Auto-combustion synthesis and electrochemical studies of La0.6Sr0.4Co0.2Fe0.8O3-delta - Ce0.8Sm0.1Gd0.1O1.90 nanocomposite cathode for intermediate temperature solid oxide fuel cells

摘要

In the present study, a nanocomposite cathode comprising Fe rich La0.6Sr0.4CO0.2Fe0.8O3-(delta) (LSCF) based pervoskite semiconductor oxide and Sm-Gd co-doped ceria rich Ce0.8Sm0.1Gd0.1O1.90 (CSGO) in the ratio of 1:1 has been successfully synthesized by a simple glycine nitrate auto combustion method. The structural properties of the two phase nanocomposite were evaluated by X-ray diffraction and Raman spectroscopy. A detailed electrical properties of co-doped LSCF-CSGO nanocomposites have been studied with a comparison of LSCF added with 10 mol% and 20 mol% Gd singly doped ceria (LSCF-GDC10 and LSCF-GDC20) nanocomposites as a function of temperature in the range of 673-1073 K at air atmosphere by AC impedance spectroscopy. The total electrical conductivity of the co-doped LSCF-CSGO nanocomposites has been found to be 0.043 S cm(-1) at 973 K which is higher than that of the LSCF composite containing singly doped compositions. The Sm co-doping in GDC phase has effectively helped to reduce the undesired electronic conduction produced in the doped ceria as the electron concentration of LSCF-CSGO was found to be - 2.62 x 10(15) cm(-3) which was lower than the electron concentration of LSCF containing singly doped nanocomposite (LSCF-GDC20, - 2 x 10(16) cm(-3)) estimated by Hall Effect measurement. The activation energy of LSCF-CSGO nanocomposite has been found to be 0.05 eV for the oxygen reduction reaction by temperature dependent Arrhenius equation. The improved electrical properties in terms of high ionic conductivity and low activation energy have been achieved through the incorporation of Sm into GDC10 electrolyte phase in LSCF nanocomposite. The combustion synthesis method has also effectively helped to produce microstructure containing large grain size (mu 6 mu m) which is beneficial for enlarging triple phase boundary (TPB) area of cathodes utilized in solid oxide fuel cells (SOFC) operated at reduced/intermediate temperature (673-973 K).