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 Computational Study of Solid-Cathode Interfaces and Coatings for Lithium-Ion Batteries(2021) Nolan, Adelaide M; Mo, Yifei; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)All-solid-state batteries, which use a solid electrolyte, are a promising technology for improving the safety of currently commercialized batteries based on liquid electrolytes. However, to enable all-solid-state batteries with high energy densities, we need to integrate solid electrolytes with high-voltage and high-capacity cathodes. The interface between solid electrolytes and high-energy cathodes is often thermodynamically unstable, which can lead to reactions and the formation of decomposition products which cause high interfacial resistance. One solution to improve resistance and poor contact at the interface is the application of a coating layer, which can act as a physical barrier between the solid electrolyte and the cathode and prevent decomposition. I performed first-principles computation and thermodynamic analyses to study the thermodynamic stability and Li-ion transport in coating layers for solid-solid interfaces. I used a high-throughput systematic analysis of phase diagrams based on a materials database to study the decomposition energy and products of reactions between coating layer chemistries and layered and high-voltage cathodes. My thermodynamic stability analysis revealed that the strong reactivity of lithiated and delithiated cathodes greatly limits the possible choice of materials that are stable with the cathode under high-voltage cycling. The computation results reaffirmed previously demonstrated coating chemistries and identified several new chemistries for high energy cathodes. In particular, I found that lithium quaternary phosphates and lithium ternary fluorides were two promising materials classes, with good stability with high-voltage cathodes and sufficient lithium content to enable Li-ion transport. I next studied the interface stability between solid electrolytes and common cathodes. The lithium garnet solid electrolytes are promising among known solid electrolytes because of their high temperature stability, good stability in air and moisture, and wide electrochemical window, but have limited stability against a variety of cathodes. To guide the development of coating layers for the garnet-cathode interface, I analyzed the stability of garnet with families of lithium ternary oxide (Li-M-O) coating chemistries and revealed factors governing the stability of materials with LLZO garnet and high-energy NMC cathodes. In addition to classifying known coating layers, I provide detailed guiding tables for coating layer selection and identify and discuss several new promising coating layer materials for stabilizing the interface between garnet and high-capacity cathodes. The crystal structure of a coating material plays a major role in transport properties such as Li-ion diffusivity and conductivity, which are required in the coating layer to achieve low interfacial resistance and good battery performance. Alumina is widely used as a coating layer in batteries and other applications, and has decent stability against a wide range of solid electrolytes and cathodes. I used first-principles molecular dynamics simulations and nudged-elastic band calculations to study Li-ion transport and migration barriers in several crystalline polymorphs and amorphous alumina. I found structural features in the Al framework, specifically the Li-Al distance variation, determined migration barriers in both crystalline and amorphous structures. Based on this structure-property relationship, I investigated how Li content, defects and off-stoichiometry changed the Li-ion transport within selected polymorphs, and suggest lowering the Al-ion content as a strategy to achieve stable and Li-diffusive alumina coatings. With this work, I provide an understanding of trends in stability between coating layers, cathodes, and the garnet solid electrolyte, new promising coating layer materials and families, and rational guidance for coating layer design and interfacial engineering for energy dense all-solid-state batteries. My thesis provides guiding principles for selecting materials with long-term cycling stability and good Li diffusivity as coatings for energy dense Li-ion batteries.Item THERMODYNAMICS AND APPLICATION OF A PAIR OF SYNTHETIC NUCLEOBASES FROM ARTIFICIALLY EXPANDED GENETIC INFORMATION SYSTEM(2016) Wang, Xiaoyu; Kahn, Jason D; Biochemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)UV-melting experiments were performed on 9-mer duplexes containing a pair of synthetic nucleobases P·Z, two members of Expanded Genetic Information System (AEGIS), or P, Z containing mismatches. Enthalpy, entropy and free energy change were derived from simulation using two-state transition model. Nearest neighbor thermodynamic parameters of trimers or tetramers containing P·Z pair or P, Z containing mismatches were derived based on known nearest neighbor parameters. Proposed structures based on thermodynamic parameters are discussed. An application using P·Z pair as reverse selection tool of desired nucleic acid secondary structure is described.Item CERAMIC AND COMPOSITE ANODES FOR HYDROCARBON-FUELED INTERMEDIATE TEMPERATURE SOLID OXIDE FUEL CELLS(2014) Gore, Colin; Wachsman, Eric; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The operation of solid oxide fuel cells (SOFCs) using hydrocarbon fuels at temperatures from 500-650 °C has been studied in this dissertation, with a focus on tailoring the fuel electrode (anode) to overcome challenges at these lower operating temperatures. The parameter space for SOFC operation on hydrogen and hydrocarbon fuels is calculated using thermodynamic methods to find equilibrium conditions. The interrelation between parameters that determine cell efficiency and stability, such as the Nernst open circuit voltage, fuel utilization, and tendency to form solid carbon as a reaction product are explored. Methane fueling is found to have a more consistent voltage than hydrogen at high fuel utilizations at temperatures below 650 °C, which correlates with increased theoretical efficiency. Reformed methane and jet fuel compositions that prevent carbon deposition are identified. SOFCs with nickel - gadolinia-doped ceria (GDC) cermet anodes are fabricated and studied using hydrogen and reformed hydrocarbon fuels to determine the kinetic limitations to SOFC operation at 650 °C and below. Operating SOFCs on reformed hydrocarbons gives comparable performance to using hydrogen as a fuel, with as little as a 5% decrease in maximum power density (MPD). Stable performance of 220 mW/cm2 while fueling with reformed jet fuel at 550 °C is observed. Porous ceramic anodes fabricated from GDC are developed to prevent the mechanical damage caused by volume changes of Ni metal in conventional, randomly-mixed cermet anodes. The mechanical properties of the porous ceramics are extensively characterized, and the electrical properties of the scaffold anode are measured after infiltrating with metals. The porous ceramics attain strengths of >100 MPa, and have similar conductance to Ni-GDC cermet anodes but with ~70% less metal. SOFCs using these anodes have a MPD within 15% of cermet anode cells in H2, but show stable operation at 120 mW/cm2 at 600 °C on methane for >72 hours while cermet anodes are destroyed by solid carbon formation. A mixed-conducting, single-phase material based on BaCeO3 was developed for possible use as a metal-free anode. The stability of the material in CO2 was improved through Zr and Nb doping on the B-site.Item How to Prove a Differential Form of the Generalized Second Law(2011) Wall, Aron Clark; Jacobson, Theodore A; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A new method is given for proving the semiclassical generalized second law (GSL) of horizon thermodynamics. Unlike previous methods, this method can be used to prove that entropy increases for arbitrary slices of causal horizons, even when the matter fields falling across the horizon are rapidly changing with time. Chapter I discusses how to define the GSL, and critically reviews previous proofs in the literature. Chapter II describes the proof method in the special case of flat planar slices of Rindler horizons, assuming the existence of a valid renormalization scheme. Chapter III generalizes the proof method to arbitrary slices of semiclassical causal horizons, by the technique of restricting the fields to the horizon itself. In the case of free fields it is clear that this restriction is possible, but for interacting fields the situation is murkier. Each of the three parts has been, or will be, separately published elsewhere.Item Properties of a DTN Packet Forwarding Scheme Inspired By Themodynamics(2010) Mathew, Bipin; La, Richard J.; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In this thesis, we develop a discrete time model of a recently proposed algorithm, inspired by thermodynamics, for message routing in Disruption Tolerant Networks (DTNs). We model the evolution of the temperature at the nodes as a stochastic switched linear system and show that the temperatures converge in distribution to a unique stationary distribution that is independent of initial conditions. The proof of this result borrows tools from Iterated Random Maps (IRMs) and Queuing theory. Lastly, we simulate the proposed algorithm, using a variety of mobility models, in order to observe the performance of the algorithm under various conditions.Item Protein folding and amyloid formation in various environments(2008-11-21) O'Brien, Edward Patrick; Thirumalai, Devarajan; Brooks, Bernard; Chemical Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Understanding and predicting the effect of various environments that differ in terms of pH and the presence of cosolutes and macromolecules on protein properties is a formidable challenge. Yet this knowledge is crucial in understanding the effect of cellular environments on a protein. By combining thermodynamic theories of solution condition effects with statistical mechanics and computer simulations we develop a molecular perspective of protein folding and amyloid formation that was previously unobtainable. The resulting Molecular Transfer Model offers, in some instances, quantitatively accurate predictions of cosolute and pH effects on various protein properties. We show that protein denatured state properties can change significantly with osmolyte concentration, and that residual structure can persist at high denaturant concentrations. We study the single molecule mechanical unfolding of proteins at various pH values and varying osmolyte and denaturant concentrations. We find that the the effect of varying solution conditions on a protein under tension can be understood and qualitatively predicted based on knowledge of that protein's behavior in the absence of force. We test the accuracy of FRET inferred denatured state properties and find that currently, only qualitative estimates of denatured state properties can be obtained with these experimental methods. We also explore the factors governing helix formation in peptides confined to carbon nanotubes. We find that the interplay of the peptide's sequence and dimensions, the nanotube's diameter, hydrophobicity and chemical heterogeneity, lead to a rich diversity of behavior in helix formation. We determine the structural and thermodynamic basis for the dock-lock mechanism of peptide deposition to a mature amyloid fibril. We find multiple basins of attraction on the free energy surface associated with structural transitions of the adding monomer. The models we introduce offer a better understanding of protein folding and amyloid formation in various environments and take us closer to understanding and predicting how the complex environment of the cell can effect protein properties.Item Using Recombinant PCR to Study Sequence Polymorphisms in a Family of Compact Albumin Binding Domains(2005-11-14) Rozak, David Anthony; Bryan, Philip N; Molecular and Cell Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Sixteen homologs of a compact albumin binding domain were previously identified in six proteins and four bacterial species. These domains, which exhibit varied affinities for different albumins, have been shown to support bacterial growth in vitro, and may contribute to host specificity. This dissertation describes the development of a robust PCR-based recombination technique, which is applied to representatives of the albumin binding domain to identify and understand the impact of sequence polymorphisms on domain stability and function. Analysis of phage-selected recombinants highlights the potential impact of multiple mutations in stabilizing the selected domains and improving albumin binding through gains in hydrophilic surface area, direct modifications to the binding interface, and subtle changes in the position of the third helix. The most common mutant was encoded by three fourths of the selected phage and exhibited 5 and 10 fold increases in human and guinea pig albumin binding constants compared to the wild type streptococcal domain (G148-GA3). This study serves to validate further the application of in vitro recombination and phage display in the analysis of sequence polymorphisms. The recombination technique itself is shown to be well suited for producing multiple recombination events among compact heterologous domains and appears to offer several advantages over traditional DNA shuffling techniques.