Photocatalytic CO ₂ Reduction Using Oxygen Vacancy‐Rich Polycrystalline TiO ₂ Conjugated with AlMo ₆ Cluster

Abstract An Anderson‐type hetero‐polyoxoanion, [Al(OH) 6 Mo 6 O 18 ] 3− (AlMo 6 ) is conjugated to the polycrystalline TiO 2 matrix (AlMo 6 @TiO 2 ) through multiple [Ti─O─Mo] linkages, characterized by various spectroscopic studies. X‐ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) studies reveal high surface oxygen vacancies with dominant Ti 3+ species in the AlMo 6 @TiO 2 . The experimentally determined band gap of 3.11 eV and conduction and valence band potential of −0.84 and 2.27 V (vs NHE), respectively, of AlMo 6 @TiO 2 is ideal to catalyze photochemical CO 2 reduction to CO and CH 4 , with significantly higher activity than bulk anatase TiO 2 . Detailed characterization and photocatalysis data show that despite having a lower lifetime of 0.39 µs for AlMo 6 @TiO 2 than 0.62 µs of bulk anatase TiO 2 , the higher photoreduction of CO 2 to CO by AlMo 6 @TiO 2 is driven by the oxygen vacancies of TiO 2 . However, the use of a 10% H 2 O‐dimethyl sulfoxide mixture leads to a change in the product selectivity to 94% CH 4 . AlMo 6 cluster is used here as a redox‐active and sufficiently bulky anionic cluster to uplift the bands of polycrystalline TiO 2 towards more negative potential, sufficiently higher than CO 2 reduction potential, and induces significant lattice defects, or vacancy sites exposed during photocatalytic CO 2 reduction with comparatively higher photochemical activity than the bulk TiO 2 .