Electrochemical and chemical characterization of NdBa1-xCo2-yFeyO5+δ cathodes for IT-SOFCs

Neodymium- and cobalt-based layered perovskite oxides with increasing Fe substitution (NdBaCo2-yFeyO5+δ, y = 0.0/0.4) were prepared via the molten citrate technique and fully characterized. The physico-chemical properties were investigated via XRD, TG-DTA, ICP-MS and cerimetric titrations. The electrical conductivity was measured and EIS was performed on symmetrical cells with GDC electrolyte. Iron substitution triggers a structural change from orthorhombic to tetragonal, and cell size increases with iron content. Co and Fe increase their average oxidation state, and the oxygen content increases with increasing Fe. The electrical conductivity is lowered by doping, with a relative maximum at y = 0.2. The y = 0.4 composition shows the lowest polarization resistance (0.17 Ω∗cm2 at 700°C). The ORR mechanism investigated by ECM and physical 1D modeling shows that the first electronation of the oxygen atom on the MIEC surface and the bulk diffusion of the oxygen vacancies in the MIEC lattice are the rate determining steps.