Bonding phase of amorphous silicate gas-tight seals for electrode-supported SOFCs

Abstract

Electrode-supported SOFCs exhibit highly electrochemical performance but they require gas-tight sealing between porous electrodes. Conventional sealing materials can sufficiently seal with dense materials such as ceramics and metals, but the sealing materials were much penetrated into porous electrodes and excess penetration caused severe gas-leakage. We have prepared insulating flexible sheets to realize gas-tight sealing against porous SOFC electrodes during fusion at 800°C. Amorphous Na2O-SiO2 spherical particles (NS particles) and amorphous SiO2 particles (S particle) were synthesized by sol-gel method, and thick sheets containing NS and S particles were obtained by tape-casting method. Porous La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) ceramics were used as a porous electrode to investigate penetration of sealing materials and identification of bonding phases. Fusion of the sheet against porous LSCF at 800°C resulted in gas-tight sealing and the formation of NaLa9(SiO4)6O2 (NLSO) phase. The formation of NLSO phase was controlled by the addition of S particles. TEC of NLSO did not show anomalous profiles which often result in severe cracks and are shown for some glasses at glass transition temperatures. Therefore, the NLSO phase would be valuable as the bonding phase between LSCF and glass seals.