Nb(5+)-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−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(0.8)Sr(0.2)Ga(0.83)Mg(0.17)O(3−δ) (LSGM) as electrolyte and SrMo(0.8)Fe(0.2)CoO(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.