Thermoelectric Material Ca3Co4O9 as a Cathode Electrode for IT-SOFCs
Kensaku Nagasawaa*, Hiroshi Nakatsugawab, Olivier Mentrec, and Mami Yamadaa
aDepartment of Applied Chemistry, Tokyo University of Agriculture and Technology (TAT)
2-24-16 Naka-cho, Koganei, Tokyo 184-8588, Japanb
Graduate School of Engineering, Yokohama National University,
79-5 Tokiwadai, Hodogaya Word, Yokohama, Kanagawa, 240-8501, Japanc
UCCS - Unite de Catalyse et de Chimie du Solide – UMR CNRS 8181, Ecole Nationale Superieure deChimie de Lille, Batiment C7a – BP90, 108, 59652, Villeneuve d'Ascq cedex, Franceken-naga@cc.tuat.ac.jp

resin

Ca3Co4O9CGO

50.0 μm

Fig. 1. SEM image of cross section of the Ca349-CGO pellet.

electrode approximates to that of CGO electrolyte. The area
specific resistance (ASR) was calculated from the total
polarization resistance Rp and electrode surface area S using
the following: ASR=(Rp×S)/2. In ambient air, the resulting
ASR values ware 4.0 Ω cm2 at 700 ºC (Fig. 2). The single
cells using Ca349 cathode ware confirmed the SOFC
generation by open circuit voltage measurements. Theseresults indicate that the Ca349 has the enough capability tocandidate of novel cathode material for IT-SOFC6).
-50-4002Z''( .cm )Intermediate Temperature Solid Oxide Fuel Cells (ITSOFCs)1) have expected to generate efficiently at 600-800ºC due to the utilization of the alloy interconnecter (e.g FeCr2)). Along with this, SOFC cathode materials have desired
properties of low polarization resistance, thermal andchemical compatibility for electrolyte and long time
durability at lower temperature.
As one of the candidates of SOFC cathode materialshas well known La1-xSrxMnO3 (LSM)3), which is shown its
high thermal and chemical stability. However, the cathodecharacteristics of LSM have drawbacks of rapidly
deterioration below 800 ºC. In the meanwhile, cobalt oxide
for the cathode materials such as Sm1-xSrxCoO3 (SSC), La1xSrxCo1-xFexO3 (LSCF) or Ba 1-xSrxCo1-xFexO3 (BSCF) haveinterested in which exhibit higher performance as the mixed
ionic and electronic conductor (MIEC) at IT region.
Calcium cobalt oxide Ca3Co4O9 (hereafter Ca349) isthe compound that has studied heretofore for candidate ofthermoelectric material due to the high seebeck coefficientand electrical conductivity and the low thermal
conductivity4). The peculiar aspect of this compound is thatits crystal structure consists of 2D misfit layer between
CoO2 (CdI2 type) and Ca2CoO3 (NaCl type) sublattices5)
differ from 3D perovskite structure for the most of SOFC
cathode materials. The aim of this work is that it determines
the thermal, chemical and electrochemical properties ofCa349 as IT-SOFC cathode material.
Polycrystalline Ca349 was prepared using solid-state
reaction at 880 ºC for 24 h from CaCO3 and Co3O4 powders.
Ca349 powder was carried out the chemical reaction tests
with Ce0.9Gd0.1O1.95 (CGO) electrolyte and XRD
measurements. Ca349 pellets ware measured thermal
expansion coefficient (TEC). Electrode slurry was madefrom powder Ca349 and organic additives, and deposited on
CGO pellets, then, heat-treated at 700 ºC. These pellets
ware performed the impedance measurements and SEM
observations. In addition, SOFC single cell generation tests
using Ca3Co4O9 cathode, which included the open circuit
voltage, the I-V characterization and the impedance
measurements ware carried out.
No chemical reaction between Ca349 electrode andCGO electrolyte at 750 ºC was observed. SEM observationof the cross section is shown in Fig. 1. It was observed thegood adherence between the electrode and the electrolyte.
Furthermore, it was found that TEC value of Ca349

1-30
260-20-1-1

500
550
600 T°C
650
700-100102030

4050607080 750Z'( .cm2)

Fig. 2. Temperature dependence of impedance spectra ofCa349 cathode in air.
References
1) J. P. P. Huijsmans, F. P. F. van Berkel, G. M. Christie,
J. Power Sources 71 (1998) 107.
2) P. Kofstad and R. Bredesen, Solid State Ionics 52(1992) 69.
3) Y. Takeda, R. Kanno, M. Noda and O. Yamamoto, J.
Electrochem. Soc. 134 (1987) 2659.
4) S. Li, R. Funahashi, I. Matsubara, K. Ueno and H.
Yamada, J. Mater. Chem. 9 (1999) 1659.
5) Y. Miyazaki, Solid State Ionics 172 (2004) 463.
6) K. Nagasawa, S. Daviero-Minaud, N. Preux, A. Rolle,
P. Roussel, H. Nakatsugawa and O. Mentre, Chem.
Mater. 21 (2009) 4738.