Mechanistic study of structural regulation and enhanced oxygen reduction performance in La0.5Sr1.5FeO4+δ cathodes via Mg doping

Abstract

To develop high-performance cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs), this study systematically investigated how magnesium doping regulates the structure and electrochemical performance of La_0.5Sr_1.5FeO_4+δ (LSF). A series of La_0.5Sr_1.5Fe_1−xMg_xO_4+δ samples (LSFM_x; x = 0, 0.025, 0.050, 0.075, and 0.100) were synthesized by the sol–gel method. XRD, XPS, SEM, and TEM results confirmed that Mg²⁺ was successfully incorporated into the LSF lattice, which promoted the formation of oxygen vacancies and effectively lowered the thermal expansion coefficient, thereby improving thermal compatibility with the electrolyte. Electrochemical measurements showed that moderate Mg doping (x = 0.050) markedly enhanced the oxygen reduction reaction (ORR) activity of the cathode. At 800 °C, the corresponding single cell delivered a peak power density of 0.60 W cm⁻², representing a 36% increase over the undoped sample, and also exhibited excellent long-term operational stability. Combined distribution of relaxation times (DRT) analysis and first-principles calculations further revealed that Mg doping improves the reversibility of oxygen migration pathways and lowers the oxygen dissociation energy barrier, thereby enhancing interfacial oxygen transport and surface exchange kinetics. These results provide an effective strategy and deeper theoretical insight for designing high-performance, highly stable SOFC cathodes through cation doping.