With the world’s increasing energy demand and the depletion of fossil fuels, there is a growing demand for the development of alternative and clean energy sources. Batteries and fuel cell technologies have been cited as next generation technologies to provide sustainable energy; however, these technologies are insufficient in supplying high power in short time periods that can be produced by oil as an energy source. In contrast, electrochemical capacitors possess fast charging/discharging capabilities with high power output. As a result, the use of electrochemical capacitors in commercial applications has generated strong interest. Examples of commercial applications include emergency back-up power, consumer electronics, and hybrid vehicles. Commercially available electrochemical capacitors are based on carbonaceous materials with high surface area, excellent electrical conductivity, and wettability which statically store the charges in pores. In contrast, pseudocapacitive materials, namely transition metals, utilize fast reversible faradaic reactions on the surface of the materials which allow for greater energy storage than carbonaceous materials. Currently, many research activities are being focused on pseudocapacitive materials in an effort to enhance their energy storage capabilities. This thesis presents research on a pseudocapacitive material: nickel hydroxide/oxide hybrid. Also, it identifies the hybrid material’s lack of conductivity which can negatively impact its capacitive performance. An addition of carbon supports is recommended to enhance the conductivity. There are two parts to this study. The first study addresses the synthesis of the nickel hybrid structures through solvothermal process and calcination. The materials are thoroughly analyzed through physical and electrochemical characterizations. The issue of using the hybrid material as pseudocapacitor electrodes are identified at this stage. The second part of the study addresses the effect of different carbon additives in the nickel hybrid material. Commonly known carbon additives are incorporated into the nickel hybrid material and analyzed through electrochemical characterization to distinguish the best carbon support for the nickel hydroxide/oxide.

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Electrochemical capacitors (ECs) have received a significant level of interest for use in the electric utility industry for a variety of potential applications. For example, ECs integrated with a power conversion system can be used to assist the electric utility by providing voltage support, power factor correction, active filtering, and reactive and active power support. A number of electric utility applications have been proposed but, to date, ECs have not been very well characterized for use in these applications. Consequently, there is a need to gain a better understanding of ECs when used in electric utility applications. ECs are attractive for utility applications because they have higher energy density than conventional capacitors and higher power density than batteries. ECs also have higher cycle life than batteries, which results in longer life spans. To better understand the system dynamics when ECs are used for utility applications requires suitable models that can be incorporated into the variety of software programs currently used to create dynamic simulations for the applications, programs such as PSPICE™, MATLAB Simulink™, and PSCAD™. To obtain a relevant simulation with predictive capability, the behavior of the EC on which the model is based must be well defined; this necessitates a thorough understanding of the electrical characteristics of these devices. This paper and the associated research focus on the use of the electrochemical impedance spectroscopy (EIS) to develop nonlinear equivalent circuit models to better understand and characterize symmetric ECs (SECs) for electric utility applications. It also focuses on the development of analytical solutions to better understand SEC efficiency and energy utilization. Representative static synchronous compensator (StatCom) systems, with and with out SECs, were simulated and discussed. The temperature effects on device ionic resistance and capacitance are covered as is the effect of temperature on maximum power transfer to a resistive load. Experimental data showed that the SEC's double-layer capacitance and ionic resistance are voltage dependent. Therefore a voltage-dependent RC network model was developed and validated and the results showed that this type of model mimicked the experimental SEC better than traditional electrical models. Analytical solutions were developed for the efficiency and energy utilization of an SEC. The analytical solutions are a function of operating voltages, constant current, and ionic resistance. The operating voltage method is an important factor in system design because the power conversion interface is typically limited by a voltage window and thus can determine the performance of SECs during charge and discharge. If the operating voltage window is not properly selected the current rating of the system can be reduced thus limiting the SECs performance. / Ph. D.

In this research, different anionic dopants were investigated for the fabrication of polypyrrole (PPy) electrode materials for electrochemical capacitors (ECs). Anionic dopants from catechol, salicylic acid and chromotropic acid family allowed for the formation of adherent PPy thin film on stainless steels current collectors by electropolymerization. Comparison between galvanostatic and pulse electropolymerization of PPy thin films was made. Pulse electropolymerization was found to provide improved impregnation of Ni plaque current collectors and formation of nanostructured coating. The electrodes prepared by pulse electropolymerization showed higher porosity, lower electrical resistance, higher capacitance and improved cyclic stability. In order to overcome the mass loading limitation for thin film PPy electrodes, chemical polymerization of PPy was investigated. The use of fine particles, prepared by the chemical polymerization method, allows impregnation of Ni foams and fabrication of porous electrodes with high materials loading. Moreover, improved capacitive performance and cyclic stability was obtained for PPy electrodes with high materials loading using new anionic dopants. To further improve the cyclic stability of PPy electrodes, multiwalled carbon nanotubes (MWCNT) were used for the fabrication of PPy-MWCNT composite materials due to their high surface area and excellent conductivity. Different dispersants as well as dispersing methods were studied in order to obtain stable MWCNT suspensions. Among those dispersants, multifunctional anionic dopants were found to benefit the formation of MWCNT suspension as well as the polymerization of PPy. A conceptually new approach has been developed for the fabrication of PPy coated MWCNT based on the use of multifunctional anionic dopants. The use of PPy coated MWCNT allowed excellent electrochemical performance for high active mass loadings, required for commercial EC applications. The electrodes and devices made of PPy coated MWCNT showed high capacitance, good capacitance retention at high charge-discharge rates and good cycling stability. The record high capacitance achieved at high charge-discharge rates is promising for the development of high power ECs. / Thesis / Doctor of Philosophy (PhD)

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.

In this research various techniques were used to study surface groups on carbon electrodes, including the spectroscopic techniques UV-Vis-NIR, FTIR, PAS, XPS and XAS, as well as the Boehm titration. The methods determined to give the best insight to the surface functionalities on the carbon were XPS, XAS and the Boehm titration. The Boehm titration methodology was standardized before use. An in situ method of examining surface groups using spectroscopy during electrochemistry was attempted. Spectroelectrochemistry is a useful way to gain information on how electrochemistry affects electrodes during experimentation; however, it was unsuccessful for the carbon used and remains to be developed. Polymerization of the copolymer of PANI and PPy as a potential electrode material for ECs was achieved by electrochemical cycling and was studied through spectroelectrochemical measurements. Overall, the research completed included the initial stages to studying electrodes for electrochemical capacitors using analytical, non-electrochemistry techniques in conjunction with electrochemistry.

Layer-by-Layer (LbL) deposition of electrochemically active materials on porous carbon electrodes is a proven method to leverage both electrochemical double-layer capacitance and pseudocapacitance for charge storage on the same electrode. LbL coatings are held together by electrostatic attraction between adjacent layers of oppositely charged molecules. Previous studies have used Keggin polyoxometalates to great effect as the anionic layer in LbL electrode modification, but little effort has been devoted to cationic material selection and LbL process optimization. This work investigated alternatives to the conventional, electrochemically inert polydiallyldimethylammonium (PDDA) cation. The use of fuchsin molecular cations in LbL deposition improved the specific energy and specific power of modified electrodes. Fuchsin cation also rendered the environmentally harmful oxidative surface activation step unnecessary for LbL deposition. Process parameters were optimized for MWCNT/Fuchsin/POM samples, and post-LbL electrochemical polymerization was found to further improve the performance of these electrodes.

The objective of this thesis is to study the effect of process conditions on structure and electrochemical properties of polyacrylonitrile (PAN)/carbon nanotube (CNT) composite film based electrodes developed for electrochemical capacitors. The process parameters like activation temperature, CNT loading in the composite films are varied to determine optimum process conditions for physical (CO2) and chemical (KOH) activation methods. The PAN/CNT precursors are stabilized in air, carbonized in inert atmosphere (argon), and activated by physical (CO2) and chemical (KOH) methods. The physical activation process is carried out by heat treating the carbon precursors in CO2 atmosphere at activation temperatures. In the chemical activation process, stabilized carbon precursors are immersed in aqueous solutions of activating media (KOH), dried, and subsequently heat treated in an inert atmosphere at the activation temperature. The structure and morphology are probed using scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy. The specific capacitance, power and energy density of the activated electrodes are evaluated with aqueous electrolytes (KOH) as well as organic electrolyte (ionic liquid in acetonitrile) in Cell Test. The surface area and pore size distribution of the activated composite electrodes are evaluated using nitrogen absorption. Specific capacitance dependence on factors such as surface area and pore size distribution are studied. A maximum specific capacitance of 300 F/g in KOH electrolyte and maximum energy density of 22 wh/kg in ionic liquid has been achieved. BET surface areas in excess of 2500 m2/g with controlled pore sizes in 1 - 5 nm range has been attained in this work.

Supercapacitors have emerged in recent years as a promising energy storage technology. The main mechanism of energy storage is based on electrostatic separation of charges in a region at the electrode-electrolyte interface called double layer. Various electrode materials including carbon and conducting polymers have been used in supercapacitors. Also, supercapacitors offer high life cycle and high power density among electrochemical energy storage devices. Despite their interesting features, supercapacitors present some disadvantages that limit their competitivity with other storage devices in some applications. One of those drawbacks is high self-discharge or leakage. The leakage occurs when electrons cross the double layer to be involved in electrochemical reactions in the supercapacitor’s electrolyte. In this work, the first research project demonstrates that the addition of a very thin blocking layer to a supercapacitor electrode, can improve the energy storage capability of the device by reducing the leakage. However, the downside of adding a blocking layer is the reduction of the capacitance. A second project developed a mathematical model to study how the thickness of the blocking layer affects the capacitance and the energy density. The model combines electrochemical and quantum mechanical effects on the electrons transfer responsible of the leakage. Based on the model, a computational code is developed to simulate and study the self-discharge and the energy loss in hypothetical devices with different thicknesses of the blocking layer. The third research project identified the optimal amount of a surfactant (Triton-X 100) that had a significant effect on the double layer capacitance and conductivity of a spin-coated PEDOT:PSS (poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate)) electrode. The effect of the concentration of the surfactant was investigated by measuring the electrochemical properties and the conductivity of different electrodes. The electrodes were fabricated with different concentrations of the surfactant. Scanning electron microscopy characterizations confirmed the structural change in the PEDOT:PSS that contributed to the capacitance and conductivity enhancement. A final research project proposed an approach on how to utilize the modified PEDOT:PSS added to different photoactive dyes to design a photoactive supercapacitor. The new approach showed the possibility of using a supercapacitor device as an energy harvesting as well as a storage device.

Room temperature molten liquids are proposed to be good alternates for volatile and harmful organic compounds. They are useful in varied areas of applications ranging from synthesis, catalysis to energy storage molten electrolytes have certain unique characteristics such as low vapour pressure, reasonably high ionic conductivity, high thermal stability and wide electrochemical window. These molten liquids can be classified in to two types depending on the nature of the species present in the liquids. One, those liquids consists only of ions (e.g) conventional imidazolium based ionic liquids and other that consists of ions and solvents (e g) acetamide eutectics. Acetamide and its eutectics from room temperature molten solvents that is unique with interesting physicochemical properties. The solvent properties of molten acetamide are similar to water, with high dielectric consist of 60 at 353 k. its acid – base properties are also similar to water, and it can solublise variety of organic and inorganic compounds as well. in the present studies room temperature molten liquids consisting of acetamide as one of the components have been prepared and used for various applications. Room temperature molten electrolytes consisting of magnesium perchlorate/magnesium triflate as one of the constituents have been used for rechargeable magnesium batteries where as those consisting of zinc perchlorate /zinc triflate have been used for zinc based rechargeable batteries. Full utilization of cathode material (y-mno2) is achieved using amide-based molten liquid as electrolyte in rechargeable zinc based batteries. Ammonium nitrate/ lithium nitrate containing electrolytes have been used for electrochemical super capacitors. They have been used as solvent cum stabilizers for metallic nanochains that can be used as substrate in surface enchanced Raman scattering studies.