Aug 13, 2011

DOE awards SBIR Phase II High-Temperature Viscous Sealing Glasses for Solid Oxide Fuel Cells

Statement of the problem or situation that is being addressed: Solid Oxide Fuel Cells (SOFCs) require hermetic seals to prevent mixing of the fuel and oxidant streams within the cell stack and to seal the stack to the system manifold. Reliable sealing materials must (a) possess viscosity-temperature characteristics that are compatible with sealing requirements and that allow for stress relaxation and ‘self-healing’ without excessive flow, under pressure, that would compromise seal integrity; (b) be chemically compatible with SOFC components and so not alter the long-term thermo-mechanical stability of the seal by forming deleterious interfacial reaction products; (c) avoid the significant volatilization of glass constituents under the SOFC operational conditions that has been associated with other sealing materials, and so alter the viscous properties of the seal or the performance of the SOFC; (d) possess dilatometric properties that are compatible with other SOFC components, and these properties must be stable over the course of the SOFC lifetime.

Objectives: The main goal of the Phase II program is to complete the development and commercialization of new ‘viscous glass’ compositions, first identified in Phase I, that are stable against crystallization and can be used to fabricate reliable, thermochemically stable, hermetic seals for solid oxide fuel cells with desired service life of 40,000 hours. At the successful completion of the project, MO-SCI Corporation will produce new hermetic sealing materials critical for the development of solid oxide fuel cells as practical alternative energy devices.

What was done in Phase I: The Phase I research successfully identified and tested several glass compositions that could be used as viscous seals for SOFCs. The glasses possess desirable viscosity characteristics and relatively low liquidus temperatures, exhibit no significant weight losses from the molten state when held in air, and survive dozens of thermal cycles.

What is planned for the Phase II project: Phase II activities will build on the Phase I accomplishments by optimizing the glass compositions, and will address the unresolved technical issues identified in Phase I, including the long-term performance of the seals and the development of a commercial sealing technology.

Commercial Applications and Other Benefits: The lack of a reliable, thermally stable, hermetic sealing system is one of the most important barriers to the commercialization of solid oxide fuel cells. A properly engineered ‘viscous glass’ sealing system could mitigate concerns about the long-term thermomechanical stability of rigid glass-ceramic seals currently under development. The Phase II work will produce such a sealing system that will allow the Solid State Energy Conversion Alliance (SECA) program to realize its goal of 40,000 hours of SOFC operational life. Improved power generation technologies will help the nation make more efficient and environmentally-responsible use of its abundant domestic coal reserves. Accordingly, the nation seeks advances in SOFC technology for Integrated Gasification Fuel Cell (IGFC) systems. IGFC systems are attractive alternatives to current technologies in large-scale stationary applications. This Phase II project will help to overcome the critical barrier to SOFC commercialization.

Key Words: viscous, sealing glass, self-healing, solid oxide fuel cell, SOFC