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• BNT (0.94Bi 0.5 Na 0.5 TiO 3 -0.06BaTiO 3) and LNT (La 0.5 Na 0.5 TiO 3) containing alkali element and conducting oxide ion were used for replacing the non-conductive LiAlO 2 matrix in MCFCs (Molten carbonate fuel cells). • Cells fabricated using both new oxides as solid matrix support show state-of-the-art electrochemical performance. • LNT sample has extended life-time and better performance than BNT sample and the good performance may related to enhanced oxygen reduction reaction kinetics. New oxide ion conductors with perovskite structures containing alkali metal were explored for use as solid support materials for MCFCs (molten carbonate fuel cells). The conductivity of two candidates, BNT (0.94Bi 0.5 Na 0.5 TiO 3 -0.06BaTiO 3) and LNT (La 0.5 Na 0.5 TiO 3), in an oxidation atmosphere, were measured and compared. The conductivity measurement of BNT in a reducing atmosphere indicated the reduction of BNT to Bi metal by a sharp change in conductivity. It limited the lifetime of the fuel cell using BNT as solid support. Fuel cell measurements using the alternative perovskite LNT showed excellent stability under fuel cell operation conditions and high-power density compared to conventional MCFC with LiAlO 2 as the solid matrix. The reason for obtaining high electrochemical performance using the LNT matrix is discussed. [ABSTRACT FROM AUTHOR]