Theses and Dissertations at Montana State University (MSU)
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Item Synthesis and characterization of boron-doped graphitic carbon for energy storage applications(Montana State University - Bozeman, College of Letters & Science, 2023) McGlamery, Devin Gray; Chairperson, Graduate Committee: Nicholas P. Stadie; This is a manuscript style paper that includes co-authored chapters.Carbonaceous materials offer great utility as a medium for electrochemical energy storage of ions or for the storage of chemical fuels. The low molecular weight of the second-row element carbon affords access to materials that express remarkably high gravimetric energy densities, and the robust nature of carbon-carbon bonds allow for good cyclability and longevity of carbon-based materials for use in energy storage applications. With the growing popularity and recent advancement of electric vehicles, current battery technologies are pushed to their limits in terms of capacities as well as in minimizing charging times. This has motivated great efforts to discover new lightweight materials that outperform what has traditionally been used in these applications. Alternative energy carriers, such as hydrogen, are also critical for the development of our energy landscape yet are plagued with their own technical challenges; mainly low volumetric energy densities and safety concerns associated with high pressure gas storage systems. Chapter 2 reviews hydrogen storage in today's society as well as provides a review of past synthetic methods to generate high boron content graphite (BC 3'); being a promising metastable material for the storage of alkali metal ions as well as for solid state hydrogen storage at near ambient conditions. Chapter 3 focuses on the discovery of a new lithium storage mechanism within a novel carbon-based material possessing a high hydrogen content that is tolerant of extremely fast charging, yet still expresses high reversible capacities. Chapter 4 presents a systematic investigation for the detection of chemical environments within BC 3' through an examination of unique spectroscopic properties that originate from the materials phonon structure. Chapter 5 explores the generation of boron and carbon binary phases by the co-pyrolysis of molecular precursors and establishes a density functional theory based approach to align the cracking temperatures of molecular feedstocks; affording access to bulk metastable materials that contain a homogeneous distribution of chemical environments. This work is concluded with an assessment of the materials investigated herein from the perspective of energy storage, as well as provides directions for future work.Item Catalysis with early and late transition metals: C-H activation at tantalocene hydrides and oxidative addition at palladium solvato complexes(Montana State University - Bozeman, College of Letters & Science, 2021) Rehbein, Steven Mark; Chairperson, Graduate Committee: Sharon Neufeldt; Matthew J. Kania and Sharon R. Neufeldt were co-authors of the article, 'Experimental and computational evaluation of tantalocene hydrides for C-H activation of arenes' in the journal 'Organometallics' which is contained within this dissertation.; Steven M. Rehbein and Sharon R. Neufeldt were co-authors of the article, 'Solvent coordination to palladium can invert the selectivity of oxidative addition' in the journal 'Organometallics' which is contained within this dissertation.Herein we present our work on transition metal catalysis using metals from two sides of the periodic table: C-H activation catalyzed by early transition metals and cross-couplings catalyzed by late transition metals. In the first part, a synergistic experimental and computational approach was employed to investigate the possibility of extending the reactivity of bent tantalocene hydrides beyond aromatic C-H activation to enable activation of aliphatic substrates. In situ monitoring of the characteristic 1 H NMR metal hydride signals in the reaction of Cp 2TaH 3 and related complexes with deuterated aromatic substrates allowed for the evaluation of reaction kinetics of catalyst decomposition, H/D exchange, and off-cycle reactions. The insight gained from in situ reaction monitoring with aromatic substrates, combined with computational analyses, allowed for the extension of this chemistry to intra- and intermolecular aliphatic C-H activation. This work represents the first example of aliphatic C-H activation by homogeneous tantalum hydrides. In the second part, we provide compelling evidence that solvent coordination to palladium during oxidative addition of chloroaryl triflates can result in an inversion of chemoselectivity of this step. Previous investigations attributed a solvent-dependent switch in chemoselectivity to the propensity of polar solvents to stabilize anionic transition states of the type [Pd(P t Bu 3)(X)]- (X = anionic ligand). However, our detailed investigations show that solvent polarity alone is not a sufficient predictor of selectivity. Instead, solvent coordinating ability is selectivity-determining, with polar coordinating and polar noncoordinating solvents giving differing selectivity, even in the absence of anionic ligands 'X'. A solvent-coordinated bisligated transition state of the type Pd(P t Bu 3)(solvent) is implicated by density functional theory calculations. This work provides a new mechanistic framework for selectivity control during oxidative addition.Item Excited state processes in ruthenium(II) polypyridyl complexes and cerium oxide nanoparticles(Montana State University - Bozeman, College of Letters & Science, 2016) Stark, Charles William; Chairperson, Graduate Committee: Patrik R. Callis; Wolfgang J. Schreier, Janice Lucon, Ethan Edwards, Trevor Douglas and Bern Kohler were co-authors of the article, 'Interligand electron transfer in heteroleptic ruthenium(II) complexes occurs on multiple time scales' in the journal 'The journal of physical chemistry A ' which is contained within this thesis.Solar driven hydrogen production from water is a sustainable alternative to fossil fuels, but suffers greatly from the large energy cost associated with splitting water. This report uses ultrafast transient absorption and other spectroscopic techniques to analyze several components that show potential for this photocatalysis, in particular observing the excited state dynamics of electron separation and recombination. In ruthenium(II) polypyridyl systems, the rate of interligand electron transfer (ILET) was found to change with time, initially behaving as an ultrafast barrierless process, but transforming into a much slower activated process as excess energy is vibrationally released over 100 ps following excitation. The change in ILET rates lead to changes in the population of localized 3 MLCT states distributed among each ligand, which are initially randomized, but favor the lower energy bipyridine ligands at longer times. Three analogous ruthenium complexes were then linked via a triazole bridge to a cobalt(II) polypyridyl center known to catalyze the formation of H 2, observing the electron transfer from ruthenium to cobalt using emission decay signals of the ruthenium complex. The electron transfer decay pathway was slower and relatively minor compared to similar ruthenium(II)-cobalt(II) systems; however, this reduced efficiency can potentially be explained by localizations on peripheral ligands, as well as a possible energy barrier on the 5-position of phenanthroline. Finally, citrate coated CeO 2 nanoparticles displayed ultrafast trapping of holes upon excitation with UV light, forming significantly deeper traps than has been observed in other metal oxides. Transient absorption signals of the excited holes decayed over hundreds of picoseconds, with lifetimes dependent on the pH of the solution, indicating that the trapping sites are influenced by the surface of the nanoparticle. The corresponding electrons appear to form long lived Ce 3+ sites, observable on timescales of minutes. The fate of these Ce 3+ sites is also pH dependent, indicating that CeO 2 may be an effective water-splitting photocatalyst under basic conditions.Item Characterization of the [FeFe]-hydrogenase : toward understanding and implementing biohydrogen production(Montana State University - Bozeman, College of Letters & Science, 2014) Swanson, Kevin Daniel; Chairperson, Graduate Committee: John W. PetersHydrogen may provide an avenue for a clean renewable fuel source, yet the methods to produce hydrogen are either extremely energy intensive, rely on fossil fuels, or require expensive noble metal catalysts. Biology may hold the keys necessary to unlocking new technologies that could change how hydrogen is produced. Microbial processes also produce hydrogen and harbor enzymes that carryout the reversible reduction of protons to hydrogen gas. These enzymes are capable of producing hydrogen at high rates comparable to platinum catalysts, but biological hydrogen catalysts can produce hydrogen using abundant elements carbon, oxygen, nitrogen, sulfur, iron, nickel and selenium. Biological hydrogen catalysts are termed hydrogenases, and though hydrogenases use abundant elements they are extraordinarily complex. This has made it difficult to construct model complexes using inorganic synthesis that can replicate the activities of their biological counterparts. One way to circumvent this problem is to use microbial hydrogen production and let microbes produce and maintain these enzymes inside a cell. Microbial hydrogen production also has the added benefit that hydrogen production could be engineered to connect with other metabolic processes such as photosynthesis and fermentation. Engineering microbes for hydrogen production could eventually allow for the production of hydrogen using inexpensive energy inputs such as solar energy or waste materials. Yet, there are many barriers that need to be overcome in order to engineer a robust microbial organism. One of the primary difficulties of developing this technology has been the oxygen sensitivity of hydrogenases. Hydrogenases when exposed to atmospheric concentrations of oxygen either completely inactivate or their rates are significantly slowed. To engineer a hydrogenase that is more amenable for microbial hydrogen production, the optimization of expressing and purifying hydrogenase enzymes has been developed. Methodologies have been developed to characterize how oxygen inactivates hydrogenase enzymes, and a new methodology has been explored to help find novel hydrogenase gene sequences that may help in engineering oxygen tolerant enzymes.