Fundamental Insights into Dye-Sensitized Interfaces for Solar Fuels Production

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  • Brady, Matthew David
    • Affiliation: College of Arts and Sciences, Department of Chemistry
Abstract
  • Solar energy has immense potential to supply clean, sustainable energy for mankind. Dye-sensitized photoelectrosynthesis cells (DSPECs) provide a promising architecture for solar energy conversion that combine molecular photocatalysts with wide band gap semiconductor materials. The focus of this thesis is to develop fundamental understandings of the interfacial and intermolecular electron transfer processes of dye-sensitized photoelectrodes. Chapter 1 introduces strategies for solar energy conversion, the operating principles of dye-sensitized photoelectrodes, and insights into possible future directions. In Chapters 2 and 3, ruthenium polypyridyl photocatalysts were examined on TiO2 and SnO2/TiO2 core/shell interfaces as photoanodes for hydrobromic acid splitting. Chapter 2 examined a single ruthenium polypyridyl photocatalyst capable of both excited-state electron injection to the semiconductor and subsequent oxidation of bromide in aqueous solution. This results in a DSPEC capable of HBr splitting for solar energy storage. Chapter 3 examines a series of four ruthenium polypyridyl photocatalysts with ground- and excited-state reduction potentials tuned through synthetic modification, demonstrating the delicate interplay of balancing a strong photoreductant with a potent oxidant for dye-sensitized HBr splitting. Chapter 4 explores [Ru(deeb)(bpz)2]2+, where deeb is 4,4’-diethylester-2,2’-bipyridine and bpz = 2,2’-bipyrazine, which undergoes fascinating ligand photosubstitution chemistry in solution in the presence of bromide. Prolonged steady state photolysis yields both the cis and trans isomers of Ru(deeb)(bpz)Br2. Chapter 5 explores a series of twenty-two ruthenium polypyridyl photocatalysts on metal oxide electrodes to understand the factors that govern desorption and electrochemically-induced degradation. This study reveals that on planar electrodes and mesoporous thin films, there is a correlation between the E (RuIII/II) reduction potential and the stability of the photocatalyst after oxidation. More positive reduction potentials result in more rapid electrochemically-induced degradation. Chapter 6 examines the intermolecular self-exchange electron transfer or “hole hopping” for a series of three ruthenium polypyridyl photocatalysts on TiO2 interfaces in the absence and presence of an insulating Al2O3 overlayer. Hole hopping is explored electrochemically through chronoabsorptometry and photochemically through transient polarization spectroscopy and time-resolved anisotropy studies. This study reveals that the insulating overlayer completely inhibits hole hopping, but still allows for photoinduced excited-state electron injection to the TiO2 acceptor states.
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Advisor
  • Meyer, Gerald J
Degree
  • Doctor of Philosophy
Degree granting institution
  • University of North Carolina at Chapel Hill Graduate School
Graduation year
  • 2020
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