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Research Papers

Sintering Mechanisms of Cobalt-Doped Ceria and Zirconia Electrolytes in Intermediate-Temperature Solid Oxide Fuel Cells

[+] Author and Article Information
Masashi Mori, Zhenwei Wang

 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, Kanagawa 253-8585, Japan

J. Fuel Cell Sci. Technol 8(1), 011007 (Nov 03, 2010) (6 pages) doi:10.1115/1.4002231 History: Received January 20, 2010; Revised June 23, 2010; Published November 03, 2010; Online November 03, 2010

Ce0.9Gd0.1O1.95 (CGO) and (ZrO2)0.89(Sc2O3)0.1(CeO2)0.01 (ScSZ) have been proposed as possible alternative electrolytes in intermediate-temperature solid oxide fuel cells (SOFCs). In this study, the mechanisms of densely sintering Co-doped CGO and ScSZ electrolytes during the SOFC fabrication process were investigated using synchrotron X-ray diffraction (SR-XRD) analysis. The addition of CoO enhanced the sintering characteristics of both CGO and ScSZ. Based on the results of the SR-XRD analysis, it was found that CGO and CoO did not form a solid solution after heat treatment at 1200°C for 10 h. On the other hand, the solubility limit of Co in ScSZ was estimated to be 3mol% after firing at 1400°C, and Co doping accelerated the conversion of the two phases of the fluorite structures with cubic and rhombohedral phases into a single cubic phase. Because no significant densification of the Co-doped ScSZ samples was observed before and after the phase change and Co diffusion, it suggests that these reaction sintering processes should not be strongly related to densification. From the results of scanning electron microscopy, Co doping suggests to assist the densification of the ScSZ samples through liquid phase sintering, similar to Co-doped CGO.

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Figures

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Figure 1

FE-TEM and SEM micrographs of starting materials: (a) CGO, (b) ScSZ, and (c) CoO

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Figure 2

Sintering characteristics of pure CGO and Co-doped CGO samples. The data of CGO and 2 mol % Co-CGO were used in Ref. 7. (a) Relative density of the samples as a function of Co content at various firing temperatures, where the holding time at the highest temperature was zero. (b) Relative density of the samples sintered at selected temperatures as a function of holding time.

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Figure 3

SEM micrographs of pure CGO and Co-doped CGO samples after firing at 1100°C without holding time: (a) CGO, (b) 1 mol % Co-doped CGO, and (c) 2 mol % Co-doped CGO

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Figure 4

SR-XRD measurement of pure CGO and Co-doped CGO samples after firing at 1100°C for 10 h. (a) 7 3 3 peak in the SR-XRD patterns: (1) 1 mol % Co-doped, (2) 2 mol % Co-doped, and (3) 3 mol % Co-doped CGO. (b) Lattice parameter as a function of CoO content.

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Figure 5

Co oxide content in CGO with CoO addition after firing at selected temperatures, as determined by SR-XRD measurements

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Figure 6

FE-TEM micrograph of 2 mol % Co-doped CGO after firing at 1400°C for 4 h. Circles denote areas of higher Co concentration. White and black circles represent >1 mol % and 0.5–1 mol %, respectively.

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Figure 7

Sintering characteristics of pure ScSZ and Co-doped ScSZ samples. (a) Relative density of thesamples as a function of Co content at various firing temperatures, where the holding time at the highest temperature was zero. (b) Relative density of the samples at selected temperatures as a function of holding time.

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Figure 8

SR-XRD measurement of pure ScSZ and Co-doped ScSZ samples after firing at 1400°C for 4 h. (a) 7 3 3 peak in the SR-XRD patterns: (1) 1 mol % Co-doped, (2) 2 mol % Co-doped, and (3) 3 mol % Co-doped ScSZ. (b) Lattice parameters as a function of CoO content.

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Figure 9

1 1 1 peak in the SR-XRD patterns of the Co-doped ScSZ samples after firing at 900°C for 1 h

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Figure 10

Each ScSZ phase content in the samples at selected temperatures for 1 h: (a) Cubic phase content as a function of firing temperature. (b) Rhombohedral phase content as a function of Co content.

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Figure 11

Co oxide content in pure ScSZ and Co-ScSZ samples after firing at selected temperatures, as determined by SR-XRD measurements

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Figure 12

SEM micrographs of pure ScSZ and Co-ScSZ samples after firing at 1100°C without holding time: (a) ScSZ, (b) 1 mol % Co-doped, (c) 2 mol % Co-doped, and (d) 3 mol % Co-doped ScSZ

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