GE Hybrid Power Generation Systems
Recent Advances in Solid Oxide Fuel Cell Technology Nguyen Minh
American Ceramic Society PCRM Seattle, WA, October 1-4, 2002 Copyright© General Electric Company 2002
SOFCs for Power Generation Applications GE Hybrid Power Generation Systems
• SOFC: Electrochemical energy conversion device based on ionic conducting oxide electrolyte
• SOFC systems for a broad spectrum of power
generation applications – Small lightweight compact devices (W-size) to large SOFC/turbine hybrid systems (MW-size)
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SOFC Power Systems GE Hybrid Power Generation Systems
7.9”
4.5”
3.3”
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Features of Solid Oxide Fuel Cell GE Hybrid Power Generation Systems
• Key features: All solid state device operating at high temperatures – Multifuel capability
Internal reforming Direct oxidation
– Solid state (mainly ceramic) device
No liquid management Design flexibility
– High-temperature operation
Hybrid with gas turbine High-quality byproduct heat
• Key technical challenges: Materials and fabrication processes to produce reliable and cost-competitive systems
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SOFC Stack Designs GE Hybrid Power Generation Systems
From Minh and Takahashi, Science and Technology of Ceramics Fuel Cells, Elsevier, 1995 M-ACerS-Seattle.ppt- 5
SOFC Materials GE Hybrid Power Generation Systems
• Most common electrolyte materials: 8 mol% yttria (Y2O3) stabilized zirconia (ZrO2) or 8YSZ
– Oxygen ion conducting (cubic phase). stability in both oxidizing and reducing –
environments Ionic conductivity about 0.1 ohm-1cm-1 at 1000°C
• Most common anode material: Ni/8YSZ cermet
– Greater than 30 vol% Ni required for conductivity; greater than 100 ohm-1cm1
– –
at 1000°C Ni provides electronic conductivity and catalytic activity 8YSZ provides ionic conductivity and catalytic activity, supports Ni particles, and improves anode thermal expansion match
• Most common cathode material: strontium doped lanthanum manganite (Sr-doped LaMnO3) (LSM) – Adequate electronic conductivity (125 ohm-1cm-1 at 1000°C) – Addition of YSZ to improve cathode activity and adherence
• Interconnect materials: doped LaCrO3 or metals
– Electronic conducting, stability in both oxidizing and reducing environments – Sr-doped LaCrO3 conductivity about 15 ohm-1cm-1 at 1000oC M-ACerS-Seattle.ppt- 6
SOFC Cost Estimates GE Hybrid Power Generation Systems
• Example:
– Projected system cost based on planar SOFCs when fully developed:
$388/kW
– Stack Costs Utilities (17.8%)
Equipment (18.7%)
Land & Building (0.9%)
Labor (12.1%)
Materials (50.5%)
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Factors Contributing to Lowering Stack Cost GE Hybrid Power Generation Systems
• Certain factors contributing to lower SOFC stack costs – Reduced operating temperatures
e.g., use of metallic interconnects
– High power density
e.g., lower material costs due to small size, lower weight
– Low- cost manufacturing processes – Direct operation on hydrocarbon fuels
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Recent Developments GE Hybrid Power Generation Systems
• • • •
Reduced-temperature electrolytes Advanced fabrication processes Engineered electrode microstructures Direct oxidation anodes for hydrocarbon fuels
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Approaches for Reduced Operating Temperature GE Hybrid Power Generation Systems
Approaches to Develop Reduced-Temperature SOFCs
Alternate Electrolytes
Thin Yttria-Stabilized Zirconia (YSZ) Electrolytes
• Advantage: Conductive Material
• Advantage: Well Known System
• Challenge: Less Know Systems
• Challenge: Thin Film Fabrication M-ACerS-Seattle.ppt- 10
Conductivity of Zirconia GE Hybrid Power Generation Systems
Dopant
Mole % Dopant
Conductivity at 1000°C
Nd2O3
15
0.01
Sm2O3
10
0.06
Y2O3
8
0.10
Yb2O3
10
0.11
Sc2O3
10
0.25
(ohm-1•cm-1)
From Minh and Takahashi, Science and Technology of Ceramics Fuel Cells, Elsevier, 1995
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Reduced -Temperature Electrolytes GE Hybrid Power Generation Systems
• Doped Ceria
– Fluorite structure – Oxygen ion conductivity
Gd-doped CeO2: 0.08 ohm-1cm-1 at 800°C
– Reduction at low oxygen partial pressure with consequent introduction of electronic conductivity
• Doped lanthanum gallate – Perovskite structure – Oxygen ion conductivity
Sr, Mg-doped LaGaO3: 0.04 ohm-1cm-1 at 800°C
– Relatively new electrolytes
• Proton conducting electrolytes
– Examples: doped BaCeO3, doped SrCeO3 M-ACerS-Seattle.ppt- 12
Performance of SOFC Cell
Peak Power Density, W/cm
GE Hybrid Power Generation Systems
1.8 1.4 1.2 0.8 0.4
650°C
Temperature
800°C
Based on single cell, 100% hydrogen as fuel
Ishihara et al, J. Electrochem Soc., 147, 1332 (2000) M-ACerS-Seattle.ppt- 13
SOFC Fabrication Processes GE Hybrid Power Generation Systems
• Deposition approach
– Formation of electrolyte layer on an electrode support by a chemical or physical process e.g., chemical vapor deposition, plasma spraying
• Particulate approach
– compaction of ceramic powder into cell components and densification at elevated temperatures e.g., tape casting, tape calendering
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Fabrication of Thin YSZ Electrolytes GE Hybrid Power Generation Systems
Deposition DepositionProcess Process
Particulate ParticulateProcess Process
•• •• •• •• ••
•• ••
•• •• ••
Sputtering Sputtering Dip Dipcoating coating Spin Spin coating coating Spray Spraypyrolysis pyrolysis Electrophoretic Electrophoretic deposition deposition Vacuum Vacuumslip slipcasting casting Electrostatic Electrostaticassisted assisted vapor vapordeposition deposition Plasma Plasmaspraying spraying
Tape Tapecasting casting Tape Tapecalendering calendering
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Tape Calendering Process GE Hybrid Power Generation Systems
Tape Forming
Rolling
Rolling Thin Electrolyte on Support Electrode Layer
Electrolyte
Bilayer
Bilayer
Support Electrode Support Electrode
Deposited Electrode Application
Firing
Cutting
M-12569.ppt
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High-Performance Anode-Supported SOFC GE Hybrid Power Generation Systems
Fracture Surface LaMnO3 Cathode
ZrO2 Electrolyte
NiO/ZrO2 Anode
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SOFC Performance
1.4
1.4
1.2
1.2 1
Voltage (V)
1 0.8
0.8
0.6
0.6
0.4
0.4
0.2
Voltage in Syngas
Voltage in H2
Power Density in Syngas
Power Density in H2
19% H2, 24% CO, 1% CO2, Bal N2
0 0
0.5
1
1.5
0.2 0
2
Power Density (W/cm²)
GE Hybrid Power Generation Systems
•• 800°C 800°Coperation operation •• Open Opencircuit circuitvoltages voltages in inagreement agreementwith with theoretical values theoretical values •• Peak Peakpower powerdensity: density:
–– 1.3 1.3W/cm² W/cm²inin ––
hydrogen hydrogen 0.85 0.85W/cm² W/cm²ininJP-8 JP-8 syngas syngas
2.5
Current Density (A/cm²)
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Pressurized SOFC Performance GE Hybrid Power Generation Systems
Experimental Data Points and Model 1.2
0.4
1 0.9
0.3
0.8 2
0.7 0.6
0.2
0.5 0.4
1
Fuel utilization
2
PD, W/cm
Cell Voltage (V), Fuel Utilization
1.1
3 atm
0.3
0.1
0.2 0.1 0
0 0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
2
Current Density, A/cm
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Electrode Performance GE Hybrid Power Generation Systems
0.7
I = 1 A/cm2 0.6
Anode Loss
Voltage Drop (V)
0.5 0.4 0.3
Cathode Loss
0.2 0.1
Electrolyte Loss 0 550
600
650
700
750
800
850
Temperature (°C)
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Controlling Factors for Cathode Performance GE Hybrid Power Generation Systems
• • • •
Distribution of reaction sites Mixed conduction Interfacial bonding Access of oxidant to electrolyte O2 Sheet Conductivity
e-
e-
Cathode
Bulk Activity O2 Interface Activity
e-
O2-
O2-
Electrolyte M-ACerS-Seattle.ppt- 21
Cathode Performance Improvement/Degradation GE Hybrid Power Generation Systems
• Performance improvement – – – –
Catalyzed interface Structured interface Highly dispersed catalyst Functional graded layers
• Performance degradation during operation – Chemical interactions – Poisoning by chromium, silica
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SOFC Cell Performance at Reduced Temperatures GE Hybrid Power Generation Systems 1.4
1.4
800C
1 Cell Voltage, V
1.2
750C
1 2
700C 650C
0.8
0.8
0.6
0.6
0.4
Power Density, W/cm
1.2
0.4
600C 0.2
0.2
Hydrogen fuel Air oxidant
0
0 0
0.5
1
1.5 Current Density, A/cm
2
2.5
3
2
•• High Highpower powerdensities densities(e.g., (e.g.,0.9 0.9W/cm² W/cm²at at650°C) 650°C)achieved achievedat atreduced reduced temperatures temperatures(
