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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.

The typical catalyst layer structure for proton exchange membrane (PEM) fuel cells has changed little over the last two decades. A new electrode design with improved control over factors such as ionic and electrical pathways, porosity, and catalyst placement, could allow the application of less expensive catalyst alternatives. In this work, a novel electrode design based on ionomer-coated carbon nanofibers is proposed and studied. Governing equations for this design were established, and a mathematical model was created and solved using MATLAB to predict the performance of the new electrode design. A parametric study was performed to identify the design variables that had the most significant effect on performance. The best performing catalyst layer design studied with this model produces a current density of 1.1 A cm-2 at 600 mV which is better than state-of-the-art cathode designs. The results offer insight into the performance of ionomer-coated carbon nanofiber catalyst layers and can guide the fabrication and testing of these promising catalyst layer structures. / Master of Science / Proton exchange membrane (PEM) fuel cells have the potential to replace traditional energy conversion systems in many applications, however their widespread adoption is currently limited by their high cost and insufficient durability. PEM fuel cells are expensive because they require the use of platinum as a catalyst. Currently, less expensive non-platinum catalysts, must be used in much higher amounts in the catalyst layer to achieve similar electrochemical activity, creating very thick catalyst layers. Traditional fuel cell catalyst layer structures are designed to be thin and perform poorly when thick enough to accommodate non-platinum catalysts. This work proposes a novel catalyst layer design based on ionomer-coated carbon nanofibers that can allow for thicker catalyst layers and much higher catalyst loadings. A mathematical model was developed for the novel catalyst layer based on first principles. The model was solved using MATLAB to predict the performance of the new catalyst layer design. A parametric study was performed to identify the critical design variables and their effect on catalyst layer performance. The best performing catalyst layer design studied with this model produced a current density of 1.1 A cm-2 at 600mV, which is better than state-of-the-art fuel cell designs. This work is meant to offer insight into the performance of an ionomer-coated nanofiber catalyst layer and to guide future research in the fabrication of high performance fuel cells based on this novel catalyst layer architecture.

Intracranial electroencephalography (iEEG) provides superior diagnostic and research benefits over non-invasive EEG in terms of spatial resolution and the level of electrophysiological detail. Post-operative Computed Tomography (CT) scans provide the precision in electrode localization required for clinical purposes; however, to use this data for basic sleep research the challenge lies in identifying the precise locations of the implanted electrodes’ recording sites in terms of neuroanatomical regions as well as reliable scoring of their sleep data without the aid of facial electrodes. While existing methods can be combined to determine their exact locations in three-dimensional space, they fail to identify the functionally relevant gray matter areas that lie closest to them, especially if the points lie in the white matter. We introduce an iterative sphere inflation algorithm in conjunction with a unified pipeline to detect the exact as well as nearest regions of interest for these recording sites. Next, for sleep scoring purposes, we establish differences observed in alpha band activity between wakefulness and rapid eye movement (REM) sleep in frontal and temporal regions of iEEG patients. Lastly, we implement an automated sleep scoring method relying on the variations in alpha and delta bands power during sleep which can be applied to large sets of iEEG data recorded without accompanying electrooculogram (EOG) and electromyogram (EMG) electrodes available across labs for use in studies pertaining to neural dynamics during sleep. / M.S. / Patients with epilepsy (a neurological disorder characterized by seizures) who do not respond to medication often undergo invasive monitoring of their brains’ electrical activity using intracranial electroencephalography (iEEG). iEEG requires a surgery in which electrodes are inserted directly into the patient’s brain for better measurements. While they are monitored, these patients offer a unique opportunity for research studies that investigate the role of sleep in various learning, memory mechanisms and other health-related areas. This is because the direct contact of the electrodes with the brain tissue provides far superior quality and resolution of brain activity data in comparison to non-invasive cap-based EEG that healthy subjects wear over their scalp. However, in order to derive meaningful conclusions from these invasive recordings, we must first know the exact areas of the brain from which each site records the electrical data. We must then be able to identify which stage of sleep the patient is in at any given point in time, to be able to successfully correlate specific sleep stage-related activity with our research objectives; these patients often lack the facial electrodes used for standard sleep scoring procedures. To solve the first problem, we present an electrode localization method along with an algorithm to determine which neighboring regions contribute most to a given site’s recorded data. For the second problem, we first establish a difference in the behavior of alpha waves in the brain between wakefulness and rapid eye movement (REM) sleep. Lastly, we present an automated method to classify sleep data into different stages based on the variation in alpha waves and delta waves found during sleep.

The present study presents the current status of research into the production of active carbons from environmental applications using waste newspaper. A number of studies have been performed to investigate the pyrolysis of waste paper ash to carbon gel.Although several studies report the production of carbon from waste tyre, bamboo, coconut shell, this study is first of its kind that for the first time, the waste newspapers have been used as a raw material for supercapacitor electrodes. A cheap raw material, and a simple method of preparation make this carbon gel more economically attractive. By carbonizing a waste paper a new carbon-carbon composite as electrode material was prepared through RF gel. The surface morphology and electrochemical characteristics of the carbon composite were investigated by Scanning Electron Microscopy, Cyclic Voltammetry, Electrochemical impedance spectroscopy and galvanostatic charge-discharge cycle tests with various current densities. The SEM study reveals that the connectivity between the grains increases during cycling thus enhances the cyclic stasitity. The CV’s suggests that there is simultaneous redox and capacitive behavior and these behaviors are highly reversible even after 8 lakh cycles. The reversibility was still maintained even in the range – 3 V to + 3 V. The charge/discharge cycle tests reveal the cycle stasitity and delivered more then 8 lakh cycles at 100 mA/cm2. The maximum specific capacitance of 300 F/g was obtained at 150 mA/cm2 current density. These results imply that this newspaper based carbon gel be used as potential candidate for supercapacitors.

京都大学 / 新制・課程博士 / 博士(工学) / 甲第25302号 / 工博第5261号 / 新制||工||2001(附属図書館) / 京都大学大学院工学研究科物質エネルギー化学専攻 / (主査)教授 安部 武志, 教授 阿部 竜, 教授 陰山 洋 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DGAM