New families of Mn+-doped SrCo1−xMxO3−δ perovskites performing as cathodes in solid-oxide fuel cells

We have investigated the effect of M = Ti4+ and V5+ doping on the crystal structure and on the thermal, electrical, and electrochemical properties of SrCo1−xMxO3−δ (x = 0.03 and 0.05) perovskite oxides performing as cathodes in solid oxide fuel cells (SOFC). The characterization of these materials included x-ray (XRD) and neutron powder diffraction (NPD) measurements. The introduction of Ti4+ and V5+ replacing Co in SrCoO3−δ leads to the stabilization of a tetragonal perovskite superstructure at room temperature with a = a0, c = 2a0 (a0≈ 3.9 Å) defined in the P4/mmm space group, containing two inequivalent Co positions. Flattened and elongated (Co,M)O6 octahedra alternate along the c axis sharing corners in a three-dimensional array (3C-like structure). The thermal expansion coefficients of SrCo0.95Ti0.05O3−δ and SrCo0.97V0.03O3−δ have been measured between 25 and 850 °C. The electrical conductivity at the SOFCs working temperatures (650-850 °C) seems to be sufficient to yield a good performance in IT-SOFC; the polarization resistance in symmetrical cells is as low as 0.016 Ω cm2 at 850 °C for M = Ti. In single test cells these materials generated a maximum power of 824 mW/cm2 at 850 °C with pure H2 as a fuel. This good performance make these systems promising candidates as cathode materials in SOFC.