Crystal chemistry and interface stability of ceria and doped SrFeO3with reduced critical raw materials

Abstract

X-ray microspectroscopy provides a powerful insight into the chemical and structural evolution of complex materials under operating conditions, providing a spatially resolved analysis of interfaces and redox processes in solid-state devices. In this work, synchrotron-based micro X-ray fluorescence (micro-XRF) and micro X-ray absorption near-edge structure (micro-XANES) at the Fe K-edge were combined to investigate SrFeO3-based perovskites co-doped with Ca, Ba, and Mo (SBCFM, SBC10FM) as well as CaFeO3-based perovskites co-doped with Sr, Ba, and Mo (CBSFM) as electrode materials for reversible intermediate-temperature solid oxide electrochemical cells (IT-SOCs). These techniques allowed detailed mapping of elemental distributions, oxidation states, and interfacial features after electrochemical polarization. Overpotential measurements revealed that SBC10FM exhibits the best performance and structural stability at 700–800 °C, while CBSFM, despite its biphasic nature, shows the lowest activation energy for oxygen ion migration (0.47 eV) and high conductivity at lower temperatures. Micro-XRF maps identified a dense interfacial layer enriched in Ca, Ba, and Fe for SBCFM, whereas SBC10FM showed no densification and only limited Ca migration. Notably, Sr segregation, typically a major degradation mechanism in Sr-based electrodes, was completely suppressed in all samples, confirming the stabilizing role of multi-doping. Micro-XANES spectra demonstrated that Fe maintained a stable mixed-valence state (+3/+4) and coordination geometry throughout the electrode and interface, indicating strong redox resilience. The enhanced pre-edge intensity suggested distortion of FeO6 octahedra and formation of oxygen vacancies, both linked to improved electrocatalytic activity. Altogether, the combined micro-XRF/micro-XANES approach elucidates local chemical mechanisms governing phase stability and performance, guiding the rational design of durable, resource-efficient electrodes for next-generation solid oxide electrochemical cells-based technologies.