Theses and Dissertations from UMD
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Item NOVEL GRAPHENE HETEROSTRUCTURES FOR SENSITIVE ENVIRONMENTAL AND BIOLOGICAL SENSING(2024) Pedowitz, Michael Donald; Daniels, Kevin; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The COVID-19 pandemic has underscored the need for rapid, mobile, and adaptable sensing platforms to respond swiftly to pandemic-level emergencies. Additionally, smog and volatile organic compounds (VOCs), which posed significant health risks during last year’s wildfires, highlight the critical need for environmental air quality monitoring. Graphene, with its high sensitivity and fast response times, shows promise as a powerful sensing platform. However, it faces challenges related to low selectivity and the complexities of device fabrication using conventional chemical vapor-deposited graphene grown on metal foil, which requires exfoliation and transfer to suitable substrates.This dissertation explores the use of epitaxial graphene, which is graphene grown from the sublimation of silicon from silicon carbide, and forming heterostructures with legacy functional materials, such as transition metal oxides and selective capture probes like antibodies and aptamers to develop rapid, ultrasensitive, and selective sensors to address critical environmental and public health challenges. Epitaxial graphene provides a single-crystal, lithography-compatible graphene substrate that retains the desirable electronic properties of graphene without the drawbacks associated with transferred materials. This work focuses on creating heterostructures using traditional functional materials, such as manganese dioxide and antibodies, to develop high-quality, selective sensors for both biological and environmental applications. The practical applications of these sensors are demonstrated and validated using techniques such as Raman spectroscopy, X-ray photoelectron spectroscopy, atomic force microscopy, scanning electron microscopy, and electrical characterization. Additionally, detailed material analysis on producing these heterostructures is provided, emphasizing their ability to be modified without damaging the underlying graphene surface. This highlights epitaxial graphene's robust and versatile nature and its potential for creating high-quality devices with relatively simple designs. Finally, these biosensors are applied to alternate antibody-antigen systems, including influenza, to enhance disease-tracking capabilities. We also explore advanced functional materials, such as protease-peptide systems, which enable the creation of on-chip chemistry systems previously unattainable with current material systems.Item Using Electric Fields to Modulate Polymeric Materials: Electro-adhesion, Electro-gelation and Electro-carving(2023) XU, WENHAO; Raghavan, Srinivasa R.; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation concerns the effects of electric fields on aqueous polyelectrolytes (solutions and gels), including those of polysaccharides and proteins. Electrical effects on such polymeric systems have not been studied in detail thus far. In this work, we apply electric fields as stimuli to trigger responses in these materials. We have discovered three novel responses: electro-adhesion of a gel to a solid electrode; electro-gelation of a polymer solution, which allows gels to be made in 3D, and localized electro-disruption of gels, which allows gels to be carved or sculpted. In our first study, we show that it is possible to adhere a soft ionic conductor (like a polymeric hydrogel) to a hard, electronically conductive electrode using a low DC voltage without any adhesive. When 5 to 10 V DC is applied between a pair of electrodes (e.g., graphite, copper, etc.) spanning a cylindrical hydrogel (e.g., acrylamide, gelatin, etc.), in 3 to 15 min, the gel strongly adheres to either or both electrodes. The ultimate adhesion strength can exceed 150 kPa and is only limited by the strength of the soft material. This hard-soft electro-adhesion applies to not only lab-synthesized hydrogels but also animal or plant tissues, such as beef, pork, apples, bananas, etc. We show that this adhesion results from electrochemical reactions that form chemical bonds between the polymers in the gel backbone and the electrode surface. Hard-soft electro-adhesion can be used to assemble hybrid materials with hard and soft compartments, which could be useful in robotics, energy storage, underwater adhesion etc. Next, we demonstrate how an electric field can be used to gel a polymer solution with spatial control thereby, we can ‘print’ gels in 3D. When a solution of alginate (an anionic biopolymer) is subjected to a DC electric field (~ 10 V) using a platinum (Pt) needle as the anode, a gel is formed right around the anode within seconds. By using a mobile anode, gel “voxels” can be formed sequentially and these merge into 3D structures. Similar electro-gelation can also be done with the cationic biopolymer chitosan, but at the cathode instead of the anode. The mechanism for gelation with both alginate and chitosan involves the polymer chains losing their charge next to the electrode. A loss of charge leads to insolubility, and insoluble domains act as crosslinks and connect the chains into networks. We have built a prototype for a 3D-printer that can translate a 3D design into a robust biopolymer gel formed by electro-gelation. Lastly, we show that an electric field applied by an electrode can be used like a knife to carve or sculpt hydrogels into 3D shapes. When we apply a DC electric field across certain gels, the gel shrinks near the anode, while water is expelled out of the gel near the cathode. Ultimately the gel shrinks by more than 50% of its original size. Such shrinkage is observed with a range of anionic gels, including both physical gels of biopolymers like agar and alginate as well as covalent gels such as sodium acrylate. If the ionic strength of the gel is high, the shrinkage does not occur. The origin of this effect lies in a combination of electroosmosis as well as pH changes near the electrodes. Finally, we show that with a focused electric field, the shrinkage can be limited to a specific location in a gel, thereby allowing us to electro-carve gels in 3D.Item ELECTROLYTE DESIGN FOR HIGH-ENERGY METAL BATTERIES(2022) Hou, Singyuk; Wang, Chunsheng; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The demand for advanced batteries surged in the past decade because they are at the heart of several tactically important technologies, such as renewable electrification grids and electric vehicles (EVs). These technologies will progressively transform our energy consumption structure toward sustainability and alleviate the global climate crisis. Unlike consumer electronics, EVs require batteries with larger energy storage to avoid "range anxiety". According to the US Advanced Battery Consortium (USABC), breakthroughs are needed to double the battery energy density and reduce the price by 50% for EVs to be competitive in the automobile market. These stringent requirements are unlikely to be met by the Li-ion batteries (LIBs) because the charge storage limits have been reached. Metal batteries using metals as anodes require no host materials and have up to ten times higher charge storage capacities. When metals with low redox potentials (Mg, Ca, and Li) are used, new battery systems that benefit from larger capacities and high cell voltages result in over 100 % leap in energy density to satisfy the USABC's goals for EV applications. On the other hand, the scarcity of materials related to LIBs raises uncertainties and doubts in the transition to electric transportation. Metals such as Mg and Ca are highly abundant in the earth crust, which potentially ensures the reliability of the energy supply in the future.Despite the exciting prospects of metal batteries, there are knowledge gaps in understanding how the electrolyte changes the behaviors of metal plating/stripping. Although electrolytes are considered inert materials in batteries, they are indispensable in maintaining ionic transport, modulating interfacial reaction kinetics, and maintaining reversible electrode reactions through the formation of solid-electrolyte interphase (SEI). In this dissertation, I detailed our efforts to establish the microscopic understanding of the electrolyte structures, SEI components, nucleation, and growth of the electroplated metal with spectroscopic techniques and physical models. These understandings guided the design of electrolytes for reversible metal anodes in practical high-energy battery applications.Item SEROTONIN SENSOR-INTEGRATED IN VITRO SYSTEMS AS RESEARCH TOOLS TO ADDRESS THE GUT BRAIN AXIS(2022) Chapin, Ashley Augustiny; Ghodssi, Reza; Bentley, William E; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The gut-brain-axis (GBA) is a bi-directional communication system between the gastrointestinal (GI) enteric nervous system and the central nervous system, capable of complex crosstalk between the gut and the brain to maintain GI homeostasis and influence mood and higher cognitive functions. Under healthy conditions, this communication is beneficial for regulating immune function, proper peristaltic motion, and hormone release related to hunger and feeding behaviors. However, GBA communication can cause co-morbid occurrence of both GI and neural disorders. For instance, chronic inflammatory conditions of the gut, such as inflammatory bowel disease (IBD) and irritable bowel syndrome (IBS), often present with symptoms of depression and anxiety. Clinical studies, animal models, and molecular research techniques have implicated serotonin (5-HT) as a key signaling molecule to both regulate GI functions and stimulate enteric nerves. These studies are limited by the inability to study sub-mucosal 5-HT on the basolateral side of the epithelium, wheremost of the 5-HT is released and acts on nerves endings. The ability to measure 5-HT release patterns in this area, at native spatial and temporal scales, within an in vitro culture of the gut epithelium, would allow researchers to distinguish 5-HT release patterns stimulated by different GI luminal conditions associated with health and disease, to better understand how these stimuli affect the brain. In this dissertation, electrochemical sensors are fabricated within two types of in vitro platforms to measure 5-HT at physiological scales (sub-micromolar concentrations). The goal of this design is to facilitate the direct detection of 5-HT released from cells cultured in the platform to improve both spatial and temporal access to basolaterally-secreted molecules and provide continuous, automated measurements over experimental time scales. 5-HT sensors fabricated on both porous and smooth cell culture substrates are demonstrated, achieving sensitivities of ~1 – 10 μA/μM and limits of detection of ~100 nM. Electrochemical characterization allow understanding of 5-HT adsorption kinetics, which was modeled to track and predict sensor fouling over continuous measurements. These sensor-integrated substrates were packaged in 3D printed structures, which allowed rapid fabrication of custom designs and were shown to be biocompatible and support growth of RIN14B cells, a model 5-HT-secreting cell line. Finally, cell-secreted 5-HT was detected at ~100 – 500 nM, corresponding to ~4 pmol 5-HT / 105 cells. Ultimately, slow adsorption kinetics prevented direct detection of 5-HT from cells cultured directly on top of the sensors, but the thorough characterization of the platform demonstrated here lays significant groundwork for future optimization of the sensing protocol.Item INVESTIGATION OF ORDERED POROUS MATERIALS FOR LITHIUM AND MAGNESIUM IONS ELECTROCHEMICAL ENERGY STORAGE(2021) Henry, Hakeem Kimani; Lee, Sangbok; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)As portable electronics and electric vehicles become a more integral part of everyday life, rechargeable electrical energy storage devices (batteries) capable of providing greater energy and power densities will soon be necessary. Lithium-ion batteries (LIBs) have dominated this area of rechargeable energy storage devices since their commercialization in 1990. However, as electronic devices continue to advance, battery technology will have to go beyond conventional lithium-ion battery systems to power these devices. Among the many possible alternatives to lithium, magnesium is a promising candidate. In comparison to lithium, magnesium is more abundant, lower in cost, and more environmentally friendly. Magnesium batteries can also utilize a Mg metal anode which offers a high volumetric capacity and low standard reduction potential. Despite the potential benefits, Mg batteries suffer from several drawbacks. The three main issuesplaguing Mg batteries are (1) a lack of practical cathodes due to slow insertion kinetics of the divalent Mg2+ ion, (2) incompatibility between Mg electrolytes and high voltage cathodes, (3) and parasitic and passivating reactions occurring at the Mg metal anode surface. The work of this dissertation aims to address the Mg2+ insertion issue by developing modified cathodes with enhanced electrochemical performance. In the first study, the effect of structure and hydration on Mg2+ intercalation into amorphous and crystalline V2O5 films was systematically investigated by electrochemical methods. It was determined that the high water content of electrodeposited V2O5 films was the primary factor impacting Mg2+ intercalation, while the crystal structure played a secondary role. In the second study, an ordered mesoporous carbon (OMC) structure was grown on the surface of carbon nanotubes (CNT) to achieve a novel electrode architecture. The hybrid carbon structure allowed for fast ion diffusion and high electronic conductivity. The porous structure also served as an excellent host for the deposition of high-capacity cathode materials for an all-in-one electrode design. In the final study, the OMC synthesis method was paired with electrodeposited V2O5 protocol to further investigate the OMC electrochemical performance. Overall, the work of this dissertation contributes to the development and commercialization of rechargeable Mg batteries by elucidating a portion of this complex chemistry.Item BEYOND LI ION: INTERFACE ENGINEERING ENABLES HIGH ENERGY DENSITY LI AND NA METAL BATTERIES(2020) DENG, TAO; Wang, Chunsheng; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The ever-increasing demand from electric vehicles and consumer electronics, as well as the expanding market of intermittent renewable energy storage, has sparked extensive research on energy-storage devices with low cost, high energy density, and safety. Although the state-of-the-art Li-ion battery (LIB) based on highly reversible intercalation chemistry has approached its theoretical limit after several decades’ incremental improvement, there is still no great progress in the exploration of alkaline metal chemistry (Li & Na) for next-generation batteries. Compared with Li-ion chemistry, alkaline metal anode is more attractive due to the extremely high capacity (3860/1166 mA g-1 for Li/Na) and low negative electrochemical potential (-3.04/-2.71 V for Li/Na vs. the standard hydrogen electrode), thus enables next-generation batteries with high energy density. To achieve this, significant advances have been made in liquid or solid-state electrolytes that cater to the high capacity Li/Na anodes and high-voltage cathodes, but performance of the battery is still not comparable to that of commercial LIB due to dendrite formation and unstable interphase formation. Such situation requires a deep exploration on the rational design of electrolytes and interfacial stability between the electrolytes and electrodes for realizing next-generation batteries. In this dissertation, I detailed our efforts in exploring new electrolyte systems and proposed some interface engineering strategies or methods to stabilize the electrolyte-electrode interfaces, thus supporting the next-generation battery chemistries beyond LIB technology. They include nonflammable fluorinated electrolytes, polymer composites electrolytes, as well as solid-state garnet-type (Li6.75La3Zr1.75Ta0.25O12) and Na-beta-alumina (β''-Al2O3) electrolytes for Li/Na metal batteries. We studied the dendrite formation and electrode-electrolyte interface stability in the corresponding chemistry, thermodynamics, as well as kinetics. Based on the learned mechanisms, we also proposed our strategies to suppress dendrite formation and realize good performance Li/Na metal batteries by forming stable electrolyte-electrode interphases. Being enabled by the fundamental and scientific breakthroughs in terms of electrochemical mechanisms, interface chemistry, as well as interface modification techniques, this work has provided insights into the development of high-energy Li/Na metal batteries for both academic and industrial communities.Item ELECTROCHEMICAL PROTECTION OF LITHIUM METAL ANODE IN LITHIUM-SULFUR BATTERIES AND BEYOND(2020) Wang, Yang; Lee, Sang Bok; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)With the growing demand of advanced energy storage devices that have high energy density and high power density to power electric vehicles and electrical grid, scientists and engineers are exploring technologies beyond conventional Li-ion batteries which have transformed the industry in the past thirty years. Li-S batteries have much higher energy density than Li-ion batteries and are gaining momentum. However, the intrinsic issues of Li-S batteries require a comprehensive systematic study of the protection of Li metal anodes to put them into practical applications. In the first study of this dissertation, we investigated using conventional electrolyte of Li-S batteries that includes 1,3-dioxolane to electrochemically pretreat Li metal anodes. We concluded that the electrochemical pretreatment of Li metal anodes generated an organic-inorganic artificial solid electrolyte interface (ASEI) layer that greatly enhanced the battery performance of the Li-S batteries. The properties of this ASEI can be tuned by manipulating the current density and cycle number of the electrochemical pretreatment. In the second study, we studied the comprehensive development and surface protection of Li10GeP2S12 (LGPS) material as solid-state electrolyte, which has ionic conductivity comparable to liquid electrolytes, potentially for solid-state Li-S batteries. Lithium phosphorus oxynitride (LiPON) was coated onto LGPS pellets by atomic layer deposition (ALD). It demonstrated great compatibility with LGPS and extends the electrochemical stability window. The third study explored the potential of transferring this electrochemical pretreatment method to the protection of other metal anodes, particularly Mg. The study discovered the surprising catalytic capability of Mg2+ in the polymerization of solvent 1,3-dioxolane (DOL). A layer with poly-DOL component was also found to grow on the surface of Mg metal anodes as a result of the electrochemical pretreatment, and the overpotential of Mg-Mg symmetric cells cycling dropped with the growth of the layer. Future studies are required to test the effectiveness of this method in Mg batteries. Overall, these studies can help to understand the surface chemistry of the electrochemically pretreated Li metal anodes, provide guidelines on the improvement of Li-S batteries and contribute to the development of solid-state Li-S batteries and multivalent metal anode batteries.Item Performance and Enhancement of Solid Oxide Fuel Cell Electrodes Via Surface Modification(2020) Robinson, Ian Alexander; Wachsman, Eric D; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Solid oxide fuel cells (SOFCs) electrochemically convert chemical fuels to usable electricity with high efficiency and can operate on any oxidizable fuel. SOFCs fuel flexibility is accompanied by clean conversion by only converting the fuel to H2O and CO2 without the production of NOx. Additionally, the design of the device allows for a facile integration of carbon capture because the exhaust from the anode and cathode are already separated, allowing for a separated CO2 stream for carbon capture. Technical limitations have prohibited the commercial deployment of SOFCs at an impactful scale and the SOFC market is currently worth <$1 billion. The high operating temperature (T>800 °C) of SOFCs limits possible applications due to high degradation rates within cell components and a high balance of plant costs to use the requisitespecialized high temperature materials. The primary limitation to using to a lower temperature SOFC is the sluggish kinetics of the air electrode or cathode oxygen reduction reaction (ORR) at lower temperatures. This work increases the activity and durability of SOFC electrodes at lower temperatures by utilizing a facile, effective, low cost surface modification technique, defect engineering, and universal cathode scaffold design. Surface modification of SOFC cathodes also prevents the deactivation of the SOFC cathode typically caused by contaminant gasses like CO2 in Sr0.5Sm0.5CoO3-δ (SSC) cathodes. The surface modification technique also shows breakthroughs in the activity of SOFC cathodes SSC and La1-xSrxCo1-yFeyO3-δ (LSCF), allowing the SOFC to operate below 600 °C. The use of an engineered porous functional layer is shown to reduce the electronic leakage current in ceria-based electrolytes. This type of functional layer also increases the overall performance and durability of a SOFC at lower temperatures. Additionally, an approach was developed to deposit any desired cathode electrocatalyst on a universal scaffold to enable low-temperature operation and is compatible with existing cell components. 1 W/cm2 at 550 °C is achieved by utilizing the scaffold infiltration approach and demonstrates that high performance operations at low temperatures is achievable. Finally, the fuel flexibility of metal-supported solid oxide fuel cells (MS-SOFCs) was demonstrated to highlight their potential applications for carbon neutral transportation.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 Improving the performance of solid polymer electrolytes for lithium batteries via plasticization with aqueous salt or ionic liquid(2019) Widstrom, Matthew; Kofinas, Peter; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The goal of this dissertation is to investigate and enable polyethylene oxide (PEO)-based solid polymer electrolytes (SPEs) for lithium batteries. Specifically, two different strategies to plasticize the PEO matrix for improving ion transport are explored. PEO has a propensity to crystallize below 60C, rendering ion motion too slow to be commercially competitive and constituting one of the main challenges of utilizing PEO SPEs as an alternative to organic liquid electrolytes. ILSPEs incorporating ionic liquids (ILs) were fabricated by blending PEO, IL, and corresponding lithium salt followed by hot-pressing the mixture into a homogenous film. Aqueous SPEs (ASPEs) were fabricated by blending a highly concentrated solution of lithium salt in water (aqueous salt) with PEO followed by hot-pressing in a similar manner. Thermal analysis and electrochemical characterization were carried out for both classes of SPEs to assess their suitability as electrolytes and to optimize their composition for performance. Additionally, engineering the interface between the SPE and electrodes remains challenging and is critical for achieving good cycling performance. Multiple approaches for quality interface creation are proposed and carried out. Optimized ILSPE compositions show resistance to oxidation and were able to achieve room temperature conductivity of 0.96 mS/cm at room temperature, a value suitable for commercial application, as well as good rate performance at room temperature cycling in Li/ ILSPE/ lithium iron phosphate configuration. ASPE compositions exhibit conductivities between 0.68 and 1.75mS/cm at room temperature, with proof-of-concept cycling in a LTO/ ASPE/ LMO configuration.