Thesis (M.S.)--University of Delaware, 2006. / Principal faculty advisor: John S. Boyer, College of Marine and Earth Studies. Includes bibliographical references.

L'oxyde de manganèse (MnO₂) est un candidat de choix comme composant de base des supercondensateurs électrochimique pour son faible coût, son caractère non polluant et sa capacité spécifique théorique élevée (~1380 F/g). Cependant, les capacités spécifiques expérimentales sont bien inférieures et se limitent aux systèmes à faibles masses actives due à la faible conductivité et la forte densité du matériau. La méthode conventionnelle de préparation d'électrode consiste en un mélange de MnO₂, de carbone activé (conductivité) et de polymère liant isolant (PTFE). Le projet s'est basé sur une nouvelle stratégie qui consiste à remplacer le noir d'acétylène (AB) par des nanotubes (CNT) et des fibres de carbone (VGCF) afin d'augmenter la conductivité et diminuer la densité du matériau. Aussi, l'utilisation d'un polymère liant échangeur d'ions (Nafion) doit permettre de vérifier si l'accessibilité des ions vers la matière active interne est favorisée. L'analyse des poudres composites (MnO₂ amorphe et les divers composants) effectuée pour la première fois par isotherme d'adsorption a montrée clairement la diminution de surface spécifique ainsi que le blocage de pores (micropores et mésopores), particulièrement pour les échantillons avec le Nafion. L'influence de ces paramètres sur la cinétique des réactions électrochimiques a été confirmée. De plus, la caractérisation des électrodes composites par voltampérométrie cyclique dans l'électrolyte 0,65M K₂SO4 a permis de confirmer que les mélanges avec CNT et ceux avec AB combinés au PTFE sont les plus performants avec des capacités spécifiques de ~165 F/g (2 mV/s), et ce, même pour des masses élevées de 45 mg/cm2. Par leur distribution poreuse et leur excellente conductivité électronique, le CNT semble être le meilleur additif conducteur. L'utilisation du Nafion ne permet cependant pas d'obtenir un mélange malléable ni une capacité spécifique supérieure. Les résultats obtenus ont permis de mettre en évidence un profil d'optimisation clair de tous les mélanges testés. ______________________________________________________________________________ MOTS-CLÉS DE L’AUTEUR : Électrochimie, supercondensateurs électrochimiques, stockage énergie, dioxyde de manganèse, électrode composite.

This thesis considers the effect of a large scale wind power introduction into an electricity system and the focus has been on the carbon dioxide emissions. Two different systems were studied, the Swedish and the Danish electricity system. When studying the Swedish electricity system different scenarios were created to see what might happen with the CO2 emissions with an introduction of a large amount of wind power. The model that was used is based on parameters such as regulating power, transmission capacity, export possibility, and the electricity generation mixes in the Nordic countries. Given that the transmission capacity is good enough, the conclusion is that the carbon dioxide emissions will be reduced with a large scale introduction of wind power. In the Danish electricity system wind power is already introduced to a large extent. The main purpose here was to investigate the development of the CO2 emissions and if it is possible to decide the actual change in carbon dioxide emissions due to the large scale introduction of wind power. The conclusions to this part are that the CO2 emissions per kWh produced electricity have decreased since the electricity generation mix has changed but the total amount of CO2 emissions fluctuates depending on weather, in a dry year less hydro power from Norway and Sweden can be used and more electricity from the fossil fuelled CHPs are generated. It has not been possible to determine the influence of the wind power on the CO2 emissions.

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The photovoltaic energy conversion system (PV cells or solar cells) has been researched over the last few decades, and new technologies have been proposed. At the same time, the synthesis of nano-scale materials has been investigated intensively from the 1990s. These new types of materials encourage the development of new PV technologies with extensive research. Dye-sensitized solar cells (DSSCs) can be a part of these efforts. Since first presented in 1991, DSSCs have become the center of attention due to their great advantages to the traditional silicon solar cells. However, it remains a challenge to develop better performing DSSCs since the efficiency of DSSCs is still much lower than that of high performance solar cells. To meet this challenge, the different types of TiO2 nanostructures in DSSCs have been studied. This thesis presents the synthesis of TiO2 hetero-structures. These structures can achieve two important factors in DSSCs. One is the electron pathway for high electron transport rate, and the other is the large surface area for the dye absorption. TiO2 hetero-structures were successfully synthesized by using a simple thermal annealing method. The synthesis method required neither a high reaction temperature nor complicated reaction processes and produced dense TiO2 nanowires and incorporating TiO2 nanoparticles with relatively short reaction time. The key parameters of growing 1-D TiO2 nanostructures were the Cu eutectic catalyst, the reaction temperatures, and the annealing time. The repetition time and the reaction temperatures were important factors for incorporating TiO2 nanoparticles. The structure and composition of as-grown samples were analyzed using an x-ray diffractometer, a scanning electron microscope, a field emission scanning electron microscope, a transmission electron microscope and an ultraviolet-visible spectroscopy. The results showed they were crystalline structures in rutile phase of TiO2. From this research, we can utilize hetero-structures as an electrode of DSSCs. We also expect that our simple and effective synthesis method can be used for growing other kinds of metal oxide nanostructures, especially for those melting temperature are high.

The performance of a Direct Methanol Fuel Cell has been experiment and analysis in this research. The performance of Direct Methanol Fuel Cell were tested by changing different parameter, such as methanol concentration, temperature, and the effect of carbon dioxide. This influence include transient and steady-state respond. Through the experiment and analysis, we hope we could understand the important factors which influence the performance of the DMFC. This experiment use Nafion® as membrane electrode assembly, and the ratio of flow channel area to total electrode area is 58%. The performance of the single cell was enhanced by increasing methanol concentration as the experiment result, no matter transient or steady-state respond. The best performance was obtained from 2M. The performance at transient or steady-state was also improved by increasing methanol/cell temperature. The product of the reaction, carbon dioxide, will cause more influence when cell work at higher current. In addition, there are few carbon dioxide which will appear as gaseous state.

The mainly research is by adding the rare-earth metal gadolinium salts with sol-gel process to form the gadolinium -doped titanium dioxide, and by forming the liquid crystal template with the non-ionic surfactant to form the mesostructure of titanium dioxide. And the research has aimed at the using different non-ionic surfactant, the different pH value, the different solvent of water/ethanol ratio, the hydrothermal process or not, and the gadolinium content. We discussed these factors how to affect the titanium dioxide in the physical property, the chemical property, or structure influence. Using the XRD to measure the mesostucture of titanium dioxide and the crystallization of titanium dioxide, and we observe the shape and particle size of titanium dioxide with SEM. We use UV-visible spectrum to observe absorption spectrum of titanium dioxide. The result discovers that surfactant effect is using triblock copolymer, poly (ethylene oxide) - poly (propylene oxide) - poly (ethylene oxide), the titanium dioxide has anatase and rutile crystallization, and particle aggregation. The pH affects the partic le size and the shape. In pH is 5.8, the titanium dioxide has anatase and rutile crystallization. In water/ethanol ratio effect, we use solvent including ethanol, the titanium dioxide has anatase and rutile. Through hydrothermal process, titanium dioxide has little brookite crystallization and the few fibrous titanium dioxides. The doping gadolinium effect is the anatase is reducing with gadolinium content increasing, and from the UV-visible spectrum, the doping gadolinium titanium dioxide has the red shift. The titanium dioxide using polyoxyethylene sorbitan monostearate and doping gadolinium has the anatase, and absorbs a longer wavelength, and when the doping content is 1% titanium dioxide has a better absorption.

Abstract: Dimeric dimethylAluminum complexes, [Me2Al(m-R)]2 (R= Me, NiPr2, NiBu2, NPh2, NHnBu, OMe) and Al(NiPr2)3 react with carbon dioxide, yielding a series of carbamato aluminum complexes: [Me2Al(m-OCMe3)]2 (1); [Me2Al(m-O2CNiPr2)]2 (2); [Me2Al(m-O2CNiBu2)]2 (3); [Me2Al(m-O2CNPh2)]2 (4); [Me2Al(m-O2CNHnBu)]2 (5); Al4Li2(m4-O)2(m-O2CNiPr2)10 (6). X-ray crystallographic determinations were performed on compounds (2), (3), (4) and (6). The general trends identitide in these structures suggest that depending upon the bonding energy of aluminum with bridge ligand and electron density on bridge ligand. One novel crystal structure (6), Al4Li2(m4-O)2(m-O2CNiPr2)10 , was found from the previous reaction in the presence of lithium chloride. These compounds were characterized with 1H, 13C NMR, IR spectroscopy, mass spectrometer, and elemental analyses.