Immobilization of a [Co(III)Co(II)(H(2)O)W(11)O(39)](7–) Polyoxoanion for the Photocatalytic Oxygen Evolution Reaction

[Image: see text] The ongoing transition to renewable energy sources and the implementation of artificial photosynthetic setups call for an efficient and stable water oxidation catalyst (WOC). Here, we heterogenize a molecular all-inorganic [Co(III)Co(II)(H(2)O)W(11)O(39)](7–) ({Co(III)Co(II)W(11)}) Keggin-type polyoxometalate (POM) onto a model TiO(2) surface, employing a 3-aminopropyltriethoxysilane (APTES) linker to form a novel heterogeneous photosystem for light-driven water oxidation. The {Co(III)Co(II)W(11)}-APTES-TiO(2) hybrid is characterized using a set of spectroscopic and microscopic techniques to reveal the POM integrity and dispersion to elucidate the POM/APTES and APTES/TiO(2) binding modes as well as to visualize the attachment of individual clusters. We conduct photocatalytic studies under heterogeneous and homogeneous conditions and show that {Co(III)Co(II)W(11)}-APTES-TiO(2) performs as an active light-driven WOC, wherein {Co(III)Co(II)W(11)} acts as a stable co-catalyst for water oxidation. In contrast to the homogeneous WOC performance of this POM, the heterogenized photosystem yields a constant WOC rate for at least 10 h without any apparent deactivation, demonstrating that TiO(2) not only stabilizes the POM but also acts as a photosensitizer. Complementary studies using photoluminescence (PL) emission spectroscopy elucidate the charge transfer mechanism and enhanced WOC activity. The {Co(III)Co(II)W(11)}-APTES-TiO(2) photocatalyst serves as a prime example of a hybrid homogeneous–heterogeneous photosystem that combines the advantages of solid-state absorbers and well-defined molecular co-catalysts, which will be of interest to both scientific communities and applications in photoelectrocatalysis and CO(2) reduction.