Novel cobalt-free layered perovskite LaBaFe2-xNbxO6-δ (x=0–0.1) as cathode for solid oxide fuel cells

Abstract To realize solid oxide fuel cells commercial applications, it is necessary to develop new cathode materials with low-cost, high electrochemical performance and high stability. In this paper, we successfully synthesize a series of Nb-doped LaBaFe2-xNbxO6-δ (x = 0, 0.05, 0.075 and 0.1) cathode materials and present a systematic investigation on their physical and electrochemical properties. In comparison to the parent LaBaFe2O6-δ material, the Nb-doped materials greatly improve the electrocatalytic activity and electrochemical performance, while possessing a suitable thermal expansion coefficient and excellent electrode stability. Among the series of samples, the LaBaFe1.925Nb0.075O6-δ cathode exhibits the lowest polarization resistance of 0.056 Ω cm2 and the largest power densities of 553 mWcm−2 at 800 °C. Additionally, the cells still maintain a favorable electrode stability without obvious electrochemical performance degradation after a test period of 50 h. According to the analysis result of the distribution of relaxation times, the oxygen partial pressure dependence studies indicate that the major determining step of the whole oxygen reduction reaction processes under lower oxygen partial pressures is the adsorption process of oxygen molecules on the electrode surface. The LaBaFe1.925Nb0.075O6-δ sample is expected to be a promising candidate cathode for solid oxide fuel cells.