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Research Papers

A Fundamental Study on the Chemical Stability of La1−xSrxCo0.2Fe0.8O3−δ Cathodes for Intermediate Temperature Solid Oxide Fuel Cells

[+] Author and Article Information
Yufeng Qiu, Jian Pu

Center for Fuel Cell Innovation,
School of Materials Science and Engineering,
State Key Laboratory of Material Processing and
Die and Mould Technology,
Huazhong University of
Science and Technology,
Wuhan 430074, China

Jian Li

Center for Fuel Cell Innovation,
School of Materials Science and Engineering,
State Key Laboratory of Material Processing and
Die and Mould Technology,
Huazhong University of
Science and Technology,
Wuhan 430074, China
e-mail: lijian@hust.edu.cn

Yihui Liu

Hubei Key Laboratory of Advanced Technology
for Automotive Components,
Wuhan University of Technology,
Wuhan 430070, China;
Hubei Collaborative Innovation Center for
Automotive Components Technology,
Wuhan University of Technology,
Wuhan 430070, China
e-mail: liuyihui@whut.edu.cn

Bin Hua

Department of Chemical and
Materials Engineering,
University of Alberta,
Edmonton, AB T6G 1H9, Canada

1Corresponding authors.

Manuscript received January 14, 2017; final manuscript received April 6, 2017; published online June 13, 2017. Assoc. Editor: San Ping Jiang.

J. Electrochem. En. Conv. Stor. 14(3), 031002 (Jun 13, 2017) (6 pages) Paper No: JEECS-17-1009; doi: 10.1115/1.4036812 History: Received January 14, 2017; Revised April 06, 2017

The chemical stability of La1−xSrxCo0.2Fe0.8O3−δ (x = 0, 0.4, 0.6, and 1) oxides before and after annealing at 750 °C in air is investigated by field emission scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and environmental transmission electron microscopy (TEM). Results indicate that Sr surface segregation has initially occurred at the sintering stage, and then, the secondary-phase particles are formed with increasing the heat-treatment time at 750 °C in air. Increasing Sr content accelerates Sr segregation on the surface, because of two driving forces including interaction forces in the crystal lattice and thermal activation. AES and XPS results reveal that Sr and Co segregations toward the surface have great contributions to the chemical instability of La1−xSrxCo1−yFeyO3−δ (LSCF) during annealing.

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Figures

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Fig. 1

XRD patterns of La1−xSrxCo0.2Fe0.8O3−δ (x = 0, 0.4, 0.6, and 1) powders, and the inset is a local part corresponding to the (110) planes

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Fig. 2

Refined XRD patterns of (a) LCF, (b) LSCF40, (c) LSCF60, and (d) SCF powders

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Fig. 3

SEM images observed on the surface of dense La1−xSrxCo0.2Fe0.8O3−δ bar samples before and after heat treatment for different times at 750 °C in air

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Fig. 4

(a) AES image on the surface of SCF bar after annealing for 200 h at 750 °C in air, and the corresponding elemental maps for (b) Sr, (c) Co, and (d) Fe

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Fig. 5

Schematic diagrams of chemical changes on the surface of SCF sample before and after annealing at 750 °C in air (the size of each part in the diagrams is not the real size)

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Fig. 6

The core-level spectra of (a) C 1 s, (b) O 1 s, and (c) Sr 3 d on the surface of dense SCF sample before and after annealing at 750 °C in air

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Fig. 7

TEM images of the SCF power after annealing for 200 h at 750 °C in air: (a) SCF powder and (b) a typical region of the segregated particle. The insets are the corresponding electron diffraction patterns obtained by FFT.

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