a promising sealing material for next-generation P-SOEC stacks.