A. James Clark School of Engineering
Permanent URI for this communityhttp://hdl.handle.net/1903/1654
The collections in this community comprise faculty research works, as well as graduate theses and dissertations.
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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 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 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 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 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.Item THE APPLICATION OF MICRODEVICES FOR INVESTIGATING BIOLOGICAL SYSTEMS(2018) Shang, Wu; Bentley, William E; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The gastrointestinal (GI) tract is a complex ecosystem with cells from different kingdoms organized within dynamically-changing structures and engaged in complex communication through a network of molecular signaling pathways. One challenge for researchers is that the GI tract is largely inaccessible to experimental investigation. Even animal models have limited capabilities for revealing the rich spatiotemporal variation in the intestine and fail to predict human responses due to genetic variation. Exciting recent advances in in vitro organ model (i.e., organ-on- chips (OOC)) based on microfluidics are offering new hope that these experimental systems may be capable of recapitulating the complexities in structure and context inherent to the intestine. A current limitation to OOC systems is that while they can recapitulate structure and context, they do not yet offer capabilities to observe or engage in the molecular based signaling integral to the functioning of this complex biological system. This dissertation focuses on developing microfluidic tools that provide access to interrogating signaling events amongst populations in the GI tract (e.g., microbes and enterocytes). First, a membrane-based gradient generator is built to establish linear and stable chemical gradients for investigating gradient-mediated behaviors of bacteria. Specifically, this platform enables the study of bacterial chemotaxis and potentially facilitates the development of genetically rewired lesion-targeted probiotics. Second, “electrobiofabrication” is coupled with microelectronics, for the first time, to create molecular-to-electronic (i.e., “molectronic”) sensors to observe and report the dynamic exchange of biochemical information in OOC systems. Last, to address the issue of poor compatibility between OOCs and sensors, we assemble OOCs with molectronic sensors in a modular format. The concept of modularity greatly reduces the system complexity and enables sensors to be built immediately before applications, avoiding functional decay of active biorecognition components after long-term device storage and use. We envision this work will “open” OOC systems for molecular measurement and interrogation, which, in turn, will expand the in vitro toolbox that researchers can use to design, build and test for the investigation of GI disease and drug discovery.Item IN-OPERANDO ELECTRON MICROSCOPY AND SPECTROSCOPY OF INTERFACES THROUGH GRAPHENE-BASED MEMBRANES(2017) Yulaev, Alexander; Leite, Marina S.; Kolmakov, Andrei; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Electron microscopy and spectroscopy (EMS) techniques enable (near-) surface and interfacial characterization of a variety of materials, providing insights into chemical/electrochemical and morphological information with nanoscale spatial resolution. However, the experimental realization of EMS in liquid/gaseous samples becomes problematic due to their incompatibility with high vacuum (HV) conditions. To perform EMS under elevated pressure conditions, electron transparent membranes made of thin C, SiO2 or/and Si3N4 are implemented to isolate a liquid/gas sample from HV environment. Nevertheless, even a few ten nanometer thick membrane deteriorates signal quality due to significant electron scattering. The other challenge of EMS consists in inaccessibility to probe solid state interfaces, e.g. solid-state Li-ion batteries, which makes their operando characterization problematic, limiting the analysis to ex situ and postmortem examination. The first part of my thesis focuses on developing an experimental platform for operando characterization of liquid interfaces through electron transparent membranes made of graphene (Gr)/graphene oxide (GO). The second part is dedicated to probing Li-ion transport at solid-state-battery surfaces and interfaces using ultrathin carbon anodes. I demonstrated the capability of GO to encapsulate samples with different chemical, physical, and biological properties and characterized them using EMS methods. I proposed and tested a new CVD-Gr transfer method using anthracene as a sacrificial layer. Characterization of transferred Gr revealed the advantages of our route with respect to a standard polymer based approach. A novel platform made of an array of Gr-capped liquid filled microcapsules was developed, allowing for a wide eld of view EMS. I showed the capability of conducting EMS analysis of liquid interfaces through Gr membranes using energy-dispersive X-ray spectroscopy, photoemission electron microscopy, and Auger electron spectroscopy. Using operando SEM and AES, I elucidated the role of oxidizing conditions and charging rate on Li plating morphology in all-solid-state Li-ion batteries with thin carbon anodes. Operando EMS characterization of Li-ion transport at battery interfaces with carbon or Gr anodes will provide valuable insights into safe all-solid-state Li-ion battery with enhanced performance.Item Solid Oxide Ionic Materials For Electrochemical Energy Conversion And Storage(2015) Ruth, Ashley Lidie; Wachsman, Eric D; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Solid state ionic materials can be utilized in components of both solid oxide fuel cells and lithium ion batteries. Solid oxide fuel cells (SOFCs) are devices used to convert chemical energy into useful electrical energy. The higher temperatures required to effectively conduct oxygen vacancies is a material limitation that prevents the implementation of this technology in today's society. Our group has developed the novel incorporation of a bilayer electrolyte utilizing the high conductivity properties of the cubic fluorite bismuth oxide material in the low temperature regime at 650 °C and below. This phase is stabilized by single and double doping of Er, Dy-W, Dy-Ce, and Dy-Gd chemistries in this study. Conductivity measurements through electrochemical impedance spectroscopy champion (Bi0.88Dy0.08Gd0.04)2O3 as the most suitable electrolyte for future testing in SOFCs. Using the bilayer system in button type cells, the layer thickness ratio is optimized for highest open circuit voltage. Using neutron diffraction was used to better understand the activation energy change in conductivity in DWSB due to phase transformation that masked oxygen ordering at lower temperatures. Stabilized bismuth oxides are incorporated into a suitable composite cathode via an in-situ nano-scale mixing with La0.8Sr0.2MnO3-δ, improving the oxygen reduction reaction kinetics. Utilizing lessons from ceramic materials synthesis in SOFCs, cathode materials for Li-ion batteries were synthesized. In previous work, LixMn2O4-yClz spinel demonstrated enhanced charge potential and discharge potential while maintaining reversibility. However the original method for synthesis was extremely cumbersome. Using the simple glycine-nitrate reaction, we could fabricate an operating button cell starting from raw powders in less than 8 hours. X-ray diffraction and x-ray fluorescence confirm spinel structure and maintenance of chlorine through ignition respectively. In demonstrating favorable charge/discharge performance and cyclability, we considered the benefits of B-site doping of the spinel. For the first time LixMn2-wFewO4-yClz was also easily synthesized and tested for more than 250 charge-discharge cycles with 98% capacity retention. Similarly, Ni is introduced to the LixMn2O4-yClz spinel in order to take advantage of the intrinsic redox couple of Ni2+/Ni4+ at 4.7V and demonstrate reversibility from 5.0 V to 2.0 V.Item SOFT HYDROGEL BATTERIES: THE DANIELL CELL CONCEPTUALIZED IN HYBRID HYDROGELS(2015) Goyal, Ankit; Raghavan, Srinivasa R; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Energy storage devices such as batteries are important elements in many electronic devices. Currently, researchers are seeking to create new electronic devices that are "soft", i.e., bendable and stretchable. However, the batteries that power such devices are still mostly hard structures. In the current thesis, we have attempted to develop a "soft" battery out of hydrogels. Specifically, we have made a soft version of the Daniell Cell, which is a classic electrochemical cell. Our design involves a hybrid gel composed of three distinct layers. The top and bottom layers are gels swollen with a zinc salt and a copper salt, respectively, while the middle layer is akin to a "salt bridge" between the two. The hybrid gel is made by a polymerization technique developed in our laboratory and it retains good mechanical integrity (i.e., the individual layers do not delaminate). Zinc and copper foils are then attached to the hydrogel, thus creating an overall battery, and its discharge performance is reported. One unique aspect of these gel batteries is that they can be dehydrated and stored in a dry form, whereupon they are no longer batteries. In this inactive state, the materials are safe and light to transport. Upon rehydration, the gels revert to being functional batteries. This concept could be useful for military or other applications where an emergency energy storage is needed.