Effect of low Cobalt doping on morphology and properties of calcium ferrite and its application as cathode in Solid Oxide Fuel

Cobaltite perovskites, such as polycrystalline complex brownmillerite oxide Ca2Fe2-xCOxO5, possess high catalytic activity with potential application as cathode materials for Solid oxide fuel cells. However, high Co concentration can lead to high thermal expansion coefficient, which makes them incompatible with widely used Zirconia electrolytes. In the present work we employ low Co concentration and elucidate the effect of morphology on the physical properties of wet chemical synthesized Ca2Fe2-xCOxO5 (x = 0,0.01, 0.03). Oxygen stoichiometry was determined from iodometry titration at room temperature. Co incorporation in the lattice, as low as 1 mol%, reveals a change in morphology and grain size. We also evaluate the role of Ca2Fe2-xCOxO5 samples as cathode material in a bilayer (Cathode/Electrolyte) based on Ce0.9Sm0302 (Samarium doped Ceria) solid electrolyte. Alternating Current (A.C) impedance spectroscopy showed variation in ionic conductivity with respect to temperature for Ca2Fe2-xCOxO5 (x = 0,0.01, 0.03) in a temperature range from 400 degrees C to 800 degrees C. Activation energy with respect to Co-doping and temperature is reported. The complex impedance plane plots show a relaxed mechanism due to grain size effect. Scaling behavior of imaginary part of impedance indicates that relaxation follows similar mechanism at various temperatures. (C) 2017 Elsevier B.V. All rights reserved.