New Electrode Materials for Symmetrical Solid Oxide Fuel Cells Based on Perovskites (La,Ca)(Fe,Co,Mg,Mo)O3-delta

摘要

The conductivity of perovskites La0.3Ca0.7Fe0.6Mg0.175Mo0.225O3 - delta (LCF6) and La0.3Ca0.7Fe0.5Mg0.25Mo0.25O3 - delta (LCF5) is studied in the temperature interval of 573-1173 K at varied oxygen partial pressure. It is found that when going from air to the reductive atmosphere (8% Ar/H-2), the conductivity of both samples at 1173 K increases from 4.6 to 25 S/cm for LCF6 and from 0.5 to 10 S/cm for LCF5. For LCF5, the conductivity is shown to be virtually independent of the oxygen partial pressure throughout the studied intervals of temperature and partial pressure, whereas for LCF6 two regions are observed. The conductivity of LCF5 remains constant at the cyclic change of the atmosphere from air to the reductive atmosphere and back. The method of impedance spectroscopy is used for studying the electrochemical behavior in air of the porous electrode based on (La,Ca)(Fe,Mg,Mo)O3 - delta deposited on the solid electrolyte of Ce0.8Gd0.2O1.9 (GDC). The polarization resistance of the electrode/electrolyte interface (R-eta) is found to be 2.7 and 3.6 ohm cm(2) for electrodes of LCF5 and LCF6, respectively, at 1173 K. The partial substitution of Co for Fe allows the R-eta value of La0.3Ca0.7Fe0.45Co0.05Mg0.25Mo0.25O3 - delta and La0.3Ca0.7Fe0.55Co0.05Mg0.175Mo0.225O3 - delta to be decreased to similar to 1.2 ohm cm(2). Moreover, these materials demonstrate the CTE values close to that of GDC and also exhibit the acceptable conductivity in both air and reductive atmosphere and, hence, can be recommended for using as the electrode material in symmetrical solid-oxide fuel cells.