Electric double layer capacitors (EDLCs) are an important class of electrical energy storage devices which store energy in the form of electric double layers. The charging mechanism is highly reversible physical adsorption of ions into the porous electrodes, which empower these devices to show a remarkable power performance (15kW/kg) and greater life expectancy (> 1 million cycles). However, they store a small amount of energy (5Wh/kg) when compared with batteries. Optimization of the performance of EDLCs based on porous activated carbons is highly challenging due to complex charging process prevailing in the Nano pores of electrodes. Molecular simulations provide information at the molecular scale which in turn can be used to develop insights that can explain experimental results and design improved EDLCs. The conventional approach to simulate EDLCs places both the electrodes and electrolyte region in a single simulation box. With present day computers, however, this one-box method limits us to system sizes of the order of nanometres whereas the size of a typical EDLC is at least of the order of micrometres. To overcome this system size limitation, a Gibbs-ensemble based Monte Carlo (MC) method was recently developed, where the electrodes are simulated in a separate simulation boxes and each box is subjected to periodic boundary conditions in all the three directions. This allows us to eliminate the electrode-electrolyte interface. The simulation of the bulk electrolyte is avoided through the use of the grand canonical ensemble. The electrode atoms in the electrode are maintained at an equal constant electric potential likewise the case in a pure conductor with the use of the constant voltage ensemble. In this thesis, the Gibbs-ensemble based MC simulations are performed for an EDLC consisting of porous electrodes. The simulations are performed with aqueous electrolytes of type MX and DX2 (where M=Na+, K+; D=Ca+2; X=Cl , F ) for a wide variety of operating conditions. The water is modelled as a continuum background with a dielectric constant value of 30. The electrodes are silicon carbide-derived carbon, whose microstructure generated from reverse MC technique, is used in the simulations. The results from these simulations help us understand the charge storage mechanism, the effect of size and valence of ions on the performance of nonporous carbon based EDLCs when the hydration effects are indignant. The thesis first demonstrates the presence of finite size effects in the simulations performed with the one-box method for KCl electrolyte. The capacitance (ratio of the charged stored on the positive electrode to the voltage applied) values obtained for KCl electrolyte with the one-box method are significantly higher than the corresponding values obtained from the Gibbs-ensemble method. This shows the presence of finite size effects in the one-box method simulations and justices the use of the Gibbs-ensemble based method in our simulations. The fundamental characteristics of aqueous electrolytes in the EDLC are analyzed with the simulation results for KCl electrolyte. In agreement with experiments and modern mean held theory, the capacitance monotonically decreases with voltage (bell-shaped curve) due to overcrowding of ions near the electrode surface. The charge storage mechanism in both the electrodes is mainly a combination of countering (ions oppositely charged to that of the electrode) adsorption and ion exchange, where coins (ions identically charged to that of the electrode) are replaced with countering. However, at higher voltages, the mechanism is predominantly counter ion adsorption because of the scarcity of coins in the electrodes. The mechanism is preferentially more ion exchange for the positive electrode because of its relatively bulky countering, Cl . The shifting of mechanism towards counter ion adsorption at higher voltages and preferential ion exchange process for the positive electrode are in qualitative agreement with the recent experimental results. The constraint of equal electric potential on all the electrode atoms of the amorphous electrode in the simulations resulted in a non-uniform average charge distribution on the electrodes. It shows that the Gibbs-ensemble simulation approach can account for the polarization effects which arises due to a complex topology of the electrodes. In agreement with earlier experiments and simulation studies, the local structure analyses of the electrodes shows that the highly conned ions store charge more efficiently. On the application of voltage difference between the electrodes, the electrolyte ions move towards higher degree of con ned regions of the electrodes indicating the charging process involves local rearrangement and rescuing of electrolyte ions. The thesis also discusses the effect of temperature and bulk concentration on the performance of EDLCs. The Gibbs-ensemble based simulations are performed for the EDLC with varying temperature and bulk concentration for the KCl electrolyte independently. In agreement with the Guo -Chapman theory and experiments, the capacitance decreases with the temperature and increases with the bulk concentration. This is because the concentration of countering in the electrodes decreases with an increase in the temperature but increases with an increase in the bulk concentration. Lastly, the effect of ion size and valency on the performance of EDLCs is analyzed. The capacitance monotonically decreases with voltage (bell-shaped curve) for all the electrolytes, except for NaF, where a maximum is observed at a non-zero finite voltage (camel-shaped curve). The capacitances of NaCl and NaF are greater than that for KCl and KF, respectively. This is because the smaller Na+ ions have more accessibility to narrow con ned regions, where the charge storage efficiency is high. As expected, the capacitance for CaCl2 and CaF2 are highest among their monovalent counterparts, NaCl and KCl; NaF and KF, respectively. This is attributed to the relatively smaller double layer thickness of the bivalent Ca+2 ions. Interestingly, at higher voltages, the capacitance for the bivalent electrolytes approaches the capacitance for the monovalent electrolytes because the concentration of Ca+2 ions in the negative electrode increases sluggishly with voltage due to a strong electrostatic repulsion between Ca+2 ions.

La demande urgente d'innovations dans le domaine du stockage de l'énergie est liée au développement récent de la production d'énergie renouvelable ainsi qu'à la diversification des produits électroniques portables qui consomment de plus en plus d'énergie. Il existe plusieurs technologies pour le stockage et la conversion électrochimique de l'énergie, les plus notables étant les batteries aux ions lithium, les piles à combustible et les supercondensateurs. Ces systèmes sont utilisés de façon complémentaire des uns aux autres dans des applications différentes. Par exemple, les batteries sont plus facilement transportables que les piles à combustible et ont de bonne densité d'énergie alors que les supercondensateurs ont des densités de puissance plus élevés et une meilleure durée de vie. L'objectif principal de ces travaux est d'étudier les performances électrochimiques d'une nouvelle famille de matériaux bidimensionnel appelée MXène, en vue de proposer de nouvelles solutions pour le stockage de l'énergie. Pour y arriver, plusieurs directions ont été explorées. Dans un premier temps, la thèse se concentre sur les supercondensateurs dans des électrolytes aqueux et aux effets des groupes de surface. La seconde partie se concentre sur les systèmes de batterie et de capacités à ions sodium. Une cellule complète comportant une anode en carbone et une cathode de MXène a été développées. La dernière partie de la thèse présente l'étude des MXènes pour les supercondensateur en milieu organique. Une attention particulière est apportée à l'étude du mécanisme d'intercalation des ions entre les feuillets de MXène. Différentes techniques de caractérisations ont été utilisées, en particulier la voltampérométrie cyclique, le cyclage galvanostatique, la spectroscopie d'impédance, la microscopie électronique et la diffraction des rayons X. / An increase in energy and power densities is needed to match the growing energy storage demands linked with the development of renewable energy production and portable electronics. Several energy storage technologies exist including lithium ion batteries, sodium ion batteries, fuel cells and electrochemical capacitors. These systems are complementary to each other. For example, electrochemical capacitors (ECs) can deliver high power densities whereas batteries are used for high energy densities applications. The first objective of this work is to investigate the electrochemical performances of a new family of 2-D material called MXene and propose new solutions to tackle the energy storage concern. To achieve this goal, several directions have been explored. The first part of the research focuses on MXene behavior as electrode material for electrochemical capacitors in aqueous electrolytes. The next part starts with sodium-ion batteries, and a new hybrid system of sodium ion capacitor is proposed. The last part is the study of MXene electrodes for supercapacitors is organic electrolytes. The energy storage mechanisms are thoroughly investigated. Different characterization techniques were used in this work, such as cyclic voltammetry, galvanostatic charge-discharge, electrochemical impedance spectroscopy, scanning electron microscopy and X-ray diffraction.

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This study focuses on the design, fabrication, and characterization of deterministically engineered, three-dimensional architectures to be used as high-performance electrodes in energy storage applications. These high-surface-area architectures are created by the robotically-assisted sequential electrodeposition of structural and sacrificial layers in an alternating fashion, followed by the removal of the sacrificial layers. The primary goal of this study is the incorporation of these highly laminated architectures into the battery electrodes to improve their power density without compromising their energy density. MEMS technologies, as well as electrochemical techniques, are utilized for the realization of these high-power electrodes with precisely controlled characteristic dimensions. Diffusion-limited models are adopted for the determination of the optimum characteristic dimensions of the electrodes, including the surface area, the thickness of the active material film, and the distance between the adjacent layers of the multilayer structure. The contribution of the resultant structures to the power performance is first demonstrated by a proof-of-concept Zn-air microbattery which is based on a multilayer Ni backbone coated with a conformal Zn film serving as the anode. This primary battery system demonstrates superior performance to its thin-film counterpart in terms of the energy density at high discharge rates. Another demonstration involves secondary battery chemistries, including Ni(OH)2 and Li-ion systems, both of which exhibit significant cycling stability and remarkable power capability by delivering more than 50% of their capacities after ultra-fast charge rates of 60 C. Areal capacities as high as 5.1 mAh cm-2 are reported. This multilayer fabrication approach is also proven successful for realizing high-performance electrochemical capacitors. Ni(OH)2-based electrochemical capacitors feature a relatively high areal capacitance of 1319 mF cm-2 and an outstanding cycling stability with a 94% capacity retention after more than 1000 cycles. The improved power performance of the electrodes is realized by the simultaneous minimization of the internal resistances encountered during the transport of the ionic and electronic species at high charge and discharge rates. The high surface area provided by the highly laminated backbone structures enables an increased number of active sites for the redox reactions. The formation of a thin and conformal active material film on this high surface area structure renders a reduced ionic diffusion and electronic conduction path length, mitigating the power-limiting effect of the active materials with low conductivities. Also, the highly conductive backbone serving as a mechanically stable and electrochemically inert current collector features minimized transport resistance for the electrons. Finally, the highly scalable nature of the multilayer structures enables the realization of high-performance electrodes for a wide range of applications from autonomous microsystems to macroscale portable electronic devices.

With the advantages of MOS monolithic technology in mind, Switched-Capacitor (SC) filter design and simulation are studied in this research. For SC circuit design, Shunt SC, bilinear, and LDI z-Transform methods are discussed. A practical design example, together with its circuit implementation, is used to check both design and simulation behaviors. For SC circuit simulation, certain methods are analyzed to compare with the Four-Port Method, from which a proposed method, STAMP, is derived. STAMP improves on the large computation time and storage space problems of other well-known programs. It has the capability of being expanded using some of the routines which are appended.

The main purpose of this thesis was to develop a printed circuit board for Autoliv Electronics AB. This circuit board should be placed in their test equipment to support some of their camera vision systems used in cars. The main task was to combine the existing hardware into one module. To be able to achieve this, the most important factors in designing a printed circuit board was considered. A satisfying power distribution network is the most crucial one. This was accomplished by using decoupling capacitors to achieve low enough impedance for all circuits. Calculations and simulations were executed for all integrated circuits to find the correct size and numbers of capacitors. The impedance of the circuit board was tested with a network analyzer to confirm that the impedance were low enough, which was the case. System functionality was never tested completely, due to delivery problems with some external equipment.

High capacitance devices were developed using rapid electrophoretic deposition (EPD) of barium titanate (BaTiO3) on ultrasonically etched nickel (Ni) substrates. The microstructural and electrical properties of films with varying thicknesses, sintering temperatures and substrate etching times were investigated to study their effect on the capacitance. Although increasing the capacitance was the primary goal, decreasing manufacturing costs and reducing environmental impact was also considered. After confirming the tetragonality and particle size of a 0.2 µm hydrothermal powder, it was dispersed in an aqueous-organic mixture of ethanol, acetone and water. A zeta potential of 50 mV was observed at the EPD pH level (6.8). Flocculation or coagulation was not likely in this situation. Therefore, mixing water with an organic solution was an effective method for reducing environmental impact while maintaining deposition quality. The presence of BaCO3 in the films was proven using X-ray diffraction. Other impurities such as TiO2 and NiO were not detected. A significant variation in the average grain size was not observed for films with different thicknesses whereas films sintered at different temperatures displayed greater variation. A bimodal pore size distribution in the samples suggested that the powder was agglomerated after deposition due to a high deposition voltage (20 V). Rapid deposition times of 2 to 8 seconds offered a potential for cost reduction compared to longer deposition times implemented in industry. Therefore the increased porosity was accepted. The dielectric constant of the films increased from 2900 to 6730 as the thickness increased from 17.75 µm to 47.5 µm. The dissipation factor decreased from 0.27 to 0.06 with increasing thickness. This behavior was attributed to a low dielectric constant interfacial layer and a higher dielectric leakage current at smaller thicknesses. The dielectric constant increased from 1700 to 6350 and the dissipation factor decreased from 0.23 to 0.04 as the sintering temperature increased from 1150°C to 1300°C. This was attributed to an increase in tetragonality with grain size and a decrease in porosity with sintering temperature. Finally, etching a substrate for 60 seconds increased its capacitance by 27.47% and using ultrasonic agitation further increased the capacitance by 8.75%. / Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2012-10-12 00:54:53.915

The Graphene term has become synonymous with layered carbon sheets having thicknesses ranging from the monolayer to stacks of about ten layers. For bulk volume production, graphite chemical exfoliation is the preferred solution. For this reason, much interest has congregated around different processes to oxidize and peel off graphite to obtain graphene oxide (GO) and its counterpart, reduced GO (rGO). The community at-large has quickly adopted those processes and has been intensively using the resulting (r)GO as active materials for a myriad of applications. Yet, partially given the absence of comparative studies in synthesis methodologies, a lack of understanding persists on how to best tailor these carbon materials for a given application. In this dissertation, the effect of using different chemical oxidation-reduction strategies for graphite, namely the impact on the structure and chemistry of GOs and rGOs is systematically discussed. Added to this, it is demonstrated that the drying step of the powdered materials cannot be neglected. Its influence is demonstrated in studies such as the optimization of capacitance of rGOs touted as electrochemical energy storage materials (Chapter 4). It is concluded that, in order to maximize the performance of GO and rGO materials for any particular application, there must be a judicious choice of their synthesis steps. Obvious as it may be for anyone working in Chemistry, this point has been surprisingly overlooked for too long by the vast majority of those working with these carbon materials.

The technical and scientific challenges to provide reliable sources energy for US and global economy are enormous tasks, and especially so when combined with strategic and recent economic concerns of the last five years. It is clear that as part of the mix of energy sources necessary to deal with these challenges, fuel cells technology will play critical or even a central role. The US Department of Energy, as well as a number of the national laboratories and academic institutions have been aware of the importance such technology for some time. Recently, car manufacturers, transportation experts, and even utilities are paying attention to this vital source of energy for the future. In this thesis, a review of the main fuel cell technologies is presented with the focus on the modeling, and control of one particular and promising fuel cell technology, aluminum air fuel cells. The basic principles of this fuel cell technology are presented. A major part of the study consists of a description of the electrochemistry of the process, modeling, and simulations of aluminum air FC using Matlab Simulink™. The controller design of the proposed model is also presented. In sequel, a power management unit is designed and analyzed as an alternative source of power. Thus, the system commutes between the fuel cell output and the alternative power source in order to fulfill a changing power load demand. Finally, a cost analysis and assessment of this technology for portable devices, conclusions and future recommendations are presented. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2013.

The development of energy storage devices has represented a significant technological challenge for the past few years. Electrochemical double-layer capacitors (EDLCs), also named as supercapacitors, are a likely competitor for alternative energy storage because of their low-cost, high power density, and high fast charge/discharge rate. The recent development of EDLCs requires them to be lightweight and flexible. There are many fabrication techniques used to manufacture flexible EDLCs, and these methods can include pre-treatment to ensure more efficient penetration of activated carbon (AC) patterns onto the substrate, or those that utilise masks for the definitions of patterns on substrates. However, these methods are inconvenient for building cost-effective devices. Therefore, it was necessary to find a suitable process to reduce the steps of manufacture and to be able to print multiple materials uniformly. This research work describes the first use of a 3D printing technology to produce flexible EDLCs for energy storage. In this research work, the four essential elements for the EDLCs substrate, current collector, activated electrode, and gel electrolyte were investigated. The AC powder was milled by ball milling to optimise the paste deposition and the electrochemical performance. A flexible composite EDLC was designed and manufactured by 3D printing. The electrochemical performance of the flexible composite EDLCs was then examined. Being highly flexible is one of the critical demands for the recent development of EDLCs. Therefore, highly flexible EDLCs were designed and manufactured by only one single extrusion process. The 3D highly flexible EDLC maintains significant electrochemical performance under a mechanical bending test. To meet the power and energy requirements, the EDLCs were connected and tested in series and parallel circuits. A supercapacitor based on printed AC material displays an area specific capacitance of 1.48 F/cm2 at the scan rate of 20 mV/s. The coulombic efficiency for the flexible EDLC was found to be 59.91%, and the cycling stability was achieved to be 56% after 500 cycles. These findings indicate that 3D printing technology may be increasingly used to develop more sophisticated flexible wearable electronic devices.