Electrode properties of a spinel family, AFe2O4 (A = Co, Ni, Cu), as new cathode for solid oxide fuel cells

Abstract

In this work, the spinel-type oxides of AFe2O4 (A = Co, Ni, Cu) prepared via a glycine–nitrate process were investigated as possible cathode materials for solid oxide fuel cells. The as prepared sample, CoFe2O4 and NiFe2O4 are cubic spinel structure, while the CuFe2O4 is tetragonal spinel structure. The XRD results show that AFe2O4 (A = Co, Ni, Cu) is chemically compatible with La0.9Sr0.1Ga0.8Mg0.2O3−δ (LSGM) at fuel cell operation temperatures. At a given temperature, the order of the electrical conductivity of the ceramic samples was CuFe2O4 > CoFe2O4 > NiFe2O4. The electrical conductivity of CuFe2O4 reaches a maximum value of 2.7 S cm−1 at 850 °C in air. The order of average thermal expansion coefficient was CuFe2O4 < NiFe2O4 < CoFe2O4 in the temperature range of 30–1000 °C in air. The thermal expansion coefficients of the AFe2O4 (A = Co, Ni, Cu) samples are very close to that of typical electrolyte materials. CuFe2O4 exhibits the smallest area specific resistance among the three samples, i.e., 0.37 Ω cm2 at 800 °C in air. Peak power density of single cells with CuFe2O4 as cathode on a 300 µm-thick LSGM electrolyte reaches 326 mW cm−2 at 800 °C. In this series, CuFe2O4 exhibits a favorable oxygen reduction reaction activity, thus it may be a promising candidate in SOFCs.