Transcript MCFC Research at USC - University of South Carolina

La0.8Sr0.2CoO3 Coated Nickel Cathodes
for Molten Carbonate Fuel Cells
Prabhu Ganesan, Hector Colon, Bala Haran,
R. E. White and Branko Popov
Department of Chemical Engineering
University of South Carolina, Columbia, SC 29208.
Presentation Outline
Objectives
 Prepare a stable cathode material with lower
solubility and comparable performance as NiO
Coating of La0.8Sr0.2CoO3 using sol-gel process
Characterization Studies
 Polarization performance
 AAS – Solubility measurements
 SEM – Microstructure analysis
 EIS
 Full cell studies
State-of-the Art Molten Carbonate Fuel Cells
Component
Material / Properties
Anode
Material
Pore size
Porosity
Thickness
Sp. Area
Cathode
Material Lithiated NiO
Pore size 6 ~ 9 mm
Porosity 80~85% as Ni
Thickness 0.5~0.8 mm
Sp. Area 0.5 m2/g
Matrix
Material
Pore size
Porosity
Thickness
Sp. Area
g-LiAlO2
0.2 ~ 0.5 mm
50~60%
0.5 mm
0.1~10 m2/g
• Sintering/Thermal Stability
- Fiber or large particles
• Phase stability
- a-LiAlO2
Current
Collector
Material
SS316
•Chromium Dissolution
- Nickel Cladding (Anode)
- Fe-Al alloys
Ni+10wt% Cr
3 ~ 6 mm
50~70%
0.5~1.5 mm
0.1~1 m2/g
Problem/Solution
• Creep/Sintering
- Ni-Al Alloy
• Electrolyte retaining
- Coating of Oxides
• NiO dissolution
- Stabilized NiO
- LiCoO2 cathode
- Modified electrolyte
Cathode Materials for Molten
Carbonate Fuel Cells
• State-of-the-art NiO(Li)
Alternate Cathodes
• LiCoO2, LiNiO2
• LiCoO2 Coated Nickel Oxide
• Ni-Ce and Ni – La2O3
• Ni-Nb Surface Alloy
• Perovskites such as La0.8Sr0.2CoO3
• Cobalt Encapsulated Nickel
• Mixed Lithium Nickel Cobalt Oxides
USC Molten Carbonate Fuel Cell
(Half Cell)
Porous Ni Cathode
Perforated SUS 304 Current Collector
USC Molten Carbonate Fuel Cell
(Full Cell)
Flow chart for Ni electrode preparation
Dispersant
+ Water
Ni Powder
Milling 24 h
Binder
Plasticizer
Milling 12 h
Milling 12 h
Filtering
De-airing
Casting
Drying
Sintering
TGA Behavior of Ni green tape
104
10
wt remaining (%)
Nickel
r = 10 oC/min
96
-10
-20
92
-30
-40
88
-50
84
-60
80
0
200
400
600
o
Temperature ( C)
-70
800
dw/dT*1000 (mg/o C)
0
100
Sintering schedule for Ni electrodes
800OC
Nitrogen
1h
800 OC
5 OC/min
400 OC
5h
400 OC
1 OC/min
230 OC
3h
230 OC
1 OC/min
1 OC/min
130 OC
1h
130 OC
Hydrogen
1 OC/min
RT
RT
Flow chart for LSC Coated Ni electrode
preparation
La, Sr, Co-Acetates
Dist.
Water
Stirring at
80o C
Ethylene
Glycol
Ni
Electrodes
Stirring
Gel
Drying in Vacuum
at 90o C
Sintering at 900o C
in Air
Citric
Acid
900 o C
800 o C
700 o C
600 o C
500 o C
400 o C
300 o C
0
20
40
2-T heta (deg.)
60
(220)
(208)
(018) (214)
(211)
(024)
(202)
Intensity (a.u)
(012)
(110)
(104)
XRD Patterns of La0.8Sr0.2CoO3 at different
temperatures
SEM Pictures of La0.8Sr0.2CoO3 coated Ni
electrode After Sintering at 900°C
Bare Ni Electrode
LSC Coated Ni Electrode
Sintered at 900o C
LSC Coated Ni Electrode after
immersion in molten carbonate
Melt for 200 hours
Magnification X 2000
Dissolution Behavior La0.8Sr0.2CoO3 coated
Ni electrode at 650o C
Ni (mole fraction) X 10 6
40
Ni from NiO
30
Ni from LSC coated Ni
20
10
0
0
45
90
135
Time (Hours)
180
225
Polarization Behavior of Ni
0.075
Polarization (, V)
0.055
650 C
700 C
750 C
0.035
0.015
-0.005
0.00
0.05
0.10
0.15
Applied Current (A/cm2 )
Effect of Temperature on Polarization Performance of NiO
0.20
Polarization Behavior of La0.8Sr0.2CoO3
coated Ni electrode
0.12
Over Potential ( )
0.10
650
700
750
0.08
0.06
0.04
0.02
0.00
30
80
130
Applie d C urre nt (mA/cm 2)
Comparison of Impedance Behavior of Ni
2.4
650 C
700 C
750 C
-Imaginary Z
1.8
1.2
0.6
0.0
0.75
1.55
2.35
3.15
3.95
Real Z
Comparison of Impedance response of NiO at different temperatures at
100 mV applied polarization potentials
EIS response for La0.8Sr0.2CoO3 coated Ni
electrode at 650°C
2.60
33:60:0
33:60:2.5
33:60:7.5
33:60:15
33:60:22.5
33:60:30
1.52
0.98
Increasing [O 2 ]
0.44
2.9
-0.10
2.4
0.7
1.2
1.7
Real Z' ( )
2.2
2.7
-Imaginary Z" ()
-Imaginary Z" ()
2.06
1.9
1.4
0:60:16
2.5:60:16
10:60:16
20:60:16
30:60:16
45:60:16
60:60:16
0.9
Increasing [CO 2 ]
0.4
-0.1
1
2
Real Z' ( )
3
EIS response for La0.8Sr0.2CoO3 coated Ni
electrode at 700°C
33:60:0
33:60:2.5
33:60:7.5
33:60:15
33:60:22.5
33:60:30
-Imaginary Z" (
1.9
1.4
0.9
In cre asin g [O 2]
0.4
2.50
-0.1
1.1
1.6
Real Z' (
1.98
2.1
-Imaginary Z"()
0.6
0:60:16
2.5:60:16
10:60:16
20:60:16
30:60:16
45:60:16
60:60:16
1.46
0.94
Increasing [CO 2 ]
0.42
-0.10
0.5
1.0
1.5
Real Z'( )
2.0
2.5
EIS response for La0.8Sr0.2CoO3 coated Ni
electrode at 750°C
-Imaginary Z" ()
1.4
0.9
33:60:0
33:60:2.5
33:60:7.5
33:60:15
33:60:22.5
33:60:30
0.4
In cre asin g [O 2]
2.60
-0.1
1.1
Real Z' ()
2.06
1.4
-Imaginary Z" ()
0.8
0:60:16
2.5:60:16
10:60:16
20:60:16
30:60:16
45:60:16
60:60:16
1.52
0.98
Increasing [CO 2 ]
0.44
-0.10
0.5
1.0
1.5
2.0
Real Z" ( )
2.5
EIS response of La0.8Sr0.2CoO3 coated
Ni electrode in Full Cell at 650°C
5:20:32
16:20:32
30:20:32
40:20:32
60:20:32
3
2
1
Incre asing [O 2]
0
-1
0:20:16
16:20:16
32:20:16
64:20:16
100:20:16
3.5
0
1
2
3
Real Z' ()
4
5
-Imaginary Z" ()
-Imaginary Z" (()
4
3.0
2.5
2.0
In cre asin g [C O 2]
1.5
1.0
0
1
2
Real Z' ()
3
Conclusions
Rate of dissolution of Ni decreased significantly
after La0.8Sr0.2CoO3 coating.
The observed increase in polarization may be due
to the decrease in porosity and change in surface
morphology.
La0.8Sr0.2CoO3 coated nickel oxides offer better
stability in MCFC cathode environment.
Acknowledgements
Financial sponsors - Dept of Energy,
National Energy Technology Laboratory