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

Emerging photocatalytic applications of cerium dioxide (CeO 2 ) include green hydrogen production, CO 2 conversion to fuels, and environmental remediation of various toxic molecules. These applications leverage the oxygen storage capacity and tunable surface chemistry of CeO 2 to photocatalyze the chosen reaction, but many open questions remain regarding the fundamental physics of photocatalysis over CeO 2 . The commonly ascribed 'bandgap' of CeO 2 (∼3.1 eV) differs fundamentally from other photocatalytic oxides such as TiO 2 ; UV light excites an electron from the CeO 2 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 CeO 2 photocatalysis and discusses commonly reported photocatalytic reactions and visible light-sensitization strategies. We detail the often misunderstood fundamental physics of CeO 2 photocatalysis and supplement previous work with original computational insights. The exceptional progress and remaining challenges of CeO 2 -based photocatalysts are highlighted, along with suggestions for further research directions based on the observed gaps in current understanding.