orea

nstitute of

eramic

ngineering &

echnology

Effect of Starting Materials on the Characteristics of (La1-xSrx) Mn1+yO3-δ Powder Synthesized by GNP

2007. 04. 26

MI-Jai Lee

KoreaKorea--America America nanonano forumforum

Electronic Materials Team

What is SOFC ?

Anode : H2+O-2 = H2O + 2e-

Cathode : 1/2O2 + 2e- = O-2

Total : H2 +1/2O2 = H2O

PrinciplePrinciple

Solid oxide fuel cell is energy conversion device that produces electricity by electrochemical.It operate at high temperature over 600℃ with pollution-free

technology.

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PrinciplePrinciple

Advantage & Disadvantage

Highest energy conversion efficiency

No need to use noble metal catalyst (600~1000℃ operation)

LNG, coal gas can be used

No problems of electrolyte loss

High quality byproduct heat

Modular construction

Potential for cogeneration

Much lower production of pollutants.

Not reliable to thermal cycleLow physiochemical stability

Advantage Disadvantage

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PrinciplePrinciple

Key Research Material Areas ?

• Nano-scale materials, and synthesis- Nano-powders- Composites

• New cathode materials- Higher conductivity- Lower polarization

• Fuel flexible anode materials- Sulfur tolerance- Various fuels

Materials Processing

• Thin films- lower temperatures- new processes

• Chemical synthesis routes for development of mixed conductors

• Investigation of complex perovskite-type oxides

• MEA fabrication and characterization(solid acids, proton conductingoxides)

General Materials

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Initial stage of glycine-metal complexation in an queous solution.

H2N - CH2 - CO

O- Sr2+

N - CH2 - C

HH

(H2O)5La2+

O

OH

CO

OHH2N - CH2 -

x(H2O)6-x

2+

Sr

Chemical Reaction ofGlycine-Nitrate Process

(a) Carboxylic Acid Group

(b) Amine Group

Experimental ProcedureExperimental Procedure

Mixing

Addition(Glycine)

Complexation

Combustion

(La0.8Sr0.2)MnO3 Powder

Calcination(400~1200℃ )

La Sr Mn

HNO3Nitrate, Oxide solution

(1mole or 1.4mole)

XRDBETThermal conductivity detctor

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Combustion of residual glycine

200 400 600 800 1000 120050

60

70

80

90

100

←Exo

Temperature (℃)

DSC

(mW

/mg)

TG

(%

)

-1.2

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

21.79%

590.9℃

211.8℃

-148.1 J/g

919.4℃

-16.75 J/g

ResultResult

(a) Nitrate solution (b) Oxide solution

DT-DSC curve of synthesized La0.8Sr0.2MnO3 powder(Stoichiometric)

Dehydration

200 400 600 800 1000 120050

60

70

80

90

100

←Exo

DSC

(mW

/mg)

Temperature (℃)

-1.2

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

TG

(%

)

18.48%

580.9℃

206.6℃

-55.32 J/g

905.1℃

-9.196 J/gOrganicdisappearance

NO3- or CO3

disappearance

Electronic Materials Team

10 20 30 40 50 60 70 802Θ (degree)

La0.8Sr0.2MnO3

Sr2MnO4

La2O3

Sr(NO3)2

As-synthesized

400℃

800℃

1000℃

(b) Oxide solution

ResultResult

10 20 30 40 50 60 70 802Θ (degree)

(a) Nitrate solution

XRD patterns of (La0.8Sr0.2)MnO3 powder (Stoichiometric)

0 2 4 6 8 10 12 140

20

40

60

80

100

Mol

%

pH

COO -

NH3+

Under pH < 1, Amine group are only existing.

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ResultResult

It has single phase after calcination at 1200℃ for 4hrs.

(La0.8Sr0.2)Mn1.4O3

XRD patterns of (La1-xSrx)Mn1.40O3 powders(Non-Stoichiometric, Nitrate Solution)

20 30 40 50 60 70 80

calcined at 1200℃

calcined at 1000℃

as-synthesized

Inte

nsity

(arb

. unit)

2Θ (degree)

(LaSr)MnO3

Secondary phase

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ResultResult

0.9 1.0 1.1 1.2 1.3 1.4 1.50.0

0.4

0.8

1.2

1.6

2.0

2.4

2.8

log(σ

/S·

cm

)

1000/T K-1

Nitrate Oxide

Nitrate solution : 4.87 S/cm at 700℃

Oxide solution : 35.7 S/cm at 700℃

Electrical conductivity of (La0.8Sr0.2)Mn1-xO3 powders

0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.62.0

2.1

2.2

2.3

2.4

2.5

log(σ

·S/c

m)

1000/T K-1

Nitrate Oxide

Nitrate solution : 210.3 S/cm at 700℃

Oxide solution : 152.7 S/cm at 700℃

(b) Non-Stoichiometric (Mn = 1.4mole)(a) Stoichiometric (Mn = 1mole)

J. Mater. Chem. 1997, 7(13)155900

Solid State Ionics 110(1998)61180800

Refs.σ (S/cm)Temp.(℃)

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ResultResult

100 200 300 400 500 600 700

H2 u

ptak

e am

ount

(A.U

. uni

t)

Tem perature(oC)

(a) (b)

Temperature programmed reduction (Non-Stoichiometric)

Temperature programmed reduction of La0.8Sr0.2Mn1-xO3 powder after calcination 1000℃ for 4hrs with different starting Materials.(a) nitrate and (b) Oxide

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ConclusionConclusion

• Case1 : Nitrate solution (La:Mn=1:1)

- LSM powders show secondary phases after calcination at 1000℃ (La2O3, Sr2MnO4)

- Average particle size is 0.90 ㎛ and BET is 26.5 m2/g

- The particles show porous structure

- Electrical conductivity shows 4.87 S/cm at 700℃ after sintered at 1200℃

• Case2 : Oxide solution (La:Mn=1:1)

- Average particle size is 9.04㎛ and BET is 16.8 m2/g

- LSM powders show a secondary phase Sr2MnO4 after calcination 1000℃ for 4hrs.

- Electrical conductivity shows 35.7 S/cm at 700℃ after sintered at 1200℃ for 4hrs.

• Case3 : Mn excess (La:Mn=1:1.4, nitrate solution)

- Average particle size is 2.46 ㎛

- The powders have good sinterability

- Deoxidization peak of the synthesized (La,Sr)MnO3+δ powders using nitrate solution appeared

at lower temperature than the synthesis powders using oxide solution, at 450℃(β-peak)

- Electrical conductivity shows 210.3 S/cm at 700℃ after sintered at 1200℃ for 4hrs.

Effect of Starting Materials on the Characteristics of(La1-xSrx)Mn1+yO3-δ Powder Synthesized by GNP