LaNi0.6Fe0.4O3-Ceria composite cathode for SOFCs operating at intermediate temperatures

We fabricated single cells with a LaNi0.6Fe0.4O3 (LNF) cathode and a scandia alumina-doped zirconia electrolyte. Cells with a cathode consisting of a current collecting LNF layer and an active layer were also fabricated by using a screen-printing technique. The active layer contained Ce0.8Sm0.2O1.9 (SDC) or Ce0.9Gd0.1O1.95 and LNF particles. The influence of the sintering temperature and particle size of LNF and SDC on the cathode properties was investigated. LNF cathodes with this active layer exhibited good levels of performance, including cathode potential, and interface resistance from the start of the operation at 800 degrees C. This configuration also improved the adhesiveness between the cathode and the zirconia electrolyte. We found that the active layer is functional when the ceria particle size is equal to or smaller than that of the LNF. Scanning electron microscope observations of the active layer showed that a high sintering temperature tends to break weak bonds around the triple phase boundary and create strongly connected bonds of LNF and ceria particles in the active layer. AC impedance measurements revealed that this microstructural change reduced the interface resistance and ohmic resistance of the cathode. The reactivity of LNF and SDC in the sintering process was also investigated by X-ray diffraction analysis. (C) 2008 The Electrochemical Society.