Dipolar Field Effect Enhanced Photochemical Reactions

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NON-TECHNICAL DESCRIPTION: Certain ceramic materials can catalyze water photolysis and produce hydrogen from water and sunlight. As a fuel for the future, hydrogen is especially attractive because it has three times the energy density of oil and its combustion does not create dangerous emissions, greenhouse gases, or radioactive byproducts. While electrical power generated from photolytic hydrogen is sustainable and generates no toxic or radioactive byproducts, it is also more expensive than the power generated by conventional systems that use fossil or nuclear fuels. This presents an exciting challenge for scientists and engineers to have a truly beneficial and widespread impact on the wellbeing of our society and environment. Therefore, the ultimate goal of this research is to develop the understanding needed to design composite materials for the lower cost synthesis of photolytic hydrogen. TECHNICAL DETAILS: Previous research has shown that when a thin titania film is supported on a ferroelectric BaTiO3 substrate, its photochemical reactivity is greater than that of bulk titania. The phenomenon is called the dipolar field effect. The dipolar field effect can potentially be used to create improved photolysis catalysts, self-cleaning materials, or materials for the photocatalytic degradation of pollutants. At the basis of any such technological developments, there must be a firm scientific understanding of the mechanism of the reactivity enhancement. Therefore, the aim of the current project is to develop a mechanistic model for the dipolar field effect. The research is guided by two hypotheses about the mechanism of the dipolar field effect. The first is that fields within the ferroelectric substrate, incompletely screened, bend the bands in the titania overlayer in such a way that electrons and holes are driven in opposite directions. The second hypothesis is that there is an ideal size for the domains that maximizes reactivity by providing adequate separation, while also preventing depolarization and providing adequate surface area. These hypotheses are being tested by quantitative microscopy experiments on idealized ferroelectric//TiO2 heterostructures. To test the generality of these findings, several exploratory experiments with ferroelectric//WO3 and ferroelectric//Fe2O3 heterostructures are also being conducted. The results of this project will provide the quantitative details necessary to confirm the proposed mechanism of the dipolar field effect and, therefore, provide the scientific basis for the design of a composite photolysis catalyst with improved efficiency. As energy prices rise, there is an increased interest in renewable and sustainable energy sources. The development of materials to efficiently catalyze the synthesis hydrogen at a reduced cost could have a transformational effect on our energy supply and economy. The project will also have impact through the education of students for careers in science and engineering. Undergraduates will be involved in this research through design groups working on a real world problems involving photochemistry.