Electrochemical properties of layered perovskite for the electrode of symmetrical solid oxide fuel cells

In this study, Co free layered perovskites SmBa(Fe1-xMnx)2O5+d (SBFMn, x = 0, 0.1, 0.3, and 0.5) were proposed as candidate electrode materials for symmetrical solid oxide fuel cells (SSOFCs), and the influence of Mn/Fe ratio on electrochemical performance, electrical conductivity behavior, and structural stability was systematically investigated. Impedance measurements using LSGM based half cells showed that SmBa(Fe0.9Mn0.1)2O5+d (SBFMn 1.8-0.2) exhibited lower area specific resistance in both air and 3.9% hydrogen atmosphere, indicating balanced and enhanced oxygen reduction reaction and hydrogen oxidation reaction activity. Electrical conductivity showed that increasing Mn content led to reduced conductivity in air and nitrogen atmospheres due to weakened M-O-M orbital overlap and decreased Fe4+ derived hole concentration. In contrast, under hydrogen atmosphere, a small degree of Mn incorporation resulted in a relative enhancement of electrical conductivity. X-ray diffraction analysis confirmed that an irreversible cubic to orthorhombic phase transition occurred exclusively under reducing conditions at approximately 450 °C, which is consistent with the conductivity decrease observed during the initial heating process and its subsequent recovery at higher temperatures. These results demonstrate that precise control of the Mn/Fe ratio enables simultaneous optimization of electrochemical activity and structural stability, providing practical design guidelines for layered perovskite electrodes in SSOFC applications.