Ca and Fe co-doped NdBaCo2O5+ double perovskites as high-performance cathodes for solid oxide fuel cells

For intermediate-temperature solid oxide fuel cells (IT-SOFCs), high electrochemical catalytic activity and a suitable thermal expansion coefficient (TEC) are essential criteria. In this investigation, simultaneous Ca and Fe co-doped NdBa1-xCaxCoFeO5+δ (NBCCF, x = 0, 0.1, and 0.2) double-perovskites were prepared and investigated as SOFC cathode materials. The introduction of Ca and Fe effectively decreased the TECs and improved the oxygen reduction activity of the cathode. The average TEC of NdBa0.9Ca0.1CoFeO5+δ (NBCCF1) at 30-850 oC was 19.1 × 10-6 K-1, which is decreased by 27.1% compared to the only Fe-doped NdBaCoFeO5+δ (NBCF). According to the distribution of relaxation time (DRT) analysis, the rate-limiting steps of the oxygen reduction reaction (ORR) include bulk diffusion and surface exchange of oxygen, and Ca doping can improve both steps. The maximum power density of the single cell with NBCCF1 as cathode reached 665 mW cm-2 at 750 oC. The polarization resistance decreased from 0.0722 to 0.0482 Ω cm2 at 800 oC. These findings indicate NBCCF1 is a viable cathode candidate for IT-SOFC.