Significant impact of nitric acid treatment on the cathode performance of Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ perovskite oxide via combined EDTA-citric complexing process

Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ (BSCF) perovskite was synthesized by the sol-gel process based on EDTA-citrate (EC) complexing method, nitric acid modified EC route (NEC) and nitric acid aided EDTA-citrate combustion process (NECC). A crystallite size of 27, 38 and 42 nm, respectively, was observed for the powders of NECC-BSCF, NEC-BSCF and EC-BSCF calcined at 1000 °C, suggesting the suppression effect of nitric acid on the crystallite size growth of BSCF. The smaller crystallite size of the powders resulted in the higher degree of sintering of the cathode. Oxygen permeation study of the corresponding membranes demonstrated that in the powder synthesis, nitric acid also had a noticeable detrimental effect on the oxygen surface exchange kinetics and on the oxygen bulk diffusion rate of the BSCF oxides. The effect of powder synthesis route on the bulk properties of the oxide was validated by the oxygen temperature-programmed desorption technique. On the whole, a decreasing cathode performance in the sequence of EC-BSCF, NEC-BSCF and NECC-BSCF was observed. A peak power density of 693 mW cm^-2 was achieved for an anode-supported cell with an EC-BSCF cathode at 600 °C, which was significantly higher than that with an NEC-BSCF cathode (571 mW cm^-2) or an NECC-BSCF cathode (543 mW cm^-2) under similar operation conditions.