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Innovative, Versatile and Cost-EffectiveSolid Oxide Fuel Cell Stack Concept
Nguyen Q. MinhCenter for Energy Research
University of California, San DiegoLa Jolla, California
18th Annual Solid Oxide Fuel Cell Project Review MeetingPittsburgh, PA
June 12-14, 2017
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Innovative, Versatile and Cost-EffectiveSOFC Stack Concept Project• Project: Innovative, Versatile and Cost-Effective Solid
Oxide Fuel Cell Stack Concept (DE-FE0026211)• DOE/NETL Project Manager: Dr. Patcharin Burke• Project Team:
– UCSD• Center for Energy Research: Dr. Nguyen Minh (PI), Dr. Yoon Ho Lee
(Postdoctoral scholar), Dr. Eduard Ron (Postdoctoral scholar)• Department of Electrical Engineering and Center for Memory and
Recording Research: Dr. Eric Fullerton, Haowen Ren (graduate student)• Department of NanoEngineering: Dr. Shirley Meng, Erik Wu (graduate
student)– FuelCell Energy
• Dr. Hossein Ghezel-Ayagh and Dr. Alireza Torabi
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Project Objective and R&D Work
• Objective: Develop and evaluate a versatile stack configuration based on a prime-surface interconnect design for a broad range of power generation applications
• R&D Work: Involve R&D activities to demonstrate fabricability, operability and affordability of the stack design
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STACK DESIGN CONCEPT
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Metal support
YSZ
Stainless steel egg carton shape
interconnectHole
LSM
YSZ
Ni
YSZ
Repeating cell unit
Cell
Interconnect
Edge seal
AirH2O, H2
AirH2O, H2
AirH2
AirH2
Stack DesignIncorporating Conventional Cells
Cathode
Stainless steel support
Anode
Electrolyte
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Features of Stack Concept
• Reduced weight and volume• Flexibility in gas flow configuration• Reduced stacking performance losses• Improved sealing• Versatility in incorporation of different types
of cell construction
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Prime-Surface Interconnect DesignMetal sheetwith openings
Metal sheetwith egg carton
shape
Metal sheetwith openings
Notch
Not in Scale
Cross Section
Assembly
FUEL
AIR
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H2O,H2
Stack Design Incorporating Sintered Cells
Sintered Cell
Prime SurfaceInterconnect
Notch
Sintered Cell
Sintered Cell
Prime SurfaceInterconnect
CathodeElectrolyteAnode
NotchEdge Seal
H2
Air Air
H2O,H2H2
Air Air
Sintered Cell
Not in Scale
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Stack DesignCross Flow Gas Manifolding
H2
H2O/H2
Air
AirNotch
Opening for Gas Access to Cell
Not in Scale
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Stack DesignIncorporating Metal-Supported Cells
H2
Repeating cell unit
Columnar electrolyte scaffold
LSC nanoparticle
Ag nanoparticle
Doped electrolyte nanoparticle
Anode
Interconnect
Metal supportElectrolyte seal
Dense electrolyte
Stainless steel support
Columnar electrolyte scaffold
Ni nanoparticle
Doped electrolyte nanoparticleAir
H2
H2O, H2
H2O, H2
Stainless steel egg carton shape
interconnectHole
Air Air
Electrolyte
Cathode
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Project Technical Activities
• Prime surface interconnect design and fabrication development
• Metal-supported cell structure development• Stack development• Stack operation demonstration• Stack cost assessment
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PRIME SURFACE INTERCONNECT DEVELOPMENT
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Preliminary Interconnect Design Assessment
• Flow distribution• Mechanical loading• Current collection• Formability
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Prime Surface Interconnect Design
Parameter ValueInterconnect height 2.5mmInterconnect sheet thickness
0.3mm
Cone angle 60o
Diameter of the cone 4mmMass of one sample(60 mm x 60 mm)
10.56 grams
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Gas Flow Distribution Modeling
• Approach: FLUENT software, LES & URANS turbulence models
• Inlet boundary conditions:Parameter ValueInlet velocity 2 m/sTemperature of the flow 800oCInterconnect design Egg carton shapeFuel type Hydrogen
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Gas Flow Patterns
• Flow is uniform with areas of boundary layer detachment in the wakes of the hills
• Flow exhibits areas of acceleration • Potentially that can be used for improved diffusion
Plane near interconnect/cell interface Plane in interconnect center
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Mechanical Loading Modeling
• Approach: ANSYS Mechanical software, modeling of loading within a stack
• Parameters:
Parameter ValueTemperature of the cell 800oCInterconnect design Egg carton shapeCell type Conventional anode-supportedNumber of cells in the stack 100Interconnect material Ferritic stainless steel
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Stress Analysis
• The appeared stresses of 3.65MPa at the bottom cell are much lower than the yield strength of ferritic stainless steel (240MPa)
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Current Collection Modeling
• Approach: Analytical calculations • Parameters:
Parameter ValueInterconnect height 2.5mmInterconnect sheet thickness
0.3mm
Cone angle 60o
Diameter of the cone 4mm
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Current Collection Losses
• Evaluation was performed for a simplified interconnect design and egg carton shape
• Egg-carton shape accounts for insignificant increase in the area-specific resistance as compared to that of a cell
• Negligible current density losses with egg carton shaped interconnects
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Interconnect Formability• Engineering drawing
produced
• Hydroforming method of production chosen
• The interconnect manufacturer BoritTM
contacted
• Positive feedback on its manufacturability received
Engineering drawing
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Prime Surface Interconnect Design Preliminary Assessment Summary
• No flow maldistribution• Stress estimated at interconnects well below
yield strength of stainless steels• Interconnect current collection without
significant losses• Formability possible with hydroforming
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METAL-SUPPORTED CELLSTRUCTURE FABRICATION
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Sputtering Process
Conventional
Reactive
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Sputtering for SOFC Cell Fabrication• Fabrication of dense and
porous layers
• Scalability
• Potential cost effectiveness
Weimar et al, PNNL Report PNNL-22732, 2013
Sputtering Target by AZO MaterialsGoldstone Vacuum Sputter System
200nm
Nano-scale Dense YSZ layer
http://www.goldstone-group.com/ http://www.azom.com/
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Fabrication of Dense YSZ Layers
Si wafer
Dense YSZ Layer
Cross Section Surface
Target Y/ZrPressure 5mtorrGas Flow 50sccm of Ar
Power 200WT-S Distance 70mm
Time 7200sec
Structure & Condition
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Fabrication of Porous YSZ StructuresStructure & Condition
Cross Section Surface
Target Y/ZrPressure 30mtorrGas Flow 50sccm of Ar
Power 200WT-S Distance 120mm
Time 7200secSi wafer
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Fabrication of Porous Ni-YSZ LayersStructure & Condition
Target Y/Zr YSZ NiPressure 30mtorrGas Flow 50sccm of Ar
Power 25W 200W 100WT-S Distance 120mm
Time 7200secSi wafer
Cross Section Surface
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Fabrication of Porous LSC-YSZ LayersStructure & Condition
Target Y/Zr LSCPressure 30mtorrGas Flow 50sccm of Ar
Power 50W 200WT-S Distance 120mm
Time 7200secSi wafer
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EDX Mapping of Deposited LSC- YSZ Layer
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Fabrication of SOFC Cell
CathodeLSC/YSZ
ElectrolyteYSZ
AnodeNi/YSZ
430n
m35
0nm
440n
m
With SE2 Detector: MorphologicalFocused image
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Fabrication of SOFC Cell
CathodeLSC/YSZ
ElectrolyteYSZ
AnodeNi/YSZ
430n
m35
0nm
440n
m
With InLens Detector: MaterialFocused image(Bright : ConductorDark : Insulator)
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Metal-Supported Cell Development Preliminary Fabrication Results Summary
• Fabrication feasibility demonstration by sputtering– Dense YSZ electrolyte layers– Porous YSZ structures– Porous Ni-YSZ layers– Porous LSC-YSZ layers– Single cell structures
• Uniform layer thickness and excellent interfaces between layers
• Electrode porosity improvements required
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Near-Term Future Work• Prime surface interconnect development
– Initiate and evaluate hydroforming of egg carton shaped interconnect and characterize fabricated samples
– Modify and optimize design• Metal-supported cell structure development
– Modify and optimize sputtering process and characterize fabricated samples
– Fabricate and characterize single cells– Fabricate cell components and single cells on metal supports
• Stack development– Initiate assembling of stacks incorporating prime surface
interconnects and sintered cells
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Acknowledgments
• DOE/NETL SOFC project management, especially Dr. Patcharin Burke
• UCSD/FCE SOFC project team