La_0.4Bi_0.4Sr_0.2FeO_3-δ as Cobalt-free Cathode for Intermediate-Temperature Solid Oxide Fuel Cell

La_0.4Bi_0.4Sr_0.2FeO_3-δ (LBSF) has previously been demonstrated to show the highest electrochemical performance in a series of bismuth doped lanthanum strontium ferrite La_0.8-xBi_xSr_0.2FeO_3-δ where 0 ≤ x ≤ 0.8 as the cathode for intermediate-temperature solid oxide fuel cells. The cobalt-free electrocatalyst LBSF is further investigated in the present study using thermogravimetric analysis, oxygen temperature-programmed desorption method, iodometric titration and high-temperature X-ray diffraction refinement methods to reveal its structural properties including oxygen non-stoichiometry coefficient (δ), valence state of Fe, and lattice parameters at the different temperatures. In addition, the oxygen reduction process on the single phase LBSF is explored using the distribution of relaxation time method based on the electrochemical impedance spectroscopy measurements conducted in oxygen partial pressure from 0.01 to 1.0 atm. The LBSF cathode electrochemical performance is effectively improved by cooperating Sm_0.2Ce_0.8O_1.9 (SDC), an oxygen ion conductor, resulting in interfacial polarization resistance less than 0.1 Ω cm² at 700°C when SDC is used as the electrolyte.