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The rising energy consumption worldwide is leading to significant increases in energy production with fossil fuels being the major energy source. The negative environmental impact of fossil fuel use and its finite nature requires the use of alternative sources of energy. Solar energy is a clean alternative energy source; however, its intermittent nature is a major impediment that needs to be reduced or eliminated by the development of cost effective energy storage. Thermal storage in tanks filled typically with molten salt at elevated temperatures is widely used in concentrating solar power plants to generate electricity during periods of low daytime solar radiation or night time. Similarly, electrical storage in batteries, etc. is used in conjunction with photovoltaic solar power plants. Electrochemical supercapacitors can be effectively used for electrical storage, either alone or in a hybrid configuration with batteries, for large scale energy storage as well as in electric vehicles and portable electronics. Unlike batteries’, supercapacitor electrodes can be made of materials that are either less toxic or biodegradable and can provide almost instantaneous power due to their unique charge storage mechanism similar to conventional capacitors found in most electronics. Unfortunately, the same storage mechanism prevents supercapacitors from having high energy density. The purpose of this dissertation is to investigate organic and inorganic electrode materials that can increase the specific capacitance and energy density of supercapacitors. Additionally, certain types of supercapacitor electrode materials store the charges at the electrode/electrolyte interface preventing any deformation of the material and thus increasing its cycle life by two to three orders of magnitude. Transition metal oxides, layered transition metal chalcogenides, and their composites with graphene and conducting polymers have been synthesized, characterized, and their electrochemical performances evaluated for suitability as electrode materials for supercapacitor applications. Morphology and crystalline structure characterization methods used, such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT-IR), were used throughout this work. Electrochemical characterization involved cyclic voltammetry (CV), constant current charge and discharge (CCCD), and electrochemical impedance spectroscopy (EIS) in two and three electrode configuration using aqueous and organic electrolytes. Ruthenium oxide-graphene (RuO2-G) electrodes were tested in the two-electrode cell configuration and exhibit an areal capacitance of 187.5 mF cm-2 in 2M H2SO4 at a RuO2:G ratio of 10:1. Due to RuO2 high toxicity, scarcity, and high cost, manganese oxide-graphene (MnO-G) was used as an alternative but its low specific capacitance remains a major stumbling block. The electrodes’ mass loading was studied in detail to understand the effects of thickness on the measured specific capacitance. Layered transition metal chalcogenides are structurally similar to graphene but possess different characteristics. Molybdenum sulfide (MoS2) is a two-dimensional material that has lower conductivity than graphene but larger sheet spacing making it easy for other materials to intercalate and form composites such as molybdenum sulfide-polyaniline (MoS2-PANI). MoS2-PANI electrodes, with different thicknesses, were measure in a three-electrode cell configuration resulting in gravimetric capacitance of 203 F g-1 for the thinnest electrode and areal capacitance of 358 mF cm-2 for the thickest electrode; all measurements performed using 1M H2SO4 aqueous electrolyte. Attempts were also made to reduce the supercapacitor self-discharge by depositing on the electrode a blocking thin layer of barium strontium titanate (BST). The results were rather inconclusive because of the large thickness of the deposited BST layer. However, they strongly suggest that a very thin BST layer could improve the overall capacitance because of the very large dielectric constant of the BST material. Additional work is required to determine its effects on self-discharge.

The generation of high current multi-MeV protons and ions by irradiation of short pulse high intense laser on an ultra-thin target has been observed and subjected great interest in recent. When ultra-thin overdense target is irradiated by focused ultraintense laser pulse, hot electrons are generated by various mechanisms and they generate energetic ion beams. In TNSA, a quasi-electrostatic field is produced on the target rear surface when the the laser pulse interacts with overdense target, driving hot electrons go torward the target rear surface. However, this mechanism results in a range of field gradients leading to a broad proton energy distribution typically. To overcome the issue, an alternative accelration mechanism has been presented to achieve the quasi-monoenergetic proton acceleration and the mechanism is called Radiation Pressure Acceleration. In the RPA, the radiation pressure push electrons into the target smoothly and setting up an electrostatic field by the laser pressure. In this thesis, we study two alternative experimental methods for the quasi-monoenergetic proton acceleration and find experimental feasibility of the presented methods from other research groups. / text

Lithium ion batteries (LIBs) play an essential role in modern life. Although relatively unknown throughout past decades, LIBs have supplanted several categories of chemically rechargeable batteries including lead-acid, nickel-cadmium and nickel-hydrogen batteries. Nowadays, LIBs dominate the market of portable electronic devices such as mobile phones, digital cameras and laptops. As the price of petroleum keeps increasing, electrically powered or assisted vehicles using LIBs are similarly gaining in the automotive market. However, current state-of-art LIBs using graphite as their electrical anode and Li metal oxides as the cathode are facing major challenges. For example, the current LIBs are approaching their capacity limit. Batteries that can maintain high charge and discharge rates are in great demand, which has not been adequately addressed by modern LIBs. Safety issues with these current batteries are being reported even from some market leaders such as Boeing and Tesla. Herein, several categories of novel anode materials have been investigated in a search for promising candidates to enable evolution of the next generation of lithium ion batteries. This research included silicon-carbon based materials, especially silicon-graphene (Si-G) materials and their derivatives, and transitional metal based materials, e.g., cobalt oxide (Co3O4). In this proposed work, Si-G composites were synthesized via a freeze-drying method; the conditions of the synthesis were controlled and adjusted to obtain a Si-G composite with the most promising morphology as well as battery performance. Based on preliminary results, graphene wrapped silicon electrodes showed significantly improved cycling performance than bare silicon electrodes. At high charge and discharge rates it was found that Si-G composites also showed superior stability and capacity retention over bare silicon electrodes. After 200 cycles, the optimized Si-G composite maintained a capacity retention close to 100%, with a capacity of 800 mAh g-1 at a 0.2 C rate and 600 mAh g-1 at a 1 C rate. This observation was a prominent increase from the performance of commercial graphite-based batteries at a theoretical capacity 372 mAh g-1. Considering the facile fabrication method and increasing use of commercial silicon nano-particles (Si-NPs) into account, Si-G composites could be a promising candidate for the anode material in LIBs. Extended work on the Si-G project also involved further decorations based on the Si-G composite synthesized from the method previously mentioned, as well as improvement on the synthesis method to make it more applicable for industrial purposes. Cobalt Oxide (Co3O4), a transitional metal oxide which has a theoretical capacity of 890 mAh g-1, draws attention as an anode material in LIBs due to its capacity compared to graphite and heavily reduced degradation compared to silicon. A novel electrode fabrication procedure was adopted in this research together with a simple material-synthesizing methodology. Similar to common silicon electrodes, Co3O4 suffers from poor electron conductivity volume change upon cycling. Herein the Co3O4 active material is directly deposited on stainless steel mesh, serving as both a current collector and a substrate for the active material. Through adapting the electrode fabrication process by directly depositing on the stainless steel electron conductor, the traditional conductive carbon material and binder requirements can be avoided. As a result, the process is reduced in both cost and complexity. The presented novel electrode design facilitates both ion diffusion and electron transportation, improving the overall performance of the material in LIBs. After 100 cycles of charge and discharge, Co3O4 on stainless steel mesh shows a capacity around 770 mAh g-1, which is more than twice that of graphite. The capacity retention was around 90% in this case.

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Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第14161号 / 工博第2995号 / 新制||工||1444(附属図書館) / 26467 / UT51-2008-N478 / 京都大学大学院工学研究科マイクロエンジニアリング専攻 / (主査)教授 立花 明知, 教授 榊 茂好, 教授 木村 健二 / 学位規則第4条第1項該当

Sound power measurements of acoustic sources are typically performed in anechoic or reverberation chambers using acoustic pressure according to international standards. The anechoic chamber creates a free-field environment where the sound power is estimated from the squared pressure integrated over some enveloping surface. The reverberation chamber produces diffuse-field conditions, where sound power is proportional to the spatially averaged squared pressure. In semi-reverberant environments, the direct and reverberant energies each contribute to the total measured field. If the kinetic and potential components of acoustic energy density are weighted appropriately, the spatial variation of the field can be significantly reduced compared to squared pressure. This generalized energy density allows an adaptation of the sound power formulation by Hopkins and Stryker to be used to make an efficient and accurate in situ sound power estimate of a noise source in a non-ideal acoustical environment. Since generalized energy density optimizes the spatial uniformity of the field, fewer measurement positions are needed compared to traditional standards. However, this method breaks down for sources that are large and extended in nature and considerably underestimates the sound power. This thesis explores the practical limits of this method related to the sound power underestimation. It also seeks to understand the special considerations necessary to achieve accurate, survey-grade sound power data of large, extended noise sources through a laboratory study of custom extended and compact sources. A modified method to accurately and efficiently measure the sound power of large, extended sources is proposed with results.

The rapid development of microelectronics has equally rapidly increased the demand for miniaturized energy storage devices. On-chip micro-supercapacitors (MSCs), as promising power candidates, possess great potential to complement or replace electrolytic capacitors (ECs) and microbatteries (MBs) in various applications. Recently, planar two-dimensional (2D) MSCs, composed of isolated thin-film microelectrodes with extremely short ionic diffusion path and free of separator on a single substrate, have become particularly attractive because they can be directly integrated with microelectronic devices on the same side of a flexible substrate to act as a standalone microsized power source. However, the areal capacities and energy densities of the 2D MSCs are commonly limited by the low voltage window and the thin layer of the electrode materials. Obviously, integrating more active material into cleverly designed three-dimensional (3D) electrode architectures will effectively increase the areal performance within a limited footprint area in spite of some loss of flexibility and cycling stability. However, it is still a big challenge to effciently and cost-effectively fabricate on-chip MSCs with high electro-chemical performance and abundant electrode structures. Here, three types of MSCs including graphene-based 2D planar MSCs, on-chip 3D interdigital MSCs and self-assembled 3D tubular MSCs were fabricated, respectively. The fabrication process, electrode materials structure and morphology, electrochemical performance, mechanical properties, integration process and difficulty, and practical application of these 2D and 3D devices are studied in detail.