Mechanism for the enhanced oxygen reduction reaction of La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ by strontium carbonate

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 SrCO₃ nanoparticles using the infiltration method. Electrochemical conductivity relaxation measurements show that SrCO₃ 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 SrCO₃, 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 SrCO₃ reduces the O₂ 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-SrCO₃ interface.