Chemical and Biomolecular Engineering Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2751
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Item INTERFACE DESIGN FOR ALL-SOLID-STATE LITHIUM METAL BATTERIES(2022) He, Xinzi; Wang, Chunsheng; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Lithium-ion batteries (LIBs) have expanded their application from electronics to electric vehicles (EVs). To ease the safety concerns and the “range anxiety”, solid-state lithium batteries (SSLBs) become a more attractive choice. The replacement of flammable and toxic liquid electrolytes with solid-state electrolytes (SSEs) makes it a safer option. The utilization and compatibility of high specific capacity materials such as sulfur cathode and lithium-metal anode increase the cell energy density. However, SSLBs still face challenges towards practical application, which mainly from the solid-solid contact nature on the interfaces. On the anode side, lithium dendrite growth and high interface resistance both hindered the longevity of the cells. On the cathode side, low initial Coulombic efficiency (CE) and low capacity utilization of sulfur obstructed the realization of high loading cathodes.In this dissertation, I addressed both challenges of dendrite and contact on the anode side by adding strontium into lithium anodes. Different from all previous metal/metal oxide coating on garnet or Li alloy anodes that form lithiophilic interlayer, a lithiophilic/lithiophobic bifunctional layer is formed to reduce the interfacial resistance and to suppress the growth of lithium dendrite, which is confirmed by comprehensive material characterizations, electrochemical evaluations, and simulations. The optimum Li-Sr | garnet | Li-Sr symmetric cells achieve a high critical current density (CCD) of 1.3 mA/cm2 and can be cycled for 1,000 cycles under 0.5 mA/cm2 at room temperature, providing a new strategy for high-performance garnet SSLB. Furthermore, I (1) verified the importance of lithiophobic on dendrite suppression by discovering and successfully constructing the highest interface energy (γ, against lithium) material ever reported among all lithium compounds that can be formed on the electrolyte | anode interface; (2) revealed the impact of anode properties on the interface by enhancing the Li self-diffusivity by a co-doping method, achieved an outperformed critical loading of 4.1 mAh/cm2 at 1.0 mA∙cm-2 at room temperature. On the cathode side, I tackled both low CE and low capacity utilization issues by promoting both Li+ and e- transportation across the cathode | SSE interface, resulting in high capacity utilization of 96.5% and high capacity retention of 88.8% after 145 cycles at a high loading of 4.0 mAh cm-2 under room temperature in Li6PS5Cl based SSLB.Item HIGH-SAFETY ELECTROLYTES DESIGN FOR HIGH ENERGY DENSITY BATTERY DEVICES(2021) Zhang, Jiaxun; Wang, Chunsheng CW; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Recently, the market share of lithium-ion batteries (LIBs) increase rapidly in the global energy market, while accidents related to fires and explosions of LIBs reported worldwide in the past several years, thus battery safety is a vital prerequisite for battery application in our daily life. The flammable organic solvent in the electrolyte of the battery is the main source that leads to fires and explosions of batteries. Designing intrinsically safe electrolytes is the key to enhancing the safety properties of batteries. Fluorinated organic electrolytes, polymer electrolytes, and aqueous electrolytes are attractive due to their inherent non- or less-combustibles. However, the energy density, cycle stability, and battery cycle life of the LIBs using the above electrolyte systems are far from commercial batteries due to poor solid electrolyte interphase (SEI) and cathode electrolyte interphase (CEI). In this dissertation, we designed SEI/CEI on anode/cathode surfaces in fluorinated organic electrolytes, polymer electrolytes, and aqueous electrolytes to enhance battery performance. Specifically, 1. By building a highly stable CEI on a high-voltage LiCoO2 cathode, we improved the energy density of fluorinated organic electrolyte batteries. 2. By introducing UV-curable polymer into the organic electrolytes, we lowered the flammability of the sodium batteries and enhanced the energy density of the sodium battery system with stable CEI on sodium cathode. 3. By limiting the water activity in the bulk electrolyte and constructing an effective SEI layer on anode surface, we expanded the electrochemical stability window of the aqueous electrolytes. We seek to understand the working mechanism of SEI/CEI in different high-safety electrolyte systems. The corresponding electrochemistry, thermodynamics, kinetics, and reaction reversibility are studied in this work.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 ACTIVE AND PASSIVE MICROFLUIDICS FOR SAMPLE DISCRETIZATION, MANIPULATION AND MULTIPLEXING(2020) Padmanabhan, Supriya; DeVoe, Don L; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The use of microfluidic technology to compartmentalize an initial sample into discrete and isolated volumes is an important step for many biological and chemical applications, that allows molecules, cells, particles, reagents, and analytes to be spatially constrained, providing unique benefits for their characterization, sorting, and manipulation with low reagent consumption. Discretization can also increase the overall throughput and enable multiplexing. In this dissertation, two platforms are described to enable microfluidic sample discretization and manipulation. First, (2D) microwell arrays fabricated in thermoplastic cyclic olefin copolymer (COP) are explored as a new approach toward the development of high throughput, low-cost components in disposable diagnostics by utilizing a passive discretization technique. Performance of various 2D array designs is characterized numerically and experimentally to assess the impact of thermoplastic surface energy, fluid flow rate, and device geometry on sample filling and discretization. The design principles are used to successfully scale up the platform without affecting device performance. Loop-mediated isothermal amplification (LAMP) on chip is used to demonstrate the platform’s potential for discretized nucleic acid testing. Next, pin spotting in nanoliter-scale 2D arrays is demonstrated as technique for high resolution reagent integration to enable multiplexed testing in diagnostics. The potential for nucleic-acid diagnostics is evaluated by performing rolling circle amplification (RCA) on chip with integrated reagents. Finally, an innovative platform enabling complex discretization and manipulation of aqueous droplets is presented. The system uses simple membrane displacement trap elements as an active technique to perform multiple functions including droplet discretization, release, metering, capture, and merging. Multi-layer polydimethylsiloxane (PDMS) devices with membrane displacement trap (MDT) arrays are used to discretize sample into nanoliter scale droplet volumes, and reliably manipulate individual droplets within the arrays. Performance is characterized for varying capillary number flows, membrane actuation pressures, trap and membrane geometries, and trapped droplet volumes, with operational domains established for each platform function. The novel approach to sample digitization and droplet manipulation is demonstrated through discretization of a dilute bacteria sample, metering of individual traps to generate droplets containing single bacteria, and merging of the resulting droplets to pair the selected bacteria within a single droplet.Item FUNCTIONAL PARTICLE GENERATION BY AEROSOL-ASSISTED PROCESSES(2018) Liang, Yujia; Ehrman, Sheryl H; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Aerosol-assisted processes are continuous with short residence times, simple operating procedures, and facile equipment requirements. They are scalable and promising for fabrication of functional particles as conductive pastes in solar cell metallization and interference packaging, electrode materials in energy storage devices, and photocatalysts in energy conversion. Although aerosol-assisted processes have long been used in manufacturing and their fundamentals have been intensively explored, further investigation is still required to better understand the particle formation mechanisms of different aerosol-assisted processes. In this dissertation, three different aerosol-assisted processes are investigated, spray pyrolysis, colloidal spray pyrolysis (CSP), and spray drying. These processes can be conducted under mild reaction conditions with simple operation procedures. The product particles are controllable. The effects of process variables on the product particles are studied. Furthermore, the prospects of applying these three aerosol-assisted processes in generating functional particles in applications, including solar cell metallization, battery, and photocatalysis are assessed. Part 1) includes Chapters 3-5. I first present Cu-Sn binary particle generation by spray pyrolysis. Through studying the particle oxidation behaviors under different reaction conditions, the Cu-Sn binary particles exhibit high oxidation-resistance. The one-dimensional and two-dimensional structures fabricated by direct printing inks containing Cu-Sn powders display low resistivity. They all suggest that Cu-Sn binary particles produced by spray pyrolysis are promising materials in the inks in printed electronics and in the conductive pastes in solar cell metallization and interference packaging. In Part 2), Chapters 6, a novel aerosol-assisted process, CSP, is developed. This process addresses one restriction of conventional spray pyrolysis which can only be used to fabricate particles from precursor solutions containing high-solubility salts. By applying CSP, tin@carbon (Sn@C) composite particles are produced with controllable interior structures. These composite particles exhibit high-performance as the anode materials for Li-ion and Na-ion batteries. In Part 3), Chapter 7, spray drying is utilized to fabricate photocatalysts from precursor solutions containing SnO2 colloids and edge-oxidized graphene oxide (eo-GO) sheets. The particle morphology, element distribution, and band structures were investigated by various tools. The photocatalytic activity of the composite particles is five times that of commercialized TiO2 (P25) in reducing CO2 into CH4.Item ELECTROCHEMICAL COMPRESSION WITH ION EXCHANGE MEMBRANES FOR AIR CONDITIONING, REFRIGERATION AND OTHER RELATED APPLICATIONS(2017) Tao, Ye; Wang, Chunsheng; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The refrigeration industry in the US are facing two main challenges. First of all, the phase down of HFCs in the future would require industries to seek alternative refrigerants which do not contribute to global warming. Secondly, the mechanical compressor in the small scale cooling system with a large energy impact is reaching its limitation due to heat transfer and manufacturing tolerances. Therefore there is an urgent need to develop a highly efficient compression process that works with environmentally friendly refrigerants. And the electrochemical compressor is developed to meet these requirement based on the following reasons. First of all, the electrochemical compressor can achieve an isothermal compression efficiency of greater than 90%. It also operates without moving parts, lubrication and noise. Most importantly, the compressor works with environmentally friendly refrigerants. In this thesis, three distinct electrochemical compression processes were studied. The first study is focused on modeling a metal hydride heat pump driven by electrochemical hydrogen compressor. The performance of the cooling-generating desorption reactor, the heating-generating absorption reactor, as well as the whole system were demonstrated. The results showed the superior performance of electrochemical hydrogen compressor over mechanical compressor in the system with optimized operating condition and COP. The second study demonstrated the feasibility of electrochemical ammonia compression with hydrogen as a carrier gas. The reaction mechanisms and the compression principle were verified and the compression efficiency was measured to be greater than 90%. The technology can be applied to ammonia vapor compression refrigeration cycle and ammonia storage. The third study is about developing and studying the electrochemical CO2 compression process with oxygen as a carrier gas. The reaction mechanism was verified and compared for both Pt and CaRuO3 electro-catalysts. And the latter was selected due to better CO2 and O2 absorption. The technology can potentially be applied in carbon dioxide transcritical refrigeration cycle and carbon capture. In conclusion, the electrochemical compression is a promising technology with higher compression efficiency and would bring a revolutionary change to the compressor engineering industry and global refrigeration and air conditioning market. It can also be used in fuel storage and separation based on the selective properties of the ion exchange membrane.Item COMPUTATIONAL FLUID DYNAMICS SIMULATIONS OF A PIPELINE ROTOR-STATOR MIXER(2017) Minnick, Benjamin Austin; Calabrese, Richard V; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Rotor-stator mixers provide high deformation rates to a limited volume, resulting in intensive mixing, milling, and/or dispersion/emulsification. CFD simulations of mixers provide flow field information that benefit designers and end users. This thesis focuses on transient three-dimensional simulations of the Greerco pipeline mixer, using ANSYS FLUENT. The modeled unit consists of two conical rotor-stator stages aligned for axial discharge flow. Flow and turbulence quantities are studied on a per stator slot and per rotor stage basis. Comparisons are made between the LES and RANS realizable k-ε model predictions at various mesh resolutions. Both simulations predict similar mean velocity, flow rate, and torque profiles. However, prediction of deformation rates and turbulence quantities, such as turbulent kinetic energy and its production and dissipation rates, show strong dependencies on mesh resolution and simulation method. The effect of operating conditions on power draw, throughput, and other quantities of practical utility are also discussed.Item THE UPGRADING OF METHANE TO AROMATICS OVER TRANSITION METAL LOADED HIERARCHICAL ZEOLITES(2017) WU, YIQING; Liu, Dongxia; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)With the boom of shale gas production, the conversion of methane to higher hydrocarbons (MTH) promises a great future as the substituent for hydrocarbon production from crude oil based processes. Among various MTH processes, direct methane aromatization (DMA) is promising since it can achieve one-step methane valorization to aromatics. The molybdenum/zeolite (Mo/MFI or Mo/MWW) has been the most active catalyst for the DMA reaction, which, however, is impeded from industrial practice due to the rapid deactivation by coke deposition. To address this challenge, in this work, transition metal loaded hierarchical 2 dimensional (2D) lamellar MFI and MWW zeolites have been studied as catalysts for the DMA reaction. The effects of micro- and mesoporosity, external and internal Brønsted acid sites, as well as particle size of 2D lamellar zeolites on the DMA reaction have been investigated. Firstly, the spatial distribution of Brønsted acid sites in 2D lamellar MFI and MWW zeolites has been quantified by a combination of organic base titration and methanol dehydration reaction. The unit-cell thick 2D zeolites after Mo loading showed mitigation on deactivation, increase in activity, and comparable aromatics selectivity to the Mo loaded 3D zeolite analogues. A detailed analysis of the DMA reaction over Mo/hierarchical MFI zeolites with variable micro- and mesoporosity (equivalent to variation in particle sizes) showed a balance between dual porosity was essential to modulate the distribution of active sites (Mo and Brønsted acid sites) in the catalysts as well as the consequent reaction and transport events to optimize performance in the DMA reaction. External Brønsted acid sites have been proposed to be the cause of coke deposition on Mo/zeolite catalysts. Deactivation of the external acid sites have been practiced to improve the catalyst performances in the DMA reaction in this work. Atomic layer deposition (ALD) of silica species was conducted on the external surface of 2D lamellar MFI and MWW zeolites to deactivate the external acid sites in Mo/2D lamellar zeolites for the DMA reaction. Another strategy to deactivate external acid sites in Mo/zeolite catalysts was the overgrowth of 2D lamellar silicalite-1 on the microporous zeolites. The as-prepared catalysts showed higher methane conversion and aromatics formation as well as higher selectivity to naphthalene and coke in comparison with Mo loaded microporous analogues.Item Lateral Capsule Migration in Microfluidic Channels(2017) Wang, Yiyang; Dimitrakopoulos, Panagiotis; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A capsule motion inside a microfluidic channel has attracted a lot of attention in recent decades owing to its important applications in industrial, pharmaceutical and physiological systems such as in cell sorting, targeted drug delivery and blood flow. In this dissertation, we computationally investigate an elastic capsule's lateral migration inside a constricted microfluidic device under Stokes flow conditions. We use the Membrane Spectral Boundary Element (MSBE) method to determine the capsule dynamics due to its high computational accuracy and versatility in dealing with complex solid geometries. In the bounded Poiseuille flow of the microfluidic constriction, a capsule, placed initially off-centered will migrate away from the wall and move toward the channel centerline. The capsule's lateral migration behavior is caused by the combination of the wall effects due to the existence of the channel boundary, the shear gradient generated by the non-linear velocity distribution of the flow, and the lift force created by the capsule deformation. We use a constricted device instead of a straight channel to do the simulations, because the capsule's lateral migration in a straight channel is too slow to be observed easily, while the existence of the converging connection of the constricted device increases the capsule's lateral velocity and thus facilitates its migration. The main goal of our research is to investigate the effects of the capsule's physical properties on its lateral migration behavior. We released various deformable capsules at different initial positions, membrane hardness, viscosity ratios, and capsule volumes inside the constricted channel and computed their deformation behavior and migration trajectories. Our results show that changing a capsule's viscosity ratio or the membrane hardness does not strongly affect the capsule's lateral migration due to the capsule's weak inner circulation. On the other hand, changing the capsule's initial position and capsule volume strongly affect its migration trajectories. Thus soft particles with different sizes can be separated and identified.Item Beyond Li ion: Rechargeable Metal Batteries based on Multivalent Chemistry(2017) Gao, Tao; Wang, Chunsheng; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The development of advanced battery technology with lower cost and higher energy density is important since various mobile applications are becoming indispensable in our daily life. While Li chemistry has approached its theoretical limit after several decades’ increment improvement, the potential of multivalent chemistry (Mg, Al, etc.) remains unexplored. Compared to Li ion chemistry, multivalent chemistry provides many intriguing benefits in terms of lowering cost and increasing energy density. First of all, minerals containing multivalent element such as Mg, Al, and etc. are much more abundant and cheaper than Li. Second, multivalent metals (Mg, Al etc.) can be directly used as anode materials, ensuring much higher anode capacity than graphite currently used in Li-ion battery. Third, the divalent or trivalent nature of the electroactive cation (Mg2+and Al3+) also promise high capacity for intercalation cathodes because the capacity of these materials are limited by their available ion occupancy sites in the crystal structure instead of its capability to accept electrons. In this dissertation, I detailed our efforts in examining some redox chemistries and materials for the use of rechargeable batteries based on multivalent metal anodes. They include intercalation cathode (TiS2) and conversion cathode (sulfur, iodine). We studied their electrochemical redox behavior in the corresponding chemistry, the thermodynamics, kinetics as well as the reaction reversibility. The reaction mechanism is also investigated with various macroscopic and spectroscopic techniques.