A Molecular Solution to Solar Fuels

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  • March 19, 2019
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  • Ashford, Dennis Lee, II
    • Affiliation: College of Arts and Sciences, Department of Chemistry
Abstract
  • Increasing demand for energy and the possible environmental impact of burning fossil fuels has resulted in the pursuit to discover a renewable energy source that circumvents these problems. The sun provides sufficient energy every hour to satisfy global energy consumption for an entire year, making it an attractive and probable long-term solution to alternative fuel sources. However, the diurnal cycle of the run requires that the energy be stored in chemical bonds which can be achieved through water oxidation (2 H2O + 4 hv --> O2 + 4 e-) and using the reductive equivalents to reduce water to hydrogen or CO2 to carbon based fuels. The absorption of solar energy is the initial step in generating solar fuels from light. Several new series of chromophores were fully characterized both in solution and derivatized on metal oxide electrodes for use in photoanodes. These complexes show that lowering the pi* acceptor orbitals results in the lowering of the excited state reduction potential (Ru3+/2+*) while leaving the ground state oxidation potential (Ru3+/2+) relatively unaffected. A new strategy to build chromophore-catalyst assemblies based on amide coupling was then devised as a way to systematically change the light harvesting chromophore, water oxidation catalyst, and the intervening spacer between the two metal centers. Photophysical analysis demonstrated that upon photoexcitation, electron injection into the conduction band of TiO2 has an efficiency of ~ 95%. Following electron injection, forward electron transfer between the two metal centers is ~ 100% efficient with 𝜏 = 145 ps. While amide coupling to build assemblies is general, it still requires multiply synthetic steps and yields assemblies that are unstable on metal oxides surface at elevated pHs. A new strategy to build spatially controlled, multi-component films on metal oxide electrodes utilizing electropolymerization. These electropolymerized films were found to be significantly more stable compared to the bare surface chromophore under photoelectrochemical conditions. In addition, electropolymerized films on a known water oxidation catalyst demonstrated that the electrocatalytic properties of the catalyst were maintained within the polymer films.
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  • In Copyright
Advisor
  • You, Wei
  • Schauer, Cynthia
  • Meyer, Thomas
  • Templeton, Joseph
  • Brookhart, Maurice
Degree
  • Doctor of Philosophy
Degree granting institution
  • University of North Carolina at Chapel Hill Graduate School
Graduation year
  • 2014
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  • Chapel Hill, NC
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  • There are no restrictions to this item.
Date uploaded
  • April 23, 2015

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