Nb ⁵⁺-Doped SrCoO _{3− δ} Perovskites as Potential Cathodes for Solid-Oxide Fuel Cells

Abstract

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− x} Nb _x O _{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 Nb ⁵⁺ doping on the thermal, electrical, and electrochemical properties of SrCo _{1− x} Nb _x O _{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 H ₂ as fuel and air as oxidant.