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High-Temperature Sealing Systems Based on Viscous Glass

Description:

High temperature (650°C to 850°C) planar solid oxide fuel cell (SOFC) stacks are comprised of alternating fuel and air chambers, which are sealed from each other and connected to fuel and air delivery manifolds, respectively. These seals are subject to a demanding set of performance criteria due to the extreme operating environment. The seals must have a low electrical conductivity, be chemically and mechanically stable in a high temperature reactive environment (moist reducing and/or oxidizing conditions), and demonstrate chemical compatibility with the cell and interconnect materials of the particular cell/stack design. Grant applications are sought to develop viscous glass-based sealing concepts for SOFCs. Ideally, the viscous glasses would maintain a softening temperature at or slightly below the lower bounds of the SOFC operating temperature (650°C) and retain suitable viscosity to the upper bound (850ºC), over the life of the seal, and be resistant to devitrification within the SOFC environment. Given that such a glass on its own may be unable to withstand the differential pressure across the seal (up to 2 psid) or the stack bearing load, it is envisioned that an engineered composite solution will be required to carry bearing loads and retain the viscous sealing material. The ultimate objective is the development of an economically-viable, manufacturable seal material followed by a composite system design that can provide sealing under all operating conditions for the life of planar SOFC stacks.

For reference purposes, the sealed perimeter for a single fuel cell-interconnect repeat unit seal is approximately 100cm. Approaches of interest should meet the following performance criteria: (1) volatile constituents in the seal should be minimized to less than 1% weight loss over 40,000 hours; (2) fuel leakage should be less than 1%, averaged over the seal area and not catastrophic for the duration of the seal life; and (3) the seal material must be capable of a service life of more than 40,000 hours and dozens of thermal cycles for stationary systems.

Phase I should focus on the identification of candidate viscous glasses and conduct rigorous analysis and experimentation to characterize crystallization, volatility, reactivity, wetting, and viscosity in the SOFC environment. Phase II would entail composite seal design and experimental validation, culminating in larger-scale testing, potentially in partnership with other SECA R&D efforts or one or more SECA Industry Teams.

Questions – contact Briggs White, Briggs.White@netl.doe.gov

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