Molecular Photoelectrocatalyts for Solar Fuel Production: Discovery, Mechanism, and Exploration

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  • March 20, 2019
Creator
  • Pitman, Catherine
    • Affiliation: College of Arts and Sciences, Department of Chemistry
Abstract
  • An exploration of the chemistry of molecular photoelectrocatalysts, beginning with the Cp*Ir(bpy) framework, is presented. Chapter 1 covers approaches to hydrogen evolution with an eye towards solar fuel production. The importance of both metal-hydride species and methods to measure metal-hydride bond strength is discussed. In Chapter 2, the central complex of this dissertation, [Cp*Ir(bpy)(H)]+, is introduced when in situ electrochemical generation permits the construction of a photoelectrocatalytic cycle. Irradiation of neutral aqueous solutions containing [Cp*Ir(bpy)(H)]+ poised at cathodic potentials produces H2 in high Faradaic efficiency. Chapter 3 presents a general synthetic scheme whereby precipitation of Cp*Ir(bpy) and analogues from water and subsequent reaction with electrophiles enabled access to a wide range of water-soluble metal-hydride and metal-alkyl complexes. Chapter 4 explores the hydricity—the hydride donor ability—of Cp*Ir(bpy)- and (arene)Ru(bpy)-based hydrides. The hydricity of [Cp*Ir(bpy-COO)(H)]– is measured using a potential-pKa cycle, and the hydricities of the metal-hydrides accessed in Chapter 3 are measured relative to this reference complex. The thermodynamic measurements presented explain why [Cp*Ir(bpy)(H)]+ is stable in neutral, aqueous solutions in the dark. Chapters 5 and 6 present results of alterations to the [Cp*Ir(bpy)(H)]+ structure. In Chapter 5, Rh is exchanged for Ir, resulting in an entirely unexpected activation of Cp*. Formation of the transient [Cp*Rh(bpy)(H)][Cl] complex leads to in the more stable species (Cp*H)Rh(bpy)(Cl). The implications of this structure on the reduction of NAD+ are discussed. In Chapter 5, the hydride ligand is exchanged for a methyl ligand making [Cp*Ir(bpy)(CH3)]+. This metal-methyl complex is characterized and its photochemical reactions are explored. Kinetic order, radical traps and clocks, and isotope labelling suggest that excitation results in homolysis of the Ir–CH3 bond.
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  • In Copyright
Advisor
  • Miller, Alexander
  • Waters, Marcey
  • Gagne, Michel
  • Brookhart, Maurice
  • Templeton, Joseph
Degree
  • Doctor of Philosophy
Degree granting institution
  • University of North Carolina at Chapel Hill Graduate School
Graduation year
  • 2017
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