Cobalt Oxide-Silica Core-Shell Nanotubes for Photodriven CO2 Reduction by H2O

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The key challenge of this project is to develop and investigate charge transport and catalytic transformations of a macroscale array of spatially separated, vertically arranged cobalt oxide-silica core-shell nanotubes for photodriven carbon dioxide reduction by water. The goal is the optimization of the photocatalytic performance for closing the photosynthetic cycle under separation of the products. In this hierarchical construct, water oxidation catalysis proceeds on the cobalt oxide surface while carbon dioxide reduction takes place at a heterobinuclear photocatalytic unit separated from the cobalt oxide nanotube by the proton permeable, oxygen blocking silica layer. Molecular wires are embedded within the silican membrane in order to allow electronic communication between the half reactions. We will study the electron and proton transport properties of the photocatalytic system. The following scopes play important roles in the electrochemical and photophysical evaluation: i) steady proton flux through a few nanometer thin (amorphous, dense phase) silica layer, ii) molecular wire mediated visible light sensitized charge flow across the silica membrane, iii) charge transfer dynamics of the hole injection process from a chromophore through the silica embedded molecular wire to the cobalt oxide catalyst, and iv) relaxation and electron transfer dynamics by implementing carbon dioxide reducing heterobinuclear charge transfer chromophores. We will place special emphasis on the identification of branching ratios of the competing processes at the different sites of the photocatalytic cycle (i.e. carbon dioxide reduction site, light absorber, silica membrane, molecular wires, water oxidation site) that will guide catalyst design improvement. Closing the photosynthetic cycle on the nanoscale under product separation is a fundamental scientific challenge, which is an approach that minimizes side and cross reactions and other efficiency degrading processes. This is essential for scalability of photosynthesis on an appropriately large scale that will have an impact on renewable solar fuels generation.