1. The Electrochemical and thermal performances of Ca3Co4O9-δ as a cathode material for IT-SOFCs
K. Nagasawa1), O. Mentré2), S. Daviero-Minaud2),
N. Preux2), A. Rolle2) and H. Nakatsugawa1)
1) Graduate School of Engineering, Yokohama National University, 79-5 Tokiwadai, Hodogaya Word, Yokohama, Kanagawa, , Japan
2) UCCS - Unite de Catalyse et de Chimie du Solide – UMR CNRS 8181, Ecole Nationale Superieure de Chimie de Lille, Batiment C7a – BP.90, 108, 59652, Villeneuve d'Ascq cedex, France
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Tours 8-10 juin 2009

2. GDR ITSOFC-PACTE Tours 8-10 juin 2009
Outline
Background
Disposition for Ca3Co4O9-δ
Cell Manufacturing
Thermal Dilatometory
Chemical Compatibility
Electrode Deposition
Preliminary Electrochemical Tests
Conclusions
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3. GDR ITSOFC-PACTE Tours 8-10 juin 2009
Back ground
Cobalt Oxide in Cathode materials for IT-SOFC
3D Perovskite
2D Perovskite
Sm0.5Sr0.5CoO3
La1-xSrxCoO3
Ba0.5Sr0.5Co1-xFexO3
　　　・
YBaCo4O7
GdBaCo2O5
showing promising cathode performances.
　mechanical incompatibility with electrolyte in TEC
　chemical incompatibility reactivity with zirconia ( IT)
GDR ITSOFC-PACTE Tours 8-10 juin 2009

4. Crystal structure and oxygen vacancy in Ca3Co4O9-δ
2D misfit layered structure X2/m(0 p 0)s0
CoO2 Hexagonal layer
High electrical conduction layer
Co valence 3+/4+
Cf. NaxCoO2-yH2O
 Ca3Co4O9 σ > 100 S/cm
Ca2CoO3 Rock salt layer
Co valence 2+/ 3+
Oxygen Vacancy
δ ～ 0 – 0.15
Possible ionic conduction O
[Ca2CoO3]pCoO2
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5. GDR ITSOFC-PACTE Tours 8-10 juin 2009
Thermal dilatometry
Temperature (ºC) .
ΔL/L0 (-)
Thermal expansion coefficient (10-6 ºC-1)
CGO
→ TEC = x 10-6 (ºC-1)
Experimental Value
Ca3Co4O9
→ TEC = 9-10 x 10-6 (ºC-1)
30CGO-Ca3Co4O9
→ TEC = x 10-6 (ºC-1)
Caliculated Theoretical Value
from HT-XRD
→ TEC = 13 x 10-6 (ºC-1)
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6. Optimizing grain size by ball milling times
initial condition (0 hour)
9 hours
12 hours
24 hours
Mean grain size 0～12 h →1.5-4 m h → m
GDR ITSOFC-PACTE Tours 8-10 juin 2009

7. Reaction test with electrolyte
YSZ(a)
750℃
100 hours
Ca3Co4O9 + or
CGO(b)
YSZ
CGO
GDR ITSOFC-PACTE Tours 8-10 juin 2009

8. GDR ITSOFC-PACTE Tours 8-10 juin 2009
Experimental
Test Cell preparation
CaCO3
Ball milling
Calcination
880℃　12h
Sintering
880℃ 24h
+ 30 wt% CGO
Ball milling
Co3O4
+ dispersant
+ acetone
Deposit
CGO pellet
Heat treating
700℃
ink
Drying in air
+ binder
+ acetone
<Cell size>
10-11 mm in diameter
1.5-2 mm thick
・XRD ・Thermal dilatometry
・SEM ・Impedance measurement
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9. GDR ITSOFC-PACTE Tours 8-10 juin 2009
SEM image
Cross section of the cell
Cell surface <Ca3Co4O9-δ electrode cell>
50.0 μm
resin
Ca3Co4O9
CGO
20.0 μm
resin
70%Ca3Co4O9-30%CGO
CGO
GDR ITSOFC-PACTE Tours 8-10 juin 2009

10. Impedance spectra of Ca3Co4O9-δ-1 1 2 6
[ in air ]
[ at 700 ºC ]
<HF>
<LF>
[ 700 ºC in air ] ASR = 4.00 Ω.cm2
GDR ITSOFC-PACTE Tours 8-10 juin 2009

11. Impedance spectra of 30CGO-Ca3Co4O9-δ-1 1 2 6
[ in air ]
[ at 700 ºC ]
<HF>
<LF>
[ 760 ºC in air ] ASR = 1.05 Ω.cm2
[ 700 ºC in air ] ASR = 1.42 Ω.cm2
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12. Activation energy →Improve low activation energy by added 30% CGO
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13. GDR ITSOFC-PACTE Tours 8-10 juin 2009
Conclusions
Good chemical compatibility with CGO (TEC, Chemical reactivity).
Good adherence between electrode and electrolyte,
no crack surface.
Relatively Low ASR value of Ca3Co4O9 and 30CGO-Ca3Co4O9 cell.
the limiting stage is the ionic conductivity for Ca3Co4O9
 Necessity for optimization of the microstructure.
(grain size optimization, use of cellulose for porosity)
 Optimization of the Oxygen conductivity (doping, … measurement of the permittivity under investigation (SPS- Toulouse, France)
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