Comparison of (Pr, Ba, Sr)FeO3-δ-SDC composite cathodes in proton-conducting solid oxide fuel cells

Three kinds of Co-free Ba0.5Sr0.5FeO3-delta (BSF), Pr0.5Ba0.5FeO3-delta (PBF), and Pr0.5Ba0.25Sr0.25FeO3-delta (PBSF) cathode materials (CMs) with cubic perovskite structure were prepared by combining EDTA-citrate process and solid state reaction. The lattice constant is the largest for BSF, and the smallest for PBSF due to the difference of Ba2+, Sr2+, and Pr3+ ionic radii. A good chemical compatibility was observed among BSF (PBF or PBSF), Sm0.2Ce0.8OFeO2-delta (SDC) and BaZr0.1Ce0.7Y0.2O3-delta (BZCY) even their mixture was co-fired at 1000 degrees C for 6 h. For single cells with NiO-BZCYIBZCY1CM-SDC (CM = BSF, PBF, or PBSF) configuration, the best electrochemical performance was obtained for PBSF at 650 degrees C and higher working temperatures while it was achieved for BSF at 600 degrees C. Analyses on the electrochemical impedance spectra show that the polarization process of H-SOFCs with PBSF-SDC composite cathode should be mainly controlled by the charge transfer and diffusion of the oxygen ions while that for both BSF-SDC and PBF-SDC might be dominated by proton behavior.