Defect-State Engineering in Doped CeO₂ for Oxygen Storage: Aliovalent Substitution, Co-Doping, and Pathway-Dependent...

CeO₂ is a representative oxygen-storage oxide because its fluorite lattice can reversibly release and reincorporate oxygen through the Ce⁴⁺/Ce³⁺ redox couple and the associated formation and annihilation of oxygen vacancies. Although doped CeO₂ has been studied extensively, the literature has often treated oxygen-storage enhancement mainly in terms of dopant identity and composition, whereas the more fundamental issue is how a given doping strategy constructs a specific defect state within the fluorite host. Here, oxygen-storage enhancement is discussed from the standpoint of defect-state engineering. The discussion focuses on three routes, as follows: rare-earth single doping, cation-anion co-doping, and route-dependent dopant incorporation. Rare-earth single doping correlates aliovalent substitution with lattice expansion, vacancy generation, and finite oxygen-storage-capacity (OSC) optima. Cation-anion co-doping further shows that simultaneous perturbation of the cationic and anionic sublattices can amplify the defect response, while also demonstrating that vacancy concentration alone does not fully account for OSC enhancement. Route-dependent doping adds an additional dimension by showing that the same dopant can produce different lattice responses, defect populations, and oxygen-release behaviors when introduced through different pathways. On this basis, the review argues that OSC in doped CeO₂ is more meaningfully rationalized through a coupled descriptor set involving lattice accommodation, Ce³⁺/Ce⁴⁺ redistribution, oxygen-vacancy abundance, and dopant incorporation pathway. Taken together, these observations shift the design logic of oxygen-storage ceria from empirical dopant screening toward deliberate defect-state construction.