Photocatalytic CO2 Reduction using Oxygen Vacancy‐rich Polycrystalline TiO2 Conjugated with AlMo6 Cluster

An Anderson‐type hetero‐polyoxoanion, [Al(OH)6Mo6O18]3‐ (AlMo6) is conjugated to polycrystalline TiO2 matrix (AlMo6@TiO2) through multiple [Ti‐O‐Mo] linkages, characterized by electron microscopic studies. X‐ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) studies reveal high surface oxygen vacancies with dominant Ti3+ species in the AlMo6@TiO2. The experimentally determined band gap of 3.11 eV, conduction‐ and valence‐band potential of ‐0.84 V and 2.27 V (vs NHE), respectively of AlMo6@TiO2 is ideal to catalyze photochemical CO2 reduction to CO, and CH4, with significantly higher activity than bulk anatase TiO2. Detailed characterization and photocatalysis data show, despite having a lower lifetime of 0.39 µs for AlMo6@TiO2 than 0.62 µs of bulk anatase TiO2, the higher photoreduction of CO2 to CO by AlMo6@TiO2 is driven by the oxygen vacancies of TiO2. However, the use of a 10% H2O‐dimethyl sulfoxide mixture leads to a change in the product selectivity to 94% CH4. AlMo6 cluster is used here as a redox‐active and sufficiently bulky anionic cluster to uplift the bands of polycrystalline TiO2 towards more negative potential, sufficiently higher than CO2 reduction potential, and induces significant lattice defects or vacancy sites exposed during photocatalytic CO2 reduction with comparatively higher photochemical activity than the bulk TiO2.