Operational requirements are 600 to 1,000 °C for thousands of hours.
John H. Glenn Research Center, Cleveland, Ohio
A solid oxide fuel cell (SOFC) is an electrochemical device that converts chemical energy into electrical power. A solid oxide electrolyzer cell (SOEC) operates in a reverse mode of SOFC, and produces O2 and H2 gases. SOFCs are being developed for a broad range of applications including portable electronic devices, automobiles, power generation, and aeronautics. The salient features of SOFCs are all-solid construction and high-temperature electrochemical reaction-based operation, resulting in clean and efficient power generation from a variety of fuels. SOFCs of two different designs, tubular and planar, are currently under development. Planar SOFCs offer several advantages such as simple manufacturing and relatively short current path, resulting in higher power density and efficiency. However, planar SOFCs and SOECs require hermetic seals. Various glass and glass-ceramics based on borates, phosphates, and silicates are being examined for SOFC seals. Silicate glasses are expected to perform superior to the borate and phosphate glasses as sealing materials.
Planar SOFCs and SOECs require hermetic seals along the edges of each cell and between the stack and gas manifolds to separate and contain fuel and oxidant within the cell and to bond cell components together. The requirements for SOFC and SOEC sealing materials are severe since the cells will operate at 600 to 1,000 °C for thousands of hours, with sealing materials exposed to both oxidizing and reducing conditions.
Quaternary silicate glasses containing MgO, CaO, Al2O3, and SiO2 have been identified as seal materials for SOFCs and SOECs. These glasses are free of the detrimental constituents such as boron and alkali metals. A representative glass composition in this quarternary system has been prepared by melting the constituents together. Properties of these quarternary silicate glasses are appropriate for use as hermetic sealing materials at operating temperatures of these devices. Seals made out of these glasses will be self-healing as operating temperatures of SOFC and SOEC are higher than the softening point of these glass sealants.
Physical, thermal, mechanical, and electrical properties of these glass sealants are compatible with those of other SOFC and SOEC components: electrolyte, cathode, anode, and interconnect.
This work was done by Narottam Bansal of Glenn Research Center.
Inquiries concerning rights for the commercial use of this invention should be addressed to NASA Glenn Research Center, Innovative Partnerships Office, Attn: Steven Fedor, Mail Stop 4–8, 21000 Brookpark Road, Cleveland, Ohio 44135. Refer to LEW-19100-1.