Nb⁵⁺-Doped SrCoO_3−δ Perovskites as Potential Cathodes for Solid-Oxide Fuel Cells

SrCoO_3−δ outperforms as cathode material in solid-oxide fuel cells (SOFC) when the three-dimensional (3C-type) perovskite structure is stabilized by the inclusion of highly-charged transition-metal ions at the octahedral positions. In a previous work we studied the Nb incorporation at the Co positions in the SrCo_1−xNb_xO_3−δ system, in which the stabilization of a tetragonal P4/mmm perovskite superstructure was described for the x = 0.05 composition. In the present study we extend this investigation to the x = 0.10–0.15 range, also observing the formation of the tetragonal P4/mmm structure instead of the unwanted hexagonal phase corresponding to the 2H polytype. We also investigated the effect of Nb⁵⁺ doping on the thermal, electrical, and electrochemical properties of SrCo_1−xNb_xO_3−δ (x = 0.1 and 0.15) perovskite oxides performing as cathodes in SOFC. In comparison with the undoped hexagonal SrCoO_3−δ phase, the resulting compounds present high thermal stability and an increase of the electrical conductivity. The single-cell tests for these compositions (x = 0.10 and 0.15) with La_0.8Sr_0.2Ga_0.83Mg_0.17O_3−δ (LSGM) as electrolyte and SrMo_0.8Fe_0.2CoO_3−δ as anode gave maximum power densities of 693 and 550 mW∙cm⁻² at 850 °C respectively, using pure H₂ as fuel and air as oxidant.