Mixed ionic-electronic conducting nanocomposite La0.8Sr0.2Ni0.4Fe0.6O3(LSNF)-Ce0.8Gd0.2O2-delta (GDC) was prepared via ultrasonic dispersion of nanocrystalline powders of perovskite and fluorite oxides in water with addition of surfactant, followed by drying and sintering up to 1300 degrees C. Analysis of the real structure of nanocomposite (studied by XRD and TEM with EDX) and its surface composition (studied by XPS) revealed moderate redistribution of elements between phases favoring their epitaxy. Results of impedance spectroscopy, oxygen isotope exchange, O-2 TPD and H-2 TPR experiments revealed a positive effect of composite interfaces on the oxygen mobility and reactivity agreeing with the ambipolar transport behavior of MIEC composite. Preliminary testing of button-size cell with functionally graded LSNF-GDC cathode layer supported on thin YSZ layer covering Ni/YSZ cermet demonstrated high and stable performance, which is promising for its practical application. (C) Koninklijke Brill NV, Leiden, 2009