ABSTRACT
Sealing of high-temperature solid oxide fuel cell (SOFC) stacks is a critical issue for maintaining the electrical performance of the fuel cell over a long period of time. Thermal stresses due to repeated heating and cooling cycles can degrade or fracture seals. Long-time material interactions and corrosion can also degrade seals. These are ongoing problems for developers of SOFCs that are used to generate electricity from hydrogen or hydrocarbon fuels. However, sealing is an even greater concern for solid oxide stacks used in a high-temperature steam electrolysis mode or solid oxide electrolysis cells (SOECs) to generate hydrogen. This steam electrolysis method essentially involves inputting electrical power into an SOFC in a reverse polarity mode [1, 2]. Because hydrogen is the primary valuable product for electrolysis and,
5.1 Introduction ................................................................................................... 213 5.2 Types of High-Temperature Seals ................................................................. 214
5.2.1 Glass Seals ........................................................................................ 214 5.2.2 Glass-Ceramic Seals ......................................................................... 217 5.2.3 Compressive Seals ............................................................................. 218 5.2.4 Metal Seals ........................................................................................ 218 5.2.5 Ceramic-Composite Seals ................................................................. 219 5.2.6 Compliant Seals ................................................................................ 219
5.3 Hydrodynamics of Leaking Seals .................................................................220 5.3.1 Theory of Seal Leaks ........................................................................220 5.3.2 Analysis of Seal Leaks ...................................................................... 223
5.4 Testing of Seal Properties and Behavior ....................................................... 227 5.4.1 Wetting ..............................................................................................228 5.4.2 Stability ............................................................................................. 229
5.4.2.1 Chemical Reactivity and Stability......................................230 5.4.2.2 Pressure-Leakage Test ........................................................ 231 5.4.2.3 Pressure-Sensor Tests for Leaks ........................................ 232
5.5 Summary and Conclusions ...........................................................................234 References .............................................................................................................. 235
due to hydrogen’s small size, the gas molecules can quickly leak out through various high-temperature seals.
