Hochfeste kupferhaltige Aluminiumlegierungen gelten gemeinhin als „schwer“ anodisierbar, deshalb werden in der vorliegenden Arbeit werkstoffseitige und prozessseitige Maßnahmen zur Verbesserung der Schichtqualität erforscht. Zur eindeutigen Abgrenzung des Einflusses der Cu-Verteilung vom Einfluss anderer Legierungselemente und Verunreinigungen wurde für die Anodisierexperimente zusätzlich zur kommerziellen Legierung EN AW-2024 die hochreine Modelllegierung AlCu4 als Untersuchungswerkstoff gewählt. Insbesondere für die Modelllegierung AlCu4 konnte erstmals eine systematische Veränderung des Schichtbildungsmechanismus beschrieben werden. Mit zunehmender Ausscheidungsbildung nimmt das Ausmaß der Sauerstoffentwicklung ab, woraus erhöhte Schichtdicken und -härten folgen. Die nach Anodisieren der warmausgelagerten Zustände erhaltenen Schichtmikrostrukturen wurden erstmals im Rahmen dieser Arbeit mittels Rasterelektronenmikroskopie beschrieben. Aufgrund reduzierter Schichtrücklösung sind auch auf der Legierung EN AW-2024 im warmaus-gelagerten und überalterten Zustand höhere Schichtdicken und -härten für eine Elektrolyttemperatur von 20 °C erzielbar. Bei einer Elektrolyttemperatur von 5 °C können die Schichtdicke und -härte vor allem durch Zugabe von Additiven zum schwefelsauren Grundelektrolyt gesteigert werden. Im Unterschied zu konventionellen organischen Additiven resultiert die Zugabe von Salpetersäure darüber hinaus in einer Absenkung der Anodisierspannung zu Prozessbeginn und damit in einer Reduzierung der erforderlichen elektrischen Energie. Mit steigender Additivkonzentration nimmt jedoch die Ritzbeständigkeit der Schichten infolge erhöhter Mikrorissigkeit ab. Es ist folglich ein Optimum aus Schichthärte und Mikrorissigkeit zu finden. / High-strength aluminum-copper alloys are generally recognized to be “hardly” anodizable. Hence, the influences of material and process parameters were investigated within this work in order to improve the coating properties. Apart from the commercial alloy EN AW-2024, the high purity model alloy AlCu4 was used for the anodizing experiments in order to distinguish between the influence of the copper distribution and the influence of other alloying elements and impurities. Regarding the model alloy AlCu4, a systematic change of the coating growth mechanism was described for the first time. The extent of oxygen evolution decreases with the intensification of the precipitation leading to increased coating thickness and hardness. In this work, the coating microstructures, resulting from the anodic oxidation of the artificially aged conditions, were described by scanning electron microscopy, for the first time. Due to reduced chemical dissolution of the coatings, higher coating thickness and hardness can also be achieved after room-temperature anodizing of the alloy EN AW-2024 in the artificially aged conditions. For hard-anodizing at an electrolyte temperature of 5 °C, the coating thickness and hardness can be particularly improved by using additives in combination with the sulfuric acid base electrolyte. Beyond that and in contrast to the effect of conventional organic additives, the addition of nitric acid enables the reduction of the anodizing voltage at the beginning of the process and therefore, the reduction of the required electrical energy. However, the scratch resistance of the coatings decreases with increasing additive concentration due to the occurrence of micro crack networks. Consequently, the coating hardness and the amount of microcracks have to be optimized in order to meet concrete application requirements.

Among the materials that can be treated in order to impart superhydrophobic properties are many originally hydrophilic metals. For this, they must undergo a sequential treatment, including roughening and hydrophobic coating. This contribution presents various preparation routes along with various characterization methods, such as dynamic contact angle (DCA) measurements, scanning electron microscopy (SEM) and spectroscopic techniques (FT–IRRAS, XPS, EIS). Micro-rough surfaces of pure and alloyed aluminum were generated most easily by using a modifie Sulfuric Acid Anodization under Intensifie conditions (SAAi). This produces a micro-mountain-like oxide morphology with peak-to-valley heights of 2 μm and sub-μm roughness components. Additionally, micro-embossed and micro-blasted surfaces were investigated. These micro-roughened initial states were chemically modifie with a solution of a hydrophobic compound, such as the reactive f uoroalkylsilane PFATES, the reactive alkyl group containing polymer POMA, or the polymer Teflo ® AF. Alternatively, the chemical modificatio was made by a Hot Filament Chemical Vapor Deposition (HFCVD) of a PTFE layer. The latter can form a considerably higher thickness than the wet-deposited coatings, without detrimental leveling effects being observed in comparison with the original micro-rough surface. The inherent and controllable morphology of the PTFE layers represents an important feature. The impacts of a standardized artificia weathering (WTH) on the wetting behavior and the surface-chemical properties were studied and discussed in terms of possible damage mechanisms. A very high stability of the superhydrophobicity was observed for the f uorinated wet-deposited PFATES and Teflo ® AF coatings as well as for some of the PTFE layer variants, all on SAAi-pretreated substrates. Very good results were also obtained for specimens produced by appropriate mechanical roughening and PTFE coating.

Объект исследования – анодированный диоксид циркония. Цель работы – электрохимический синтез нанотубулярных структур диоксида циркония и исследование их люминесцентных и абсорбционных свойств. Методы исследования – растровая электронная микроскопия, рентгенофазовый анализ, абсорбционная и фотолюминесцентная спектроскопия. Новизна работы – исследована фотолюминесценция анодированного диоксида циркония в диапазоне температур 6.2-700 К. Показано, что интенсивность свечения в области 375 – 600 нм возрастает с уменьшением температуры до 30 К. Спектры свечения описываются двумя пиками гауссовой формы с максимумами Emax = 2.28 и 2.75 эВ и полуширинами ω = 0.77 и 0.67 эВ, соответственно. Измерены спектры диффузного отражения образцов до и после отжига. Посредством построения Тауца рассчитана энергия края оптического поглощения нанотубулярного диоксида циркония Eg = 5.4 ± 0.1 эВ. Возможная область применения анодированного диоксида циркония – матрицы солнечных батарей и фотокатализаторы. / The object of investigation is anodized zirconia. The aim of the work is the electrochemical synthesis of nanotubular zirconia structures and the study of their luminescence and absorption properties. The methods of investigation are scanning electron microscopy, X-ray phase analysis, absorption and photoluminescence spectroscopy. The novelty of the work is the photoluminescence of anodized zirconia in the temperature range of 6.2-700 K. It is shown that the luminescence intensity increases with decreasing temperature to 30 K. The emission spectra are described by two peaks of a Gaussian shape with maxima Emax = 2.28 and 2.75 eV and halfwidths ω = 0.77 and 0.67 eV, respectively. A possible field of application of anodized zirconia is the matrix of solar cells and photocatalysts. Spectra of diffuse reflection of samples before and after annealing were measured. By means of the Tauc plot, the energy of the edge of the optical absorption of nanotubular zirconium dioxide Eg = 5.4 ± 0.1 eV is calculated. A possible field of application of anodized zirconia is the matrix of solar cells and photocatalysts.

A problemática envolvendo os efluentes têxteis decorre principalmente da elevada coloração que apresentam, devido à presença de corantes que além de serem quimicamente estáveis, podem ser tóxicos e/ou carcinogênicos. Logo, quando são descartados in natura no meio ambiente causam problemas estéticos e, sobretudo, ambientais mesmo em baixas concentrações, além da possibilidade de serem nocivos à saúde humana e dos animais. Neste contexto, o objetivo deste trabalho foi estudar a degradação eletroquímica de dois corantes têxteis, Reativo Azul 19 (RA-19) e o Reativo Preto 5 (RP-5) via Oxidação Anódica (OA), utilizando ânodos de Diamante Dopado com Boro (DDB) suportados em titânio ou em nióbio, via processo Eletro-Fenton (EF) e pela combinação dos processos com H2O2 eletrogerado e OA (CP), usando um eletrodo de Carbono Vítreo Reticulado (CVR) como cátodo. As degradações foram realizadas em célula eletroquímica de um compartimento e em reator de fluxo do tipo filtro-prensa com dois compartimentos. A eficiência das degradações foi monitorada pelas técnicas de espectrofotometria no UV-VIS, Cromatografia Líquida de Alta Eficiência (CLAE) e análise do teor de Carbono Orgânico Total (COT). As variáveis estudadas foram densidade de corrente (10-100 mA cm-2 em célula e 4-41 mA cm-2 em reator), dopagem do eletrodo de DDB/Ti (5.000 e 15.000 ppm B/C), concentração inicial dos íons Fe2+ (0-0,10 mmol L-1) e dos corantes (10-250 mg L-1). As degradações dos corantes apresentaram uma cinética de pseudo ordem zero; exceto quando o corante RP-5 foi degradado pelo processo EF, sendo o melhor ajuste ao modelo de pseudo primeira ordem. Além disso, em iguais condições eletroquímicas o corante RP-5 foi degradado em menor tempo em relação ao RA-19; sendo que em todos os processos estudados os corantes foram totalmente removidos. Considerando a OA em célula com os eletrodos de DDB/Ti, a degradação foi positivamente influenciada pelo aumento da densidade de corrente e dopagem do eletrodo, especialmente em relação a cinética. Além disso, os corantes RA-19 e RP-5 foram completamente removidos em 35 e 50 min de eletrólise quando 100 mA cm-2 foi aplicada ao eletrodo de DDB/Ti dopado com 15.000 ppm relação B/C. Em 2 h, 37% em mineralização foi observado para ambos os corantes e a toxicidade do RA-19 diminuiu contra as bactérias Vibrio fischeri. Ainda nessa condição total mineralização foi alcançada após 8 h de degradação. A remoção de COT foi favorecida utilizando o reator contendo os eletrodos de DDB/Nb e CVR ao invés da célula eletroquímica, chegando a percentuais de 84 e 82% em 30 e 90 min para os corantes RA-19 e RP-5 que foram removidos em 7,5 e 5 min, respectivamente, quando a densidade de 41 mA cm-2 foi aplicada ao DDB/Nb durante a degradação via exclusivamente OA. Entre os processos realizados no reator, o EF foi o energeticamente mais favorável, promovendo remoção em COT de 60 e 74% para os corantes RA-19 e RP-5 com consumo energético de 204 e 208 kWh kg-1, além disso, a completa remoção dos corantes ocorreu em 15 e 7,5 min, respectivamente, quando o eletrólito continha íons Fe2+ na concentração de 0,10 mmol L-1 e aplicando-se -0,4 V vs Ag/AgCl ao eletrodo de CVR. Na degradação os corantes via CP o RA-19 e RP-5 foram completamente removidos em 30 e 15 min com mineralização de 72 e 82% em 90 min associada a consumos energéticos de 562 e 745 kWh kg-1, respectivamente, quando 41 mA cm-2 foi aplicada ao DDB/Nb. Por fim, concluiu-se que os resultados das degradações dos corantes foram promissores, já que rápida remoção dos corantes foi observada, além da parcial mineralização. Logo os processos propostos podem ser aplicados na remoção dos corantes em água; sendo necessários realizar mais estudos, principalmente em relação ao material eletródico e configuração do sistema eletroquímico visando a aplicação industrial. / The main problem involving the textile wastewater is theirs high coloration since they present dyes, which are chemically stable and can be toxic and/or carcinogenic. Therefore, when the textile wastewater are discarded in nature in the environment, even in low concentrations, they may cause not only aesthetic and environmental problems, but also can be harmful to human and animal health. In this context, the aim of the study was to evaluate the electrochemical degradation of two textile dyes, Reactive Blue 19 (RB-19) and Black 5 (RB-5) via Anodic Oxidation (AO) using as anodes Boron Doped Diamond electrodes (BDD) supported on titanium or niobium, via Electro-Fenton (EF) process and by combination of processes with electrogenerated H2O2 and AO (CP) using a Reticulated Vitreous Carbon electrode (RVC) as cathode. The degradations assays were carried out in an electrochemical cell with one compartment and in a filter-press flow reactor with two compartments. The efficiency of degradation was monitored by UV-VIS spectrophotometry, High Performance Liquid Chromatography (HPLC) and analysis of Total Organic Carbon (TOC). The variables studied were current density (10-100 mA cm-2 for cell and 4-41 mA cm-2 for reactor), doping of the BDD/Ti electrodes (5,000 e 15,000 ppm B/C), initial concentration of the Fe2+ ions (0-0,10 mmol L-1) and dyes (10-250 mg L-1). The kinetic results showed that the removal of dyes followed the model of pseudo zero order; except when the RB-5 dye was degraded by EF process, which the best fitted was to pseudo first order model. Furthermore, for equal conditions the RB-5 was degraded in less time in comparison to the RB-19. In addition, the dyes were fully removed in all the processes studied. Regarding the AO in cell with BDD/Ti, the degradation was positively influenced by the increasing in current density and doping of the electrode, primarily the kinetics parameters. In addition, total removal of RB-19 and RB-5 was achieved in 35 and 50 min of electrolysis when 100 mA cm-2 was applied to the electrode doped with 15,000 ppm ratio B/C. In 2 h, 37% in mineralization was attained for both dyes and the toxicity effect of the RB-19 decreased against the bacteria Vibrio fischeri. In this condition, total TOC removed was also reached after 8 h. The TOC removal was enhanced using the reactor fitted with BDD/Nb and RVC instead of the electrochemical cell, achieving TOC removal of 84 and 82% in 30 and 90 min for RB-19 and RB-5 which were removed in 7.5 and 5 min, respectively, when 41 mA cm-2 was applied to the BDD/Nb in the degradation exclusively via AO. Among the processes carried out in the reactor, the EF was the energetically most favourable since TOC removal of 60 and 74% for RB-19 and RB-5 with energy consumption of 204 and 208 kWh kg-1 were noted. In addition, the RB-19 and RB-5 were completely removed in 15 and 7.5 min, respectively, when the electrolyte containing 0.10 mmol L-1 of Fe2+ ions and -0.4 V vs Ag/AgCl was applied to CVR electrode. The combination of processes with electrogenerated H2O2 and AO for degradation of the dyes removed the RB-19 and RB-5 in 30 and 15 min with mineralization of 71.6 and 81.8% in 90 min associated to energy consumptions of 562 and 745 kWh kg-1 respectively, when 41 mA cm-2 was applied to BDD/Nb. Therefore, the degradation results of the dyes were promised since quickly removal of the dyes and partial mineralization were observed hence the proposed processes could be used to remove the dyes from water. However, more studies are needed to enable an industrial application, especially regarding the electrode material and configuration of the electrochemical system.

A problemática envolvendo os efluentes têxteis decorre principalmente da elevada coloração que apresentam, devido à presença de corantes que além de serem quimicamente estáveis, podem ser tóxicos e/ou carcinogênicos. Logo, quando são descartados in natura no meio ambiente causam problemas estéticos e, sobretudo, ambientais mesmo em baixas concentrações, além da possibilidade de serem nocivos à saúde humana e dos animais. Neste contexto, o objetivo deste trabalho foi estudar a degradação eletroquímica de dois corantes têxteis, Reativo Azul 19 (RA-19) e o Reativo Preto 5 (RP-5) via Oxidação Anódica (OA), utilizando ânodos de Diamante Dopado com Boro (DDB) suportados em titânio ou em nióbio, via processo Eletro-Fenton (EF) e pela combinação dos processos com H2O2 eletrogerado e OA (CP), usando um eletrodo de Carbono Vítreo Reticulado (CVR) como cátodo. As degradações foram realizadas em célula eletroquímica de um compartimento e em reator de fluxo do tipo filtro-prensa com dois compartimentos. A eficiência das degradações foi monitorada pelas técnicas de espectrofotometria no UV-VIS, Cromatografia Líquida de Alta Eficiência (CLAE) e análise do teor de Carbono Orgânico Total (COT). As variáveis estudadas foram densidade de corrente (10-100 mA cm-2 em célula e 4-41 mA cm-2 em reator), dopagem do eletrodo de DDB/Ti (5.000 e 15.000 ppm B/C), concentração inicial dos íons Fe2+ (0-0,10 mmol L-1) e dos corantes (10-250 mg L-1). As degradações dos corantes apresentaram uma cinética de pseudo ordem zero; exceto quando o corante RP-5 foi degradado pelo processo EF, sendo o melhor ajuste ao modelo de pseudo primeira ordem. Além disso, em iguais condições eletroquímicas o corante RP-5 foi degradado em menor tempo em relação ao RA-19; sendo que em todos os processos estudados os corantes foram totalmente removidos. Considerando a OA em célula com os eletrodos de DDB/Ti, a degradação foi positivamente influenciada pelo aumento da densidade de corrente e dopagem do eletrodo, especialmente em relação a cinética. Além disso, os corantes RA-19 e RP-5 foram completamente removidos em 35 e 50 min de eletrólise quando 100 mA cm-2 foi aplicada ao eletrodo de DDB/Ti dopado com 15.000 ppm relação B/C. Em 2 h, 37% em mineralização foi observado para ambos os corantes e a toxicidade do RA-19 diminuiu contra as bactérias Vibrio fischeri. Ainda nessa condição total mineralização foi alcançada após 8 h de degradação. A remoção de COT foi favorecida utilizando o reator contendo os eletrodos de DDB/Nb e CVR ao invés da célula eletroquímica, chegando a percentuais de 84 e 82% em 30 e 90 min para os corantes RA-19 e RP-5 que foram removidos em 7,5 e 5 min, respectivamente, quando a densidade de 41 mA cm-2 foi aplicada ao DDB/Nb durante a degradação via exclusivamente OA. Entre os processos realizados no reator, o EF foi o energeticamente mais favorável, promovendo remoção em COT de 60 e 74% para os corantes RA-19 e RP-5 com consumo energético de 204 e 208 kWh kg-1, além disso, a completa remoção dos corantes ocorreu em 15 e 7,5 min, respectivamente, quando o eletrólito continha íons Fe2+ na concentração de 0,10 mmol L-1 e aplicando-se -0,4 V vs Ag/AgCl ao eletrodo de CVR. Na degradação os corantes via CP o RA-19 e RP-5 foram completamente removidos em 30 e 15 min com mineralização de 72 e 82% em 90 min associada a consumos energéticos de 562 e 745 kWh kg-1, respectivamente, quando 41 mA cm-2 foi aplicada ao DDB/Nb. Por fim, concluiu-se que os resultados das degradações dos corantes foram promissores, já que rápida remoção dos corantes foi observada, além da parcial mineralização. Logo os processos propostos podem ser aplicados na remoção dos corantes em água; sendo necessários realizar mais estudos, principalmente em relação ao material eletródico e configuração do sistema eletroquímico visando a aplicação industrial. / The main problem involving the textile wastewater is theirs high coloration since they present dyes, which are chemically stable and can be toxic and/or carcinogenic. Therefore, when the textile wastewater are discarded in nature in the environment, even in low concentrations, they may cause not only aesthetic and environmental problems, but also can be harmful to human and animal health. In this context, the aim of the study was to evaluate the electrochemical degradation of two textile dyes, Reactive Blue 19 (RB-19) and Black 5 (RB-5) via Anodic Oxidation (AO) using as anodes Boron Doped Diamond electrodes (BDD) supported on titanium or niobium, via Electro-Fenton (EF) process and by combination of processes with electrogenerated H2O2 and AO (CP) using a Reticulated Vitreous Carbon electrode (RVC) as cathode. The degradations assays were carried out in an electrochemical cell with one compartment and in a filter-press flow reactor with two compartments. The efficiency of degradation was monitored by UV-VIS spectrophotometry, High Performance Liquid Chromatography (HPLC) and analysis of Total Organic Carbon (TOC). The variables studied were current density (10-100 mA cm-2 for cell and 4-41 mA cm-2 for reactor), doping of the BDD/Ti electrodes (5,000 e 15,000 ppm B/C), initial concentration of the Fe2+ ions (0-0,10 mmol L-1) and dyes (10-250 mg L-1). The kinetic results showed that the removal of dyes followed the model of pseudo zero order; except when the RB-5 dye was degraded by EF process, which the best fitted was to pseudo first order model. Furthermore, for equal conditions the RB-5 was degraded in less time in comparison to the RB-19. In addition, the dyes were fully removed in all the processes studied. Regarding the AO in cell with BDD/Ti, the degradation was positively influenced by the increasing in current density and doping of the electrode, primarily the kinetics parameters. In addition, total removal of RB-19 and RB-5 was achieved in 35 and 50 min of electrolysis when 100 mA cm-2 was applied to the electrode doped with 15,000 ppm ratio B/C. In 2 h, 37% in mineralization was attained for both dyes and the toxicity effect of the RB-19 decreased against the bacteria Vibrio fischeri. In this condition, total TOC removed was also reached after 8 h. The TOC removal was enhanced using the reactor fitted with BDD/Nb and RVC instead of the electrochemical cell, achieving TOC removal of 84 and 82% in 30 and 90 min for RB-19 and RB-5 which were removed in 7.5 and 5 min, respectively, when 41 mA cm-2 was applied to the BDD/Nb in the degradation exclusively via AO. Among the processes carried out in the reactor, the EF was the energetically most favourable since TOC removal of 60 and 74% for RB-19 and RB-5 with energy consumption of 204 and 208 kWh kg-1 were noted. In addition, the RB-19 and RB-5 were completely removed in 15 and 7.5 min, respectively, when the electrolyte containing 0.10 mmol L-1 of Fe2+ ions and -0.4 V vs Ag/AgCl was applied to CVR electrode. The combination of processes with electrogenerated H2O2 and AO for degradation of the dyes removed the RB-19 and RB-5 in 30 and 15 min with mineralization of 71.6 and 81.8% in 90 min associated to energy consumptions of 562 and 745 kWh kg-1 respectively, when 41 mA cm-2 was applied to BDD/Nb. Therefore, the degradation results of the dyes were promised since quickly removal of the dyes and partial mineralization were observed hence the proposed processes could be used to remove the dyes from water. However, more studies are needed to enable an industrial application, especially regarding the electrode material and configuration of the electrochemical system.

Aujourd'hui, les structures basées sur les matériaux ferromagnétiques sont largement utilisées pour différentes applications: mémoires magnéto-résistives à accès non séquentiel, capteurs magnétiques et également nouveaux composants électroniques et dipositifs spintroniques. La tendance générale de l'électronique moderne est une réduction de la dimension des éléments à l'échelle submicronique. Ainsi, les nanostructures magnétiques sont d'un grand intérêt et leurs méthodes de fabrication et propriétés sont étudiées activement.Le but principal de ce travail est la préparation et la recherche expérimentale et théorique des propriétés de nanostructures magnétiques pour applications aux composants magneto-résistifs et phononiques. La lithographie à sonde locale (SPL) et la lithographie par faisceau d’électrons (EBL) ont été utilisées pour la fabrication des nanostructures. De premiers pas ont également été réalisés en fabrication des cristaux phononiques sensibles au champ magnétique. / Nowadays, structures based on ferromagnetic materials are largely used for different applications: random access magneto-resistive memories, magnetic sensors, and also new electronic components and spintronic devices. The general trend of modern electronic is the reduction of dimensions down to submicronic scales. Therefore, the magnetic nanostructures are of great interest and their methods of fabrication and properties largely studied.The main goal of this work is the preparation and experimental and theoretical research on properties of magnetic nanostructures for applications in magnetoresistive and photonic devices. The Scanning Probe Lithography (SPL) and Electron Beam Lithography (EBL) were used for the nanostructures fabrications. First steps were also achieved in fabrication of phononic cristals sensitive the magnetic field.

Im Mittelpunkt dieser Arbeit steht die selektive Funktionalisierung von Siliziumoxidnanostrukturen auf alkyl-passivierten Siliziumoberflächen welche durch rasterkraftmikroskopisch induzierte lokale anodische Oxidation (LAO) erzeugt werden. Bei der gezielten Immobilisierung von funktionalen Molekülen auf den Strukturen werden zwei verschiedene Routen verfolgt – Anbindung von ionischen Farbstoffen über elektrostatische Wechselwirkungen sowie stufenweise kovalente chemische Anbindung von bi-funktionalen Verbindermolekülen und Farbstoffen. Eine Untersuchung der hergestellten funktionalen Strukturen erfolgt mittels Rasterkraftmikroskopie, Raster-Kelvin-Mikroskopie sowie zeitaufgelöster Fluoreszenzmikroskopie und-spektroskopie. Durch zwei unabhängige Methoden kann gezeigt werden dass die Ladungen im lokalen Oxide vergleichsweise stabil sind und die elektrostatische Anbindung somit auch noch nach Tagen möglich sein sollte. Das Verhalten der elektrostatisch angebundenen Farbstoffe hängt stark von deren Art ab. Während es bei Rhodamin 6G nur zu einer minimalen spektralen Änderung im Vergleich zur Lösung kommt so zeigen spermin-funktionalisierte Perylenbisimidfarbstoffe eine deutliche H-Aggregation und Ausbildung von Excimerzuständen. Diese Zustände sind eindeutig thermisch aktiviert und zeigen eine wesentlich höhere Aktivierungsenergie als bei allen anderen bisher untersuchten Perylenaggregaten sowie eine Hysterese bei Temperaturveränderung. Die physikalische Ursache für dieses Phänomen liegt allem Anschein nach in der elektrostatischen Anbindung selbst welche ein instabiles Gleichgewicht mit der Wechselwirkung der Moleküle untereinander bildet. Eine geordnete kovalente Anbindung von funktionalen Silanmolekülen an die mittels LAO erzeugten Strukturen erfordert sehr definierte Prozessparameter. Die spektroskopische Untersuchung von an die funktionalen Silane chemisch angebundenen Fluoresceinfarbstoffen lässt indirekte Schlüsse auf deren Belegungsdichte und damit die Qualität der Silanmonolage zu.

Developed rechargeable batteries are urgently required to make more efficient use of renewable energy sources to support our modern way of life. Among all battery types, lithium batteries have attracted the most attention because of the high energy density (both gravimetric and volumetric), long cycle life, reasonable production cost and the ease of manufacturing flexible designs. Indeed, electrode material characteristics need to be improved urgently to fulfil the requirements for high performance lithium ion batteries. TiO2-based anodes are highly promising materials for LIBs to replace carbon due to fast lithium insertion/extraction kinetics, environmentally-friendly behavior, low cost and low volume change (less than 4%) therewith, high structural stability as well as improved safety issues are obtained. Nevertheless, the low ionic and electric conductivity (≈ 10−12 S m−1) of TiO2 represent the main challenge. In short, the present work aims at developing, optimization and construction of novel anode materials for lithium ion batteries using materials that are stable, abundant and environmentally friendly. Herein, both of two-phase Ti80Co20 and single phase Ti-Sn alloys (with different Sn contents of 1 to 10 at.%) were used to fabricate highly ordered, vertically oriented and dimension-controlled 1D nanotubes of mixed transition metal oxides (TiO2-CoO and TiO2-SnO2) via a straight-forward anodic oxidation step in organic electrolytes containing NH4F. Surface morphology and current density for the initial nanotube formation are found to be dependent on the crystal structure of the alloy phases. Various characterization tools such as SEM, EDXS, TEM, XPS and Raman spectroscopy were used to characterize the grown nanotube films. The results reveal the successful formation of mixed TiO2-CoO and TiO2-SnO2 nanotubes under the selected voltage ranges. The as-formed nanotubes are amorphous and their dimensions are precisely controlled by tuning the formation voltage. The electrochemical performance of the grown nanotubes was evaluated against a Li/Li+ electrode at different current densities. The results revealed that TiO2-CoO nanotubes prepared at 60 V exhibited the highest areal capacity of ~ 600 µAh cm–2 (i.e. 315 mAh g–1) at a current density of 10 µA cm–2. At higher current densities TiO2-CoO nanotubes showed nearly doubled lithium ion intercalation and a coulombic efficiency of 96 % after 100 cycles compared to lower effective TiO2 nanotubes prepared under identical conditions. To further improve the electrochemical performance of the TiO2-CoO nanotubes, a novel ternary carbon nanotubes (CNTs)@TiO2-CoO nanotubes composite was fabricated by a two-step synthesis method. The preparation includes an initial anodic fabrication of well-ordered TiO2-CoO NTs from a Ti-Co alloy, followed by growing of CNTs horizontally on the top of the oxide films using a simple spray pyrolysis technique. The unique 1D structure of such a hybrid nanostructure with the inclusion of CNTs demonstrates significantly enhanced areal capacity and rate performances compared to pure TiO2 and TiO2-CoO NTs without CNTs tested under identical conditions. The findings reveal that CNTs provide a highly conductive network that improves Li+ ion diffusivity promoting a strongly favored lithium insertion into the TiO2-CoO NT framework, and hence results in high capacity and extremely reproducible high rate capability. On the other hand, the results demonstrate that TiO2-SnO2 nanotubes prepared at 40 V on a Ti-Sn alloy with 1 at.% Sn display an average 1.4 fold increase in areal capacity with excellent cycling stability over more than 400 cycles compared to the pure TiO2 nanotubes fabricated and tested under identical conditions. The thesis is organized as follows: Chapter 1: General introduction, in which the common situation of energy demand, along with the importance of lithium ion batteries in renewable energy systems and portable devices are discussed. A brief introduction to TiO2-based anode in lithium ion batteries and the genera strategies for developing TiO2 anodes are also presented. The scope of this thesis as well as the main tasks are summarized. Chapter 2: The basic concepts of lithium ion batteries with an overview about their main components are discussed, including a brief information about the anode materials and the crystal structure of TiO2 anode. A detailed review for TiO2 nanomaterials for LIBs including the fabrication methods and the electrochemical performance of various TiO2 nanostructures (nanoparticles, nanorods, nanoneedles, nanowires and nanotubes) as well as porousTiO2 nanostructures is presented. The fabrication of TiO2 nanotubes by anodic oxidation, along with the growth mechanism are highlighted. The factors affecting the electrochemical performance of anodically fabricated pure TiO2, TiO2/carbon composites and TiO2-mixed with another metal oxide are reviewed. Chapter 3: In this chapter, the synthesis of TiO2-CoO, (CNTs)@TiO2-CoO and TiO2-SnO2 nanotubes, along with the characterization techniques and the electrochemical basics and concepts are discussed. Chapter 4: Detailed results and discussion of synthesis, characterizations and the electrochemical performance of TiO2-CoO nanotubes and ternary (CNTs)@TiO2/CoO nanotube composites are presented. Chapter 5: Detailed results and discussion of synthesis, characterizations and the electrochemical performance of ternary (CNTs)@TiO2-CoO nanotube composites are explained. Chapter 6: Detailed results and discussion of synthesis, characterizations and the electrochemical performance of TiO2-SnO2 nanotubes are presented. Chapter 7: Summarizes the results presented in this work finishing with realistic conclusions, and highlights interesting work for the future. / Um die zur Aufrechterhaltung unserer modernen Lebensweise unabdingbaren erneuerbaren Energiequellen effizient nutzen zu können, werden hochentwickelte wiederaufladbare Batterien dringend benötigt. Lithium-Ionenbatterien gelten aufgrund ihrer hohen Energiedichte (sowohl gravimetrisch als auch volumetrisch), ihrer langen Lebensdauer, moderater Produktionskosten und aufgrund der Möglichkeit, vielfältige Konzepte einfach herstellen zu können, als vielversprechend. Dennoch müssen die Elektrodenmaterialien dringend verbessert werden, um den Ansprüchen an zukünftige hochentwickelte Lithium-Ionenbatterien gerecht zu werden. TiO2-basierte Anoden gelten aufgrund ihrer schnellen Lade- und Entladekinetik, ihres umweltfreundlichen Verhaltens und niedriger Kosten als aussichtsreiche Alternativen zu Kohlenstoffen. Durch die geringe Volumenänderung beim Lithiumeinbau (unter 4%) werden außerdem eine hohe strukturelle Stabilität und erhöhte Sicherheit gewährleistet. Die hauptsächlichen Herausforderungen stellen die niedrige ionische und elektrische Leitfähigkeit (≈ 10−12 S m−1) von TiO2 dar. Zusammengefasst liegt das Ziel der vorliegenden Arbeit in der Entwicklung, Optimierung und Herstellung neuartiger Anodenmaterialien für Lithium-Ionenbatterien unter Verwendung stabiler, verfügbarer und umweltfreundlicher Materialien. In dieser Arbeit wurden sowohl zweiphasiges Ti80Co20 und einphasige Ti-Sn-Legierungen (mit verschiedenen Sn-Gehalten zwischen 1 und 10 at-%) zur Herstellung hochgeordneter, vertikal orientierter eindimensionaler Nanoröhren aus gemischten Übergangsmetalloxiden (TiO2–CoO und TiO2–SnO2) mittels anodischer Oxidation in NH4F-haltigen organischen Elektrolyten genutzt. Dabei wurden Abhängigkeiten der Oberflächenmorphologie und der Stromdichte für die Bildung der Nanoröhren von der Kristallstruktur der zugrundeliegenden Legierung beobachtet. Vielfältige Methoden wie REM, EDXS, TEM, XPS und Ramanspektroskopie wurden genutzt, um die Nanoröhren zu charakterisieren. Die Ergebnisse zeigen, dass gemischte TiO2-CoO und TiO2-SnO2 Nanoröhren in den gewählten Spannungsfenstern erfolgreich gebildet werden konnten. Die so hergestellten Nanoröhren sind amorph und in ihren Dimensionen präzise durch die Wahl der Spannung einstellbar. Eine elektrochemische Beurteilung der Nanoröhren erfolgte durch Tests gegen eine Li/Li+-Elektrode bei veschiedenen Stromdichten. Die Resultate zeigen, dass TiO2-CoO-Nanoröhren, welche bei 60 V hergestellt wurden, die höchsten Flächenkapazitäten von ~ 600 µAh cm–2 (d.h. 315 mAh g–1) bei einer Stromdichte von 10 µA cm–2 aufweisen. Bei höheren Stromdichten zeigen TiO2-CoO-Nanoröhren nahezu verdoppelte Lithiuminterkalation und eine Coulomb-Effizienz von 96 % nach 100 Zyklen, verglichen mit weniger effektiven TiO2–Nanoröhren, welche unter identischen Bedingungen hergestellt wurden. Um die elektrochemischen Eigenschaften der TiO2-CoO-Nanoröhren weiter zu verbessern, wurde ein neuer Komposit aus Kohlenstoff-Nanoröhren und TiO2-CoO-Nanoröhren ((CNT)s@TiO2/CoO) durch eine zweistufige Synthese hergestellt. Die Herstellung beinhaltet zunächst die anodische Bildung geordneter TiO2/CoO-Nanoröhren, ausgehend von einer Ti-Co-Legierung, gefolgt von einem horizontalen Kohlenstoff-Nanoröhren-Wachstum auf dem Oxid mittels einer simplen Sprühpyrolyse. Die einzigartige 1D-Struktur einer solchen hybriden Nanostruktur mit eingebundenen CNTs zeigt deutlich erhöhte Flächenkapazitäten und Belastbarkeiten im Vergleich zu Nanoröhren aus TiO2 und TiO2/CoO-Nanoröhren ohne CNTs, die unter identischen Bedingungen getestet wurden. Die Ergebnisse zeigen, dass die CNTs ein hochleitfähiges Netzwerk bilden, welches die Diffusion von Lithium-Ionen und deren Einbau in die TiO2/CoO-Nanoröhren begünstigt und somit hohe Kapazitäten und reproduzierbare hohe Belastbarkeiten bewirkt. Außerdem zeigen die Resultate, dass TiO2-SnO2 Nanoröhren, welche bei 40 V auf einer Ti-Sn-Legierung mit 1 at.% Sn hergestellt wurden, im Mittel eine 1,4-fache Erhöhung der Flächenkapazität und eine exzellente Zyklenstabilität über mehr als 400 Zyklen, verglichen mit unter identischen Konditionen hergestellten und getesteten TiO2-Nanoröhren, zeigen. Die Arbeit ist wie folgt organisiert: Kapitel 1: Allgemeine Einführung, in der die Energienachfrage und die Bedeutung von Lithium-Ionenbatterien in erneuerbaren Energiesystemen und tragbaren Geräten diskutiert wird. Eine kurze Einleitung zu TiO2-basierten Anoden in Lithium-Ionenbatterien und allgemeine Strategien zur Entwicklung von TiO2-Anoden werden ebenfalls gezeigt. Das Ziel der Arbeit und hauptsächliche Aufgaben werden zusammengefasst. Kapitel 2: Das grundlegende Konzept der Lithium-Ionenbatterie mit einem Überblick über ihre Hauptkomponenten wird diskutiert. Dies beinhaltet auch eine kurze Darstellung der Anodenmaterialien und der Kristallstruktur von TiO2-Anoden. Eine detaillierte Übersicht über TiO2-Nanomaterialien für LIB, welche Herstellungsmethoden und die elektrochemische Performance verschiedener TiO2-Nanostrukturen (Nanopartikel, Nanostäbe, Nanonadeln, Nanodrähte und Nanoröhren) und poröser TiO2-Nanostrukturen beinhaltet, wird gezeigt. Die Bildung von TiO2-Nanoröhren durch anodische Oxidation und der Wachstumsmechanismus werden hervorgehoben. Faktoren, welche die elektrochemische Performance anodisch hergestellter TiO2-Materialien, TiO2/Kohlenstoff-Komposite und TiO2 als Gemisch mit anderen Metalloxiden beeinflussen, werden diskutiert. Kapitel 3: In diesem Kapitel werden die Synthese von TiO2-CoO, (CNTs)@TiO2/CoO und TiO2-SnO2-Nanoröhren, die Charakterisierungsmethoden, elektrochemische Grundlagen und Konzepte diskutiert. Kapitel 4: Detaillierte Resultate und die Diskussion der Synthese, Charakterisierung und der elektrochemischen Performance der TiO2-CoO- Nanoröhren und der ternären (CNTs)@TiO2/CoO-Nanoröhrenkomposite werden gezeigt. Kapitel 5: Detaillierte Resultate und die Diskussion der Synthese, Charakterisierung und der elektrochemischen Performance der der ternären (CNTs)@TiO2/CoO-Nanoröhrenkomposite werden diskutiert. Kapitel 6: Detaillierte Resultate und die Diskussion der Synthese, Charakterisierung und der elektrochemischen Performance von TiO2-SnO2-Nanoröhren werden gezeigt. Kapitel 7: Eine Zusammenfassung der Resultate, die in dieser Arbeit gezeigt wurden und Schlussfolgerungen, sowie interessante Ansatzpunkte für zukünftige Arbeiten werden präsentiert.

Developed rechargeable batteries are urgently required to make more efficient use of renewable energy sources to support our modern way of life. Among all battery types, lithium batteries have attracted the most attention because of the high energy density (both gravimetric and volumetric), long cycle life, reasonable production cost and the ease of manufacturing flexible designs. Indeed, electrode material characteristics need to be improved urgently to fulfil the requirements for high performance lithium ion batteries. TiO2-based anodes are highly promising materials for LIBs to replace carbon due to fast lithium insertion/extraction kinetics, environmentally-friendly behavior, low cost and low volume change (less than 4%) therewith, high structural stability as well as improved safety issues are obtained. Nevertheless, the low ionic and electric conductivity (≈ 10−12 S m−1) of TiO2 represent the main challenge. In short, the present work aims at developing, optimization and construction of novel anode materials for lithium ion batteries using materials that are stable, abundant and environmentally friendly. Herein, both of two-phase Ti80Co20 and single phase Ti-Sn alloys (with different Sn contents of 1 to 10 at.%) were used to fabricate highly ordered, vertically oriented and dimension-controlled 1D nanotubes of mixed transition metal oxides (TiO2-CoO and TiO2-SnO2) via a straight-forward anodic oxidation step in organic electrolytes containing NH4F. Surface morphology and current density for the initial nanotube formation are found to be dependent on the crystal structure of the alloy phases. Various characterization tools such as SEM, EDXS, TEM, XPS and Raman spectroscopy were used to characterize the grown nanotube films. The results reveal the successful formation of mixed TiO2-CoO and TiO2-SnO2 nanotubes under the selected voltage ranges. The as-formed nanotubes are amorphous and their dimensions are precisely controlled by tuning the formation voltage. The electrochemical performance of the grown nanotubes was evaluated against a Li/Li+ electrode at different current densities. The results revealed that TiO2-CoO nanotubes prepared at 60 V exhibited the highest areal capacity of ~ 600 µAh cm–2 (i.e. 315 mAh g–1) at a current density of 10 µA cm–2. At higher current densities TiO2-CoO nanotubes showed nearly doubled lithium ion intercalation and a coulombic efficiency of 96 % after 100 cycles compared to lower effective TiO2 nanotubes prepared under identical conditions. To further improve the electrochemical performance of the TiO2-CoO nanotubes, a novel ternary carbon nanotubes (CNTs)@TiO2-CoO nanotubes composite was fabricated by a two-step synthesis method. The preparation includes an initial anodic fabrication of well-ordered TiO2-CoO NTs from a Ti-Co alloy, followed by growing of CNTs horizontally on the top of the oxide films using a simple spray pyrolysis technique. The unique 1D structure of such a hybrid nanostructure with the inclusion of CNTs demonstrates significantly enhanced areal capacity and rate performances compared to pure TiO2 and TiO2-CoO NTs without CNTs tested under identical conditions. The findings reveal that CNTs provide a highly conductive network that improves Li+ ion diffusivity promoting a strongly favored lithium insertion into the TiO2-CoO NT framework, and hence results in high capacity and extremely reproducible high rate capability. On the other hand, the results demonstrate that TiO2-SnO2 nanotubes prepared at 40 V on a Ti-Sn alloy with 1 at.% Sn display an average 1.4 fold increase in areal capacity with excellent cycling stability over more than 400 cycles compared to the pure TiO2 nanotubes fabricated and tested under identical conditions. The thesis is organized as follows: Chapter 1: General introduction, in which the common situation of energy demand, along with the importance of lithium ion batteries in renewable energy systems and portable devices are discussed. A brief introduction to TiO2-based anode in lithium ion batteries and the genera strategies for developing TiO2 anodes are also presented. The scope of this thesis as well as the main tasks are summarized. Chapter 2: The basic concepts of lithium ion batteries with an overview about their main components are discussed, including a brief information about the anode materials and the crystal structure of TiO2 anode. A detailed review for TiO2 nanomaterials for LIBs including the fabrication methods and the electrochemical performance of various TiO2 nanostructures (nanoparticles, nanorods, nanoneedles, nanowires and nanotubes) as well as porousTiO2 nanostructures is presented. The fabrication of TiO2 nanotubes by anodic oxidation, along with the growth mechanism are highlighted. The factors affecting the electrochemical performance of anodically fabricated pure TiO2, TiO2/carbon composites and TiO2-mixed with another metal oxide are reviewed. Chapter 3: In this chapter, the synthesis of TiO2-CoO, (CNTs)@TiO2-CoO and TiO2-SnO2 nanotubes, along with the characterization techniques and the electrochemical basics and concepts are discussed. Chapter 4: Detailed results and discussion of synthesis, characterizations and the electrochemical performance of TiO2-CoO nanotubes and ternary (CNTs)@TiO2/CoO nanotube composites are presented. Chapter 5: Detailed results and discussion of synthesis, characterizations and the electrochemical performance of ternary (CNTs)@TiO2-CoO nanotube composites are explained. Chapter 6: Detailed results and discussion of synthesis, characterizations and the electrochemical performance of TiO2-SnO2 nanotubes are presented. Chapter 7: Summarizes the results presented in this work finishing with realistic conclusions, and highlights interesting work for the future.:1. Introduction and scope of the thesis 15 1.1 Batteries for renewable energy systems and portable devices 15 1.2 TiO2-based anodes in lithium ion batteries 17 1.3 Strategies for developing TiO2 anodes 17 1.4 Scope of work 19 1.5 Tasks 20 2. Basics and literature review 23 2.1 Lithium ion battery system 23 2.2 Anode materials 26 2.3 Crystal structure of TiO2 28 2.4 TiO2 nanomaterials for LIBs 30 2.4.1 TiO2 nanoparticles 30 2.4.2 TiO2 nanoneedles 36 2.4.3 Porous TiO2 nanostructures 39 2.5 TiO2 nanotubes prepared by electrochemical anodization 44 2.6 The mechanism of nanotube formation by anodic oxidation 47 2.7 Anodically fabricated TiO2 nanotubes as anodes in LIBs 49 2.7.1 Anodization electrolyte 50 2.7.2 Amorphous and crystalline TiO2 anodes 50 2.7.3 Influence of the nnealing atmospheres of TiO2 52 2.7.4 Free-standing TiO2 nanotube membranes 54 2.7.5 TiO2 nanotubes/carbon composites 55 2.7.6 Mixed oxide nanotubes 55 3. Materials and methods 61 3.1 Methodology 61 3.1.1 Synthesis of TiO2-CoO and TiO2 nanotubes 61 3.1.2 Synthesis of CNTs@TiO2-CoO NT composite 62 3.1.3 Synthesis of TiO2-SnO2 and TiO2 nanotubes 63 3.2 Characterization techniques 64 3.2.1 X-ray diffraction (XRD 64 3.2.2 Scanning electron microscopy (SEM 65 3.2.3 Energy-dispersive X-ray spectroscopy (EDXS 65 3.2.4 Transmission electron spectroscopy (TEM 66 3.2.5 X-ray photoelectron spectroscopy (XPS 66 3.2.6 Raman spectroscopy 67 3.2.7 Nitrogen sorption isotherms 67 3.2.8 Inductively coupled plasma optical emission spectroscopy (ICP–OES 68 3.3 Basic definitions and electrochemical concepts 68 3.3.1 Faraday’s law 68 3.3.2 Capacity 69 3.3.3 Discharging 69 3.3.4 Charging 69 3.4 Electrochemical techniques 70 3.4.1 Cyclic voltammetry 70 3.4.2 Galvanostatic discharging/charging cycling 70 3.4.3 Electrochemical impedance spectroscopy (EIS 71 3.5 Electrode preparation and measurement conditions 71 3.5.1 TiO2-CoO nanotube electrodes 71 3.5.2 CNTs@TiO2 and CNTs@TiO2/CoO NTs electrodes 72 3.5.3 TiO2-SnO2 nanotube electrodes 73 4. TiO2-CoO as anodes in lithium ion batteries 75 4.1 Introduction 76 4.2 Characterization 76 4.2.1 Phase identification of as cast Ti-Co alloy 76 4.2.2 Time-current density relationship 79 4.2.3 Morphology of the fabricated TiO2-CoO nanotubes 81 4.2.4 Phase identification of the fabricated TiO2-CoO nanotubes 85 4.2.5 Specific surface area of the fabricated TiO2-CoO nanotubes 87 4.2.6 Chemical state in the grown TiO2-CoO nanotubes 89 4.2.7 Raman spectroscopy of TiO2-CoO nanotubes 91 4.3 Electrochemical testing of TiO2-CoO electrodes 92 4.3.1 Cyclic voltammetry 92 4.3.2 Galvanostatic cycling with potential limitation 93 4.3.3 Electrochemical impedance spectroscopy (EIS) 97 4.3.4 Structural stability TiO2-CoO anodes over cycling 98 4.4 Summary of chapter 4 99 5. Ternary CNTs@TiO2-CoO nanotube composites: improved anode materials for LIBs 101 5.1 Introduction 102 5.2 Characterization 103 5.2.1 Morphology and Raman analysis of the fabricated CNTs@TiO2-CoO NTs 103 5.2.2 XRD analysis of the fabricated TiO2-CoO NTs before and after CNTs coating 106 5.3 Electrochemical properties 107 5.3.1 Cyclic voltammetry 107 5.3.2 Galvanostatic cycling with potential limitation 109 5.3.2 Electrochemical impedance spectroscopy (EIS 112 5.4 Summary of chapter 5 114 6. TiO2-SnO2 nanotubes as anodes in lithium ion batteries 115 6.1 Introduction 116 6.2 Characterization 117 6.2.1 ICP-OES analysis of the as-cast Ti-Sn alloys 117 6.2.2 SEM analysis of the as-cast Ti-Sn alloys 117 6.2.3 Phase analysis of the as-cast Ti-Sn alloys 118 6.2.4 Morphology of the fabricated TiO2-SnO2 nanotubes 121 6.2.5 XPS investigation of the grown TiO2-SnO2 nanotubes 127 6.2.6 Raman spectroscopy of TiO2-SnO2 nanotubes 129 6.3 Electrochemical Testing 130 6.3.1 Cyclic voltammetry 130 6.3.2 Galvanostatic cycling with potential limitation132 6.3.3 Specific surface area of the fabricated TiO2-SnO2 nanotubes135 6.3.4 Electrochemical impedance spectroscopy (EIS) and rate performance tests of the fabricated TiO2-SnO2 nanotubes 137 6.4 Summary of chapter 6140 7. Summary and outlook 141 7.1 Summary 141 7.2 Outlook 143 Appendix 145 Bibliography 157 List of figures 183 Glossary 191 Publications 193 Curriculum vitae 195 Acknowledgment 199 Declaration 201 / Um die zur Aufrechterhaltung unserer modernen Lebensweise unabdingbaren erneuerbaren Energiequellen effizient nutzen zu können, werden hochentwickelte wiederaufladbare Batterien dringend benötigt. Lithium-Ionenbatterien gelten aufgrund ihrer hohen Energiedichte (sowohl gravimetrisch als auch volumetrisch), ihrer langen Lebensdauer, moderater Produktionskosten und aufgrund der Möglichkeit, vielfältige Konzepte einfach herstellen zu können, als vielversprechend. Dennoch müssen die Elektrodenmaterialien dringend verbessert werden, um den Ansprüchen an zukünftige hochentwickelte Lithium-Ionenbatterien gerecht zu werden. TiO2-basierte Anoden gelten aufgrund ihrer schnellen Lade- und Entladekinetik, ihres umweltfreundlichen Verhaltens und niedriger Kosten als aussichtsreiche Alternativen zu Kohlenstoffen. Durch die geringe Volumenänderung beim Lithiumeinbau (unter 4%) werden außerdem eine hohe strukturelle Stabilität und erhöhte Sicherheit gewährleistet. Die hauptsächlichen Herausforderungen stellen die niedrige ionische und elektrische Leitfähigkeit (≈ 10−12 S m−1) von TiO2 dar. Zusammengefasst liegt das Ziel der vorliegenden Arbeit in der Entwicklung, Optimierung und Herstellung neuartiger Anodenmaterialien für Lithium-Ionenbatterien unter Verwendung stabiler, verfügbarer und umweltfreundlicher Materialien. In dieser Arbeit wurden sowohl zweiphasiges Ti80Co20 und einphasige Ti-Sn-Legierungen (mit verschiedenen Sn-Gehalten zwischen 1 und 10 at-%) zur Herstellung hochgeordneter, vertikal orientierter eindimensionaler Nanoröhren aus gemischten Übergangsmetalloxiden (TiO2–CoO und TiO2–SnO2) mittels anodischer Oxidation in NH4F-haltigen organischen Elektrolyten genutzt. Dabei wurden Abhängigkeiten der Oberflächenmorphologie und der Stromdichte für die Bildung der Nanoröhren von der Kristallstruktur der zugrundeliegenden Legierung beobachtet. Vielfältige Methoden wie REM, EDXS, TEM, XPS und Ramanspektroskopie wurden genutzt, um die Nanoröhren zu charakterisieren. Die Ergebnisse zeigen, dass gemischte TiO2-CoO und TiO2-SnO2 Nanoröhren in den gewählten Spannungsfenstern erfolgreich gebildet werden konnten. Die so hergestellten Nanoröhren sind amorph und in ihren Dimensionen präzise durch die Wahl der Spannung einstellbar. Eine elektrochemische Beurteilung der Nanoröhren erfolgte durch Tests gegen eine Li/Li+-Elektrode bei veschiedenen Stromdichten. Die Resultate zeigen, dass TiO2-CoO-Nanoröhren, welche bei 60 V hergestellt wurden, die höchsten Flächenkapazitäten von ~ 600 µAh cm–2 (d.h. 315 mAh g–1) bei einer Stromdichte von 10 µA cm–2 aufweisen. Bei höheren Stromdichten zeigen TiO2-CoO-Nanoröhren nahezu verdoppelte Lithiuminterkalation und eine Coulomb-Effizienz von 96 % nach 100 Zyklen, verglichen mit weniger effektiven TiO2–Nanoröhren, welche unter identischen Bedingungen hergestellt wurden. Um die elektrochemischen Eigenschaften der TiO2-CoO-Nanoröhren weiter zu verbessern, wurde ein neuer Komposit aus Kohlenstoff-Nanoröhren und TiO2-CoO-Nanoröhren ((CNT)s@TiO2/CoO) durch eine zweistufige Synthese hergestellt. Die Herstellung beinhaltet zunächst die anodische Bildung geordneter TiO2/CoO-Nanoröhren, ausgehend von einer Ti-Co-Legierung, gefolgt von einem horizontalen Kohlenstoff-Nanoröhren-Wachstum auf dem Oxid mittels einer simplen Sprühpyrolyse. Die einzigartige 1D-Struktur einer solchen hybriden Nanostruktur mit eingebundenen CNTs zeigt deutlich erhöhte Flächenkapazitäten und Belastbarkeiten im Vergleich zu Nanoröhren aus TiO2 und TiO2/CoO-Nanoröhren ohne CNTs, die unter identischen Bedingungen getestet wurden. Die Ergebnisse zeigen, dass die CNTs ein hochleitfähiges Netzwerk bilden, welches die Diffusion von Lithium-Ionen und deren Einbau in die TiO2/CoO-Nanoröhren begünstigt und somit hohe Kapazitäten und reproduzierbare hohe Belastbarkeiten bewirkt. Außerdem zeigen die Resultate, dass TiO2-SnO2 Nanoröhren, welche bei 40 V auf einer Ti-Sn-Legierung mit 1 at.% Sn hergestellt wurden, im Mittel eine 1,4-fache Erhöhung der Flächenkapazität und eine exzellente Zyklenstabilität über mehr als 400 Zyklen, verglichen mit unter identischen Konditionen hergestellten und getesteten TiO2-Nanoröhren, zeigen. Die Arbeit ist wie folgt organisiert: Kapitel 1: Allgemeine Einführung, in der die Energienachfrage und die Bedeutung von Lithium-Ionenbatterien in erneuerbaren Energiesystemen und tragbaren Geräten diskutiert wird. Eine kurze Einleitung zu TiO2-basierten Anoden in Lithium-Ionenbatterien und allgemeine Strategien zur Entwicklung von TiO2-Anoden werden ebenfalls gezeigt. Das Ziel der Arbeit und hauptsächliche Aufgaben werden zusammengefasst. Kapitel 2: Das grundlegende Konzept der Lithium-Ionenbatterie mit einem Überblick über ihre Hauptkomponenten wird diskutiert. Dies beinhaltet auch eine kurze Darstellung der Anodenmaterialien und der Kristallstruktur von TiO2-Anoden. Eine detaillierte Übersicht über TiO2-Nanomaterialien für LIB, welche Herstellungsmethoden und die elektrochemische Performance verschiedener TiO2-Nanostrukturen (Nanopartikel, Nanostäbe, Nanonadeln, Nanodrähte und Nanoröhren) und poröser TiO2-Nanostrukturen beinhaltet, wird gezeigt. Die Bildung von TiO2-Nanoröhren durch anodische Oxidation und der Wachstumsmechanismus werden hervorgehoben. Faktoren, welche die elektrochemische Performance anodisch hergestellter TiO2-Materialien, TiO2/Kohlenstoff-Komposite und TiO2 als Gemisch mit anderen Metalloxiden beeinflussen, werden diskutiert. Kapitel 3: In diesem Kapitel werden die Synthese von TiO2-CoO, (CNTs)@TiO2/CoO und TiO2-SnO2-Nanoröhren, die Charakterisierungsmethoden, elektrochemische Grundlagen und Konzepte diskutiert. Kapitel 4: Detaillierte Resultate und die Diskussion der Synthese, Charakterisierung und der elektrochemischen Performance der TiO2-CoO- Nanoröhren und der ternären (CNTs)@TiO2/CoO-Nanoröhrenkomposite werden gezeigt. Kapitel 5: Detaillierte Resultate und die Diskussion der Synthese, Charakterisierung und der elektrochemischen Performance der der ternären (CNTs)@TiO2/CoO-Nanoröhrenkomposite werden diskutiert. Kapitel 6: Detaillierte Resultate und die Diskussion der Synthese, Charakterisierung und der elektrochemischen Performance von TiO2-SnO2-Nanoröhren werden gezeigt. Kapitel 7: Eine Zusammenfassung der Resultate, die in dieser Arbeit gezeigt wurden und Schlussfolgerungen, sowie interessante Ansatzpunkte für zukünftige Arbeiten werden präsentiert.:1. Introduction and scope of the thesis 15 1.1 Batteries for renewable energy systems and portable devices 15 1.2 TiO2-based anodes in lithium ion batteries 17 1.3 Strategies for developing TiO2 anodes 17 1.4 Scope of work 19 1.5 Tasks 20 2. Basics and literature review 23 2.1 Lithium ion battery system 23 2.2 Anode materials 26 2.3 Crystal structure of TiO2 28 2.4 TiO2 nanomaterials for LIBs 30 2.4.1 TiO2 nanoparticles 30 2.4.2 TiO2 nanoneedles 36 2.4.3 Porous TiO2 nanostructures 39 2.5 TiO2 nanotubes prepared by electrochemical anodization 44 2.6 The mechanism of nanotube formation by anodic oxidation 47 2.7 Anodically fabricated TiO2 nanotubes as anodes in LIBs 49 2.7.1 Anodization electrolyte 50 2.7.2 Amorphous and crystalline TiO2 anodes 50 2.7.3 Influence of the nnealing atmospheres of TiO2 52 2.7.4 Free-standing TiO2 nanotube membranes 54 2.7.5 TiO2 nanotubes/carbon composites 55 2.7.6 Mixed oxide nanotubes 55 3. Materials and methods 61 3.1 Methodology 61 3.1.1 Synthesis of TiO2-CoO and TiO2 nanotubes 61 3.1.2 Synthesis of CNTs@TiO2-CoO NT composite 62 3.1.3 Synthesis of TiO2-SnO2 and TiO2 nanotubes 63 3.2 Characterization techniques 64 3.2.1 X-ray diffraction (XRD 64 3.2.2 Scanning electron microscopy (SEM 65 3.2.3 Energy-dispersive X-ray spectroscopy (EDXS 65 3.2.4 Transmission electron spectroscopy (TEM 66 3.2.5 X-ray photoelectron spectroscopy (XPS 66 3.2.6 Raman spectroscopy 67 3.2.7 Nitrogen sorption isotherms 67 3.2.8 Inductively coupled plasma optical emission spectroscopy (ICP–OES 68 3.3 Basic definitions and electrochemical concepts 68 3.3.1 Faraday’s law 68 3.3.2 Capacity 69 3.3.3 Discharging 69 3.3.4 Charging 69 3.4 Electrochemical techniques 70 3.4.1 Cyclic voltammetry 70 3.4.2 Galvanostatic discharging/charging cycling 70 3.4.3 Electrochemical impedance spectroscopy (EIS 71 3.5 Electrode preparation and measurement conditions 71 3.5.1 TiO2-CoO nanotube electrodes 71 3.5.2 CNTs@TiO2 and CNTs@TiO2/CoO NTs electrodes 72 3.5.3 TiO2-SnO2 nanotube electrodes 73 4. TiO2-CoO as anodes in lithium ion batteries 75 4.1 Introduction 76 4.2 Characterization 76 4.2.1 Phase identification of as cast Ti-Co alloy 76 4.2.2 Time-current density relationship 79 4.2.3 Morphology of the fabricated TiO2-CoO nanotubes 81 4.2.4 Phase identification of the fabricated TiO2-CoO nanotubes 85 4.2.5 Specific surface area of the fabricated TiO2-CoO nanotubes 87 4.2.6 Chemical state in the grown TiO2-CoO nanotubes 89 4.2.7 Raman spectroscopy of TiO2-CoO nanotubes 91 4.3 Electrochemical testing of TiO2-CoO electrodes 92 4.3.1 Cyclic voltammetry 92 4.3.2 Galvanostatic cycling with potential limitation 93 4.3.3 Electrochemical impedance spectroscopy (EIS) 97 4.3.4 Structural stability TiO2-CoO anodes over cycling 98 4.4 Summary of chapter 4 99 5. Ternary CNTs@TiO2-CoO nanotube composites: improved anode materials for LIBs 101 5.1 Introduction 102 5.2 Characterization 103 5.2.1 Morphology and Raman analysis of the fabricated CNTs@TiO2-CoO NTs 103 5.2.2 XRD analysis of the fabricated TiO2-CoO NTs before and after CNTs coating 106 5.3 Electrochemical properties 107 5.3.1 Cyclic voltammetry 107 5.3.2 Galvanostatic cycling with potential limitation 109 5.3.2 Electrochemical impedance spectroscopy (EIS 112 5.4 Summary of chapter 5 114 6. TiO2-SnO2 nanotubes as anodes in lithium ion batteries 115 6.1 Introduction 116 6.2 Characterization 117 6.2.1 ICP-OES analysis of the as-cast Ti-Sn alloys 117 6.2.2 SEM analysis of the as-cast Ti-Sn alloys 117 6.2.3 Phase analysis of the as-cast Ti-Sn alloys 118 6.2.4 Morphology of the fabricated TiO2-SnO2 nanotubes 121 6.2.5 XPS investigation of the grown TiO2-SnO2 nanotubes 127 6.2.6 Raman spectroscopy of TiO2-SnO2 nanotubes 129 6.3 Electrochemical Testing 130 6.3.1 Cyclic voltammetry 130 6.3.2 Galvanostatic cycling with potential limitation132 6.3.3 Specific surface area of the fabricated TiO2-SnO2 nanotubes135 6.3.4 Electrochemical impedance spectroscopy (EIS) and rate performance tests of the fabricated TiO2-SnO2 nanotubes 137 6.4 Summary of chapter 6140 7. Summary and outlook 141 7.1 Summary 141 7.2 Outlook 143 Appendix 145 Bibliography 157 List of figures 183 Glossary 191 Publications 193 Curriculum vitae 195 Acknowledgment 199 Declaration 201

Durch elektrochemische Impedanzspektroskopie während der anodischen Oxidation von Aluminium werden in der vorliegenden Arbeit die elektrochemischen Vorgänge während der Oxidbildung quantitativ und zeitabhängig untersucht. Es wird ein Modell vorgeschlagen und diskutiert, welches das Impedanzverhalten während der anodischen Oxidation in Schwefel-, Oxal- und Phosphorsäure über einen großen Bereich von Konzentrationen und Stromdichten abbilden kann. Aus den gewonnenen Ergebnissen werden die kapazitive Wirkung der Sperrschicht am Porengrund, der Eintritt von Ladungsträgern in die Sperrschicht, der Ionentransport durch die Sperrschicht sowie die Oxidbildungsreaktion selbst als wesentlich für das Impedanzverhalten identifiziert. Die ermittelten Zusammenhänge und Konstanten können als Grundlage für Modellvorstellungen dienen, welche das Verhalten elektrischer Prozessgrößen und die Ausbildung der charakteristischen Oxidstruktur bei der anodischen Oxidation von Aluminium verknüpfen. / In the present work, the electrochemical subprocesses of the oxide formation on aluminium by anodic oxidation are investigated using electrochemical impedance spectroscopy. The time dependence of the impedance behaviour and the quantitative relations between the process parameters and the impedance behaviour are considered. A model for the representation of the electrochemical behaviour during the anodic oxidation in sulphuric, oxalic and phosphoric acid is proposed and discussed for a wide range of anion concentrations and current densities. On the basis of the obtained results, the capacitive effect of the barrier layer, the charge transfer resistance of the barrier layer, the ion transport within the barrier layer and the oxide formation are identified as the dominating effects for the impedance behaviour. The established relations can serve as a basis for models, which interrelate both the electrochemical behaviour and the geometrical formation of the characteristic pore structure.