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Chemical Technology DivisionArgonne National Laboratory
Argonne Activity Overview
Michael KrumpeltMichael KrumpeltJames RalphJames RalphTerry CruseTerry Cruse
Argonne National LaboratoryArgonne National Laboratory
Presented atSECA Core Technology Review
February 19-20, 2003Sacramento, CA
Argonne National Laboratory
Chemical Technology DivisionArgonne National Laboratory
Nothing Is Permanent But Change
Completed: -Cathode Development
Continuing: -Exploration of alloy composition for bipolar plates
New: -Investigate Cr Poisoning-Develop diesel reforming catalysts-Review detection methods for defects
Chemical Technology DivisionArgonne National Laboratory
Technical Issues
Bipolar Plate Materials• Stainless steels are protected by a Cr2O3 layer, but
in flowing moist air the Cr2O3 becomes volatile
Cr2O3 + 3/2O2 + 2H2O 2 CrO2(OH)2
• Composition of steels cannot be easily changed
Chemical Technology DivisionArgonne National Laboratory
Technical Issues (2)
Chromium Volatization• Poisoning of the cathode has been observed to
be more rapid at 700ºC than 800ºC.
Diesel Reforming• Catalysts are poisoned by sulfur and loose
activity• Avoiding carbon formation
Chemical Technology DivisionArgonne National Laboratory
Results: Cathodes
Temperature/°C650 700 750 800
ASR
/ Ω. c
m2
0.1
1
10
100
1000
La0.8Sr0.2MnO3
0.8 0.2 3
Pr0.8Sr0.2FeO3
La0.6Sr0.25FeO3
La Sr FeO
LSF better than LSM
PrSF shows further improvement over LSM
La-deficient La0.6Sr0.25FeO3displays significant improvement over stoichiometric LSF
Chemical Technology DivisionArgonne National Laboratory
La-Deficient Ferrite Cathodes
La- and total A-site-deficiency between 5-20 mol% achieve significantly lower ASR values compared to stoichiometric LSF
Increasing Sr-doping in La-deficient LSF further improves ASR
Target ASR obtained at 800°C using La0.6Sr0.25FeO3
Temperature/ °C650 700 750 800
ASR
/ Ω. c
m2
0.1
1
10 (La0.8Sr0.2)0.8FeO3
La0.7Sr0.2FeO3
La0.7Sr0.25FeO3
La0.65Sr0.25FeO3
La0.6Sr0.25FeO3
Target ASR
Chemical Technology DivisionArgonne National Laboratory
Stability of Argonne LSF CathodesNo reactivity observed between stoichiometricor non-stoichiometric LSF and YSZ using XRD: Reactivity experiment performed at 1200°C for 1 week on compacted powders
2Θ (°)
20 30 40 50 60 70 80
Inte
nsity
(Cou
nts/
sec)
0
50
100
150
200La0.75Sr0.25FeO3+YSZLa0.6Sr0.25FeO3+YSZ
LSF LSF
LSF
LSF
LSF
LSF
LSF
YSZ
YSZ
YSZ
YSZ
YSZ YSZ
Chemical Technology DivisionArgonne National Laboratory
Lower Cost Ferrite Cathodes
Switching La for other rare earths has shown further improvements
Replacing pure lanthanum with a cheaper but less pure lanthanum concentrate resulted in similar ASR values
Temperature/°C650 700 750 800
ASR
/ Ω. c
m2
0.1
1
10
Simulated Concentrate Ln0.7Sr0.25FeO3 #1Simulated Concentrate Ln0.7Sr0.25FeO3 #2La0.7Sr0.25FeO3
#1 – La(68.7%), Ce(3.4%), Pr(4.7%), Nd(23.2%)
#2 - La(63.5%), Ce(6.35%), Pr(8.73%), Nd(22.5%)
Chemical Technology DivisionArgonne National Laboratory
Cathode ASR Comparison
0.01
0.1
1
10
100
400 500 600 700 800 900 1000
Temperature/ °C
ASR
/ Ω.c
m2
YSZANL LSFCGOLSGM
(1997-2002)
Chemical Technology DivisionArgonne National Laboratory
Benefits of Argonne LSF Cathodes
Iron is cheapest of transition metals normally considered on the B-site of the perovskite
Slurry coated cathodes are simple and cheap
NO additional processing steps are used to obtain acceptable performance, e.g. interlayers, impregnation, graded structures
Chemical Technology DivisionArgonne National Laboratory
Argonne’s ApproachPowder metallurgy approach offers the ability to quickly make unique alloy compositions, a wide range of structures and compositionally graded materials allowing for different alloys under both environments.
Argonne’s 3 Primary Groups of Focus– Fe-Cr Alloys With Rare Earth Additions– Ferritic Alloys Without Chromium– Compositionally Graded Cermets
Chemical Technology DivisionArgonne National Laboratory
Thermal Expansion of Alloys Compared to 8YSZ
8
9
10
11
12
13
14
15
16
100 200 300 400 500 600 700 800Temperature (C)
Coe
ffici
ent o
f The
rmal
Exp
ansi
on (*
10-6
cm
/cm
/K)
8YSZ434L (16wt% Cr)E-Brite (26wt% Cr)Fe-25CrFerritic Alloy w/o CrT-441 (18wt% Cr)
Chemical Technology DivisionArgonne National Laboratory
Ferritic Stainless Steels
0
3
6
9
12
15
1 2 3 4 5 6 7 8 9 1 0 1 1 1 2 1 3 1 4
ASR
(Ohm
s*cm
^2)
Fe-2
5Cr
Fe-2
5Cr-
2La-
1.28
YFe
-25C
r-1L
a-0.
64 Y
Fe-2
5Cr-
1 Y-
0.16
Sr
Fe-2
5Cr-
2 Y
Fe-2
5Cr-
1Y
Fe-2
5Cr-
2La-
0.32
Sr
Fe-2
5Cr-
1 La
-0.1
6Sr
Fe-2
5Cr-
2La
Fe-2
5Cr-
1La
434
(Fe-
17C
r-1M
o-1M
n-1S
i)
Fe-2
5Cr-
3Mn-
1 La
-0.6
4 Y-
0.32
SrFe
-25C
r-2
La-1
.28
Y-0.
62 S
r
Fe-2
5Cr-
1La-
0.64
Y-0.
31Sr• Rare earth additions
improve ASR and should stabilize oxide scale
• La appears more effective at improving ASR
• Y appears more effective at improving oxidation resistance
• Sr enhances electrical conductivity
0
3
6
9
12
1 2 3 4 5 6 7 8 9 1 0 1 1 12 13 14
Wei
ght G
ain(
mg/
cm^2
)
Fe-2
5Cr
Fe-2
5Cr-
2La-
1.28
Y
Fe-2
5Cr-
1La-
0.64
Y
Fe-2
5Cr-1
Y-0
.16
Sr
Fe-2
5Cr-2
Y
Fe-2
5Cr-
1YFe-2
5Cr-2
La-0
.32
Sr
Fe-2
5Cr-
1 La
-0.1
6Sr
Fe-2
5Cr-2
La
Fe-2
5Cr-1
La
Fe-2
5Cr-
3Mn-
1 La
-0.6
4 Y-
0.32
Sr
Fe-2
5Cr-2
La-
1.28
Y-0
.62
Sr
Fe-2
5Cr-
1La-
0.64
Y-0.
31Sr
434
(Fe-
17C
r-1M
o-1M
n-1S
i)
Compositions in weight percent
Chemical Technology DivisionArgonne National Laboratory
Ferritic Alloys Without Chromium
• Limited Selection of Elements that stabilize ferritic phase.
• Possible Mixed Oxide Scales– FeXO4 (wolframite structure).– FeXO4 (rutile structure)– FeX2O6 (trirutile structure)
• Addition of Ni– Possible Formation of NiX2O6
(trirutile structure).• Addition of Ni with La or Y
– Possible Formation of XNiO3(perovskite structure).
• Consider additions and oxides other than those of ferritic stabilizers
• Produce a stable oxide• Dope to enhance electrical
conductivity
020406080
100120140160180200
1 2 3 4 5 6 7 8 9 1 0 1 1 1 2
Wei
ght G
ain
(mg/
cm^2
)
434
Ni added,complete oxidation
0
10
20
30
40
50
60
70
1 2 3 4 5 6 7 8 9
ASR
(Ohm
s*cm
^2)
434
Chemical Technology DivisionArgonne National Laboratory
LaSrCrO3-Ferritic Stainless Steel Composites
• Simple mixing: some segregation during processing
• Mechanical alloying of LaSrCrO3 with starting elements: produced to fine a powder.
• Presently attempting to pre-alloy elements then mix in LaSrCrO3, short time and lower energy.
Chemical Technology DivisionArgonne National Laboratory
Future Plans
• Have nano-phase LSF prepared and supply samples
• Explore alloys with low chromium volatization
• Compare “time to failure” of SOFC for various bipolar plate materials
• Explore perovskites as diesel reforming catalysts