Synthesis and characterization of Sr₂Fe_1.4Ni_0.1Mo_0.5-xNb_xO_6-Δ (x = 0, 0.05, 0.1, and 0.15) cathodes for solid oxide fuel cells

Nb modified Sr₂Fe_1.4Ni_0.1Mo_0.5-xNb_xO_6-δ (SFNi_0.1MNb_x, x = 0, 0.05, 0.1, and 0.15) materials are synthesized by the one-step combustion method, and their characteristics are investigated. According to the X-ray diffraction (XRD), all samples present single perovskite structures and scanning electron microscope (SEM) results indicate that all samples possess uniform porous structures. Additionally, the electrode conductivity is improved by doping Nb on the B′ site of SFNi_0.1M. From the X-ray photoelectron spectroscopy (XPS) results, the ratios of Fe²⁺/Fe³⁺ and Mo⁶⁺/Mo⁵⁺ vary with the Nb content, which leads to the conductivity change of SFNi_0.1MNb_x materials. For all the samples, SFNi_0.1MNb_0.05 exhibits the best electrochemical performance with the lowest polarization resistance of 0.11 Ω cm² and the highest power density of 1260 mW cm⁻² 800 °C in humidified H₂. The results indicate that SFNi_0.1MNb_x is a promising type of candidate cathode for solid oxide fuel cells.