High Performance Flexible Reversible Solid Oxide Fuel
CellJie Guan, Badri Ramamurthi, Jim Ruud, Jinki Hong, Patrick Riley, Nguyen
Minh
GE Global Research CenterMay 16, 2006
Project ID:PDP34This presentation does not contain any proprietary or confidential information
DE-FC36-04GO14351
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Hydrogen Program Review, 05/16/2006
Overview
• Project start date: October 2004• Project end date: September
2006• Percent complete: 75%
• Barriers addressed– K. Electricity Costs– G. Capital Costs– H. System Efficiency
• Total project funding–DOE share: $1,252,683–Contractor share: $616,993
• Funding received in FY05: $575,198• Funding for FY06: $677,485
Timeline
Budget
Barriers
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Hydrogen Program Review, 05/16/2006
Objectives
• Demonstrate a single modular stack that can be operated under dual modes–Fuel cell mode to generate electricity from a variety of fuels
–Electrolysis mode to produce hydrogen from steam
• Provide materials set, electrode microstructure, and technology gap assessment for future work
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Hydrogen Program Review, 05/16/2006
Approaches
BASELINE
MATERIALS
SELECTION
REVERSIBLE
STACKS
REVERSIBLE
SINGLE CELLS
FUEL FLEXIBLE
REVERSIBLE
ELECTRODES
Conventional
SOFC
Based
Materials
REVERSIBLE
SOFC
DEMO
Planar Design
Metallic
Interconnect
Electrode Supported
Cells Operating
At <800 o C
Reversible
Multifuel Anode
and
Reversible Electrodes
PROGRAM
ELEMENTS
CONCEPTS
COST
ESTIMATE
Assessment of
SOFC Material
Properties Relevant
to Reversible
Operation
Electrode
Configuration
Microstruture
Composition
Catalytic Activity
Thin Electrolyte
Electrode Supported
Cells Made by
Calendering
Half Sealed
Planar DesignAPPROACHES
BASELINE
MATERIALS
SELECTION
REVERSIBLE
STACKS
REVERSIBLE
SINGLE CELLS
FUEL FLEXIBLE
REVERSIBLE
ELECTRODES
Conventional
SOFC
Based
Materials
REVERSIBLE
SOFC
DEMO
Planar Design
Metallic
Interconnect
Electrode Supported
Cells Operating
At <800 o C
Reversible
Multifuel Anode
and
Reversible Electrodes
PROGRAM
ELEMENTS
CONCEPTS
COST
ESTIMATE
Assessment of
SOFC Material
Properties Relevant
to Reversible
Operation
Electrode
Configuration
Microstruture
Composition
Catalytic Activity
Thin Electrolyte
Electrode Supported
Cells Made by
Calendering
Half Sealed
Planar DesignAPPROACHES Technology Analysis
Key challenges:– Performance for cost and efficiency– Low degradation for reliability
Technical focuses:– Reversible electrode modeling– Electrode compositions and
microstructure engineering
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Hydrogen Program Review, 05/16/2006
Cell Configuration
•SOFCs have the flexibility, running under power generation mode and hydrogen production mode•High temperature solid oxide steam electrolysis can lower the electricity consumption
Fuel, CH4, H2, etc.
Oxidant, air.
Power Generation Mode
Load
e
eCH4 + 4O2- → 2H2O +CO2 + 8e-
2O2 + 8e- → 4O2-
Hydrogen Production Mode
e
e
Pow
er
Steam Hydrogen
Oxygen
2H2O + 4e- → 2H2 + 2O2-
2O2- → O2 + 4e-
~60 μm~7 μm
~300 μm
Oxygen Electrode, PerovskiteElectrolyte, YSZ
Hydrogen Electrode, Ni/YSZ
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Hydrogen Program Review, 05/16/2006
Stack Configuration
Oxygen electrodeElectrolyte
Hydrogen electrode
Interconnect (IC)
Cell
Interconnect (IC)
Cell Module Multi-cell Stack
Cell/ICsRepeat units
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Hydrogen Program Review, 05/16/2006
Oxygen Electrode Performance
• Screened several lanthanum strontium manganites (LSM), lanthanum strontium ferrites (LSF), and lanthanum strontium cobalt iron oxides (LSCF) as oxygen electrodes
• Under both modes, electrode performance increases in the order of LSCF>LSF>LSM/YSZ
800C 200 sccm H2 ~50% H2O
0.00
0.25
0.50
0.75
1.00
1.25
1.50
1.75
-3 -2 -1 0 1 2 3
J (A/cm2)
E (V
), U
tiliz
atio
n LSM-1LSM-2LSF-1LSF-2LSCFUtilization
Electrolyzer
Fuel CellSteam Utilization
Fuel Utilization
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Hydrogen Program Review, 05/16/2006
Oxygen Electrode Performance Stability
• Excess performance degradation was observed with LSM/YSZ as the oxygen electrode in electrolysis mode (SOEC) mainly due to electrode delamination
• LSCF and LSF showed better performance stability in electrolysis mode than LSM/YSZ electrode
800 C
0
200
400
600
800
1000
1200
1400
0 20 40 60 80 100
Time (hrs)
ASR
(moh
m-c
m2 )
LSM SOEC
LSM SOFCLSF SOECLSCF SOECLSF SOFCLSCF SOFC
LSM/YSZ Oxygen electrode
Hydrogen electrodeElectrolyte
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Hydrogen Program Review, 05/16/2006
Oxygen Electrode Reversibility
• Vacancy diffusion and activation at the oxygen electrode/electrolyte interface are different for fuel cell mode and electrolysis mode
• Higher current densities can lead to depletion of vacancies at the interface in electrolysis mode
• Experimental data matched well with non-symmetrical vacancy model
Non-symmetrical vacancy model
Non-symmetrical vacancy model
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Hydrogen Program Review, 05/16/2006
Operation Mode Cyclic Ability
• Evaluated cell performance for fuel cell mode alone, electrolysis mode lone, and fuel cell/electrolysis cyclic mode
• Similar degradation in fuel cell (SOFC), electrolysis (SOEC) and cyclic modes (rSOFC) – perhaps enhanced electrolysis degradation
800 C 50%H2O/50%H2
0
100
200
300
400
500
600
700
800
900
1000
0 100 200 300 400
Time (hrs)
ASR
(moh
m-c
m2 )
SOFC
SOEC
rSOFC
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Hydrogen Program Review, 05/16/2006
Hydrogen Electrode PerformanceFuel cell mode
Electrolysis mode
• Higher polarization losses predicted under electrolysis mode mainly due to difference of diffusion
• Thinner electrode and smaller particles preferred
Conditions:T = 800 CFuel = 50/50 H2/H2OActive layer thickness= 16 μmActive layer particle size=0.8 μm
Region I – H2/H2O diffusion and reaction limitedRegion II – Reaction limitedRegion III – Ion conduction and reaction limited
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Hydrogen Program Review, 05/16/2006
• At 800°C, internal reforming kinetic was fast
• CH4 conversion measured (gas chromatography) > 98%, agrees well with thermodynamic prediction
• Thermodynamic calculations defined carbon deposition boundary
Thermodynamic Prediction of Carbon Deposition BoundaryThermodynamic Prediction of Carbon Deposition Boundary
Hydrogen Electrode Internal Reforming
X is the distance from the fuel inlet along the channel and L is the total channel length
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Hydrogen Program Review, 05/16/2006
• Performance (I-V curve) with internal reforming similar to that with 64% H2/36%N2 fuel
• Improved cells efficiency and potential system simplification with internal reforming
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
100 200 300 400 500Current Density (mA/cm2)
Cel
l Vol
tage
(V)
64% H2 - 36% N2
20% CH4 - 30% H2O - 50% N2
Performance with Internal Reforming
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Hydrogen Program Review, 05/16/2006
• LSCF performed better than LSM/YSZ electrode
• Substantial degradation rate reduction achieved with LSCF oxygen electrode in electrolysis mode
• Improved performance with electrode material selection and process engineering
Module Performance Improvement
0.4
0.6
0.8
1.0
1.2
1.4
1.6
-600 -400 -200 0 200 400 600Current Density (mA/cm2)
Cel
l Vol
tage
(V)
Electrolysis Fuel Cell
Baseline Bilayer + Baseline Oxygen Electrode
Supercell Bilayer + LSCF-SDC Oxygen Electrode
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
0 20 40 60 80 100 120Hours in Electrolysis Degradation Test
ASR
(ohm
-cm
2)
Baseline Bilayer + Baseline Oxygen Electrode
Supercell Bilayer + LSCF-SDC Oxygen Electrode
0.1
1
10
100
1000
0 0.5 1 1.5
Electrolysis ASR (ohm-cm2)
% In
crea
se in
Vol
tage
/ 10
00 h
ours
Technology Feasibility Demo
Reduced Cost, Increased Efficiency
Impr
oved
Rel
aibi
lity
Baseline:LSM-1YSZ-Ni
YSZ-Ni microstructure enginnering
Alternative LSM-2Active LSCF
Processing Improvement
Materials and Process Optimization
Commerical Viable
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Hydrogen Program Review, 05/16/2006
Multi-cell Stack Performance
• Built and tested 3-cell stacks under power generation and electrolysis mode for more than 1000 hrs
• Hydrogen production measured and the measured value close to the predicted
• Cell-cell performance variation needs to be addressed
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
-700 -600 -500 -400 -300 -200 -100 0 100 200 300 400 500 600 700Current Density (mA/cm2)
Stac
k Vo
ltage
(V)
Electrolysis Fuel Cell
0.0
0.4
0.8
1.2
1.6
2.0
2.4
2.8
0 40 80 120 160 200 240 280 320Current Density (mA/cm2)
H2
Flow
Rat
e (L
/min
)
Fuel Exhaust H2 Flow Predicted
Fuel Exhaust H2 Flow Measured
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Hydrogen Program Review, 05/16/2006
Future Works
• Demonstrated multi-cell stack operation and assess performance under reversible operating conditions
• Estimate hydrogen production cost ($/kg H2)• Conduct technology assessment and gap
analysis
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Hydrogen Program Review, 05/16/2006
Summary• Oxygen electrode development
–Performance: LSCF>LSF>LSM–“Irreversibility” of oxygen electrode observed, associated with
differences in vacancy diffusion and activation at electrode/electrolyte interface
• Hydrogen electrode development–Internal reforming with Ni-YSZ modeled and demonstrated –Higher polarization loss under electrolysis mode expected, mainly
due to difference of H2 and H2O diffusion
• Module and stack development–Module and stack performance improved by electrode engineering–Initial multi-cell stacks tested and hydrogen generation demonstrated
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Hydrogen Program Review, 05/16/2006
Acknowledgement
This research was supported in part by DOE award DE-FC36-04GO14351. This support does not constitute an endorsement by DOE of the views expressed in the article.