BaCeO3-based proton conductor BaCe0.5Zr0.3Y0.16Zn0.04O3-delta(BCZYZn) was adopted as a part of the oxide-carbonate composite electrolyte. The total ionic conductivity of BCZYZn-carbonate composite is 0.28 S cm(-1) at 500 degrees C. Perovskite oxide SrFe0.7Mn0.2Mo0.2O3-delta was developed and used as cathode. It was found that SrFe0.7Mn0.2Mo0.2O3-delta exhibits a primitive cubic structure with space group Pm (3) over barm(221); a = 3.8790(1) angstrom, v = 58.364(1) angstrom(3). The electrical conductivity of SrFe(0.7)Mno(0.2)Mo(0.1)O(3-delta) is 15-26 S cm(-1) in the temperature range 400-700 degrees C measured by d.c. method. Single cell with BCZYZn-carbonate composite electrolyte and SrFe0.2Mn0.2Mo0.2O3-delta cathode was fabricated and tested with humidified H-2 (similar to 3 vol H2O) as fuel and air as oxidant. A similar configuration cell with lithiated NiO cathode was also constructed for comparison. It was found that neither BaCe0.5Zr0.3Y0.26Zn0.04O3-delta nor SrFe0.7Mn0.2Mo0.1O3-delta is chemically compatible with (Li,Na)(2)CO3. The fuel cell performance is not as good as those based on doped ceria-carbonate electrolytes.