The Electrochemical and thermal performances of Ca3Co4O9-δ
as a cathode material for IT-SOFCs
K. Nagasawa1), O. Mentre2), 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, 240-8501, Japan
2)
UCCS - Unite de Catalyse et de Chimie du Solide – UMR CNRS 8181, Ecole Nationale Superieure deChimie de Lille, Batiment C7a – BP.90, 108, 59652, Villeneuve d'Ascq cedex, France

22Z''(Ω.cm )Z''(Ω.cm )The decreasing of the working temperature for intermediate temperature solid oxide fuel cells(IT-SOFC’s) is such that the cathode has turned out to provide the major source of electrical loss.
Recently, layered double perovskites with ordering of oxygen vacancies such as LBaCo2O5+δ
(L=lanthanide) [1] have been presented as promising cathode materials, highlighting the important roleof their 2D-characteristics in the electrochemical process.
Here, we present recent results on the 2D-Ca3Co4O9-δ (Ca349) for cathode application for ITSOFCs. This misfit-compound is most known for its thermoelectric properties [2] while, to ourknowledge no solid-electrochemical properties been investigated so far. Ca349 is built up fromsandwiching [CdI2]-type and rock-salt slabs according to the formula [CoO2][Ca2CoO3-δ]0.62, the rocksalt layers being oxygen deficient and potentially mixed conductors. Here, Ca349 could be considered
as a natural intergrowth between electronic and potential O2- conducting units. It makes of thiscompound and excellent candidate for SOFC cathode.
Both the thermal expansion coefficient (9-10×10-6 K-1) and chemical stability tests (no reaction
between palletized mixed phases after 100h at 1023 K) show an excellent compatibility between thetitle compound and CGO electrolyte, while YSZ was immediately discarded due to the formation ofCaZrO3. The preliminary electrochemical tests have been performed on symmetricalelectrode/CGO/electrode cells with electrode = pure Ca349 and composite 30 %CGO-70%Ca3Co4O9(30CGO). Thin electrode layers were deposited on dense CGO by ink painting and firing at 700°C.
Impedance spectroscopy measurements versus temperature and oxygen partial pressure wereperformed, leading to promising results. The total polarization resistance (ASR) obeys to an Arrhenius
behavior with activation energy Ea = 1.55 and 1.23 eV, on air, for Ca349 and 30CGO respectively. It isassorted with ASR values around 3Ω.cm2 at 700°C for Ca349 but it is remarkable that, at this point,
no particular effort has been provided to(a)
(b)
-4-50
optimize the microstructure and porosity of theelectrode, nor to reduce its thickness (typically-40-301030µm). However, for 30CGO, the ASR value
122-30becomes 0.75Ωcm (Fig. 1) at 7OO°C with an
201-1-266-1-1
improvement of the ionic diffusion process,0 -1-20500
500
1550
550-1
evidenced as a function of the working pO2.
6600 T°C -1
600 T°C-10650650
To conclude, it was understood that
700
700
0 10 20 30 400
1 2 3 4 5 650 60 70 80 750
both TEC and preliminary electrochemical
7 8 9 750
Z'(Ω.cm )Z'(Ω.cm )measurements indicate the misfit 2D-Ca3Co4O9-δFig. 1. Temperature dependence of impedance spectra
as promising original cathode material for ITof pure Ca 3Co4O9 (a) and 30CGO (b)SOFCs.
22[1] A. Tarancon, S. J. Skinner, R. J. Chater, F. Hernandez-Ramirez and J. A. Kilner, J. Mater. Chem., 17, (2007) p.
3175.
[2] Siwen Li, Ryoji Funahashi, Ichiro Matsubara, Kazuo Ueno and Hiroyuki Yamada, J. Mater. Chem., 9, (1999) p.
1659.