ИСТИНА

A major target in the development of solid-oxide fuel cells (SOFC) is the decrease of their operating temperature down to 550-750oC (intermediate temperature SOFC or IT-SOFC). For this purpose standard cathode material based on Sr doped LaMnO3 (LSM) should be replaced by oxygen-deficient perovskites with 3d-elements like Fe, Co, Ni or Cu. Requirements for cathode materials for IT-SOFC include high electronic and oxide-ion conductivities, high catalytic activity for oxygen reduction, thermal expansion coefficient (TEC) match with that one for electrolyte and absence of chemical interaction with neighbouring components of fuel cell. In the present study influence of the crystal structure and chemical composition on the properties of perovskite-related cobalt and copper oxides important for their use as cathode materials for IT-SOFC are discussed. Complex perovskite-related cobaltates with Co3+ fit perfectly to the majority of the requirements for cathode materials for IT-SOFC listed above. However, they posses high TEC due to thermally activated transition between low (LS) and high-spin (HS) state of Co3+. One of the ways to decrease their TEC is to reveal cobaltates with HS Co3+ in ground state. Such compounds can be found among cobaltates with brownmillerite-type structure. Cuprates R2CuO4, R – rare-earth cation with layered crystal structures contain perovskite slab alternating with rock-salt slab (R=La, so called Т-phase) and fluorite slab (R=Nd-Gd, so called T’-phase) are considered as prospective cathode materials for IT-SOFC due to their low TEC (~12 ppm K-1) and moderate high-temperature conductivity (>100 S/cm for Pr2CuO4). Correlation between the presence of the particular structural slab in the crystal structure of layered cuprates and their high-temperature oxide-ion conductivity is discussed.