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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Nanostructured Materials for Energy Storage and Conversion

Ji, Xiulei January 2009 (has links)
Efficient, cost effective, and environmentally friendly energy storage and conversion systems are highly desirable to meet ever increasing demands. Nanostructured materials have attracted great interest due to their many superior characteristics in these energy applications. These materials, typically nanoporous or nanostructured, exhibit faster charge transports, better contact, and sometimes new electrochemical reactivity, which leads to their high energy density, high power and/or great catalytic performances. A series of functional nanostructured materials have been fabricated with new synthetic schemes. Nanoporous materials technology and solid state electrochemistry have been attempted to be integrated in this study. New functional nanoporous materials have been sought for electrochemical purposes. By employing a simple dilution strategy, homogeneously sized, ordered mesoporous silica nanorods (SBA-15), spanning about 10 porous channels in width and ranging from 300 to 600 nm in length were prepared. By employing SBA-15 nanorods as a template, ordered mesoporous carbon (OMC) CMK-3 nanorods were prepared. These porous nanorods exhibit enhanced mass transfer kinetics in their applications owing to their short dimensions. To improve the electronic conductivity of OMC and exploit otherwise wasted copolymer surfactant cross-linked in the channels of as-synthesized SBA-15, direct graphitic mesoporous carbon (termed as DGMC) were synthesized from the copolymer surfactant by employing transition metals (Fe, Co, Ni) as a catalyst. DGMC exhibit three orders higher conductivity and better thermal stability than non-graphitic OMC materials. A series of nanostructured composites were fabricated by employing OMC as structure backbones and/or electronic conduits. DGMC/MoO2 as a Li ion battery anode exhibits a reversible capacity more than twice the value that a graphite anode can provide. Due to the confined and nanosized dimensions of the MoO2, the composite exhibits a cycle life with no capacity fading. Polymer modified OMC/sulfur interwoven nanostructures were prepared and applied as a cathode in Li-S batteries. The nanostructure displays all of the benefits of confinement effects at a small length scale. The nanostructure provides not only high electronic conductivity but also great access to Li+ ingress/egress for reactivity with the sulfur. The tortuous pathways within the framework and the surface polymer strongly retard the diffusion of polysulfide anions out from the channels into the electrolyte and minimize the loss of active mass in the cathode, resulting in a stabilized cycle life at reasonable rates. The Li-S batteries can supply up to near 80% of the theoretical capacity of sulfur (1320 mA∙h/g). This represents more than five times the specific capacity of conventional intercalation Li ion batteries. The assembly process for OMC/S is simple and broadly applicable, conceptually providing new opportunities for materials scientists for tailored design that can be extended to many different electrode materials. Size-controlled supported metal and intermetallic nanocrystallites are of substantial interest because of their wide range of electrocatalytic properties. These intermetallics are normally synthesized by high temperature techniques; however, rigorous size control at high temperature is very challenging. A simple and robust chemically controlled process was developed for synthesizing size controlled noble metal, or bimetallic nanocrystallites, embedded within the porous structure of OMC. The method is applicable to a wide range of catalysts, namely bimetallic PtBi but also including Pt, Ru, Rh and Pd. By using surface-modified OMC, nanocrystallites are formed with monodisperse sizes as low as 1.5 nm, that can be tuned up to 2 and 3.5 nm (equivalent to the channel size of OMC) by thermal treatment. The method is also tailored for the deposition of catalysts on conventional fuel-cell carbon supports. OMC-PtBi nanohybrids were investigated as catalysts for formic acid oxidation for the first time. OMC-PtBi catalysts show an absence of CO poisoning. The excellent catalytic properties can be attributed to the successful catalyst preparation and the faithful practice of the “ensemble effect” at the nanoscale level. A new agitation-friction methodology was developed to prepare the nano-OMC/S composite. The method is completely different from any conventional impregnation which requires the voluntary molecular mobility of guest phases. The method relies on frictional forces, and the hydrophobic attraction of the mixing components. This is the first example of a nanoporous solid which can be infiltrated by another solid phase at room temperature. The C/S nanocomposite exhibits not only better Pt ion sorption kinetics than its bulk counterpart, but also a higher pseudo-second-order rate constant than chitosan sorbents.
2

Nanostructured Materials for Energy Storage and Conversion

Ji, Xiulei January 2009 (has links)
Efficient, cost effective, and environmentally friendly energy storage and conversion systems are highly desirable to meet ever increasing demands. Nanostructured materials have attracted great interest due to their many superior characteristics in these energy applications. These materials, typically nanoporous or nanostructured, exhibit faster charge transports, better contact, and sometimes new electrochemical reactivity, which leads to their high energy density, high power and/or great catalytic performances. A series of functional nanostructured materials have been fabricated with new synthetic schemes. Nanoporous materials technology and solid state electrochemistry have been attempted to be integrated in this study. New functional nanoporous materials have been sought for electrochemical purposes. By employing a simple dilution strategy, homogeneously sized, ordered mesoporous silica nanorods (SBA-15), spanning about 10 porous channels in width and ranging from 300 to 600 nm in length were prepared. By employing SBA-15 nanorods as a template, ordered mesoporous carbon (OMC) CMK-3 nanorods were prepared. These porous nanorods exhibit enhanced mass transfer kinetics in their applications owing to their short dimensions. To improve the electronic conductivity of OMC and exploit otherwise wasted copolymer surfactant cross-linked in the channels of as-synthesized SBA-15, direct graphitic mesoporous carbon (termed as DGMC) were synthesized from the copolymer surfactant by employing transition metals (Fe, Co, Ni) as a catalyst. DGMC exhibit three orders higher conductivity and better thermal stability than non-graphitic OMC materials. A series of nanostructured composites were fabricated by employing OMC as structure backbones and/or electronic conduits. DGMC/MoO2 as a Li ion battery anode exhibits a reversible capacity more than twice the value that a graphite anode can provide. Due to the confined and nanosized dimensions of the MoO2, the composite exhibits a cycle life with no capacity fading. Polymer modified OMC/sulfur interwoven nanostructures were prepared and applied as a cathode in Li-S batteries. The nanostructure displays all of the benefits of confinement effects at a small length scale. The nanostructure provides not only high electronic conductivity but also great access to Li+ ingress/egress for reactivity with the sulfur. The tortuous pathways within the framework and the surface polymer strongly retard the diffusion of polysulfide anions out from the channels into the electrolyte and minimize the loss of active mass in the cathode, resulting in a stabilized cycle life at reasonable rates. The Li-S batteries can supply up to near 80% of the theoretical capacity of sulfur (1320 mA∙h/g). This represents more than five times the specific capacity of conventional intercalation Li ion batteries. The assembly process for OMC/S is simple and broadly applicable, conceptually providing new opportunities for materials scientists for tailored design that can be extended to many different electrode materials. Size-controlled supported metal and intermetallic nanocrystallites are of substantial interest because of their wide range of electrocatalytic properties. These intermetallics are normally synthesized by high temperature techniques; however, rigorous size control at high temperature is very challenging. A simple and robust chemically controlled process was developed for synthesizing size controlled noble metal, or bimetallic nanocrystallites, embedded within the porous structure of OMC. The method is applicable to a wide range of catalysts, namely bimetallic PtBi but also including Pt, Ru, Rh and Pd. By using surface-modified OMC, nanocrystallites are formed with monodisperse sizes as low as 1.5 nm, that can be tuned up to 2 and 3.5 nm (equivalent to the channel size of OMC) by thermal treatment. The method is also tailored for the deposition of catalysts on conventional fuel-cell carbon supports. OMC-PtBi nanohybrids were investigated as catalysts for formic acid oxidation for the first time. OMC-PtBi catalysts show an absence of CO poisoning. The excellent catalytic properties can be attributed to the successful catalyst preparation and the faithful practice of the “ensemble effect” at the nanoscale level. A new agitation-friction methodology was developed to prepare the nano-OMC/S composite. The method is completely different from any conventional impregnation which requires the voluntary molecular mobility of guest phases. The method relies on frictional forces, and the hydrophobic attraction of the mixing components. This is the first example of a nanoporous solid which can be infiltrated by another solid phase at room temperature. The C/S nanocomposite exhibits not only better Pt ion sorption kinetics than its bulk counterpart, but also a higher pseudo-second-order rate constant than chitosan sorbents.
3

Research and Development of a Smart Li-Battery Management System

Hung, Yu-Huan 29 June 2005 (has links)
This research proposes a smart battery management system applied to Li-Battery. The system not only can monitor the batteries for all kinds of parameters but also modify them by users. Besides, in estimating the residual capacity of Li-ion batteries, an automatic measurement platform is set up in order to record the data of Li-battery in different kinds of charge-discharge condition and to analysis the characteristics. In monitoring used battery capacity, Modified-Coulomb-Measuring method is proposed and it can accurately estimate the residual capacity according to the effect of output current and environment temperature. In addition to estimate the residual capacity accurately, Smart Battery System can record the information of Li-batteries over a long period of time, and the log files can be used for further battery characteristics analysis.
4

Synthese von Metallnitrid- und Metalloxinitridnanopartikeln für energierelevante Anwendungen / Synthesis of metal nitride and metal oxynitride nanoparticles for energy related applications

Milke, Bettina January 2012 (has links)
Ein viel diskutiertes Thema unserer Zeit ist die Zukunft der Energiegewinnung und Speicherung. Dabei nimmt die Nanowissenschaft eine bedeutende Rolle ein; sie führt zu einer Effizienzsteigerung bei der Speicherung und Gewinnung durch bereits bekannte Materialien und durch neue Materialien. In diesem Zusammenhang ist die Chemie Wegbereiter für Nanomaterialien. Allerdings führen bisher die meisten bekannten Synthesen von Nanopartikeln zu undefinierten Partikeln. Eine einfache, kostengünstige und sichere Synthese würde die Möglichkeit einer breiten Anwendung und Skalierbarkeit bieten. In dieser Arbeit soll daher die Darstellung der einfachen Synthese von Mangannitrid-, Aluminiumnitrid-, Lithiummangansilicat-, Zirkonium-oxinitrid- und Mangancarbonatnanopartikel betrachtet werden. Dabei werden die sogenannte Harnstoff-Glas-Route als eine Festphasensynthese und die Solvothermalsynthese als typische Flüssigphasensynthese eingesetzt. Beide Synthesewege führen zu definierten Partikelgrößen und interessanten Morphologien und ermöglichen eine Einflussnahme auf die Produkte. Im Falle der Synthese der Mangannitridnanopartikel mithilfe der Harnstoff-Glas-Route führt diese zu Nanopartikeln mit Kern-Hülle-Struktur, deren Einsatz als Konversionsmaterial erstmalig vorgestellt wird. Mit dem Ziel einer leichteren Anwendung von Nanopartikeln wird eine einfache Beschichtung von Oberflächen mit Nanopartikeln mithilfe der Rotationsbeschichtung beschrieben. Es entstand ein Gemisch aus MnN0,43/MnO-Nanopartikeln, eingebettet in einem Kohlenstofffilm, dessen Untersuchung als Konversionsmaterial hohe spezifische Kapazitäten (811 mAh/g) zeigt, die die von dem konventionellen Anodenmaterial Graphit (372 mAh/g) übersteigt. Neben der Synthese des Anodenmaterials wurde ebenfalls die des Kathodenmaterials Li2MnSiO4-Nanopartikeln mithilfe der Harnstoff-Glas-Route vorgestellt. Mithilfe der Synthese von Zirkoniumoxinitridnanopartikeln Zr2ON2 kann eine einfache Einflussnahme auf das gewünschte Produkt durch die Variation derReaktionsbedingungen, wie Harnstoffmenge oder Reaktionstemperatur, bei der Harnstoff-Glas-Route demonstriert werden. Der Zusatz von kleinsten Mengen an Ammoniumchlorid vermeidet, dass sich Kohlenstoff im Endprodukt bildet und führt so zu gelben Zr2ON2-Nanopartikeln mit einer Größe d = 8 nm, die Halbleitereigen-schaften besitzen. Die Synthese von Aluminiumnitridnanopartikeln führt zu kristallinen Nanopartikeln, die in eine amorphe Matrix eingebettet sind. Die Solvothermalsynthese von Mangancarbonatnanopartikel lässt neue Morphologien in Form von Nanostäbchen entstehen, die zu schuppenartigen sphärischen Überstrukturen agglomeriert sind. / The development of new methods toward alternative clean energy production and efficient energy storage is a hot topic nowadays. In this context nanoscience has an important role to find suitable ways of increasing the efficiency of storage and production of energy of already known materials and new materials. However, until now the most well-known syntheses of MnN0,43 and Zr2ON2 nanoparticles lead to undefined particles. A simple, cheap and safe synthesis would offer the possibility of broader applications and scalability. We herein present the so-called urea-glass route which is used as a sol-gel process. This synthetic route leads to well-defined particle sizes, novel particle morphologies and allows the tailoring of the desired products. In the case of the synthesis of manganese nitride nanoparticles (MnN0,43), nanoparticles with a core-shell structure are obtained, their use as conversion materials in batteries is first introduced. On the other hand, the formation of zirconium oxynitride nanoparticles (Zr2ON2) can be easily influenced by varying the reaction conditions such as the amount of urea or the reaction temperature. The addition of small amounts of salt prevents the formation of carbon in the final product, leading to yellow Zr2ON2 nanoparticles with a size of d = 8 nm which show semiconductor behavior.
5

Étude structurale et électrochimique de films de LiCoO2 préparés par pulvérisation cathodique : application aux microaccumulateurs tout solide

Tintignac, Sophie 16 December 2008 (has links)
Au cours de ce travail de thèse, nous avons mis au point un procédé d'élaboration reproductible de films minces de LiCoO2 par pulvérisation cathodique radio fréquence. L'étude paramétrique nous a permis de déterminer les conditions de dépôt optimales ainsi que les conditions de traitement thermique post-dépôt les plus adaptées afin d'aboutir aux meilleures propriétés électrochimiques pour ces électrodes. Une fois optimisés, les films minces ont été étudiés en électrolyte liquide et nous avons notamment évalué l'influence sur les performances électrochimiques de l'épaisseur du film, de la densité de courant employée, ainsi que des bornes de potentiel utilisées. Nous avons mis en évidence un excellent comportement des films sur une large gamme d'épaisseurs et régimes. La capacité obtenue pour un film de 3,6 µm à 10 µA.cm-2 est de 240 µAh.cm-2. Une étude par microspectrométrie Raman permet de montrer que les changements structuraux induits par les processus électrochimiques sont mineurs et limités à une élongation réversible des liaisons Co-O dans l'axe d'empilement. L'intégration d'un film de 450 nm d'épaisseur dans un microaccumulateur tout solide (LiCoO2/LiPON/Li) a confirmé les excellents résultats obtenus en électrolyte liquide avec une capacité de 25 µAh.cm-2. Là encore, le comportement du film reste inchangé pour des densités de courant élevées allant jusqu'à 800 µA.cm-2. Le cyclage du microaccumulateur à 10 µA.cm-2 a été maintenu pendant plus de 800 cycles sans perte notable de capacité. Pour la première fois on démontre que des films minces de LiCoO2 élaborés par pulvérisation cathodique et recuits à 500°C peuvent être utilisés dans un microaccumulateur au lithium tout solide avec des performances proches de la théorie / This PhD-work has led to a reproducible elaboration process of LiCoO2 thin films by radio frequency sputtering. We determined the optimum deposition parameters and post-annealing conditions that lead to the best electrochemical properties for the thin electrodes. These optimized films have then been characterized in liquid electrolyte. In particular, the effect of the film thickness, the current rate and the oxidation voltage limit on the electrochemical performances have been studied. The films demonstrate an excellent behaviour for a large range of thicknesses and current rates. The galvanostatic cycling at 10 µA.cm-2 of a 3,6 µm thick film results in a specific capacity of 240 µAh.cm-2. A Raman spectrometry study has shown that structural changes induced by lithium insertion/deinsertion were weak and limited to a reversible stretching of the Co-O bondings along the stacking axis. The integration of a 450 nm thick film in an all-solid-state microbattery (LiCoO2/LiPON/Li) confirmed the excellent results obtained in liquid electrolyte with a capacity of 25 µAh.cm-2. Once again, the thin film behaviour is unchanged for current rates up to 800 µA.cm-2. The microbattery has been cycled at 10 µA.cm-2 for more than 800 cycles without significant capacity losses. This is the first time that 500°C annealed LiCoO2 films elaborated by radio frequency sputtering are successfully integrated in an all-solid-state lithium microbattery with performances close to the theoretical ones

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