Theses & Dissertations

Permanent URI for this collection


Recent Submissions

Now showing 1 - 5 of 179
  • Item
    Mechanical Exfoliation of Expanded Graphite and Functionalization with Palladium Nanoparticles for Hydrogen Storage
    (University of Guelph, ) Chow, Darren; Chen, Aicheng
    Due to the clear effect of fossil fuels on the environment, alternative sources of energy must be considered. One alternative is hydrogen which is abundant and does not produce greenhouse gasses. The advent of a hydrogen economy is a challenge due to the requirement of a safe and efficient storage method. In this thesis, a graphene-based nanomaterial was prepared through liquid phase exfoliation of expanded graphite (EG) followed by functionalization with palladium nanoparticles (Pd-NP) as a solid-state hydrogen storage material. Specifically, high-shear mixing and probe-tip sonication produced palladium functionalized sonicated EG (Pd-sEG) and palladium functionalized sheared EG (Pd-ShEG). A variety of characterization methods were used, and the hydrogen storage ability was assessed through electrochemical studies. It was determined the hydrogen desorption charge was 50.4 mC cm-2 for Pd-sEG, and 41.2 mC cm-2 for Pd-ShEG, notably improving the performance over base materials of Pd-EG (29.6 mC cm-2) and Pd-NP (19.2 mC cm-2).
  • Item
    Room Temperature Pulsed Laser Deposition and Annealing of Yttria-Stabilized Zirconia Thin Films for Use in Intermediate Temperature Solid Oxide Fuel Cells
    (University of Guelph, ) Smith, David; Thomas, Daniel
    To study the effect of adatom energy on the crystallization and topography of yttria-stabilized zirconia (YSZ) thin films deposited at room temperature by pulsed laser deposition (PLD), YSZ films were deposited by PLD at room temperature onto SiO terminated Si (100) substrates and broken in half, with one half being annealed at 300 °C for 10 hours in an ambient atmosphere. The target to substrate distance (TSD) and the background gas (O2) pressure were varied for each deposition. The films were analyzed by X-ray diffraction (XRD) to determine crystallinity, ellipsometry to determine topography, and X-ray photoelectron spectroscopy (XPS) to determine elemental composition. All as-deposited YSZ films have been found to be amorphous. A blast wave model fits the experimental findings well, describing the TSD-pressure boundary at which the amorphous films crystallize when annealed at 300 °C. The topography of the deposited material follows the expected cosnϴ distribution for all films. The dependence of n on TSD indicates that the films are likely sputtered by the high-energy plume material at a TSD below 5 cm at an O2 pressure of 20mTorr and 4 cm at 50mTorr. All deposited YSZ films were found to have the expected Y:Zr ratio.
  • Item
    Utilizing DFT Methods to Predict Relative Stability Constants of Ruthenium (II) Complexes
    (University of Guelph, ) Salmon, Kyle; Schlaf, Marcel
    This study utilized DFT calculations in Gaussian G16 to determine the relative stability constants of ruthenium-based complexes. The methods used include the M06-2X functional, def2svp and def2tzvp basis sets, and the PCM and SMD models with two solvent systems of interest: water and acetonitrile. Obtaining relative stability constants of the corresponding coordination reactions required collection of the sum of free energies and employed Hess’ Law to calculate G of the complexation reactions. ∆G: ∆G reaction = ∑∆G products - ∑∆G reactants The relative stability constants were then determined using the van’t Hoff equation. ∆G=RTlnK A relative stability scale, allowing semi-quantitative prediction of stabilities for Ru (II) complexes with a range of chelating ligands in solvation was accomplished. Thus, allowing a more tailored approach to many synthetic and homogeneous catalysis projects that rely on the – at least – qualitative prediction of complex stability constants that are very difficult to determine experimentally.
  • Item
    Physicochemical properties of Mn Incorporated Spinels
    (University of Guelph, ) Farshidfar, Farshad; Ghandi, Khashayar
    This thesis is aimed at tuning chemical and physical properties of spinels via a novel approach of manganese incorporation. Oxide spinels benefit from 1) hosting diverse cations at 4 and 6-coordinated sites; and 2) dual functionality of shared anionic oxygen in electron transport and surface reactivity. In other words, redox reactions over transition metal oxide spinels take advantage of charge transport in the bulk and mass exchange phenomena on the surface. Both rates of bulk charge transport and surface mass exchange depend on anion-cation interaction. Variability of manganese oxidation state and the impact of Jahn-Teller active Mn3+O6 are the most significant features affecting bulk properties as well as surface reactivity. This thesis establishes a meaningful correlation between activation energy of electron hopping and the rate of oxygen evolution reaction. Both features follow a volcano plot versus eg occupancy at octahedral site in the range of 0-2. Such a correlation is one of the novelties brought about by this thesis. The effect of calcination and post calcination on the structural and electrical properties of MgFe2O4 is investigated. An oxygen free atmosphere is introduced as the most suitable environment to collect densified crystallites of magnesium ferrite at 850 ˚C. A DC electrical conductivity instrument was developed to evaluate the mechanism of electron hopping under controlled atmospheres. The instrumental approach allows us to evaluate the electron exchange interaction managed by cation-anion interactions. In situ evaluation of redox kinetics of such ceramic material is another feature of the instrument, providing novel insights into additional chemical and electrical properties. Both single and multi-phase approaches of manganese incorporation in MgFe2O4 are considered here, along with applications pertaining to catalysis, electrocatalysis, energy storage, and sensors. In this thesis, an advanced composite of porous Mn3O4 in dense MgFe2O4 matrix is introduced and the effect of Mn diffusion into ferrite spinel is further investigated.
  • Item
    Enzymatic Electro-reduction of Carbon Dioxide to Formate by Directly Immobilized NAD+-independent Formate Dehydrogenase
    (University of Guelph, ) Elmahdy, Reem; Chen, Aicheng; Lipkowski, Jacek
    Global warming has been raising concerns for the state of the climate and the resulting adverse effects, due to the rise in levels of greenhouse gases including methane, nitrous oxide and carbon dioxide. As the atmospheric concentration of carbon dioxide has been rapidly increasing each year, it is pertinent to work on the decrease of such levels through the development of renewable methods of electricity generation and development of efficient methods of conversion of CO2 to chemicals. Electrochemical conversion of CO2 into reduced C1 compounds is a useful technique to reduce carbon dioxide levels as it is easy to select the appropriate reaction conditions. As electrochemical reduction of CO2 is associated with low product selectivity and efficiency due to competition with hydrogen evolution reactions, enzymatic electroreduction of carbon dioxide can be utilized due to the high selectivity of enzymes. This thesis demonstrates novel approaches to the direct immobilization of metal-independent formate dehydrogenases on electrode surfaces to facilitate the direct catalysis of carbon dioxide reduction to formate, without the need for NADH/NAD+ cofactors.