The multi-electron processes of CO₂ reduction and H₂O oxidation, which constitute the essential reactions of sunlight to fuel conversion (artificial photosynthesis) require efficient coupling of light absorber and catalyst. Using all-inorganic heterobinuclear units such as ZrOCo anchored on high surface area silica, we have developed photodeposition methods for the directional assembly of nanometer sized catalyst clusters for H₂O oxidation or CO₂ reduction with proper coupling to the binuclear light absorber. Copper oxide nanoclusters were assembled adjacent to the Zr acceptor sites of the heterobinuclear unit, and light driven reduction of CO₂ upon excitation of the ZrOCo unit demonstrated. Illumination of the ZrOCo chromophore coupled to a metal oxide nanocatalyst for H₂O oxidation affords closing of the photocatalytic cycle in the absence of sacrificial agents. Time resolved FT-IR spectroscopy provided detailed mechanistic insight into the multi-electron reactions of H₂O oxidation and CO₂ reduction on the metal oxide catalyst surfaces under reaction conditions, with surface intermediates and their kinetics uncovered for the first time.

To achieve CO₂ photoreduction by H₂O under product separation on the nanoscale, Co₃O₄-SiO₂ core-shell nanotubes were developed in which the inner surface acts as efficient water oxidation catalyst while the nanoscale silica layer with embedded molecular wires serves as a proton conducting, gas impermeable separation membrane with tight control of electron transport. Completing the photocatalytic cycle on the nanoscale seeks to minimize side reactions and efficiency degrading transport processes. Characterization of the assembly by transient spectroscopy and photoelectrochemical measurements will be discussed.

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