Argonne Activity Overview - National Energy Technology ......Argonne National Laboratory Stability of Argonne LSF Cathodes No reactivity observed between stoichiometric or non-stoichiometric

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


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


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


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


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


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


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


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%)


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)


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


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


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)


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


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


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.


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

Documents

Argonne Activity Overview - National Energy Technology ......Argonne National Laboratory Stability of Argonne LSF Cathodes No reactivity observed between stoichiometric or non-stoichiometric