Browsing by Author "Ferraris, John P."
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Item Carbon Nanofibers Derived From Polymer Blends as Electrodes for High Performance Supercapacitors(2021-12-01T06:00:00.000Z) Malekpour, Soheil; Ferraris, John P.; Dragovic, Vladimir; Balkus, Jr., Kenneth J.; Smaldone, Ronald A.; Stefan, Mihaela C.Nowadays, generation and storage of energy is vital in our life. Supercapacitors as one the energy storage devices are safe and can store high amount of energy and deliver it in a fast manner. Also, they can be used in a wide range of temperatures and show a high cyclability, which make them proper candidates for broad range of applications. However, compared to other common energy storage systems such as batteries, their energy density is low. Carbon materials are known as the most common materials for making electrodes for supercapacitors. To achieve supercapacitors with high energy density it is important to use the right materials as electrodes with proper morphologies. Two main energy storage mechanisms include electric double layer capacitance which energy is stored electrostatically, in the interface of electrode and electrolyte and pseudocapacitance, in which fast redox reactions occur at or near surface of electrodes. In double layer capacitors, high surface area and controlled pore size and pore distribution is required hence, choice of carbon precursors to obtain these properties is essential. Chapter 1 gives basic information about energy storage systems and mechanisms involved in supercapacitors. Also, carbon nanofibers as one of the popular materials for making electrodes are introduced and how they are made is explained. Chapter 2 introduces polymer blends derived from polyacrylonitrile (PAN) and polymethacrylic acid (PMAA) as suitable candidates for making high surface area carbon fibers with high performance. It shows PMAA can be used as a new degrading polymer which, blended with PAN, can result in phase-separation in carbon fibers. Chapter 3 describes fabricating hybrid materials as electrodes for supercapacitors using PANPMAA blend as carbon source and cobalt oxide. It is shown how using PMAA as a chelating polymer can enhance the distribution and uniformity of metal oxide nanoparticles on the carbon fibers which improve the performance of supercapacitors compared to the ones that are made only with PAN.Item Changing Brain Networks Through Non-Invasive NeuromodulationTo, Wing Ting; De Ridder, Dirk; Hart, John, Jr.; Vanneste, Sven; Wang, Zijie; Perananthan, Sahila; Panangala, Samitha D.; Ferraris, John P.; Balkus, Kenneth J.; To, Wing Ting; Hart, John, Jr.; Vanneste, SvenBackground/Objective: Non-invasive neuromodulation techniques, such as repetitive Transcranial Magnetic Stimulation (rTMS) and transcranial Direct Current Stimulation (tDCS), have increasingly been investigated for their potential as treatments for neurological and psychiatric disorders. Despite widespread dissemination of these techniques, the underlying therapeutic mechanisms and the ideal stimulation site for a given disorder remain unknown. Increasing evidence support the possibility of non-invasive neuromodulation affecting a brain network rather than just the local stimulation target. In this article, we present evidence in a clinical setting to support the idea that non-invasive neuromodulation changes brain networks. Method: This article addresses the idea that non-invasive neuromodulation modulates brain networks, rather than just the local stimulation target, using neuromodulation studies in tinnitus and major depression as examples. We present studies that suppo rt this hypothesis from different perspectives. Main Results/Conclusion: Studies stimulating the same brain region, such as the dorsolateral prefrontal cortex (DLPFC), have shown to be effective for several disorders and studies using different stimulation sites for the same disorder have shown similar results. These findings, as well as results from studies investigating brain network connectivity on both macro and micro levels, suggest that non-invasive neuromodulation affects a brain network rather than just the local stimulation site targeted. We propose that non-invasive neuromodulation should be approached from a network perspective and emphasize the therapeutic potential of this approach through the modulation of targeted brain networks.Item Design and Synthesis of Polymer Nanocomposites for Additive Manufacturing(May 2023) Perera, Sachini Dilinika 1992-; Penev, Kaloyan; Smaldone, Ronald A; Ferraris, John P.; Biewer, Michael C.; Gassensmith, Jeremiah J.Additive manufacturing or 3D printing is a process where the materials are deposited in a layer- by-layer fashion according to a pre-designed computer aided file to fabricate required geometries. There are a wide range of materials from thermoplastics, polymeric resins, metals, alloys, nanocomposites, to hydrogels that have been used in 3D printing, as well as several different types of processes are available for 3D printing. Fused filament fabrication, ink jet printing, stereolithography (SLA) and digital light projection (DLP) can be recognized as the most popular and affordable techniques. This manufacturing technique is very promising as a user friendly, customizable setup without the need to manufacture through expensive molding processes or producing waste from subtractive manufacturing methods such as milling. Even though it possesses all the advantages, poor interlayer adhesion, limited mechanical properties, low resolution and rough surface finish is limiting its applications at large scale. Vat photopolymerization 3D printing techniques provide better resolution as high as 10 μm for the printed parts from SLA and DLP compared to other 3D printing techniques. Here, a photo resin that contains photocurable monomers and oligomers, crosslinkers are polymerized in a print vat using UV irradiation in the presence of a photoinitiator. The photo printed structures show fine resolution and smooth surface finish, yet the mechanical properties of the printed parts are inadequate for end use applications. To address this limitation different approaches were taken and studied, thus the overall goal of this research was to enhance properties of 3D printed objects and to develop methodologies to improve photo printing processes that would ultimately improve intrinsic properties of the photo printed materials. Chapter 1 of the dissertation provides a literature review about 3D printing techniques, materials, and the limitations of additive manufacturing. This chapter further discusses the approaches taken to overcome the limitations by introducing ways to improve the mechanical properties. Chapter 2 describes our work in enhancing mechanical properties through a nanofiller derived from Kevlar and how we successfully 3D printed photoresin formulations using stereolithography without compromising printability. We discuss a methodology that can be used to incorporate unprocessable fibrous fillers in a resin formulation. Chapter 3 provides insights about how supramolecular interactions provide 3D printable materials with noncovalent cross-linking and stimuli-responsive properties to improve their processability and functionality. We evaluated urea formulations with aliphatic and aromatic sidechains and showed physical evidence for the presence of hydrogen bonding using variable temperature Fourier transform infrared (VT-ATR-FTIR) spectroscopy and van’t Hoff analysis. The self- healing efficiency of these formulations was characterized by measuring the recovery of their tensile mechanical properties. Chapter 4 describes our approach to process Metal Organic-Frameworks in vat photopolymerization. A new method is introduced to construct complex structures with fine features by integrating high loading weight percentages of MOF crystals to a photocurable acrylate formulation. Through free radical polymerization in a DLP setup, MOF loaded nanocomposites were 3D printed, and its catalytic performances were studied.Item Development of Graphene-like Carbons for Energy Storage and the Sequestration of Lanthanide and Actinide Elements(2021-12-01T06:00:00.000Z) Brown, Alexander Travis; Balkus, Jr., Kenneth J.; Akbar, Mohammad; Ferraris, John P.; Stefan, Mihaela C.; Yang, Duck J.Porous materials are solids which contains voids also known as pores. Porous materials are used in a variety of applications that require a high surface area as well as controllable pore sizes and pore architectures. Porous silica and carbons can be used in applications like as drug delivery, gas separations, energy storage, and the sequestration of elements. Particularly, porous carbona can be synthesized by chemical vapor deposition and can have exceptional porosity as well as high electrical conductivity. The development of carbons that have both high porosity and high electrical conductivity has surged since the discovery of graphene-like carbons. The ability to form various type of porous carbons and understanding of the underlying growth mechanism is a trending research topic. Furthermore, porous carbons can be used for extracting and selectively separating rare earth elements, which are critical elements vital to the production of magnets, batteries, metals, catalysts, glass, lighting, pigments, ceramics, aerospace products, and various other textiles. Herein various high surface area and electrically conductive porous carbons are synthesized and characterized; and a mechanism for the carbon synthesis is proposed. Then the porous carbons are evaluated for the performance in liquid-solid extractions of lanthanide and actinide elements and supercapacitors applications.Item Extraction of Seismic Properties and Models From, and Full Waveform Inversion of, Dispersed Seismic Waves(2022-12-01T06:00:00.000Z) Ren, Li; Zhu, Hejun; Ferraris, John P.; McMechan, George A.; Ferguson, John F.; Stern, Robert J.Surface waves, which propagate along boundaries between two different media, play an important role in resolving geological structures of different scales targeted from global seismology, exploration seismology, geotechnical engineering, to nondestructive testing. Over the past half century or so, different methods have been explored to process and invert surface waves for underground model properties, especially the shear wave velocity. However, there are still many problems waiting to be solved. Conventional dispersion curve inversion (DCI) is limited to 1-D model assumption and has increased uncertainty when the structure is complicated. It also requires picking of dispersion curves from field data, which is often a labor intensive process. Although, methods in the framework of full waveform inversion of surface waves yield models with good resolution, both laterally and vertically when carefully implemented and applied, they are computationally intensive and can easily suffer from the cycle skipping problem. Wave-equation based dispersion curve inversion method combine some of the advantages of those in conventional dispersion curve inversion and full waveform inversion, but also requires picking of dispersion curves from both field and synthetic data. This dissertation focuses to partially solve some of the above issues and leads to more work that can be done in the future. To automate the picking of dispersion curves from surface waves, which is required for many approaches for shallow-subsurface characterization using surface waves, my first project presents a convolutional-neural-network (CNN) based machine learning approach to automatically pick the curves for the fundamental and higher modes along the two azimuths of any 2D seismic profile. Various attributes such as amplitudes, coherency, and local phase velocity as well as frequency and wavenumber of dispersion curves are derived; different sub-sets of these are tested in the CNN training process to assess the best combinations. We use a U-net architecture that is modified to convert the conventional 2D image segmentation problem in the (f,k) domain into direct multi-mode curve fitting and a subsequent picking process. To make the automatic picking algorithm more practical, we (1) introduce a second loss function that combines conventional wavenumber residuals and curve slope residuals; (2) use the transfer learning strategy, in which the network is pre-trained with synthetic data and then with a relatively small portion of the field data, to improve the efficiency of the algorithm; (3) evaluate two categories of uncertainty, the epistemic uncertainty from the method itself and input data, and uncertainty from non-deterministic factors such as random initialization of model weights and random shuffle of samples in training in the CNN, and in GPU parallelism. The epistemic uncertainty is an important indicator of the picking quality and can be used as a weighting of data in subsequent inversion; (4) perform post-processing to determine the effective dispersive frequency range of the picked curves by using different criteria, such as long/short moving average ratios (MAR) of squared picked wavenumbers, posterior uncertainty etc. The effectiveness of the automatic picking process is demonstrated in this study through applications to a field OBN dataset where different modes of Scholte waves were recorded. To reduce cycle skipping in FWI and to increase resolution of the estimated model, my second project develops and illustrates concurrent elastic full-waveform inversion (FWI) of P and S body waves and Rayleigh waves using interleaved envelope- and waveform- based misfit functions, in a gradually-increasing frequency, multi-scale, inversion strategy, to estimated both lateral and horizontal variations of models, which breaks the 1D assumption of conventional DCI. Computing correlation coefficients between the observed and predicted data, and between the inverted and correct models, provides quantitative measures of the composite contributions, of the starting model, the chosen data flow, and the depth extent of the solution space, to the fits of the corresponding solutions. Treating the whole wavefield as a single data set means that it is not necessary to separate, or even to identify, different types of body and surface waves.Item Fabrication and Characterization of Aging Resistant Carbon Molecular Sieve Membranes for C₃ Separation Using High Molecular Weight Crosslinkable Polyimide, 6FDA-DABA(Elsevier B.V.) Karunaweera, Chamaal; Musselman, Inga H.; Balkus, Kenneth J.; Ferraris, John P.; Karunaweera, C.; Musselman, Inga H.; Balkus, Kenneth J.; Ferraris, John P.Although propylene/propane separation remains a challenge for industrial processes, carbon molecular sieve membranes (CMSMs) have the potential to replace traditional separation methods. A high molecular weight crosslinkable polyimide was utilized to fabricate CMSMs, which showed pure gas permeabilities in excess of 400 barrers with propylene/propane selectivities as high as 25. Mixed gas (C₃H₈:C₃H₆ 50:50) measurements yielded a propylene permeability of 257 barrers and a selectivity of 20. CMSMs from thermally precrosslinked polymer precursors demonstrated a 98% propylene permeability retention after aging for 20 days under vacuum. Active gas flow conditions resulted in slightly lower permeability retention (92.5%) after 15 days of testing. ©2019 Elsevier B.V.Item Fabrication of Carbon Nanofiber Electrodes Using Poly(acrylonitrile-co-vinylimidazole) and Their Energy Storage Performance(Springer, 2019-02-02) Jung, K. -H; Kim, S. J.; Son, Y. J.; Ferraris, John P.; Ferraris, John P.For electrodes in electrochemical double-layer capacitors, carbon nanofibers (CNFs) were prepared by thermal treatment of precursor polymer nanofibers, fabricated by electrospinning. Poly(acrylonitrile-co-vinylimidazole) (PAV) was employed as a precursor polymer of carbon nanofibers due to the effective cyclization of PAV polymer chains during thermal treatment compared to a typical precursor, polyacrylonitrile (PAN). PAV solutions with different comonomer compositions were prepared and electrospun to produce precursor nanofibers. Surface images obtained from scanning electron microscopy showed that their nanofibrous structure was well preserved after carbonization. It was also confirmed that electrospun PAV nanofibers were successfully converted to carbon nanofibers after the carbonization step by Raman spectroscopy. Carbon nanofiber electrodes derived from PAV showed higher specific capacitances and energy/power densities than those from PAN, which was tested by coin-type cells. It was also shown that PAV with an acrylonitrile/vinylimidazole composition of 83:17 is most promising for the carbon nanofiber precursor exhibiting a specific capacitance of 114 F/g. Their energy and power density are 70.1 Wh/kg at 1 A/g and 9.5 W/kg at 6 A/g, respectively. In addition, pouch cells were assembled to load the higher amount of electrode materials in the cells, and a box-like cyclic voltammetry was obtained with high capacitances. © Korean Carbon Society 2019.Item High Performance Electrode Materials From Carbon Nanofibers with Tunable Pore Architectures(2019-08-30) Panangala, Samitha Dilhani; Ferraris, John P.Alternative energy sources are required in order to address the depletion and environmental concerns associated with non-renewable energy sources. Uncertainty and sporadic nature of renewable energy sources such as wind and solar, intensify the need of energy storage to supply a secure reliable energy throughout the day. Therefore the energy storage has drawn much attention in the science community. Among various energy storage devices, electrochemical double layer capacitors (EDLCs) also known as supercapacitors have superior properties like excellent performance, rapid charge-discharge, high power densities, along with long cycle life. But EDLCs possess low energy densities (<10 Wh/kg) which limit their use in real world applications. Therefore current research is focused on increasing the energy density of EDLCs while maintaining the existing attractive properties. EDLCs with high energy densities are an emerging field of energy storage. EDLCs rely on the pure electrostatic forces formed at the electrode/electrolyte interface. High surface area carbon and electrolytes with higher working voltage window are the key components to improve the energy density of EDLCs. Novel polyimide (PI) precursors were synthesized and tested for electrochemical performance. The polymers were electrospun to obtain polymer fibers to yield carbon nanofibers (CNFs) upon pyrolysis. The effect of in-situ porogen was analyzed and utilized for preparation of high surface area CNFs. PI with the best performance (6FDA-DABA) was blended with polyacrylonitrile (PAN) and the electrochemical performance was analyzed. PAN and 6FDA-DABA are immiscible and strenuous to incorporate higher amounts of 6FDA-DABA. A better way to incorporate higher amounts of immiscible polymers and obtain uniform morphologies is polymer compatibilization. Before compatibilizing PAN and 6FDA-DABA it was required to study the kinetic behavior of the activation reaction (CO2 oxidation of carbon at 1000 °C) of known compatibilized immiscible polymer blend; which mimics the behavior of PAN and 6FDA-DABA. Therefore a polybenzimidazole (PBI) and 6FDD (6FDA-DAM:DABA) blend was chosen and the kinetic behavior was studied before and after compatibilizing with 2-methylimidazole (2-MI). Chapter 1 interprets the introduction which summarizes the history of supercapacitors, energy storage principles, preparation of high surface area carbon and the use of electrolytes with high working voltage windows. Chapter 2 explicates the novel polyimide precursors for EDLCs. The effect of in-situ porogen was studied and the electrochemical performance of CNFs before and after CO2 activation is described. Chapter 3 describes the behavior of the highest performing polymer (6FDA-DABA) with PAN. Polymer blends comprising PAN and 6FDA-DABA were tested for the electrochemical performance before and after CO2 activation. Chapter 4 elucidates the kinetic behavior associated with CO2 oxidation of CNFs derived from electrospun compatibilized polymer blends of PBI and 6FDD. The rate constants, activation energies were calculated which concluded as the oxidation react becomes faster upon compatibilization of the immiscible polymer blend.Item High Surface Area Carbon Nanofibers Derived from Electrospun Pim-1 for Energy Storage Applications(2013-11-21) Bonso, Jeliza S.; Kalaw, Grace Jones D.; Ferraris, John P.; Bonso, Jeliza S.; Kalaw, Grace Jones D.; Ferraris, John P.Electrochemical double layer capacitors (EDLCs) utilize electrodes with high surface area to achieve high-energy storage capability. In this study, flexible and freestanding carbon nanofibers derived from PIM-1, a microporous polymer with high free volume, were prepared by pyrolysis of the electrospun polymer. A BET surface area of 546 m² g⁻¹ was obtained upon carbonization of the electrospun PIM-1 fibers. After further heat treatments such as steam-activation and annealing, the surface area increased to 1162 m² g⁻¹. These carbon fibers were directly used as electrodes without the use of binders in a coin cell (CR2032) configuration and were characterized by cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy. The activated and annealed fibers gave a specific capacitance of 120 F g⁻¹ at a scan rate of 10 mV s⁻¹ using 1,3-ethylmethylimidizaolium bis(trifluoromethanesulfonyl) imide as the ionic liquid electrolyte. From the galvanostatic charge-discharge test, the supercapacitor exhibited energy and power densities of 60 W h kg ⁻¹ (active material) and 1.7 kW kg⁻¹, respectively, at a current density of 1 A g⁻¹. High power application of this device was demonstrated by its 77% retention of the energy density (47 W h kg⁻¹) at a higher discharge current density of 5 A g⁻¹.Item High-Performance Membrane Materials for Industrial Gas Separations(2019-08-30) Karunaweera, Chamaal; Ferraris, John P.Membrane-based gas separation is a potential alternative for expensive and energy intensive conventional separation techniques such as pressure swing adsorption and cryogenic/fractional distillation. Polymer and carbon molecular sieve (CMS) membranes are two commonly studied types of membranes for gas separations. Despite their ease of application and relatively inexpensive nature, polymer membranes suffer from the gas permeability/selectivity trade-off, and they are also highly susceptible to plasticization. On the other hand, physical aging in CMS membranes results in less efficient separations over time, as a result of reduced permeabilities. This dissertation describes approaches to overcome the above problems in polymer and CMS membranes. The first chapter briefly describes current trends and concerns in membrane-based gas separations. This chapter also discusses the importance of membrane-based gas separations as an alternative for conventional gas separation techniques. The second chapter explains the utilization of a thermally crosslinkable polymeric precursor to fabricate aging resistant CMS membranes under simulated industrial conditions. Synthesis of a high molecular weight, thermally crosslinkable polymer, 6FDA-DABA, is reported for the first time. The fabrication technique for aging resistant CMS membranes described is simple and relatively inexpensive compared to previously reported aging prevention techniques. The CMS membranes show excellent propylene/propane separation properties (propylene permeability of 257 Barrer and propylene/propane selectivity of 20) with about 92% permeability retention after 15 days. The third chapter reports the fabrication and characterization of novel carbon-carbon composite membranes (a type of CMS membranes) from a compatibilized immiscible polymer blend, polybenzimidazole (PBI)/6FDA-DAM:DABA (6FDD). Morphology control of the PBI:6FDD immiscible polymer blend is the key to obtaining membranes with higher gas permselectivities, which is an effective way to overcome the gas permeability/selectivity trade-off. In addition, this trade-off can be addressed by converting the morphology controlled immiscible polymer blends into carbon-carbon composite membranes. The synergistic effect of polymer blending and carboncarbon composite membrane fabrication is investigated for H2/CO2 separations. Morphology controlled carbon-carbon composite membranes showed an approximately three-fold increase in both H2 permeability and H2/CO2 selectivity in comparison to the membrane without morphology control. The fourth chapter explains how an immiscible polyimide blend can be converted to a miscible polymer blend using a reactive small molecule compatibilizer. This technique allows the fabrication of CO2/CH4 separation membranes with excellent plasticization resistance and gas permselectivities. Thermal crosslinking of the polymer blend membranes improves the plasticization resistance. Plasticization resistance is greater for the crosslinked miscible polymer blends in comparison to the crosslinked immiscible polymer blends.Item Kinetic Stability of Bulk LiNiO₂ and Surface Degradation by Oxygen Evolution in LiNiO₂-Based Cathode Materials(Wiley-VCH Verlag Gmbh, 2018-11-02) Kong, Fantai; Liang, Chaoping; Wang, Luhua; Zheng, Yongping; Perananthan, Sahila; Longo, Roberto C.; Ferraris, John P.; Kim, Moon J.; Cho, Kyeongjae; Kong, Fantai; Liang, Chaoping; Wang, Luhua; Zheng, Yongping; Perananthan, Sahila; Longo, Roberto C.; Ferraris, John P.; Kim, Moon J.; Cho, KyeongjaeCapacity degradation by phase changes and oxygen evolution has been the largest obstacle for the ultimate commercialization of high-capacity LiNiO₂-based cathode materials. The ultimate thermodynamic and kinetic reasons of these limitations are not yet systematically studied, and the fundamental mechanisms are still poorly understood. In this work, both phenomena are studied by density functional theory simulations and validation experiments. It is found that during delithiation of LiNiO₂, decreased oxygen reduction induces a strong thermodynamic driving force for oxygen evolution in bulk. However, oxygen evolution is kinetically prohibited in the bulk phase due to a large oxygen migration kinetic barrier (2.4 eV). In contrast, surface regions provide a larger space for oxygen migration leading to facile oxygen evolution. These theoretical results are validated by experimental studies, and the kinetic stability of bulk LiNiO₂ is clearly confirmed. Based on these findings, a rational design strategy for protective surface coating is proposed.Item Novel Binder-Free Electrode Materials for Supercapacitors Utilizing High Surface Area Carbon Nanofibers Derived from Immiscible Polymer Blends of PBI/6FDA-DAM:DABA(Royal Society of Chemistry, 2018-06-01) Abeykoon, Nimali C.; Garcia, Velia; Jayawickramage, Rangana A.; Perera, Wijayantha; Cure, Jeremy; Chabal, Yves J.; Balkus, Kenneth J.; Ferraris, John P.; 0000 0000 4239 3958 (Chabal, YJ); 0000-0002-3225-0093 (Ferraris, JP); Abeykoon, Nimali C.; Garcia, Velia; Jayawickramage, Rangana A.; Perera, Wijayantha; Cure, Jeremy; Chabal, Yves J.; Balkus, Kenneth J.; Ferraris, John P.Carbon nanofibers with high surface area have become promising electrode materials for supercapacitors because of their importance in increasing energy density. In this study, a high free volume polymer, 6FDA-DAM:DABA (6FDD) was blended with polybenzimidazole (PBI) in different ratios to obtain different compositions of PBI/6FDD immiscible polymer blends. Freestanding nanofiber mats were obtained via electrospinning using blend precursors dissolved in N,N-dimethylacetamide (DMAc). Subsequently, carbonization, followed by CO₂ activation at 1000 °C was applied to convert the fiber mats into porous carbon nanofibers (CNFs). The addition of 6FDD shows significant effects on the microstructure and enhancement of the surface area of the CNFs. The obtained CNFs show specific surface area as high as 3010 m² g⁻¹ with pore sizes comparable to those of the electrolyte ions (PYR₁₄TFSI). This provides good electrolyte accessibility to the pore of the carbon materials resulting in enhanced energy density compared to the CNFs obtained from pure PBI. Electrodes derived from PBI:6FDD (70 : 30) exhibited outstanding supercapacitor performance in coin cells with a specific capacitance of 142 F g⁻¹ at the scan rate of 10 mV s⁻¹ and energy density of 67.5 W h kg⁻¹ at 1 A g⁻¹ (58 W h kg⁻¹ at 10 A g⁻¹) thus demonstrating promising electrochemical performance for high performance energy storage system.Item Optimization of polybenzimidazole-based nanofibers for supercapacitor electrode applications(2013-05-21) Charlton, John; Bonso, Jeliza S.; Ferraris, John P.; The University of Texas at Dallas. Office of Undergraduate Education.; The University of Texas at Dallas. Office of Research.Electrochemical capacitors (supercapacitors) are energy storage devices characterized by high energy and power densities with long cycle stability. Supercapacitor research focuses on improving the device's energy density to be more competitive with existing battery technology. Because of their large power. densities, supercapacitors may find application anywhere a quick charge of electricity is needed, like regenerative braking systems or consumer electronics. Supercapacitors store energy in the electrochemical double-layer. When a substrate is charged in an electrolytic solution, the substrate will attract the oppositely charged electrolyte ion. This interaction forms a double-layer and is the mechanism of charge storage for supercapacitors. Since charge storage depends on this electrode/electrolyte interface, the electricity a supercapacitor can store is directly proportional to its available surface area. In this work, carbon nanofibers from the precursor polymer polybenzimidazole (PBI) were produced through electrospinning to achieve high surface area electrodes. After the fibers are produced, they undergo a series of treatments to improve their surface area. In addition, ammonium bicarbonate is used as a sacrificial pore-generating agent (porogen) to produce cavities capable of accommodating more ions. Energy is related to capacitance through the equation E = ½ CV², so energy storage can be improved with a higher working voltage. The ionic liquid ethylmethylimidazolium bis(trifluoromethylsulfonyl)imide was chosen as the electrolytic solution with a working voltage of 4.1V.Item Preparation of Functionalized Graphenes and Their Performance for Corrosion Resistance and Synthesis of Vanadium Nitridecarbon Nanofiber Mats and Their Application for Asymmetric Supercapacitor Electrodes(2020-12-01T06:00:00.000Z) Wunch, Melissa Ann; Yang, Duck Joo; Cao, Yan; Balkus, Jr., Kenneth J.; Ferraris, John P.; Smaldone, RonaldCarbon materials have been researched in a wide range of applications, including energy storage, corrosion protection, catalyst support, etc. Though many people have studied properties of carbon with/without modification, research in the synthesis of functionalized carbon and carbon composites therefrom will be important. This dissertation outlines the synthesis of functionalized graphene, development of graphene composites, and metal nitride-carbon nanofiber composites and their application for electrode for super-capacitor. Graphene is single layer carbon-based material known for its multifunctional properties (e.g. hydrophobicity, mechanical strength, etc.). This work studies application of graphene through functionalization of mechanically exfoliated graphene and functionalized graphene use for corrosion resistance. Functionalization of graphene is first discussed in the eco-friendly synthesis of aminated mechanically exfoliated graphene (MEG). Here we are able to directly functionalize MEG with amine groups using glycerol as the reaction medium and urea as the amine source. The aminated MEG (AG) also showed enhanced dispersion stability in organic solvents and aquous-solvent mixtures for >60 days. In the second area, we discussed how functionalized graphenes affected surface properties and corrosion resistance when composited with a polymer coating. Graphene, aminated graphene (AG), and fluorinated graphene (FG) were studied for corrosion resistance. Both AG and FG exhibited enhanced corrosion resistance when composited with a 2K urethane coating. Composite coating with FG showed a 94% increase in corrosion resistance versus graphene at a concentration of 4% by weight of solids. These materials also enhanced the surface properties of the coating. Electrochemical analysis of composite coatings showed that through inclusion of functionalized graphenes (AG or FG), barrier and adhesion properties were strengthened. Both FG and AG composite coatings showed an increase in contact angle versus graphene, with FG resulting in a hydrophobic surface (>90o ) at 4wt%. This project shows a step towards the potential removal of sacrificial zinc as a barrier for corrosion resistance of steel substrate. The increase in energy consumption over the last decade has led to research in the development of alternative energy storage devices which can meet the demand. Supercapacitors have garnered increased attention in this field due to their ability to provide high power and high energy. Electrodes within these devices can consist of two different materials, carbon or pseudocapacitive material. While carbon-based supercapacitors, or EDLCs, can provide high power density, they suffer from low energy densities. This has led researchers to study composite, or hybrid electrodes which combine the high power EDLC material with a high energy pseudocapacitive material (e.g. metal oxide or metal nitride). In the third area, we assembled and tested hybrid-asymmetric devices using activated vanadium nitride-carbon nanofiber (VN-CNF) electrodes. The VN was made using vanadium oxide (V2O5) nanoflowers by a new synthesis method. Composite electrodes were made by electrospinning of a poly(acrylonitrile-co-itaconic acid) (PANIA) solution with the vanadium oxide (V2O5) nanoflowers dispersed within it to produce freestanding mats. VN-CNF freestanding mats were used as anode material and CNF as the cathode when assembling the device. Ionic liquid electrolyte 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (Pyr14TFSI) with 0.5M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was used, which widens the operating voltage window (>3.5V) compared with aqueous (e.g. KOH or Na2SO4) or organic electrolytes (e.g. TEA-BF4 in ACN). Chapter 1 introduces the material graphene, its properties, and methods of synthesis. In this section we also review methods of functionalization and application in the field of corrosion protection. Chapter 2 describes the eco-friendly method of functionalization of mechanically exfoliated graphene (MEG) with amine groups and the effect of these groups on dispersion stability in organic solvents and aqueous-solvent mixtures are studied. Chapter 3 studies the effect of graphene, aminated graphene (AG), and fluorinated graphene (FG) on surface properties and corrosion resistance when composited with a urethane coating. Contact angle measurements and electrochemical analysis were performed to determine which graphene and concentration provides best corrosion resistance. Chapter 4 introduces supercapacitors and the concepts behind the different types. This section describes charge storage mechanisms of the pseudocapacitors and discusses different aspects of metal oxides and nitrides. Chapter 5 describes the preparation of vanadium nitride-carbon nanofiber (VN-CNF) composite electrodes and analysis of their electrochemical properties. Charge contributions and storage mechanisms for each sample was studied to understand the mechanism in which their charge is stored (e.g. intercalative or pseudocapacitive/capacitive).Item Pyrrole Based Donor-acceptor Building Blocks for Organic Field-effect Transistors(2020-12-01T06:00:00.000Z) Gamage, Prabhath Lakmal; Biewer, Michael C.; Stefan, Mihaela C.; Lv, Bing; Ferraris, John P.; Smaldone, Ronald A.The class of organic semiconductors is a definite contender for replacing high-cost silicon semiconductors owing to unique advantages such as solution processability, flexibility, lightweight, low cost, and the ability to do multiple structural modifications. Hence, a remarkable amount of scientific research has been carried out to improve the electronic properties of these materials. Throughout the past two decades, many improvements in the field have achieved by designing novel building blocks. There remains the possibility, however, for performance improvement through areas that has paid less attention in both conventional and non-conventional building blocks. Because of the appealing performance of organic semiconductors, it is highly desirable to seek and develop new building blocks for the next generation of organic electronics. In this dissertation, the fundamentals, history, and recent developments of conventional and nonconventional materials are covered briefly in the first chapter. Operation principles, charge transport of organic field effect transistors is introduced. Compared to conventional thiophenebased -electron donor materials, promising non-conventional pyrrole-based donor materials employed in organic field effect transistors are discussed and summarized. Chapter 2 describes the effect on organic field effect transistor (OFET) properties of a donor-acceptor polymer consist of a branched ester functionalized bithiophene copolymerized with thiophene vinyl thiophene donor. The influence on frontier molecular orbital energy levels, UV-vis absorption, electrochemical properties, OFET parameters and morphological effects were investigated. In chapter 3, the effect of furan spacer group on a thieno[3,2-b]pyrrole and diketopyrrolopyrrole based copolymer is discussed. Upon changing similar flanking groups, the polymer showed a high hole mobility of 0.42 cm2 /V s while the on-to-off ratio exhibited a drastic improvement 105 . Chapter 4 describes the incorporation of selenium hetero atom in the pyrrole fused rings to yield seleno[3,2-b]pyrrole based small molecules replacing thieno[3,2-b]pyrrole to extend the knowledge of OFETs activity of seleno[3,2-b]pyrrole in banana shaped small molecules. They exhibited moderate charge carrier properties 10-2 cm2 /V s hole mobility. In the Chapter 5 (attached as an appendix), a study on oxidative degradation of polypropylene mesh in Escherichia coli (E. coli.) environment is disscussed. Medical implants of polypropylene (PP) mesh have demonstrated biodegradation inside the body. Among the many possible factors, bacterial colonization is believed to be one of the causes for biodegradation. To gain insights on this hypothesis PP mesh samples were tested in Luria-Bertani broth containing E. coli and the experimental results demonstrated qualitative and quantitative bioerosion, confirming the oxidative degradation in vitro.Item Solution-free Ion Exchange on Lead Halide Perovskite Thin-film and Infrared Characterization(2022-08-01T05:00:00.000Z) Fan, Victor; Quevedo-Lopez, Manuel; Balkus Jr., Kenneth J.; Ferraris, John P.Lead halide perovskite is an emerging material for photovoltaic applications with the standard formula ABX3. CsPbBr3 has outstanding stability compared to other lead halide perovskite materials. Lead halide perovskite band gap energy is tunable by ion exchange in the B (lead) and X(halogen) sites. Close-Spaced Sublimation (CSS) is a scalable Physical Vapor Deposition (PVD) method that can be used for CsPbBr3 thin-film manufacturing and ion exchanging on CsPbBr3 thin-film. This thesis investigates the CsPbBr3 thin-film ion exchange on the B and X sites in the CSS system and applies the infrared spectrum as a novel tool to characterize the treated CsPbBr3 thin-films.Item Supercapacitor Electrode Materials Comprising Uniformly Dispersed Chromium Nitride/ Carbon Fiber Composite(2022-05-01T05:00:00.000Z) Rifat, Samia; Ferraris, John P.; Balkus Jr., Kenneth J.; Nielsen, Steven O.; Pantano, PaulNowadays, researchers and industrial designers are looking for an eco-friendly alternative energy source to fulfill the increasing need for energy and reduce environmental pollution. Electricity based on energy storage devices can be a way of solving the crisis. Among different energy storage devices, the faster charging and discharging speeds or higher power densities, working in a wider range of temperatures, and longer cycle life of supercapacitor make them attractive for several applications. The commercially available supercapacitors are mostly electric double-layer capacitors (EDLCs) and to a lesser degree of pseudocapacitors. Recently, researchers have been focusing on hybrid supercapacitors (HSCs) due to their ability to combine the properties of both EDLCs and pseudocapacitors to expand the applications. Engineered carbon nanofibers can be coupled with conductive metal nitrides to form composites and used as electrode materials for supercapacitor applications. In this work, a new hybrid nanocomposite of carbon fibers and chromium nitride (CFs/CrN) was fabricated as electrode materials, where polyacrylonitrile (PAN) was utilized as the carbonizing materials and polymethyl methacrylic acid (PMAA) as the sacrificial agents. Here, pore-forming agents, PMAA, assisted in improving the supercapacitor's performance by increasing the electrode materials' surface area. Also, growing CrN nanoparticles in the fiber contributed by the pseudocapacitance from proton adsorption. Furthermore, the chelation ability of the PMAA might be beneficial for the homogeneous distribution of CrN all over the CFs. Furthermore, the use of aqueous electrolytes and comparatively low-cost transition metal materials lowered the fabrication costs, and the utilization of the electrospinning technique makes CFs/metal nitrides composite electrodes freestanding and readily produced. Chapter 1 describes a detailed introduction to supercapacitors, including a brief description of the storage principle of EDLCs, pseudo capacitors, and hybrid supercapacitors and their advantages and disadvantages. It also describes the basics of the electrospinning process, thermal treatments, and aqueous electrolytes, all of which were applied to fabricate the supercapacitors using CFs and metal nitrides composite-based electrodes. Chapter 2 represents the fabrication of CFs and chromium nitrides composites using polymer blends containing PAN and PMAA and Cr precursor as a source of chromium. This chapter also describes the characterization of synthesized PAM-PMAA-CrN electrode materials and their electrochemical performance and analysis. The highest capacitance was obtained from PANPMAA-CrN based electrode 159 F/g at 5 mV/s. Also, the highest energy densities of 13.26 Wh/Kg at 1.2 V were obtained from the PAN-PMAA-CrN and CNFs based asymmetric device. Furthermore, the PAN-PMAA-CrN electrode showed higher stability with 80.4% capacitance retention after 10000 cycles.Item Supercapacitor Electrode Materials from Highly Porous Carbon Nanofibers with Tailored Pore Distributions(2017-05) Abeykoon, Nimali Chathurika; Ferraris, John P.Environmental and human health risks associated with the traditional methods of energy production (e.g., oil and gas) and intermittency and uncertainty of renewable sources (e.g., solar and wind) have led to exploring effective and alternative energy sources to meet the growing energy demands. Electricity based on energy storage devices are the most promising solutions for realization of these objectives. Among the energy storage devices, electrochemical double layer capacitors (EDLCs) or supercapacitors have become an attractive research interest due to their outstanding performance, especially high power densities, long cycle life and rapid charge and discharge times, which enables them to utilize in many applications including consumer electronics and transportation, where high power is needed. However, low energy density of supercapacitors is a major obstacle to compete with the commercially existing high energy density energy storage device such as batteries. The fabrication of advanced electrodes materials with very high surface area from novel precursors and utilization of electrolytes with higher operating voltages are essential to enhance energy density of supercapacitors. In this work, carbon nanofibers (CNFs) from different polymer precursors with new fabrication techniques are explored to develop highly porous carbon with tailored pore distributions to match with employed ionic liquid electrolytes (which possess high working voltages), to realize high energy storage capability. Novel electrode materials derived from electrospun immiscible polymer blends and synthesized copolymers and terpolymers were described. Pore distributions of CNFs were tailored by varying the composition of polymers in immiscible blends or varying the monomer ratios of copolymer or terpolymers. Chapter 1 gives the detailed introduction of supercapacitors including history and storage principle of EDLCs, fabrication of carbon nanofiber based electrodes and electrolytes employed for EDLCs. It also explains the necessity and the advantages of tailored high surface area nanofibers as an electrode materials for supercapacitors. Chapter 2 describes the preparation of high surface area carbon nanofibers using polymer blends containing PAN and PMMA and introduces an effective and simple strategy to improve the surface area of CNFs by using a sacrificial polymer, PMMA. Chapter 3 describes blending of high fractional free volume polymer, 6FDA-DAM: DABA (3:2) into PBI to increase surface area and by using the higher etch rate of 6FDA-DAM: DABA in the blend to optimize pore distribution of CNFs. Chapter 4 introduces a novel approach to increase surface area of CNFs without any physical or chemical activation by using an in situ porogen containing copolymer P(AN-co-IA). The concept developed here avoids unnecessary and complex extra activation steps when fabricating carbon nanofibers which leads to lower char yield and uncontrollable pore sizes. Chapter 5 describes enhancement of surface area by using terpolymer P(AN-VIM-IA) to develop a new precursor. This approach is further advantageous since terpolymer can combine superior electrochemical properties of homopolymer, PAN and P(AN-co-IA) and P(AN-co-VIM). Chapter 6 describes the use of commercially available small molecule compatibilizer 2-MI to tailor pore architecture of carbon fiber derived from the immiscible blend of PBI/6FDD to match with the ion sizes of ionic liquid electrolytes thereby increasing the surface area of the CNFs that is accessible to electrolytes.Item Sustainability Centered Photoresin Design for 3D Printing Using Dynamic Covalent Chemistry(August 2023) Cortes Guzman, Karen Paola 1994-; Smaldone, Ronald A.; Zhang, Chuanwei; Stefan, Mihaela C.; D'Arcy, Sheena; Ferraris, John P.Contemporary society is and will be facing from now on, worrying environmental challenges that reflect the actions from current and previous generations with a lesser sense of environmental awareness. As science and technology advance, it is our responsibility to learn and do better to ensure we stop and prevent future damage to the earth, carrying on sustainability principles into every step we take forward. The design of new materials is especially important in today’s state of the world because physical tangible materials like plastic, represent the most visibly detrimental callings for action. Numerous sustainable alternatives from feedstocks to end-of-life management have been explored over the last couple of decades, which have paved the way for more eco- conscious design of plastics. Abiding by these sustainability centered strategies will avoid worsening the already alarming plastic crisis and will be a great starting point for future generations to move forward. As society develops and advances technologically, the design of new polymeric materials requires the consideration for compatibility with the latest technological developments, to make sure that these new materials could be candidates to replace existing non sustainable ones. In plastic manufacturing, 3D printing technologies show great promise for adoption as the default methods in the near future, based on their versatility, resolution, on demand production and sustainability attributes. 3D printing allows rapid prototyping, creation of complex parts, diverse applications, and democratization of manufacturing. In terms of sustainability, 3D- printing’s on demand production capabilities, significantly reduce the need for transportation, storage and waiting time, which overall reduces the carbon footprint of the final products. There are some challenges for ensuring that the products from 3D printing technologies do not represent a threat to the environment and these could be addressed through different actions in each step of the process. Selection of renewable feedstocks obtained through sustainable processes is required since the beginning design stages. Compatibility with the best resolution 3D printing technologies like vat photopolymerization 3D printing, will ensure the products perform to expectations, reducing the possibility of creating waste before their use. Vat photopolymerization 3D printing like stereolithography (SLA) or digital light projection (DLP), mostly produce thermosetting polymers which usually lack the ability to be recycled, and due to their thermal and chemical resistance, they could represent a threat to the environment after their end-of-life if not correctly disposed. To overcome this challenge, efforts to create vat photopolymerization printed thermosets, are to be accompanied with a sustainable end-of-life disposal mechanism in mind. Lately, disposal mechanisms like reprocessing, degrading and chemical recycling, have been made possible through incorporating the use of dynamic covalent chemistry (DCC) in the synthetic design. The research presented in this dissertation includes sustainability alternatives for every step of the photo-resin design process, to create materials with low environmental impact, compatible with DLP 3D printing. Chapter 1 provides background information on the current environmental challenges associated with plastics, as well as literature examples on how DCC has endowed 3D printed materials with smart properties and mechanical performance that make them competitive, as well as disposal possibilities to handle the materials at their end-of-life without representing a threat to the environment. Chapter 2 describes the design of five bio-based resins for DLP printing with self-healing capabilities through the use of DCC. Transimination exchange reactions were chosen as the dynamic reactions based on their excellent performance without requiring the addition of a catalyst. These five resins possess bio-based content, are DLP printable, show varied mechanical performances, have self-healing and reprocessability capabilities. Chapter 3 describes the design of three completely bio-based photoresins using monomers derived from lignin, and a crosslinker with beta-hydroxy moieties that allows transesterification reactions to occur with assistance of a catalyst. Through dynamic transesterification reactions the resulting DLP printed thermosets exhibit self-healing and one of the formulations can be readily reprocessed with above 70% recovery of the mechanical performance. A post processing annealing step, improves the mechanical strength of the materials, increasing the competitiveness of these bio- based materials with conventional oil derived alternatives. Chapter 4 describes the development of resins with 70 wt % bio-based content using lignin, vanillin, and soybean oil. Methacrylated lignin has multiple hydroxy moieties that can be activated with the use of a catalyst to perform transesterification exchanges. These dynamic behaviors allowed the thermosets to self-heal and be reprocessed lowering their environmental impact. Chapter 5 includes the design of two resin formulations polymerized through thiol-ene chemistry, which enables degradation and chemical recyclability of the resulting thermosets. These two thermosets were synthesized with bio-based feedstocks and posses imine moieties capable of performing transamination reactions for self-healing behaviors. This research aims to describe sustainable alternatives for every step of the process of designing new polymeric materials, competitive through their smart properties, mechanical performance and compatibility with DLP 3D printing.Item Synthesis and Characterization of Metal-organic Frameworks for Potential Uses in Cancer Therapy(2021-12-01T06:00:00.000Z) Vizuet Mata, Juan Pablo; Balkus Jr., Kenneth J.; Kim, Tae Hoon; Ferraris, John P.; Novak, Bruce M.; Smaldone, Ronald A.Metal-organic frameworks (MOFs) are crystalline materials, characterized for their high surface areas and defined pore architectures. These materials, first synthesized and characterized in the 1990s, have seen an increase interest due to their inherent properties. As a result of their hybrid nature, MOFs can be used in a wide range of applications, from catalysis and gas storage, to drug delivery and cancer therapy. While commonly using transition metals as building blocks, using lanthanide as their metal centers further increases the range of MOF applications. Using holmium in these materials could potentially create an improved cancer therapy method by delivering both a radiation source and a radiosensitizer to the cancer sites. This work in particular focuses on the synthesis and characterization of several frameworks, with the focus of using these materials for cancer therapy applications.