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Georgia Tech - SSI&EC
Meilin Liu
School of Materials Science &Engineering
Georgia Institute of Technology
Atlanta, GA 30332-0245
Presented to Electrical Energy Systems and
Sustainability WorkshopGeorgia Tech
November 29 – December 1, 2000
Fuel Cell TechnologyStatus, Challenges, and Opportunities
Georgia Tech - SSI&EC
Outline
• Introduction• Polymer Electrolyte Membrane Fuel Cells
– Current technology– Applications: Portable/vehicle– Challenges/opportunities
• Solid Oxide Fuel Cells (SOFCs)– Current technology – Applications:Stationary/distributed/EV– Challenges/opportunities
• Concluding Remarks
Georgia Tech - SSI&EC
Fuel in Oxidant in
Depleted fuel Depleted oxidant
Electrolyte
(Ionic conductor)
CathodeAnode
H+
Anionconductor
H2
O2
H2O
H2O
Loade’
O2
H2
Schematic of an individual fuel cell
Georgia Tech - SSI&EC
Advantages of Fuel CellsOver conventional Technologies
High efficiencyInternal combustion engine: <30% Fuel cell: 50% electrical, 85% overall (SOFC)
Environmental friendlyEmits H2O or CO2 without pollutantsEmits as much as 60% less CO2 than coal plant
Noise-free and no site restrictionNo mechanical friction or moving parts
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PEMFCs: Challenges & Opportunities
Efficient catalysts insensitive to impurities in the fuel such as CO;
Efficient catalysts that promote a high rate of oxygen reduction;
Alternative catalysts less expensive than Pt to reduce the cost.
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A Planar Solid Oxide Fuel Cell
End Plate
Anode
Electrolyte
Cathode
Bipolar Separator
AnodeRepeatingunit
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A Tubular Solid Oxide Fuel Cell
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Characteristics of GDC Powder by GNPCharacteristics of GDC Powder by GNP
1m
b
4m
Easy to densify92% at 1250oC/5 hrs95% at 1350oC/5 hrs
Large surface area
Compositional homogeneity
Loose agglomeratesFoam-like structureFill density 0.059 g/cm3
120th of theoretical value
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Microstructures of Dry-Pressed FilmsMicrostructures of Dry-Pressed Films
30m
cathode
electrolyte
anode
~15 m
GDC film
Substrate
~8 m
10m
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2m
Dense SDC
2m
Porous SSC and 10 v%SDCCathode
Changrong Xia, Fanglin Chen and Meilin Liu, Electrochemical and Solid State letters, 4(5) A52-A54 (2001).
SOFCs Fabricated by Screen-Printing
Porous Ni-SDCAnode
2m
electrolyte
anode
cathode
A single cell
30m
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Single cell performance of SDC-electrolyte SOFC
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.60.0
0.2
0.4
0.6
0.8
1.0
1.2
600oC 550
oC 500
oC 450
oC 400
oC
Cel
l Vol
tage
, V
Current Density, A/cm2
0.0
0.1
0.2
0.3
0.4
0.5
Pow
er d
ensi
ty, W
cm2
Georgia Tech - SSI&EC400 450 500 550 600
0
2
4
6
8
10
Electrolyte resistance Electrodes polarization Total resistance
Res
ista
nce,
cm
2
Temperature, oC
1.1 1.2 1.3 1.4 1.50.01
0.1
1
10
Electrolyte Electrodes
Ea=32kJmol-1
Ea=11
5kJm
ol-1
Res
ista
nce,
cm
2
1000/T, k-1
0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.00.0
0.2
0.4 a
600oC
550oC
500oC
Im Z
, cm
2
Re Z, cm2
Significance of Interfacial ResistancesSignificance of Interfacial Resistances
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SOFCs: Challenges & Opportunities
• Nonstructural electrodes and interfaces to enhance performance, especially anodes for alternative fuels;
• Cost-effective fabrication processes to dramatically reduce the cost; $4,000$400/KW;
• Efficient catalysts insensitive to impurities in the fuel such as H2S.
• New electrolytes with high ionic conductivities at low temperaturesinexpensive materials,longer life;
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Mesoporous Materials
Meso-porous materials---porous inorganic solids with pore size 2-50nm
Preparation -- surfactant templating mechanism
Remarkable properties:Narrow pore size distributionPore size tunable (from 2nm to 50 nm)Large surface area (~1000 m2/g)
Surfactant
Inorganic precursor
Applications:Catalysis, selective separations, absorption medium, sensors, Electrodes for lithium batteries, fuel cells, and gas sensors.
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Formation of Mesoporous SnO2
Cetyltrimethylammonium bromide
pH=10 2- [Sn(OH)6]
SnCl4
+
H3C
CH3
N Br-
CH3 2-
[Sn(OH)6]
N+
+N
Electrostatic interaction
Tin chloride
N+
+N
[Sn(OH)6] 2- N
+
+N
N+
+ N
N
+
+N
N +
+N
N+
+N
C
2- [Sn(OH)6]
2- [Sn(OH)6]
2- [Sn(OH)6]
2- [Sn(OH)6]
[Sn(OH)6] 2-
Micelle formationS+I- interaction
N
N
NN
N
N
NN N
N
N
N
Sn
Sn
Sn O
O
O
OSn
Sn
O
O Sn
Sn
Sn
Sn O
O
O
OSn
Sn
O
O Sn
O
O
O
OOO
OO
O
O
O
O
Aging
Calcining
10 nmTEM image of SnO2
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Preparation of Mesoporous YSZ-NiO
OO
MM M
O
O
OO
O
O
O
OM
M
M O
O
O
O
O
OM
M
M
O
O
OO
O
O
MM
M
O
O
O
O
O
O
M
MM
O
O
OO
O
O
MM
M
O
O
O
O
O
OM
M
MO
OO
O
O
OM
M
M
O
O
-PPO
(Surfactant)
(PEO) m(PPO)n (PEO)m
ZrOCl2 YCl3+ NiCl2+
(Inorganic species)
YCl3ROH
OHR
YCl
ClCl
HO YCl2 HO R+
H O2
-PEO
RO YCl2 + HCl
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TG-DSC, XRD of Mesoporous YSZ-NiO
0.5 1.5 2.5 3.5 4.5
Inte
nsity
As-synthesized
500 oC/2hr
20 30 40 50 60 70 80
500 oC/2 hr
As-synthesized
oo
o o oo
x
x
x
x
o—YSZx—NiO
2 (degree)
30
40
50
60
70
80
90
100
0 200 400 600Temperature (oC)
Weig
ht ch
ange
(%)
-30
-20
-10
0
10
20
Heat
flow
(mW
)
TG
DSC
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TEM and BET of Mesoporous YSZ-NiO
TEMBET
20 nm
020406080
100120140160180
0 0.2 0.4 0.6 0.8 1Relative pressure (P/Po)
Vol
ads
orbe
d (c
c/g,
ST
P)
2 8 14
108 m2/g4.5 nm
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Micrographs of PS & Sr0.5Sm0.5CoO3
500 nm
Polystyrene Spheres
500 nm
Sr0.5Sm0.5CoO3
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Concluding Remarks
Fuel Cells are the most efficient/cleanest technology for conversion of chemical to electrical energy;
PEMFC and SOFC are the most versatile system for various applications;
Cost reduction is the key to successful commercialization of fuel cells;
Fuel cells will significantly influence our everyday life in the years to come.
