The Effect of Oxygen Partial Pressure and Composition on the Oxygen Reduction Reaction Properties of Ba0.5Sr0.5Fe1-XCuxO3-δ as a Cathode for Solid Oxide Fuel Cells

Abstract

Solid oxide fuel cells (SOFCs) face hurdles in market acceptability due to their high operating temperatures, which typically ranges from 750 oC – 1000 oC. Thus, current research is moving towards lowering the operating temperature to an intermediate temperature range from 500 oC - 700 oC by developing intermediate temperature (IT)-SOFCs. However, during IT operation, conventional cathodes show sluggish oxygen reduction reaction (ORR) kinetics. Till now, perovskite-type oxides have been at the forefront because of their mixed ionic electronic conductive (MIEC) nature. Additionally, Co-based perovskites have shown high catalytic activity for ORR in IT-SOFC cathodes. However, Co-leads to additional cost, high thermal expansion coefficient and toxicity. In this study, ORR properties of the Co-free perovskite-type Ba0.5Sr0.5Fe1-x Cu x O3-δ (x = 0.05 and 0.2) (BSFCu) cathodes were investigated by utilizing electrochemical impedance spectroscopy (EIS). BSFCu powders were synthesized through the sol-gel method with a final sintering temperature of 1050 °C. Powder X-ray diffraction was used test chemical compatibility between BSFCu and La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) powders up to 1100 °C in air. Symmetrical cells of the following configurations BSFCu-LSGM/LSGM/BSFCu-LSGM were prepared for electrochemical measurements using varying ratios of cathode to electrolyte. Using a well-controlled set up, the effect of pO2 on the area specific resistance (ASR) for ORR of symmetrical cells was studied. BSFCu0.05-LSGM/LSGM/BSFCu0.05-LSGM showed the lowest ASR of 0.03 Ω/cm2 under ambient air at 800 °C, when sintered at 1000 °C. These ASR values are competitive with typical values for Co-based cathodes as reported in the literature. Thermo-gravimetric analysis, under O2/Ar atmospheres showed reversible oxygen intake/release capability of BSFCu powders, making them potential candidates for applications in oxygen-storage technologies.