How to achieve effective separation of water oxidation and fuel generation catalysis sites by an ion conducting, gas impermeable membrane at the nanoscale, as in the case of natural photosynthesis, is one of the major challenges for the development of a high efficiency artificial photosynthesis system. This is because there are various crossover reactions and charge recombination processes involved in the multi-electron transfer catalytic reactions. Our group has proposed to assemble an artificial photosynthetic unit composed of vertically aligned and asymmetrically functionalized catalytic cobalt oxide nanotube arrays featuring p-oligo(phenylenevinylene) molecular wires embedded in an ultrathin silica shell membrane to meet the aforementioned challenge. The inner wall of the cobalt oxide nanotubes serves as the water oxidation site and the silica shell serves as the separation membrane. Catalysts for fuel generation can be deposited on the exposed surface of the silica shell and the molecular wires mediate the charge transfer across the silica membrane. Our recent work already demonstrated that the charge separation and transport are feasible in such an artificial photosynthesis unit. Our latest progress toward investigating the proton transfer and gas blocking properties of the silica shell membrane will be discussed. Our initial results revealed that ca. 4 nm thin silica membrane is capable of blocking oxygen permeation while still conducting protons. The proton transport property was systematically investigated by electrochemical techniques and electrochemical impedance spectroscopy. The knowledge learned from our studies will be invaluable to optimize artificial photosynthesis system performance and may open doors to a wide range of applications which require robust separation membranes with specific electronic and ionic transport property.

Investigation of nanometer scale silica films as the robust proton conducting, gas impermeable membrane for artificial photosynthesis

248th National Meeting (2014)

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