Symmetric cells consisting of the LaNi 0.6 Fe 0.4 O 3 (LNF)-Sm 0.2 Ce 0.8 O 1.9 (SDC) composite cathodes and 8 mol%Y 2 O 3 -stabilized ZrO 2 (YSZ) electrolyte have been investigated in order to evaluate the oxygen reduction performance of the composite cathode by AC impedance analysis. Cell performance and cathodic overvoltage were examined for cells consisting of the Ni-YSZ cermet anode, YSZ electrolyte, and composite cathode. The addition of 50 wt% SDC to LNF resulted in the lowest polarization resistance. A cell using the 50 wt% LNF + 50 wt% SDC composite cathode showed the maximum power density and the cathodic overvoltage for this cell showed as half as lower than that for a cell using the LNF cathode under the same condition. Enhancement of the electrochemical performance in the LNF-SDC composite cathode is most likely to be caused by the SDC particles connecting LNF particles with the electrolyte surface.

Polarization resistance of LaNi 0.6 Fe 0.4 O 3 (LNF) cathode has been investigated in relation to its electrical conductivity and thermochemical stability. Electrochemical properties of a solid oxide fuel cell using LNF as the cathode were compared to those using La 0.8 Sr 0.2 MnO 3 (LSM). Temperature dependence of the cathodic polarization resistance is discussed in terms of its thermochemical stability. The electrical conductivity of bulk LNF sample was measured with the four-probe DC method at different oxygen partial pressures. Phase identification for the LNF powder samples treated at 900 o C in the atmosphere of oxygen and argon was studied with time dependency of heat treatment by X-ray diffraction analysis. Although the rhombohedral crystal structure of the starting phase was maintained, the electrical conductivity of LNF sensitively changed with the partial pressure of oxygen.