Insights into charge storage and ion transport mechanisms in cerium-based metal-organic frameworks, composites, and their derivatives for supercapacitor applications: A review

Cerium-based metal-organic frameworks (Ce-MOFs) have attracted growing interest as electrode materials for advanced supercapacitors owing to their redox-active metal nodes, defect-rich structures, and highly tunable porosity. The reversible Ce 3+ /Ce 4+ redox couple, along with the oxygen vacancy formation, allows rapid and reversible Faradaic charge storage commonly referred to as surface-controlled pseudocapacitive behaviour. This review provides a critical analysis of the fundamental mechanisms and dynamic processes that dictate the charge transport in Ce-based MOFs with particular emphasis on electron hopping between cerium centers, ion diffusion via interconnected pore systems, and interfacial charge-transfer reactions under electrochemical working conditions. The roles played by framework topology, linker chemistry, defect density, and morphology in regulating electronic conductivity and ionic mobility are discussed, and key structure–mechanism–performance relationships are highlighted. Recent progress in both operando and in situ characterization methods, together with theoretical and computational studies, is summarized to explain the real-time dynamics of oxidation states and transport processes during charge-discharge cycling. Additionally, the innovative approaches, like defect engineering, nanoscale morphological control, and hybridization with conductive matrices, are considered to be effective in overcoming intrinsic conductivity limitations. Finally, the current challenges and future research directions are presented to guide rational design development of high-performance Ce-MOF-based electrodes towards enhanced supercapacitor applications.