Advanced electrochemical impedance spectroscopy for high-performance solid oxide fuel cells: A critical review

Solid oxide fuel cells (SOFCs) are promising high-efficiency electrochemical systems, yet their performance and durability depend on complex, temperature-dependent processes occurring across electrodes, electrolytes, and interfaces. Electrochemical impedance spectroscopy (EIS) has become a central diagnostic tool for resolving these processes and guiding SOFC optimization. This review provides a focused and critical examination of advanced EIS methodologies for SOFCs. After outlining fundamental principles, instrumentation, and data representations, we highlight modern analysis approaches, including KK consistency validation and distribution of relaxation times (DRT) for deconvoluting overlapping polarization processes. We summarize EIS findings across major SOFC components such as LSM-YSZ and MIEC cathodes, Ni-based anodes, oxygen-ion–conducting electrolytes (YSZ, ScSZ, GDC, SDC, LSGM), interconnects, and sealants, emphasizing how impedance features relate to charge-transfer kinetics, mass-transport limitations, grain-boundary effects, and interfacial reactions. Special attention is given to degradation mechanisms, including carbon deposition, Ni coarsening, sulfur poisoning, and electrode/electrolyte delamination, supported by frequency-resolved analysis. Integrating EIS with complementary techniques (XRD, SEM/TEM, spectroscopy) further links microstructural evolution to impedance response. This review establishes a component-resolved framework for interpreting SOFC impedance behavior and outlines future opportunities in operando EIS, data-driven analysis, and stack-level diagnostics for next-generation SOFC systems. © 2026 Elsevier Ltd.