Glass-ceramic sealants for planar IT-SOFC: A bilayered approach for joining electrolyte and metallic interconnect

To develop suitable sealants for planar anode-supported intermediate temperature solid oxide fuel cells (IT-SOFC) operating at around 800 degrees C, several glass-ceramic compositions based on the RO-Al2O3-SiO2 (R=Ba,Ca) system have been prepared and investigated. Thermal, chemical, and electrical properties of the glass ceramics along with crystallization behavior and bonding characteristics of parent glasses with yttria-stabilized zirconia (YSZ) electrolyte and ferritic steel-based interconnect Crofer22APU are studied. The glass transition temperatures (T-g) of the developed glasses are within 600-635 degrees C. By varying the alkaline-earth metal content, the coefficient of thermal expansion (CTE) values can be tailored between that of YSZ and Crofer22APU. Based on the crystallization behavior, a single glass seal having matching CTE with Crofer22APU and a bilayer glass seal having different CTE values within the range of 10-13x10(-6)/K are found to be effective for metal-metal and metal-electrolyte sealing, respectively. The electrical resistivities of the sealants are quite high (rho(800 degrees C)> 10(5) Omega cm), and under sandwiched condition between two metals, the developed glasses are found to maintain this high resistivity even after 100 h of operation. A low helium leak rate value (< 10(-6) Pa m(2) s(-1)) has been observed for most of the developed glasses. (c) 2008 The Electrochemical Society