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Research Papers

Oxygen Nonstoichiometry and Electrochemical Properties of GdBaCo2xFexO6δ Double Perovskite Cathodes

[+] Author and Article Information
Dmitry S. Tsvetkov

Department of Chemistry, Ural State University, Lenin Avenue 51, Ekaterinburg 620083, Russiadmitrii.tsvetkov@usu.ru

Nadezhda S. Saricheva, Vladimir V. Sereda, Andrey Yu. Zuev

Department of Chemistry, Ural State University, Lenin Avenue 51, Ekaterinburg 620083, Russia

J. Fuel Cell Sci. Technol 8(4), 041006 (Mar 28, 2011) (4 pages) doi:10.1115/1.4003631 History: Received March 16, 2010; Revised December 06, 2010; Published March 28, 2011; Online March 28, 2011

Mixed ionic- and electronic-conducting perovskite-type oxides are the state-of-the-art materials for high-temperature solid-state electrochemical devices such as solid oxide fuel cells (SOFCs), oxygen membranes, and sensors. Many of such materials are cobaltite-based oxides. Recently, double perovskites REBaCo2O5.5±δ, where RE is a trivalent rare earth and the oxygen content δ varies in wide range, have received a great attention as attractive materials for such application. Many interesting phenomena, such as giant magnetoresistance, charge ordering, and metal-insulator transition, have been observed in these compounds. Powder samples of GdBaCo2xFexO6δ(x=0;0.2) were synthesized by glycerol-nitrate method. Oxygen nonstoichiomentry of oxides GdBaCo2xFexO6δ(x=0;0.2) was measured by the thermogravimetric (TG) method as a function of temperature in the range of 251100°C in air. Total conductivity of aforementioned oxides was studied by the four-probe dc-method as a function of temperature in the range of 251100°C in air. Polarization resistance of double perovskite cathodes was investigated by impedance spectroscopy in symmetrical cell of the type electrode|electrolyte|electrode. “Metal-insulator” transition was found at 80°C in GdBaCo2O6δ, whereas it was not observed in iron-doped sample GdBaCo1.8Fe0.2O6δ due to the increase in oxygen content upon Fe-doping. At high temperatures, both double perovskites have almost the same total conductivity. Chemical interaction was found to decrease the performance of GdBaCo2xFexO6δ cathodes in YSZ-based SOFCs due to the chemical interaction between electrolyte and cathode materials, which significantly increases their polarization resistance. Behavior of total conductivity of oxides GdBaCo2xFexO6δ(x=0;0.2) with temperature was explained by assuming small polaron charge transfer. The particularity of the latter is larger mobility of electron holes as compared with that of electrons. Increase in cathode performance was shown in the case of YSZ covered by the Ce0.8Sm0.2O2 layer in comparison with pure Zr0.9Y0.1O2 electrolyte.

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Figures

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Figure 1

XRD pattern of GdBaCo2O6−δ

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Figure 2

Total conductivity of double perovskites GdBaCo2−xFexO6−δ(x=0;0.2) versus temperature in air

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Figure 3

Oxygen nonstoichiometry of double perovskites GdBaCo2−xFexO6−δ(x=0;0.2) versus temperature in air

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Figure 4

Typical impedance data for cell (1) with GdBaCo2O6−δ cathode and Ce0.8Sm0.2O2−δ electrolyte

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Figure 5

Equivalent scheme for impedance data analysis

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Figure 6

Polarization resistance of GdBaCo2−xFexO6−δ(x=0;0.2) cathodes versus temperature

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