A defective iron-based perovskite cathode for high-performance IT-SOFCs: Tailoring the oxygen vacancies using Nb/Ta co-doping

The sluggish kinetics of the electrochemical oxygen reduction reaction(ORR) in intermediatetemperature solid oxide fuel cells(IT-SOFCs) greatly limits the overall cell performance. In this study,an efficient and durable cathode material for IT-SOFCs is designed based on density functional theory(DFT) calculations by co-doping with Nb and Ta the B-site of the SrFeO3-δperovskite oxide. The DFT calculations suggest that Nb/Ta co-doping can regulate the energy band of the parent SrFeO3-δand help electron transfer. In symmetrical cells, such cathode with a SrFe0.8Nb0.1Ta0.1O3-δ(SFNT) detailed formula achieves a low cathode polarization resistance of 0.147 Ω cm2at 650 °C. Electron spin resonance(ESR)and X-ray photoelectron spectroscopy(XPS) analysis confirm that the co-doping of Nb/Ta in SrFeO3-δB-site increases the balanced concentration of oxygen vacancies, enhancing the electrochemical performance when compared to 20 mol% Nb single-doped perovskite oxide. The cathode button cell with NiSDC|SDC|SFNT configuration achieves an outstanding peak power density of 1.3 W cm-2at 650 °C.Moreover, the button cell shows durability for 110 h under 0.65 V at 600 °C using wet H2as fuel.