Strontium doped lanthanum cobalt ferrite (LSCF) is a widely applied electrocatalyst for the oxygen reduction reaction (ORR) in solid-oxide fuel cells (SOFCs) operated at intermediate temperatures. Sr surface segregation in long-term operation has been reported to have contradicting effects that either degrade or improve the reaction. Thus, it is critical to understand the mechanism of surface Sr compounds on ORR kinetics. This work aims to verify the effect and propose the mechanism by decorating SrCO nanoparticles using the infiltration method. Electrochemical conductivity relaxation measurements show that SrCO particles improve the chemical oxygen surface exchange coefficient by up to a factor of 100. The electrochemical performance is significantly improved by the infiltration of SrCO, which is comparable to those obtained by typical electrocatalysts including precious metals such as Pd and Rh. Distribution of relaxation time (DRT) analysis shows that the performance enhancement is strongly related to the improved kinetics of charge transfer and oxygen incorporation processes. Density functional theory calculations show that the surface SrCO reduces the O dissociation energy barrier from 1.01 eV to 0.33 eV, thus enhancing the ORR kinetics, possibly through changing the charge density distribution at the LSCF-SrCO interface.

La0.4Bi0.4Sr0.2FeO3-δ (LBSF) has previously been demonstrated to show the highest electrochemical performance in a series of bismuth doped lanthanum strontium ferrite La0.8-xBixSr0.2FeO3-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 Sm0.2Ce0.8O1.9 (SDC), an oxygen ion conductor, resulting in interfacial polarization resistance less than 0.1 Ω cm 2 at 700 °C when SDC is used as the electrolyte.