Artificial photosystems that accomplish the complete cycle of converting CO2 and H2O to fuel on the shortest possible length scale – nanometers – avoid efficiency degrading ion transport resistance losses, unwanted side reactions, and balance of systems requirements while opening up an immense design space for scale-up. We are developing a Co oxide-silica core-shell nanotube array in which each core-shell tube operates as a complete, independent photosynthetic unit. The ultrathin silica membrane separates the Co oxide H2O oxidation catalyst from light absorber and CO2 reduction sites and transmits protons but blocks O2. Precise control of electron transport across the insulating silica membrane is accomplished by embedded molecular wires with properly chosen orbital energetics. After demonstrating the synthesis and structural characterization of square inch sized core-shell arrays, we have quantitatively evaluated the proton conductivity, O2 blocking, and charge transport properties of the core-shell nanowall using analogous planar constructs. Electrochemical impedance spectroscopy revealed orders of magnitude higher capacity for H+ flux across the oxide wall than required at highest solar intensity, while ultrathin silica completely blocks O2. The structure and orientation of silica embedded p-oligo(phenylene vinylene) (3 aryl units) molecular wires upon casting into silica and after prolonged electron flux were elucidated by a combined polarized FT-IRRAS and grazing angle ATR FT-IR spectroscopy. Embedded wires with proper HOMO and LUMO energetics for exploring a 2-photon tandem system driven heterobinuclear light absorbers were synthesized and their electron transport properties evaluated by photoelectrochemical methods and transient optical spectroscopy. Mechanisms of CO2 reduction at Cu and bimetallic nanoparticles, assembled by photodeposition at heterobinuclear light absorbers on the silica shell surface, are being elucidated by time-resolved FT-IR spectroscopy, with the goal of using the structural knowledge of transient surface intermediates for guiding catalyst modifications to enable reduction beyond CO to more energy dense products.

Inorganic core-shell nanotube array for CO2 photoreduction by H2O

2019 Spring National Meeting

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