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Synthesis, structural analysis, chemical stabilities and electrochemical measurements of a new Fe-doped barium calcium niobates (Fe-BCNs) family as promising mixed conductors for SOFCs were reported. The Fe-BCNs, prepared by conventional solid state method, exhibited as single phases which can be indexed as Fm-3m (space group no. 225) structure with cell parameter a ~ 8.4 Aå by PXRD and SAED. The Fe-BCNs showed superior chemical stability in pure CO2 gas at 800oC for 24 h, boiling H2O for 72 h, 30 ppm H2S at 600oC for 24 h and pure CH4 gas at 600oC for 12 h, confirmed by PXRD. The highest total conductivity of 1.3 × 10-2 Scm-1 (Ea~0.5eV) was found for Ba2Ca0.787Fe0.566Nb0.646O6-δ at 400oC in air.

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In this paper, we report our steps forward in the search of proton conducting metal oxides possessing disordered perovskite-type and B-site ordered double perovskites for application in solid oxide fuel cells (SOFCs) and mixed proton-electron conductors as anodes for SOFCs. Role of A- and B- site cations in the perovskite structures on electrical properties and their corresponding chemical stability in CO2, H2S and H2O have been studied. Partial substitution of the parent phase is one of the most effective and popular approaches in which certain ions in the lattice are replaced by foreign species. However, "the right recipes" are not usually obvious; optimization on the functional physical and chemical properties is often based upon "the trial and error" strategy. Here, we review our progress since 2005 in the development of the proton conducting solid oxide fuel cells (H-SOFCs).