M = Ir⁴⁺,Ta⁵⁺-Doped SrCo_0.95M_0.05O_3-δ Perovskites: Promising Solid-Oxide Fuel-Cell Cathodes

In this work, two perovskites (SrCo0.95Ir0.05O3-δ and SrCo0.95Ta0.05O3-δ) have been prepared, characterized, and tested as cathode materials for intermediate-temperature solid-oxide fuel cells, producing maximum power densities of 600 and 300 mW cm–2 at 850 °C, respectively. The introduction of only a 5% of highly charged cations like Ir4+ and Ta5+ at the Co sites of the SrCoO3−δ system stabilizes a tetragonal polytype, at room temperature, and improves some essential properties such as the electrical conductivity or the polarization resistances with the electrolyte. These two materials have been characterized by X-ray diffraction and neutron powder diffraction (NPD) at 25 °C; an in situ NPD analysis was carried out from 200 to 800 °C for SrCo0.95Ta0.05O3-δ in order to study the thermal evolution of the crystal structure. In complement, the chemical or mechanical compatibility of these materials with La0.8Sr0.2Ga0.83Mg0.17O3-δ electrolyte, and a thermogravimetric analysis from 25 to 900 °C are investigated. Finally, a XPS study confirms the surface oxidation states of Co, Ta, and Ir in the SrCo0.95Ir0.05O3-δ and SrCo0.95Ta0.05O3-δ perovskite specimens.