Nanostructured CeO 2 photocatalysts: optimizing surface chemistry, morphology, and visible-light absorption.

Emerging photocatalytic applications of cerium dioxide (CeO2 ) include green hydrogen production, CO2 conversion to fuels, and environmental remediation of various toxic molecules. These applications leverage the oxygen storage capacity and tunable surface chemistry of CeO2 to photocatalyze the chosen reaction, but many open questions remain regarding the fundamental physics of photocatalysis over CeO2 . The commonly ascribed 'bandgap' of CeO2 (∼3.1 eV) differs fundamentally from other photocatalytic oxides such as TiO2 ; UV light excites an electron from the CeO2 valence band into a 4f state, generating a polaron as the lattice distorts around the localized charge. Researchers often disregard the distinction between the 4f state and a traditional, delocalized conduction band, resulting in ambiguity regarding mechanisms of charge transfer and visible-light absorption. This review summarizes modern literature regarding CeO2 photocatalysis and discusses commonly reported photocatalytic reactions and visible light-sensitization strategies. We detail the often misunderstood fundamental physics of CeO2 photocatalysis and supplement previous work with original computational insights. The exceptional progress and remaining challenges of CeO2 -based photocatalysts are highlighted, along with suggestions for further research directions based on the observed gaps in current understanding.