Nb-Doped SrCoO Perovskites as Potential Cathodes for Solid-Oxide Fuel Cells.

SrCoO 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 SrCoNbO system, in which the stabilization of a tetragonal / perovskite superstructure was described for the = 0.05 composition. In the present study we extend this investigation to the = 0.10-0.15 range, also observing the formation of the tetragonal / structure instead of the unwanted hexagonal phase corresponding to the 2H polytype. We also investigated the effect of Nb doping on the thermal, electrical, and electrochemical properties of SrCoNbO ( = 0.1 and 0.15) perovskite oxides performing as cathodes in SOFC. In comparison with the undoped hexagonal SrCoO phase, the resulting compounds present high thermal stability and an increase of the electrical conductivity. The single-cell tests for these compositions ( = 0.10 and 0.15) with LaSrGaMgO (LSGM) as electrolyte and SrMoFeCoO as anode gave maximum power densities of 693 and 550 mW∙cm at 850 °C respectively, using pure H₂ as fuel and air as oxidant.