A novel Ba0.95La0.05Fe0.9Nb0.1O3−δ ceramic electrode for symmetrical solid oxide fuel cells

Abstract

There are few reports about symmetrical electrodes based on BaFeO_3−δ-parent oxides. In this study, a novel Ba_0.95La_0.05Fe_0.9Nb_0.1O_3−δ (BLFN) ceramic electrode is developed for use as an electrode for symmetrical solid oxide fuel cells (S-SOFCs). The X-ray diffraction (XRD) result reveals that the Nb dopant can keep the cubic perovskite structure of the BLFN material stable against wet hydrogen reduction due to the steady valence state of Nb and the strong Nb–O bond. The maximum electrical conductivities of the BLFN material are 4.91 and 1.58 S cm⁻¹ in air and 5% H₂/Ar, respectively. Electrochemical impedance spectra (EIS) studies discovered the outstanding catalytic activity of the BLFN electrode toward the hydrogen oxidation reaction and oxygen reduction reaction. Polarization resistances at 750 °C are as low as 0.055 and 0.148 Ω cm² in air and hydrogen, respectively, far lower than those of reported symmetrical electrodes. The analysis of the distribution of relaxation times (DRT) for EIS under different P_O2 and P_H2 indicates that the rate-limiting steps of the BLFN electrode are determined by the hydrogen adsorption/dissociation process for the anode and the dissociation of adsorbed oxygen for the cathode, respectively. The single S-SOFC achieves a high peak power density of 581 mW cm⁻² and low polarization resistance of 0.096 Ω cm² at 800 °C. These results indicate that the BLFN material is a potential candidate for S-SOFC electrode applications.