Electronic Theses and Dissertations

Date of Award

1-1-2022

Document Type

Dissertation

Degree Name

Ph.D. in Chemistry

Department

Chemistry and Biochemistry

First Advisor

Jonah W. Jurss

Second Advisor

Jared Delcamp

Third Advisor

James Cizdziel

Relational Format

dissertation/thesis

Abstract

Modern society and technological advancements rely on a reliable and continuous supply of energy. The sun has always been the ultimate source of energy and mediated by mother nature; however, the continued reliance and use of fossil fuel resources (i.e. coal, oil, and natural gas) is causing increasingly negative environmental effects. For instance, the emission of tons of greenhouse gases from fossil fuel combustion is a leading cause of global warming, rising sea levels, and human health issues. Indeed, the concentration of CO2, a product of combustion, recently exceeded 415 ppm, rising from a pre-industrial level of less than 300 ppm. Establishing renewable energy (solar, wind, hydroelectric) sources as viable alternatives to conventional fossil fuels is promising, yet very difficult to achieve due to the largely diffuse and intermittent nature of these energy sources. This harvested renewable energy can power catalytic processes to convert readily-available substrates into value-added chemicals and/or fuels as a sustainable approach to solving our existing energy problems. The use of CO2 as a raw material for energy storage via electrocatalytic or photocatalytic processes can reduce the burden of accumulated atmospheric CO2 and establish a carbon-neutral energy cycle. Importantly, the electrons and protons that are needed for CO2 reduction to fuels must also be supplied sustainably. Water oxidation is the oxidative half-reaction that is coupled to the fuel forming reductive half-reaction in both natural and artificial photosynthesis where the only by-product is molecular oxygen. In this thesis, molecular complexes have been investigated for electrochemical and photochemical CO2 reduction to CO and formate as well as for water oxidation catalysis to dioxygen. Known catalysts for CO2 reduction often suffer from poor selectivity, low catalyst durability, and high overpotentials. In this context, a novel macrocyclic copper complex was developed and studied to obtain mechanistic insight. The electronic structure and observed activity was compared to the previously reported nickel and cobalt derivatives. The experimental and computational results suggest a unique decomposition pathway is accessible under electrocatalytic conditions. Next, a collaborative study was undertaken to evaluate the catalytic activity of nickel and copper complexes featuring a bis(pyridylimino)isoindoline ligand. The stability of these complexes was assessed and the product distribution as a function of time provided evidence for distinct CO2 reduction activity that could be assigned to a homogeneous catalyst. Next, the photocatalytic CO2 reduction activity of a series of cobalt complexes supported by a non-macrocyclic ligand and tunable macrocycles was studied. The effects of variable reaction conditions on the observed product distribution were systematically investigated to provide insight into the factors that govern product selectivity. Finally, two dinuclear ruthenium complexes were prepared and investigated for both chemical and electrochemical water oxidation catalysis.

Available for download on Wednesday, August 16, 2023

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