Solid Oxide Fuel Cells:
gy, and Applications
pp
Science,, Technology,
S David Dvorak Ph D P E
S. David Dvorak, Ph.D, P.E.
20 June 2008
Summer School on ‘Materials for the Hydrogen Economy’
Reykjavik, Iceland
Outline
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Characteristics and Basic Operation
Multifuel Capability
Cell Designs
Materials
l
Performance
Applications
High Temperature Electrolysis
High Temperature Electrolysis
2
Characteristics of SOFC Systems
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•
•
•
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Multifuel capability with minimal gas cleanup
capability with minimal gas cleanup
High quality exhaust heat
Good reaction kinetics
Good reaction kinetics
High power density
Slow startup / response time
Slow startup / response time
Materials issues
Thermal cycling issues
Thermal cycling issues Sealing issues
3
SOFC: Basic Operation
Anode Reaction:
H2 + O
+ O2‐ → H2O + 2e
O + 2e‐
O
Overall Reaction:
ll R ti
H2 + ½ O2 → H2O
Cathode Reaction:
½ O2 + 2e
+ 2e‐ → O2‐
4
Multifuel Capability
• Hydrocarbon Reforming
– CnHm + nH2O → ((n + m/2)H
/ ) 2 + nCO
• Coal Gasification
– C + H2O → H2 + CO • Biomass Gasification:
– (C6H10O5)n + 7nH2O → 6nCO2 + 12nH2
• Carbon Deposition:
– Methane Pyrolysis
Methane Pyrolysis
– Boudouard disproportination
– Reverse Gasification CH4 + H
+ H2O → C + 2H
C + 2H2
2CO → C + CO2
CO + H2 → C + H2O
5
Anode Reactions: Hydrocarbon
y
Fuels
• Steam Reformation of Methane:
– CH4 + H2O → 3H2 +CO ΔHo = 206 kJ/mole
• W
Water Gas Shift:
t G Shift
– CO + H2O → H2 + CO2 • Oxidation Reactions:
– Hydrogen y g
– Carbon Monoxide ΔHo = ‐36 kJ/mole
H2 + O2‐ → H2O + 2e‐
CO + O2‐ → CO2 + 2e‐
6
Enthalpy and Entropy For Hydrogen Oxidation
H2 + ½O2 → H2O
ΔH( T) =
∑ ΔH ( T) − ∑
ΔS( T) =
ΔH f ( T ) = ΔH 0f + ∫ c p ( T )dT
Reactants
T0
T
∑ S( T ) − ∑ S( T )
Products
S(T) = S + ∫
0
Reactan ts
cp ( T )
T0
-200
0
-220
-50
Entrop
py (J/mol-K)
Enthalpy (kJ/mol)
ΔHf ( T)
f
Products
T
-240
-260
T
dT
-100
-150
-280
-200
-300
300
400
500
600
Temperature (K)
700
800
300
400
500
600
700
800
Temperature (K)
7
Gibbs Free Energy and Thermodynamic
Potential (E) as functions of temperature
H2 + ½O2 → H2O
ΔG
E=−
2F
ΔG = ΔH - TΔS
1.30
-200
Revers
sible Cell Voltag
ge
Gibbs F
Free Energy (kJ
J/mol)
-190
-210
-220
-230
1.25
1.20
1.15
1.10
1.05
1.00
-240
300
400
500
600
Temperature (K)
700
800
300
400
500
600
700
800
Temperature (K)
8
0
14
1.4
‐50
1.2
‐100
100
Gibbs
1
‐150
Enthalpy
0.8
E
‐200
200
0.6
‐250
0.4
‐300
0.2
‐350
0
300
400
500
600
700
800
Potential (Volt)
Energy (kJ/mol)
SOFC Thermodynamics
y
900 1000 1100 1200
Temperature (K)
9
Temperature Effects
• An increase in temperature – reduces the thermodynamic potential – Improves electrode kinetics
– Increases ionic conductivity of electrolyte
Kordesch & Simader, Fuel Cells and Their Applications, VCH, 1996
10
Cell Designs
• Tubular Design
– Lower Power Density
L
P
D it
– Easier to seal
• Planar Design
– Higher Power Density
Hi h P
D it
– Harder to Seal
11
Planar Cell Configurations
g
• Electrolyte Supported Cells (ESC)
– Thick electrolyte (120μm)
– 800oC ‐1000oC
ANODE
ELECTROLYTE
CATHODE
• Anode Supported Cells (ASC)
Anode Supported Cells (ASC)
– Anode 0.6mm thick
– 600oC ‐900oC
– Thin electrolyte (higher ionic Thin electrolyte (higher ionic
conductivity at lower temperatures
• Porous Metal Substrate Cells (PMSC)
– Corrosion
Corrosion resistant ferretic
resistant ferretic stainless steel stainless steel
(0.5 to 1 mm)
– 600oC ‐700oC
– Thin Electrolyte (3YSZ) ( 2 –
Thin Electrolyte (3YSZ) ( 2 – 4 μm)
4 μm)
ANODE
ELECTROLYTE
CATHODE
ANODE
ELECTROLYTE
CATHODE
SUBSTRATE
12
Tubular Cell Development
p
Siemens Power Group
• Circular to flattened tubes(HPD5)
• Corrugated Delta9 cell (500mA/cm
g
(
/ 2)
13
SOFC Stack Performance
0.44 A/cm2 @ 0.69V
0.3 W/cm2
14
SOFC materials
• Severe
Severe material environment
material environment
– Chemical stability
– Mechanical Stability
Mechanical Stability
– Microstructural Stability
• Electrolyte
• Anode
• Cathode
• Interconnect
15
SEM Image: Electrolyte Supported Cell
Cathode →
Electrolyte →
Anode →
• Anode Nickel Oxide / YSZ Cermet
• Electrolyte 8YSZ (8% Yttria Stabilized Zirconia)
• Cathode: Lanthanum Strontium Manganite (LSM) L 0.6Sr
La
S 0.4MnO
M O3
16
SEM Image: Anode Supported Cell
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Anode support structure (Ni / 8YSZ cermet) 600μm
Anode functional layer (Ni / 8YSZ) 10μm
Electrolyte (8YSZ) 5μm
Electrolyte (8YSZ) 5μm
YDC Intermediate Layer (Ce0.8Y0.2O1.9) 3μm :
– Prevents the formation of low‐conducting phase at YSZ/LSCF interface
LSCF (La0.6Sr0.4Co0.2Fe0.8O3) Cathode 25μm
Reference: www.ecn.nl
17
SOFC Applications
pp
• SOFC Technology is scaleable over a wide range of power requirements
requirements:
– Portable Power (20W – 1.5kW)
– Auxiliary Power (5kW –
Auxiliary Power (5kW 10kW)
– Combined Heat and Power (CHP) (2kW – 10kW)
– Stationary Power (25kW –
Stationary Power (25kW – 250kW)
• SOFC
SOFC Systems are applicable where there is a need for:
Systems are applicable where there is a need for:
– Fuel Flexibility
– High quality waste heat
High quality waste heat
18
SOFC Applications:
Portable Power
• 250 Watt Battery Charger, 250 Watt Battery Charger
– Kerosene fuel
– Tubular cell design
T b l
ll d i
– 15,2 x 25,4 x 30,5 cm
www.mesoscopic.com, www.toto.co.jp
19
SOFC Applications:
pp
Auxiliary
y Power
• In the US, idling trucks consume about one billion gallons of fuel annually
of fuel annually • SOFC APU systems providing heat and electrical power could cut fuel used while idling by 85%
DELPHI 5 kW APU
• CPOX Reformer
f
• Cathode Air HEX
Stack
• 30 cells (two per APU)
• 9 kg, 2.5 liters
www.greencarcongress.com
20
SOFC Applications:
Combined Heat and Power
• Partnership
Partnership between Dantherm, Htceramix
between Dantherm, Htceramix
• System designed around 1kW integrated SOFC module (HotBox™)
(
)
www.leblogenergie.com
21
SOFC Co-Generation: Example
• 109 kW Electricity
• 69 kW of hot water for district heatingg
• Operated on natural gas in Netherlands and Germany for 20.000 hours
www.powergeneration.siemens.com
22
SOFC / Gas Turbine Hybrid:
S t
System
S
Schematic
h
ti
• Produces steam and power
23
Thermodynamic Efficiency
Carnot Cycle Efficiency Reversible Thermodynamic Efficiency
ε carnot
TL
= 1−
TH
100
90
80
Efficiency [%]
E
ε thermo
ΔG
=
ΔH
70
60
50
40
Max Efficiency (LHV)
Max.
30
Carnot Limit
20
10
0
0
200
400
600
800
1000
Temperature [degC]
24
Efficiency
y of SOFC/GT Hybrid
y
Systems
y
25
SOFC / Gas Turbine Hybrid: Example
220 kW Proof of Concept Demonstrator
• 200 kW from SOFC stack
• 20 kw from microturbine
• Operated at the National Fuel Cell Research Center, Irvine CA for 3500 hours with 53% electrical efficiency
Irvine, CA, for 3500 hours with 53% electrical efficiency
www.powergeneration.siemens.com
26
Future Gen, integrated Hydrogen, Power Production,
and
dC
Carbon
b S
Sequestration
t ti R
Research
h IInitiative
iti ti
• Goals (2020)
– Design , construct, and operate a 275 MW power plant that produces electricity and hydrogen with near zero emissions
– Produce electricity at only 10% more than non‐
sequestered power plant
– Produce hydrogen at $0.48/kg
• Key features:
– Coal gasification produces syngas (H2, CO, CO2, H2O, . . .)
– Hydrogen separated out of syngas, compressed
– Depleted syngas
D l t d
used as fuel for SOFC / GT Hybrid system
d f l f SOFC / GT H b id t
– Use of ion conducting ceramics for H2, O2 separation
27
FutureGen Simplified Process Flow Diagram
Williams, et. Al. J. Power Sources 159 (2006) 1241 ‐ 1247
28
High-Temperature
g
p
Electrolysis
y
(SOEC)
(
)
Electron
Flow
_
e
Hydrogen
Oxygen
H2
O2
O2H2 O
Oxygen Ions
Water
Cathode
Cathode Reaction:
H2O + 2e‐ → H2 + O2‐
Electrolyte
Anode
Overall Reaction:
Overall Reaction:
Anode Reaction:
O2‐ → ½ O2 + 2e‐
H2O → H2 + ½ O2
29
Electrolyzer and Fuel Cell Performance
2.5
Cell Voltage
C
e
2.0
1.5
Electrolyser Cell
Fuel Cell
1.0
0.5
0.0
0
1
2
3
4
Current Density [A/cm2]
30
Energy Demand for Water and Steam Electrolysis
• Energy needed to electrolyze water: ∆H = ∆G + T ∆S
• At high temperatures, the addition of heat (T∆S) reduced the electricity needed (∆G) for electrolysis
Mingyi, et. Al., J. Pwr. Sources 2008
31
Conventional Water Electrolysis:
Energy Flow Diagrams
Donitz, et. Al., Int. J. Hydrogen Energy 13 (5) 283 – 287, 1988 32
High Temperature Water Electrolysis:
E
Energy
Fl
Flow Di
Diagrams
• “Hot Elly” autothermal operation
• “Hot Elly” with additonal high‐temperature heat
33
High
g Temperature
p
Electrolysis
y
• At 800 – 1000oC the electrical energy required to split water is reduced
lit t i d d by about 25%
b b t 25%
• In addition to thermodynamic effectgs, improved electrode kinetics red ce req ired oltages
electrode kinetics reduce required voltages
• System complexity and materials issues remain serious challenges
serious challenges.
34