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Research Papers

# Oxygen Nonstoichiometry and Electrochemical Properties of $GdBaCo2−xFexO6−δ$ 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

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

## Abstract

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 $GdBaCo2−xFexO6−δ$$(x=0;0.2)$ were synthesized by glycerol-nitrate method. Oxygen nonstoichiomentry of oxides $GdBaCo2−xFexO6−δ$$(x=0;0.2)$ was measured by the thermogravimetric (TG) method as a function of temperature in the range of $25–1100°C$ in air. Total conductivity of aforementioned oxides was studied by the four-probe dc-method as a function of temperature in the range of $25–1100°C$ 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 $GdBaCo2O6−δ$, whereas it was not observed in iron-doped sample $GdBaCo1.8Fe0.2O6−δ$ 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 $GdBaCo2−xFexO6−δ$ 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 $GdBaCo2−xFexO6−δ$$(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

Figure 1

XRD pattern of GdBaCo2O6−δ

Figure 2

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

Figure 3

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

Figure 4

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

Figure 5

Equivalent scheme for impedance data analysis

Figure 6

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

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