Structural and performance regulation of Ce-doped mono and bimetallic transition metal oxides toward supercapacitors: advances and prospects

Recent advances in energy storage technologies and progress towards the future “electric” era underscore the growing demand for sustainable energy storage devices, such as batteries and supercapacitors (SCs), to meet society's acute energy needs. SCs are particularly notable due to their high-power density, long cycle life, and fast charging and discharging capability. To further improve the performance of SC devices, tremendous research efforts are focusing on advanced materials, engineered nanostructures, optimized fabrication methods, and innovative device architecture. In this context, designing advanced electrode materials, particularly Ce-doped mono and bimetallic TMOs, is crucial for achieving enhanced structural stability, flexibility, and durability. Incorporating Ce into the TMO lattice can modify its intrinsic physicochemical properties by inducing defect states, oxygen vacancies, and interactions between Ce 3+ /Ce 4+ species and the host TMO ions. These modifications can influence electrical conductivity, band-gap characteristics, electrochemically active sites, and charge-storage performance. This review critically discusses the proposed charge-storage mechanisms in Ce-doped TMOs and their structure-property-performance relationships, with an emphasis on defect-induced active sites, Ce 3+ /Ce 4+ interactions, and charge-transfer kinetics. Furthermore, key factors influencing electrochemical performance, including dopant concentration, surface area and morphology, band gap, and synthetic strategies, are critically analyzed. Recent progress in Ce-doped mono and bimetallic TMOs and their composites is discussed, focusing on improving supercapacitor performance, rate capability, charge transfer kinetics, and cyclic stability. This review also highlights challenges related to Ce stability, degradation, synthesis scalability, and realistic device-level validation, and outlines future research priorities for developing reliable Ce-doped TMO based supercapacitor electrodes.