BA, Oberlin College, 2014, Physics and Astronomy

Metal-Organic Frameworks, or MOFs, are an exciting class of nanoporous crystalline materials with applications that include hydrogen storage and hydrogen isotope separation. The dynamics of adsorbed molecular hydrogen in the prototypical material known as MOF-5 have previously been studied using infrared spectroscopy. However, the rovibrational spectrum of the isotopologues, HD, and D2 were obscured due to overlap with the MOF peaks. Overtone infrared spectroscopy in conjunction with a diffuse reflectance geometry is used to observe the spectrum of H2, HD and D2. The overtone spectrum is shown to facilitate the identification of hydrogen peaks. Further, the spectrum of trapped H2 near the crystallographic metal site is greatly enhanced relative to other sites and displays a greater intensity relative to the fundamental spectrum than is seen in gas phase hydrogen. The ability of the MOF to catalyze ortho to para conversion of trapped species is also discussed.

Committee: Stephen FitzGerald (Advisor) Subjects: Chemistry; Condensed Matter Physics; Molecular Physics; Physics; Quantum Physics

Master of Science, The Ohio State University, 2023, Animal Sciences

The finite nature of natural gas, along with environmental and health problems arising from combustion of fossil fuels, have spurred interest in development of clean and renewable alternative energy sources. Biohydrogen (H2) production through acetone-butanol-ethanol (ABE) fermentation by solventogenic Clostridium species, offers a promising way to achieve the goal of substituting fossil fuels with clean renewable energy sources. Low H2 yield and productivity with ABE fermentation by solventogenic Clostridium species is a major barrier to commercialization of biohydrogen. Consequently, metabolic engineering strategy is among the methods researchers have been exploring to develop industrially applicable H2 producing strains. This study, therefore, explored simultaneous deletion of negative transcription regulator (iscR) and overexpression of Fe-Fe hydrogenase genes (hydA) in C. beijerinckii NCIMB 8052 and C. pasteurianum ATCC 6013 to enhance H2 production. Specifically, chapter 3 (objective 1) explored metabolic engineering strategy to improve H2 production in C. beijerinckii. Using allele exchange construct for homologous recombination, simultaneous deletion of iscR from isc operon and overexpression of Fe-Fe hydA in the iscR locus in C. beijerinckii was conducted. The 2 copies of hydA in C. beijerinckii (hydAi and hydAii) were overexpressed separately in C. beijerinckii to generate recombinant strains: C. beijerinckii_hydAi and C. beijerinckii_hydAii. This strategy led to 1.2- and 1.3-fold increases in the growth of C. beijerinckii_hydAi and C. beijerinckii_hydAii, respectively, compared to C. beijerinckii_wildtype. Surprisingly, there was 2.9-, 1.5-, 1.4- and 1.7-fold decreases in acetone, butanol, ethanol, and total ABE produced, respectively, by C. beijerinckii_hydAi compared to C. beijerinckii_wildtype. Similarly, there was 3.7-, 1.7-, 1.9-, and 1.7-fold decreases in acetone, butanol, ethanol, and total ABE produced, respectively, by C. beijerinckii_hydAii (open full item for complete abstract)

Committee: Thaddeus Ezeji Dr. (Advisor) Subjects: Molecular Biology

Doctor of Philosophy, The Ohio State University, 2006, Chemistry

Enzymes owe the stability of their folded conformations to the cooperativity of many non-bonded interactions and this three-dimensional structure is necessary for the functions they perform. We should be able to capitalize on the globular shape, well-defined structure and controllable size of dendrimers to develop highly selective dendritic catalysts, but because of conformational flexibility, there are no dendrimers that exploit long-range coorperativity to increase catalyst specificity. We have constructed dendritic wedges using pyridine-2,6-dicarboxamide as the focal branching unit to rigidify the dendritic structure through conformational preferences of the subunit and intramolecular hydrogen-bonding interactions. When chiral terminal groups are used, cooperativity between subunits amplifies the small energetic difference between diastereomeric helical states and leads to a shift in the equilbrium toward one helical sense and these dendrons develop a bias for M-type helicity at the second and third generation that is dependent on solvent and temperature. 2,6-Pyridine-diacarboxyamide (pydam) is replaced with 2,6-pyridine-diimine (pydim) at the focal point of the dendron. This allows for selective metal binding in the interior of the dendron, far removed form the chiral terminal groups. The goal will be to determine if and how the chirality is transferred via the helical conformation from the periphery to the coordination site. The synthesis of a dendritic ligand that will be complexed to transition metals such as ruthenium, copper, zinc, and nickel is described. The focus of future work will be to determine whether or not conformational chirality can be used in enantioselective catalysis and if the coupled conformations of the terminal groups can increase the energetic difference between diastereomeric metal-substrate complexes and competing transition states.

Committee: Jon Parquette (Advisor) Subjects: Chemistry, Organic

Master of Sciences (Engineering), Case Western Reserve University, 2012, Chemical Engineering

About 94 million tons of hydrogen is consumed annually as a chemical feedstock worldwide. Hydrogen is also a promising energy carrier. As both a chemical feedstock as well as a renewable energy carrier, very pure hydrogen is required. Electrochemical hydrogen pump cells operating at 120°C - 180°C with a polybenzimidazole membrane imbibed with phosphoric acid were investigated for the electrochemical purification and pressurization of hydrogen. In this device, dilute or impure hydrogen gas is oxidized at the anode, the proton product crosses the membrane to the cathode where they are reduced to form hydrogen gas. It was found that the pump cell could purify simulated reformate containing 3% CO. A cell voltage of 0.145 V, or 0.03 W/cm2, was required to operate the cell at 150°C and 0.2 A/cm2. This corresponds to 7.7 watt-hours per mole of hydrogen pumped which is 1,000 – 10,000 times smaller than conventional purification techniques such as pressure swing adsorption. It was also found that the electrochemical pump cells could purify and pressurize the simulated reformate to at least 20 psi above the inlet pressure with only one 50 cm2 lab prototype cell. With cell pressure differentials above 5 psi, there was an undetermined amount of hydrogen back diffusion across the membrane. The ability of the pump cell to operate continuously over 20 hours was also investigated. Operating at current densities above 0.4 A/cm2 resulted in a decrease in the membrane conductivity. The membrane conductivity could be recovered to some degree by reversing the electrodes (i.e. the anode became the cathode and vice versa). These effects are thought to be due to the phosphoric acid building up in the electrodes, reducing electrode performance and facilitating phosphoric acid loss from the membrane.

Committee: Robert Savinell PhD (Advisor); Jesse Wainright PhD (Committee Member); Chung-Chiun Liu PhD (Committee Member) Subjects: Alternative Energy; Chemical Engineering

Doctor of Philosophy, The Ohio State University, 2022, Chemical Engineering

Hydrogen sulfide (H2S) is a hazardous pollutant, primarily formed during the processing of crude fossil fuels. Considering the detrimental effects of H2S, it is imperative to decompose it into harmless products. The state-of-the-art Claus process enables elemental sulfur recovery from H2S but converts H-content into low-value product- steam instead of valuable hydrogen (H2) due to its oxidative chemistry route. In this research work, H2S decomposition into H2 and elemental sulfur is explored using a sulfur looping scheme through two sub-steps—sulfidation and regeneration. The commercially viable H2 production from H2S demands superior H2S conversion and a sulfur carrier design exhibiting good reactivity and recyclability at minimal energy consumption. Additionally, understanding H2S decomposition reaction mechanism at the molecular scale as well as system level investigations are crucial for the material optimization and process design. The research work presented in the thesis thus focuses on the sulfur carrier design and process development which are investigated from both the fundamental and commercial aspects to meet these requirements. Chapter 2 focuses on the development of iron sulfide (FeS)-based sulfur carriers wherein the inherent low reactivity of FeS towards H2S decomposition is modified through dopant incorporation. A low concentration (2%) dopant addition is found to cause a dramatic reactivity improvement without much increase in material cost while preserving the phase integrity of FeS. The reaction pathways and electronic structures are analyzed using density functional theory to understand the role of dopants towards reactivity improvement. Additionally, a preliminary strategy is proposed for potential dopant selection through experimental and theoretical techniques. In Chapter 3, an innovative approach with nickel sulfide (Ni3S2)-based sulfur carriers utilizing CO2 for its regeneration is explored to reduce the overall energy footprint of (open full item for complete abstract)

Committee: Prof. Liang-Shih Fan (Advisor); Prof. Andre F. Palmer (Committee Member); Prof. Lisa M. Hall (Committee Member); Prof. Jerry Lio (Committee Member) Subjects: Chemical Engineering

Master of Science in Engineering, Youngstown State University, 2020, Department of Civil/Environmental and Chemical Engineering

Plastic waste management is one of the environmental problems facing the United States and the world at large. This project suggests solutions to the problem by using the plastic waste to produce a green and clean energy which will reduce the amount of plastic waste as well as making the environment a haven. With the increase in pollution level, the world is adopting the use of clean and green fuel. This work considers using steam reforming of volatile products from pyrolysis of high-density polyethylene (HDPE) at 500°C to mass-produce hydrogen gas. 50 metric tonnes/day of waste HDPE plastic and 7841litre/ day of generated steam feed will be converted into 5,128.2 metric tonnes of pure hydrogen gas per year using a adiabatic, fixed-bed catalytic reactors operating at 649.3°C and 1 bar. The catalyst is a commercial Ni in the form of 0.4-0.8m particle size.

Committee: Douglas Price PhD (Advisor); Pedro Cortes PhD (Committee Member); Park Byung-Wook PhD (Committee Member) Subjects: Alternative Energy; Chemical Engineering; Energy; Environmental Engineering

Doctor of Philosophy, The Ohio State University, 2020, Welding Engineering

Dissimilar metal weld butter layers are used in the oil and gas industry as transition joints to eliminate the need for post weld heat treatment (PWHT) following field welding of high strength steels. Over the past two decades there have been multiple failures of nickel based Alloy 625 butter welds on 8630 steel manifolds during subsea service while under cathodic protection. These failures were attributed to hydrogen assisted cracking (HAC) along brittle carbides that precipitate in the nickel alloy during onshore PWHT. In response to the field failures, the oil and gas industry began using low alloy steel (LAS) or C-Mn steel overlays in place of nickel overlays to mitigate the detrimental effects of carbon diffusion during PWHT. Using a LAS butter weld introduces a new dissimilar interface at the LAS/Alloy 625 closure weld, which could potentially be susceptible to HAC. This research investigated the HAC susceptibility of LAS butter welds joined to F65 steel pipes using nickel based Alloy 625 filler wire in the as-welded condition. Four different weld mock ups were investigated in this work. Each of the weld mock ups utilized slightly different closure welding procedures. Metallurgical characterization along with environmental testing using the Delayed Hydrogen Cracking Test (DHCT) was used to investigate the hydrogen assisted cracking behavior of the different interfaces. Metallurgical characterization was performed in order to identify the microstructure along the fusion boundary. Three different types of fusion boundary morphologies were observed in this work: a continuous fusion boundary, a discontinuous fusion boundary and the interpass morphology. The continuous fusion boundary morphology contained a sharp and well-defined interface between the CGHAZ and the planar growth region of the transition zone. The discontinuous morphology contained a partially mixed zone (PMXZ) between the steel CGHAZ and planar growth region. Weld metal swirls located at th (open full item for complete abstract)

Committee: Boian Alexandrov (Advisor); Antonio Ramirez (Committee Member); Boyd Panton (Committee Member) Subjects: Materials Science

Doctor of Philosophy, The Ohio State University, 2019, Welding Engineering

This work builds upon the previous research regarding hydrogen assisted cracking (HAC) of low alloy steel to nickel-base filler dissimilar metal welds (DMWs). In particular, this work is focused on DMWs commonly experienced in offshore oil and gas production systems in subsea use. The HAC tendency of these welds has been attributed to formation of susceptible microstructures at the fusion boundary during welding. As such, a post-weld heat treatment (PWHT) is utilized to temper these microstructures as well as relieve residual stresses. However, these microstructures can persist even after PWHT due to the steep compositional gradient driving migration of carbon from the base metal toward the fusion boundary and into the partially mixed zone (PMxZ) of the weld. The degree to which this migration occurs is a function of materials selection (base metal and filler metal) as well as weld and PWHT procedure. Due to this phenomenon, there is a balance that must be found to provide tempering of the susceptible microstructures that form during welding and limiting the formation of new susceptible microstructures during PWHT. Previous research has established a test method in the form of the delayed hydrogen cracking test (DHCT) which can delineate the effects of materials combination, weld procedure, and PWHT on HAC of DMWs. This test's qualitative ranking of susceptibility agreed well with industry experience. The current study worked towards refining the test methodology investigating the effects of test parameter influence on realized results. Of the investigated variables, it was found that how the test samples are coated is of primary importance where a consistently exposed fusion boundary scheme providing the most repeatable result in test. Additionally, a comparison was made between the test hydrogen charging condition which uses a dilute acid and constant current density of 10mA/cm2 and the service environment which is seawater with a constant potential (-8 (open full item for complete abstract)

Committee: Boian Alexandrov Ph.D (Advisor); Antonio Ramirez Ph.D (Committee Member); Carolin Fink Ph.D (Committee Member); Matthew Hamilton Ph.D (Committee Member) Subjects: Engineering; Materials Science

Master of Science, The Ohio State University, 2019, Chemical Engineering

Fossil fuel power plants often generate sulfur species such as hydrogen sulfide or sulfur dioxide due to the sulfur content of the raw feedstocks. To combat the associated environmental, processing, and corrosion issues, facilities commonly utilize a Claus process to convert hydrogen sulfide to elemental sulfur and water. Unfortunately, the Claus process suffers in efficiency from a thermal oxidation, or combustion, step and high equilibrium reaction temperatures. In this work, two different chemical looping process configurations towards recovering sulfur and H2 are investigated: (1) 3 reactor system (SR) for sulfur recovery; (2) 2 reactor system (SHR) for sulfur and H2 recovery. Since, H2 yield and sulfur recovery in a single thermal decomposition reactor in the SHR system is limited by low H2S equilibrium conversion, a staged H2 separation approach is used to increase H2S conversion to H2 using a staged separation methodology. Steady-state simulations and optimization of process conditions are conducted in Aspen Plus v10 simulation software for the chemical looping process configurations and the Claus process. An energy and exergy analysis is done for the chemical looping and Claus processes to demonstrate the relative contribution to exergy destruction from different unit operations as well as overall exergy and energy efficiency. The two chemical looping process configurations are compared against the Claus process for similar sulfur recovery in a 629 MW integrated combined cycle gasification power plant. The SHR system is found to be the most attractive option due to a 97.11% exergy efficiency with 99.31% H2 recovery. The overall energy and exergy efficiencies of this chemical looping system are 14.74% and 21.54% points higher than the Claus process, respectively, suggesting more efficient use of total input energy.

Committee: Liang-Shih Fan PhD (Advisor); Bhavik Bakshi PhD (Committee Member) Subjects: Energy; Engineering

Doctor of Philosophy, The Ohio State University, 2018, Welding Engineering

Subsea high pressure equipment used in production of oil and gas is routinely clad with nickel base alloys for corrosion protection. In the equipment with partial clad for sealing purpose, dissimilar metal interfaces are possibly exposed to the production fluids containing H2S. After cladding, a high hardness heat affected zone (HAZ) is produced in the base metal adjacent to the fusion boundary and is possibly susceptible to hydrogen assisted cracking (HAC) and sulfide stress cracking (SSC). National Association of Corrosion Engineers (NACE) standard MR0175/International Standard Organization (ISO) 15156 requires that HAZ hardness should be less than 22 HRC or 250 VHN. Postweld heat treatment (PWHT) is applied to reduce the HAZ hardness to meet this requirement. However, PWHT causes the carbon to diffuse from the base metal to the weld metal and pile up in a narrow region adjacent to the fusion boundary, possibly causing interface embrittlement. Also, prolonged PWHT can overtemper the base metal and impair its strength. Therefore, the optimal PWHT conditions need to be determined, which reduce the HAZ hardness to meet the industry standard, do not harm base metal strength, and do not increase the HAC and SSC susceptibility near or at the fusion boundary. In this work, nickel base Alloy 625 overlays on F22 (2.25Cr-1Mo) steel and AISI 8630 steel, or F22/625 and 8630/625 dissimilar metal welds (DMWs), were studied. A wide range of PWHT conditions indicated by Hollomon-Jaffe Parameter (HJP) was investigated to determine an optimal balance between HAZ softening and interface embrittlement. Vickers hardness testing revealed that the CGHAZ hardness decreases with the HJP increase due to martensite decomposition. There is a secondary hardening effect in F22 CGHAZ. The hardness of the planar growth zone (PGZ) of the interface and the weld metal increases with HJP, and the PGZ hardness increases at a higher rate than the weld metal. Nanoindentation and optical microsc (open full item for complete abstract)

Committee: John Lippold (Advisor); Boian Alexandrov (Committee Member); David Phillips (Committee Member) Subjects: Engineering; Materials Science; Metallurgy

BA, Oberlin College, 2017, Physics and Astronomy

In this thesis we provide an introduction to the use of Metal-Organic Frameworks (MOFs) for hydrogen storage and for the separation of hydrogen isotopologues, H2 and D2. MOFs are a class of materials comprised of `building-block' metal-oxide clusters connected by organic ligands, which have the capacity to adsorb molecules such as hydrogen through weak, physisorptive mechanisms. We provide some background on the quantum mechanical structure of hydrogen isotopologues, the structure of a few state-of-the-art MOFs, the quantum mechanics of infrared spectroscopy, and the desorption dynamics of adsorbates generally. We provide a description of the experimental apparatus and procedure used in this work to acquire thermal desorption (TD) and simultaneous, in situ infrared (IR) spectra. Notably, this apparatus makes use of a pressure gauge to record TD spectra—to the best of the author's knowledge, this is the first time such an apparatus has been created and shown to produce reproducible, physically-informative TD spectra. We demonstrate the potential of this novel spectroscopic technique on three MOFs, as we report their respective TDS and IR signatures. The agreement between our TDS and IR techniques is remarkable, as is the amount of information apparent in the TD spectra, and the agreement of our TD spectra with those in the literature. With our simple technique we are able to clearly distinguish the TD spectra of H2 and D2, allowing for the evaluation of MOFs with respect to their isotopologue separating ability. In addition to a proof of concept as to the proficiency of the experimental apparatus, this work presents two main findings: that the desorption of hydrogen isotopologues from MOFs does not follow the coverage-independent Polanyi-Wigner equation, and that stronger binding MOFs exhibit diminishing returns with respect to their ability to separate hydrogen isotopologues via temperature programming. As we argue on several occasions in this thesis, the TD s (open full item for complete abstract)

Committee: Stephen FitzGerald (Advisor) Subjects: Materials Science; Physical Chemistry; Physics; Quantum Physics

Doctor of Philosophy (PhD), Ohio University, 2013, Chemical Engineering (Engineering and Technology)

Given the abundance of ammonia in domestic and industrial wastes, ammonia electrolysis is a promising technology for remediation and distributed power generation in a clean and safe manner. Efficiency has been identified as one of the key issues that require improvement in order for the technology to enter the market phase. Therefore, this research was performed with the aim of improving the efficiency of hydrogen production by finding alternative materials for the cathode and electrolyte. 1. In the presence of ammonia the activity for hydrogen evolution reaction (HER) followed the trend Rh>Pt>Ru>Ni. The addition of ammonia resulted in lower rates for HER for Pt, Ru, and Ni, which have been attributed to competition from the ammonia adsorption reaction. 2. The addition of ammonia offers insight into the role of metal-hydrogen underpotential deposition (M-Hupd) on HER kinetics. In addition to offering competition via ammonia adsorption it resulted in fewer and weaker M-Hupd bonds for all metals. This finding substantiates the theory that M-Hupd bonds favor HER on Pt electrocatalyst. However, for Rh results suggest that M-Hupd bond may hinder the HER. In addition, the presence of unpaired valence shell electrons is suggested to provide higher activity for HER in the presence of ammonia. 3. Bimetals PtxM1-x (M = Ir, Ru, Rh, and Ni) offered lower overpotentials for HER compared to the unalloyed metals in the presence of ammonia. The activity of HER in the presence of ammonia follows the trend Pt-Ir>Pt-Rh>Pt-Ru>Pt-Ni. The higher activity of HER is attributed to the synergistic effect of the alloy, where ammonia adsorbs onto the more electropositive alloying metal leaving Pt available for Hupd formation and HER to take place. Additionally, this supports the theory that the presence of a higher number of unpaired electrons favors the HER in the presence of ammonia. 4. Potassium polyacrylate (PAA-K) was successfully used as a substitute for aqueous KOH for a (open full item for complete abstract)

Committee: Gerardine Botte Ph.D. (Advisor); Howard Dewald Ph.D. (Committee Member); David Ingram Ph.D. (Committee Member); Valerie Young Ph.D. (Committee Member); Kevin Crist Ph.D. (Committee Member) Subjects: Chemical Engineering; Chemistry; Energy; Engineering

Master of Science (MS), Wright State University, 2012, Chemistry

Computational modeling using classical grand canonical Monte Carlo simulations and first-principles calculations were carried out to study the adsorption of molecular hydrogen on nanoporous carbon modeled by the slit- pore geometry. It has previously been shown that hydrogen adsorption on pristine porous carbon has dependence on pore size and that an optimum pore size, which exhibits the maximum mass uptake, exists. There have been suggestions that doping graphitic nanocarbon structures with Pd enhances their adsorption capacity. The pore-size dependence of this change in adsorption brought about by Pd and the conditions at which improvement in adsorption can occur have not been extensively addressed to date. In this work, we perform computational modeling to examine hydrogen adsorption on pristine carbon and Pd-doped carbon nanopores. First-principles calculations were used to generate minimized configurations of the sorbent system while grand canonical Monte Carlo simulations modeled the finite temperature and pressure adsorption of hydrogen. We perform simulations at 298 K and pressures of 0.01 MPa, 1 MPa, and 5 MPa for systems with Pd to C ratios of 1:32, 1:18 and 1:8. Among the systems examined, pristine carbon at 5 MPa exhibited the highest mass uptake at 4.2 wt % adsorption capacity. This is consistent with the expectation that as the gas reservoir pressure increases, the adsorption capacity also increases. The presence of Pd resulted to enhancement in adsorption only at 0.01 MPa, the lowest pressure investigated. For the maximum adsorption of 4.2 wt% at 5 MPa, the heat of adsorption was calculated to be 8 kJ/mol. The target heat of adsorption value for hydrogen storage materials is 25 kJ/mol, and this was achieved for the 1:8 Pd:C ratio at a pore size of 6 Angstroms, but the system showed a lower adsorption capacity of 1.5 wt%.

Committee: Rachel Aga PhD (Advisor); Paul Seybold PhD (Committee Member); Ioana Sizemore PhD (Committee Member) Subjects: Physical Chemistry

Master of Science in Engineering (MSEgr), Wright State University, 2010, Renewable and Clean Energy

The energies and temperature-dependent dynamics of hydrogen and lithium chemisorption on a silicon nanosheet, called silicene, were studied using density functional theory and molecular-dynamics (MD) simulations. Silicene has a buckled honeycomb structure, and has been fabricated as suspended monolayer sheets and nanoribbons in recent experiments. We calculated the adsorption energies of hydrogen and lithium on silicene for different adsorption ratios between 3.1% and 100%. The studies will clarify the characteristics of these novel and promising nanomaterials, and pave the way for their applications. For Hydrogen, the adsorption energy had a maximum of 3.01 eV/H for complete hydrogenation, and decreased by 24.5 % to 2.27 eV/H for single atom adsorption on a 32-silicon-atom supercell. It was determined that the preferred hydrogen adsorption patterns were clusters. Molecular dynamics simulations revealed the stability of adsorption configurations at 300K. The electronic structure of these stable configurations could be modified and controlled through partial and complete hydrogenations, and a transformation from zero-gap semiconductor to insulator was observed. For lithium on silicene, the adsorption energy had a maximum of 2.23 eV/Li for 50% lithiation and decreased by 29.6% to 1.57 eV/Li for 100% lithiation. For partial Lithium adsorptions up to 50%, the preferred adsorption sites were hollow sites on top of silicon hexagons. This preference changed as more lithium atoms were introduced. At a 100 % adsorption ratio, the lithium atoms adsorbed to sites directly above or below the silicon atoms. Unlike hydrogenated silicene, the band structure of each partially lithiated structure was shown to be that of a metal. Combining hydrogen and lithium adsorptions, it was shown that silicene-Li nanocompounds can be considered for hydrogen storage.

Committee: Amir Farajian PhD (Advisor); Amer Maher PhD (Committee Member); Daniel Young PhD (Committee Member) Subjects: Materials Science

Doctor of Philosophy, University of Toledo, 2008, Physics

Textured back reflector (BR) is an essential component used in substrate type solar cells for light trapping, which enhances the long wavelength absorption. Most commonly used BR consists of a reflecting metal layer(s) of Ag and/or Al and a transparent conducting oxide (TCO) layer such as ZnO. This type of BR, if properly textured, can lead to about 20% increase in the short-circuit current and cell efficiency. A widely used technique for producing the BR is sputtering due to its simplicity and easy operation for large area thin film solar cell applications. The TCO layer needs to be thick enough (>500 nm) to reach a textured structure and to prevent the metal in the BR from diffusing into the solar cell layers. Thus, the ZnO deposition becomes the bottleneck in the BR process. Significant efforts have been putting on developing novel techniques that can produce ZnO coatings with better texture and high deposition rate. To address the above issue electrodeposition was employed to coat ZnO film, because it gives high deposition rate at low cost. A systematic study of conventional electrodeposition was performed. Further improvements for the electrodeposition process have done to eliminate some of the problems associated with conventional electrodeposition. In addition highly textured BR produced by electrodeposited ZnO changes the electrical structure of the device. The necessity to consider these factors when fabricating solar cells on highly textured BR was emphasized using PVOPTICS and AMPS modeling.Hydrogen is considered to be the fuel of the future. Subsequently there are many attempts of generating H2 by environmentally friendly means. One such proposed system is photo-electrochemical cell (PEC) consist of transparent conducting corrosion resistive (TCCR) layer, a-Si:H solar cell and catalytic layer. The research work done to identify the potential TCCR layers and fabrication of porous nickel catalyst layer will be discussed.

Committee: Xunming Deng PhD (Advisor); Robert W. Collins PhD (Committee Member); Song Cheng PhD (Committee Member); Sanjey V. Khare PhD (Committee Member); Ahalapitiya H. Jayatissa PhD (Committee Member) Subjects: Physics

Master of Science (MS), Ohio University, 2007, Mechanical Engineering (Engineering)

Since solid oxide fuel cells can operate on fuel containing both hydrogen and carbon monoxide, it may prove possible to remove hydrogen from syngas streams for other purposes and allow the fuel cell to operate with higher carbon monoxide levels. In this study, electrolyte-supported solid oxide fuel cells were tested using hydrogen, syngas, and hydrogen-depleted syngas (HDS) as fuel sources. It was found that reducing the hydrogen flow rate by 50% while maintaining an equivalent fuel utilization rate increases the polarization of the electrode by less than 5%. Carbon deposition was avoided when the water content of the fuel reflected that of actual syngas. The drop in the ideal voltage plus the increase in the resistance of the cell equated to a measured loss in power density of 7.8%.

Committee: Gregory Kremer (Advisor) Subjects: Engineering, Mechanical

Master of Science (MS), Ohio University, 2007, Mechanical Engineering (Engineering)

Use of hydrogen as an automotive fuel has been successfully demonstrated for the use but they are not ready for consumers yet. One of the major problems associated with the use of hydrogen as an automotive fuel is the storage of hydrogen on-board. Hydrostatic Pressure Retainment (HPR) is an innovative gaseous storage concept which consists of a number of small hollow spherical bubbles arranged within a solid mass similar to a sponge-like structure. These spherical bubbles or the inner-matrix can be arranged in similar fashion as the three basic packing structures of crystalline metals: Simple Cubic (SC), Body Centered Cubic (BCC) and Face Centered Cubic (FCC). In a HPR vessel, suitable configuration for the inner-matrix and feasibility study of different materials is a crucial design step. This thesis investigates the feasibility of different materials for inner-matrix using an ideal BCC microstructure and also achieves one of the milestones of the HPR research by finding and analytically supporting the suitable configuration for the HPR inner-matrix, using Finite Element Analysis.

Committee: Hajrudin Pasic (Advisor) Subjects:

BA, Oberlin College, 2012, Physics and Astronomy

The hydrogen molecule ion is the simplest molecule, consisting of only two protons and an electron. As such, understanding this problem is essential in order to extend quantum mechanical techniques to more complex molecules such as the next simplest hydrogen molecule. The non-ionized hydrogen molecule represents the simplest system with only axial symmetry exhibiting Pauli exclusion principle effects due to the two identical electrons (fermions) in the neutral molecule. Both molecules have been treated in great detail both experimentally and theoretically and the nature of their solutions and energies are well understood. Dimensional scaling of the problem can provide insight into the nature of the exact solutions to a system. For example, the problem may be solvable in certain dimensions other than three due to the simplicity of the problem or some symmetry that is present in other dimensionalities. In the present work, the former results in the hydrogen molecule ion being exactly solvable in closed form in one dimension. Solutions for the energies for a scaling of the hydrogen molecule ion Hamiltonian done by Herschbach et. al. and by Lopez et. al. [M. Lopez-Cabrera, A. L. Tan, and J. C. Loeser, J. Phys. Chem., 1993, 97, 2467-2478. and D. D. Frantz and D. R. Herschbach, J. Chem. Phys., 1990, 92, 6668-6686.] results in the energy for the three-dimensional problem being bounded by the D→1 and D→ ∞ limits, both of which can be solved in closed form. [T. C. Scott, M. Aubert-Frecon, and J. Grotendorst, Chemical Physics, 2006, 324, 323-338.] In the present work, a model of the one-dimensional hydrogen molecule ion is developed in which the charge distributions and electric fields are both mathematically fully described in one dimension. The wavefunctions governing the spacial coordinate for this model were found to be combinations of Airy functions of the first type and the wavefunctions for a free particle (sine and cosine functions) and the energies were found to be (open full item for complete abstract)

Committee: Daniel Styer (Advisor) Subjects: Physics

Doctor of Philosophy, Miami University, 2024, Chemistry and Biochemistry

Carbon is a highly versatile material which can form different bonding structures each with very specific properties. High sp3 hybridized carbon like diamond and diamond-like carbon (DLC) are characterized by high hardness, chemical inertness, and thermal stability. These properties are utilized in many industries as protective coatings, abrasives, and insulators. Although diamond and DLCs are semiconductors with limited electrical conductivity, dopants incorporated into their structures facilitate electron transfer. Combining the acquired electrical conductivity with the inherent material properties expands upon the viable applications. Although they share similar properties due to their bonding structures, diamond and DLCs differ in various ways, including their manufacturing process, surface morphology, and electrical properties. Recently, boron doped diamond (BDD) and tetrahedral amorphous carbon (ta-C) have gained popularity as electrochemical sensors, each with advantages and disadvantages. They exhibit excellent electrochemical properties with wider potential windows and low background currents. Although recent advances in diamond growth have reduced temperature and pressure conditions, substrates still reach temperatures over 750°C. BDD is characterized by a rough polycrystalline structure, adding to the intricacies of electrochemical detection. Meanwhile, ta-C thin films are coated onto substrates in a vacuum system with substrate temperatures remaining below 100°C. Doped ta-C is characterized by a very smooth surface with low friction, but the electrochemical properties are not as well studies. In this project, we explore the electrochemical properties of BDD and doped ta-C. A nanoparticle modification was used to increase the sensitivity of BDD to hydrogen peroxide (H2O2), an important biomolecule in the inflammation process and in cellular signaling. H2O2 is also implicated as a molecule which participates in oxidative stress, possibly leading to n (open full item for complete abstract)

Committee: Cory Rusinek (Advisor); Niel Danielson (Committee Chair); Rock Mancini (Committee Member); Eric Sikma (Committee Member); Catherine Almquist (Committee Member) Subjects: Chemistry; Materials Science

Master of Science, The Ohio State University, 1950, Graduate School

Committee: Not Provided (Other) Subjects: