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Research Papers

Evaluation of SrTi1−x Cox O3 Perovskites (0 ≤ x ≤ 0.2) as Interconnect Materials for Solid Oxide Fuel Cells

[+] Author and Article Information
Masashi Mori1

Zhenwei Wang, Nobuyuki Serizawa

 Central Research Institute of Electric Power Industry, 2-6-1 Nagasaka, Yokosuka, Kanagawa 240-0196 Japan

Takanori Itoh

AGC Seimi Chemical Co., Ltd., 3-2-10 Chigasaki, Chigasaki-shi, Kanagawa-ken 253-8585 Japan

1

Corresponding author.

J. Fuel Cell Sci. Technol 8(5), 051010 (Jun 20, 2011) (6 pages) doi:10.1115/1.4003761 History: Received May 18, 2010; Revised November 23, 2010; Published June 20, 2011; Online June 20, 2011

The compatibility of SrTi1− x Cox O3 perovskites (0 ≤ x ≤ 0.2) was evaluated for use as interconnect materials in solid oxide fuel cells (SOFCs). Although SrTi1− x Cox O3 perovskites have a single perovskite phase in the range of 0 ≤ x ≤ 0.2, it was observed for SrTi0.8 Co0.2 O3 that Co element agglomerated at the grain boundary during sintering. The dense SrTi0.8 Co0.2 O3 sample was destroyed and included Sr2 TiO4 as a secondary phase after reducing treatment at 1000 °C. As a result of Co doping, the linear thermal expansion coefficient (TEC) increased remarkably with increasing Co content, but the TEC of SrTi0.9 Co0.1 O3 was comparable with those of SOFC cathodes and anodes. Co doping of SrTiO3 effectively increased electrical conductivity in air, whereas the conductivity of Co-doped SrTiO3 in a reducing atmosphere was much lower than that in air. This suggests that the Co ions3+/4+ in the perovskites were earlier reduced into Co2+ ions, compared to Ti4+ ions.

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Figures

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Figure 1

Experimental equipment for electrical conductivity measurement of the SrTi0.9 Co0.1 O3 placed in an SOFC atmosphere

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Figure 2

XRD patterns of SrTi1− x Cox O3 perovskites after reducing at 1000 °C for 20 h in the H2 atmosphere: (a) x = 0.05, (b) x = 0.1, (c) x = 0.2. The symbols (×) represent the second phase.

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Figure 3

Lattice parameters of of SrTi1− x Cox O3 perovskites with cubic symmetry before and after reducing at 1000 °C in the H2 atmosphere

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Figure 4

Relative density of SrTi1− x Cox O3 as a function of firing temperature, where the holding time at the highest temperature was 5 h

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Figure 5

SEM micrographs of surface section of the dense samples after firing at 1400 °C. (a) SrTi0.95 Co0.05 O3 . (b) SrTi0.9 Co0.1 O3 .

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Figure 6

Dense SrTi0.8 Co0.2 O3 sample after firing at 1400 °C. Bright parts represent Co element. (a) SEM micrograph of surface section. (b) Co element distribution of EDX map.

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Figure 7

Amount of oxygen deficiencies in SrTi1− x Cox O3−δ in air and in the H2 atmosphere, when the oxygen deficiency of the unfired Co-doped perovskites is assumed to be zero at 25 °C. (a) In air during the 1st heating cycle. (b) In the H2 atmosphere during the first heating cycle. (c) In the H2 atmosphere during the first cooling cycle.

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Figure 8

XANES spectra of SrTi0.9 Co0.1 O3−δ perovskites as sintered and reduced, and reference materials. (a) Co K-edge. (b) Ti K-edge.

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Figure 9

Thermal expansions of SrTi1− x Cox O3 in air, and in the H2 atmosphere during the first/second heating cycles, respectively. (a) In air during the 1st heating cycle. (b) In the H2 atmosphere during the first heating cycle. (c) In the H2 atmosphere during the second heating cycle.

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Figure 10

Differential coefficient of thermal expansion – temperature curves of (i) SrTiO3 and (ii) SrTi0.9 Co0.1 O3 in air and in the H2 atmosphere during the first cycles, respectively. (a) In air. (b) In the H2 atmosphere.

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Figure 11

TEC values of SrTi1− x Cox O3 in the temperature range from 50 to 1000 °C in air and in the H2 atmosphere

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Figure 12

Arrhenius plots of electrical conductivity in air, in the 30%H2 -N2 atmosphere and in a dual atmosphere. (a) SrTi0.95 Co0.05 O3 . (b) SrTi0.9 Co0.1 O3

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Figure 13

Arrhenius plots of electrical conductivity of SrTi0.9 Co0.1 O3 tablet with thickness of 0.4 mm in air and in the 30%H2 -N2 atmosphere and in a dual atmosphere

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