UMD Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/3
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a given thesis/dissertation in DRUM.
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Item ELECTRIFIED HIGH-TEMPERATURE MANUFACTURING AND APPLICATIONS IN ENVIRONMENTAL SCIENCE(2023) Li, Shuke; Hu, Liangbing; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)High temperature processes hold great potential for material and chemical manufacturing.On the one hand, high temperature can help overcome energy barriers and thus effectively convert precursors to desired products. On the other hand, high temperature can also boost the reaction rate and improve synthesis efficiency. Recent development of electrified high temperature technologies by our group further revealed the important role played by non-equilibrium conditions on nanomaterial and chemical syntheses. For example, Joule-heating of carbon-based materials through a programmable electrical signal can offer spatial and temporal temperature profiles, which can be used to manipulate the chemical reaction pathways. For another example, tunable heating duration and quenching rates can be used to achieve a range of compositions and structures of nanoparticles. In this dissertation, two specific applications of the electrified high temperature technology will be explored, including: (1) Thermal shock synthesis of multielemental nanoparticles as selective and stable catalysts; and (2) Efficient biomass upgrading via pulsed electrical heating. Supported nanoparticle (NP) catalysts are widely used for various reactions. However, it remains challenging to synthesize high quality NPs with accurate morphologically and structure control. In this part of the research, NP catalysts with morphology or structural design were prepared by high temperature thermal shock methods. Ultra-small and high-loading carbon supported Pt3Ni NPs: Strong electrostatic effect was introduced between metal salts and carbon particles that can largely improve anchoring and dispersion of the precursors, thereby achieving high NP loading (40 wt%) as well as small NP size and good distribution (1.66 ± 0.56 nm). This method is not only limited to bimetallic NPs synthesis or NPs on carbon black but can be extended to a range of NP compositions on various substrate materials, thus providing a general strategy for developing ultrafine and high-loading NPs as electrocatalysts for various reactions. Sustainable aviation fuels (SAFs) are essential to meet future air travel demand while reducing the carbon footprint. Among many potential feedstocks to produce SAFs, lignin stands out as it is an abundant and renewable aromatic biopolymer that is usually treated as a waste material from the paper industry. However, converting lignin to SAFs by conventional thermochemical processes has been challenging due to poor control on the reaction pathway which leads to undesired product distribution. In this study, a programmed electrified heating method was designed and used to break down large lignin molecule to small aromatic molecules with targeted product distribution. A controlled heating step offers sufficient energy input to break down lignin molecules to smaller fragments without excessive secondary reactions toward undesired species such as coke. The lignin thermal decomposition products were evaluated as potential precursor for SAFs generation. This process can be further extended to process other biomass materials such as algae and sawdust to value-added chemicals.Item REACTION MECHANISMS AND INTERFACE CHARACTERISTICS OF ELECTRODE AND ELECTROLYTE MATERIALS FOR MAGNESIUM BATTERIES(2020) Sahadeo, Emily; Lee, Sang Bok; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Rechargeable magnesium (Mg) batteries are an emerging electrical energy storage technology proposed as an alternative to current Lithium-ion (Li-ion) batteries. Mg batteries have the potential to provide more energy than current Li-ion systems due to the high volumetric capacity and low reduction potential of Mg metal, in addition to higher abundance and cheaper cost of Mg compared to Li metal. However, there are many challenges regarding Mg battery chemistry and materials that must be resolved before they can be successfully commercialized. The work in this dissertation addresses a few of these challenges, including poor Mg2+ diffusion in MnO2 cathodes, interfacial limitations at the Mg anode and MnO2 cathode surfaces, and the development of solid-state electrolytes as an alternative to liquid electrolytes that passivate the Mg anode interface. These issues are investigated from a fundamental chemical and electrochemical standpoint to help improve future design of rechargeable Mg batteries. In the first study, the electrochemical reactions and charge storage mechanism of electrodeposited MnO2 cathodes in water-containing organic electrolyte are explored using X-ray photoelectron spectroscopy. These results demonstrate the key role that water plays in enabling the reversible insertion/extraction of Mg2+ from the MnO2. Second, a heterogeneous electrode structure, PEDOT/MnO2 coaxial nanowires, is utilized to study the effect of conductive polymer surface layers on the MnO2, specifically regarding the effect on the cathode’s cyclability and power performance as well as the overall charge storage mechanism. Additionally, to investigate the potential for anode protection on Mg metal, ALD Al2O3 is deposited on different Mg metal substrates to determine whether it can improve Mg deposition and stripping at the Mg anode and prevent electrolyte degradation on the Mg surface. While it does not demonstrate the ability to effectively protect the anode during cycling, the results herein can help inform further protection layer development. Finally, the catalytic ability of Mg2+ salts is reported for the ring-opening polymerization of 1,3-dioxolane, moving toward exploring this polymer’s potential to be utilized as a solid-state electrolyte. The findings here give fundamental insights into materials’ properties that can be further utilized to design Mg batteries with high-voltage cathodes.Item Nanomaterials for Garnet Based Solid State Energy Storage(2018) Dai, Jiaqi; Hu, Liangbing; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Solid state energy storage devices with solid state electrolytes (SSEs) can potentially address Li dendrite-dominated issues, enabling the application of metallic lithium anodes to achieve high energy density with improved safety. In the past several decades, many outstanding SSE materials (including conductive oxides, phosphates, hydrides, halides, sulfides, and polymer-based composites) have been developed for solid-state batteries. Among various SSEs, garnet-type Li7La3Zr2O12 (LLZO) is one of the most important and appealing candidates for its high ionic conductivity (10-4~10-3 S/cm) at room temperature, wide voltage window (0.0-6.0V), and exceptional chemical stability against Li metal. However, its applications in current solid state energy storage devices are still facing various critical challenges. Therefore, in this quadripartite thesis I focus on developing nanomaterials and corresponding processing techniques to improve the comprehensive performance of solid state batteries from the perspectives of electrolyte design, interface engineering, cathode improvement, and full cell construction. The first part of the thesis provides two novel designs of garnet-based SSE with outstanding performance enabled by engineered nanostructures: a 3D garnet nanofiber network and a multi-level aligned garnet nanostructure. The second part of the thesis focuses on negating the anode|electrolyte interfacial impedance. It consists of several processing techniques and a comprehensive understanding, through systematic experimental analysis, of the governing factors for the interfacial impedance in solid state batteries using metallic anodes. The third part of the thesis reports several processing techniques that can raise the working voltage of Li2FeMn3O8 (LFMO) cathodes and enable the self-formation of a core-shell structure on the cathode to achieve higher ionic conductivity and better electrochemical stability. The development and characterization of a solid state energy storage device with a battery-capacitor hybrid design is included in the last part of the thesis.Item NANO STRUCTURED MATERIALS FOR ENERGY APPLICATIONS(2017) Liu, Lu; Zachariah, Michael R; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation addressed the applications of nanostructured materials as oxygen carriers (OCs) and catalysts in poly lactic acid (PLA) thermal decomposition. In chapter 1~4, the stability and cyclibility of metal oxides and supported metal oxides as OCs were evaluated in an isothermal fixed bed reactor at different temperatures for 50 cycles with methane as fuel, up to 15h while their structural, physical and chemical properties were identified using XRD, SEM, TEM, BET, XPS and Ar/H2-TPR. In chapter 5, aerosol synthesized Bi2O3 was found to be a useful catalyst in thermal PLA decomposition, which could lower the on-set decomposition temperature by ~75 T. The developed study protocol could be applied to various metal oxides and polymers to study their catalytic thermal decompositions as well.Item SYSTEM MODELING AND MATERIAL DEVELOPMENT FOR STANDALONE THERMOELECTRIC POWER GENERATORS(2014) Huang, Dale Hsien-Yi; Yang, Bao; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation addresses the need to develop a scalable and standalone power generator for personal, commercial, and military transportation and communication systems. The standalone thermoelectric power generator (TPG) converts heat to electrical power in a unique way that does not draw on conventional power sources like batteries. A TPG is comprised of four main components: a heat source, thermoelectric modules, a heat sink, and thermal insulation. For system modeling and materials development purposes, the dissertation invented the first pyrophoric heated standalone TPG, solid-state renewable heat source, and two-component nanocomposite thermoelectric power generation material. In this work, the first pyrophoric heated standalone thermoelectric power generator was designed, fabricated, and tested. The bases of the system were four porous silicon carbide combustors for the exothermic reaction of pyrophoric iron powder with oxygen. These combustors provided a heat source of 2,800 to 5,600 W to the heat sinks (through TE modules) at conditions suitable for a standalone, pyrophoric iron fueled TE power generator. The system integrated with 16 commercial bismuth telluride thermoelectric modules to produce 140 to 280 W of electrical power with a TE power conversion efficiency of ~5%. This demonstration represents an order-of-magnitude improvement in portable electrical power from thermoelectrics and hydrocarbon fuel, and a notable increase in the conversion efficiency compared with other published works. To optimize the TE heat-to-power conversion performance of the TPG, numerical simulations were performed with computational fluid dynamics (CFD) using FLUENT. The temperature dependent material properties of bismuth telluride, effects of air flow rate (6 – 14 m/s) at 300 K, and effects of thermoelectric element thickness (4 – 8 mm) on temperature gradient generated across the module are investigated under constant power input (7.5 W). The obtained results reveal that all geometric parameters have important effect on the thermal performance of thermoelectric power generation module. The optimized single TE element thickness is 7 mm for electrical power generation of 0.47 W at temperature difference of 138 K. The TE heat-to-power conversion efficiency is 6.3%. The first solid-state renewable heat source (without the use of hydrocarbons) were created with porous silicon carbide combustors coated with pyrophoric 1-3 micron-sized iron particles mixture. The thermal behavior and ignition characteristics of iron particles and mixtures were investigated. The mixture include activate carbon and sodium chloride, in which iron is the main ingredient used as fuel. The final mixture composition is determined to consist of iron powder, activate carbon, and sodium chloride with a weight ratio of approximately 5/1/1. The mixture generated two-peak DSC curves featured higher ignition temperatures of 431.53°C and 554.85°C with a higher heat generation of 9366 J/g than single iron particles. The enhancement of figure-of-merit ZT or efficiency of thermoelectric materials is dependent on reducing the thermal conductivity. This dissertation synthesized and characterized the advanced two-component Si-Ge nanocomposites with a focus on lowering the thermal conductivity. The ball-milled two-component Si-Ge material demonstrated 50% reduction in thermal conductivity than the single component material used in the radioisotope thermoelectric generators and 10% reduction than the p-type SiGe alloy.