Journal
CHEMISTRY OF MATERIALS
Volume 25, Issue 11, Pages 2264-2273Publisher
AMER CHEMICAL SOC
DOI: 10.1021/cm400759f
Keywords
cobalt oxide; silica; core-shell nanoparticle; molecular wires; visible light; hole transport; transient optical spectroscopy
Funding
- Helios Solar Energy Research Center
- Office of Science, Office of Basic Energy Sciences of the U.S. Department of Energy [DE-AC02-05CH11231]
- National Center for Electron Microscopy
- U.S. Department of Energy
- Netherlands Organization for Scientific Research (NWO)
- Lawrence Berkeley National Laboratory
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In an artificial photosynthetic system, separation of the catalytic sites for water oxidation from those of carbon dioxide reduction by a gas impermeable physical barrier is an important requirement for avoiding cross and back reactions. Here, an approach is explored that uses crystalline Co3O4 as an oxygen evolving catalyst and a nanometer-thin dense phase silica layer as the separation barrier. For controlled charge transport across the barrier, hole conducting molecular wires are embedded in the silica. Spherical Co3O4(4 nm)-SiO2(2 nm) core-shell nanoparticles with p-oligo(phenylenevinylene) wire molecules (three aryl units, PV3) cast into the silica were developed to establish proof of concept for charge transport across the embedded wire molecules. FT-Raman, FT-infrared, and UV-Visible spectroscopy confirmed the integrity of the organic wires upon casting in silica. Transient optical absorption spectroscopy of a visible light sensitizer (ester derivatized [Ru(bpy)(3)](2+) complex) indicates efficient charge injection into Co3O4-SiO2 particles with embedded wire molecules in aqueous solution. An upper limit of a few microseconds is inferred for the residence time of the hole on the embedded PV3 molecule before transfer to Co3O4 takes place. The result was corroborated by light on/off experiments using rapid scan FT-IR monitoring. These observations indicate that hole conducting organic wire molecules cast into a dense phase, nanometer thin silica layer offer fast, controlled charge transfer through a product-s'epurating oxide barrier.
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