The Influence of Charged Interfaces on the Enhanced Photochemical Reactivity of Composites

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NON-TECHNICAL DESCRIPTION: Hydrogen is an attractive fuel for energy production because it has a high energy density and its combustion generates only water vapor, leaving no carbon bearing or radioactive by-products. However, unlike fossil or nuclear fuels, it cannot be mined from the earth; hydrogen must be synthesized. Photolysis, or light-driven water-splitting, is a promising renewable method to synthesize hydrogen. However, the best currently available processes are inefficient and, because of this, they are not competitive with conventional fuel sources. One of the fundamental problems is that no single material possesses the combination of properties needed to efficiently split water. This project is based on the idea that a composite, that combines materials with synergistic properties, will be able to catalyze water photolysis more efficiently and currently available materials.TECHNICAL DETAILS: This project aims to test the hypothesis that by controlling charges at interfaces in oxide heterostructures, it is possible to build in mechanisms to separate photogenerated electron-hole pairs and thereby increase the efficiency of photolysis (water-splitting). The project builds upon recent discoveries of the composite catalyst effect for enhanced photochemical reactivity and has the ultimate goal of developing a sustainable fuel source. The hypothesis is being tested by studying a combination of planar oxide heterostructures, ideal for controlled measurements, and heterostructured oxide powders that would be required for any practical implementation. Fe2O3 and TiO2 films will be supported on a variety of ABO3-type substrates (for example, LaAlO3, SrTiO3, BaTiO3, PbTiO3, BiFeO3, and FeTiO3); by choosing the appropriate phase and orientation, it is possible to control the spectral range of absorption, the carrier type, and whether or not there is a potential difference at the interface deriving from ferroelectricity, polar terminations. The effects of band offsets will also be explored in compounds in the pseudo-binary Cu2O-Fe2O3 system. Cross sectional scanning potential (Kelvin probe) microscopy is being used to map potential differences at the buried interfaces and these measurements are being compared to photoelectrochemical measures of reactivity and efficiency. Experiments are also being conducted to examine the effects of length scale on the properties of the heterostructures. The research will be an integral part of the education of graduate and undergraduate Materials Science and Engineering students.