Abstract One of the critical issues in designing and fabricating a high performance planar solid oxide fuel cell (pSOFC) stack is the development of the appropriate materials and techniques for hermetically sealing the metal and ceramic components. A second critical issue is ensuring that the brittle ceramic cell constituents, i.e. the electrodes and electrolyte, exhibit high mechanical reliability by mitigating potential sources of thermal-mechanically induced stresses that can lead to fracture during operation and/or shutdown. A foil-based sealing approach is currently being developed that appears to offer good hermeticity and mechanical integrity, while minimizing the generation of high stresses in either of the joint's substrate materials. Based on the concept's viability, demonstrated in prior experimental work, numerical analyses were conducted to evaluate the behavior and benefits of the seal in a configuration prototypic of current pSOFC stack designs. This paper presents recent results from finite element (FE) simulations of a planar cell using the foil-based seal, along with companion analyses of the more conventionally employed glass-ceramic and brazed joints. The stresses and deformations of the components were evaluated at isothermal operating and shutdown temperatures. The results indicate that the foil seal is able to accommodate a significant degree of thermal mismatch strain between the metallic support structure and the ceramic cell via elastic deformations of the foil and plasticity in the foil-to-cell braze layer. Consequently the cell stresses in this type of seal are predicted to be much lower than those in the glass-ceramic and brazed designs, which is expected to lead to improved stack reliability. This ability to accommodate large thermal strain mismatches allows the design requirement of thermal expansion matching between ceramic and metal stack components to be relaxed and expands the list of candidate materials that can be considered for the metal frames and interconnects.
[1]
Lieh-Kwang Chiang,et al.
Thermal stress analysis of a planar SOFC stack
,
2007
.
[2]
S. Campanari,et al.
Comparison of Finite Volume SOFC Models for the Simulation of a Planar Cell Geometry
,
2005
.
[3]
J. Malzbender,et al.
Curvature of Planar Solid Oxide Fuel Cells during Sealing and Cooling of Stacks
,
2006
.
[4]
Jeffrey W. Fergus,et al.
Sealants for solid oxide fuel cells
,
2005
.
[5]
M. Khaleel,et al.
Three-dimensional thermo-fluid electrochemical modeling of planar SOFC stacks
,
2003
.
[6]
Hui Yang,et al.
Dynamic TGA–FTIR studies on the thermal stability of lithium/graphite with electrolyte in lithium-ion cell
,
2007
.
[7]
J. Hardy,et al.
Reactive Air Brazing: A Novel Method of Sealing SOFCs and Other Solid-State Electrochemical Devices
,
2005
.
[8]
K. S. Weil,et al.
Effects of thermal cycling and thermal aging on the hermeticity and strength of silver–copper oxide air-brazed seals
,
2005
.
[9]
S. Singhal.
Solid Oxide Fuel Cells
,
2003
.
[10]
Guilan Wang,et al.
3-D model of thermo-fluid and electrochemical for planar SOFC
,
2007
.
[11]
K. S. Weil,et al.
The state-of-the-art in sealing technology for solid oxide fuel cells
,
2006
.
[12]
Tomoo Iwata,et al.
Analysis of Fuel Utilization Performance of Round Substrate, Planar Solid Oxide Fuel Cells
,
1998
.
[13]
J. Malzbender,et al.
Fracture test of thin sheet electrolytes for solid oxide fuel cells
,
2007
.
[14]
Michael Stelter,et al.
Engineering aspects and hardware verification of a volume producable solid oxide fuel cell stack design for diesel auxiliary power units
,
2006
.