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Theoretical investigation of the structure and stability of neutral and cationic TixOy cluster series (where y =2x-1, 2x, 2x+1) have been performed. The lowest lying structures for the neutral clusters are usually found in the singlet state. Generally, in bulk and in the case of the neutral TixOy clusters, the 2x cluster series is relatively more abundant than the 2x-1 and the 2x+1 cluster series. But in the case of cationic TixOy clusters, the 2x-1 series is more abundant. To understand the origin of the stability of the TixO2x-1+ clusters, we use density functional theory within the NRLMOL set of codes. Different analyzing factors such as ionization potential, TiO2 removal energy, oxygen removal energy, binding energy per atom and HOMO-LUMO gap have been used to examine the relative stability of TixO2x-1+ clusters. After analyzing the above criteria, we find that the ionization potential and HOMO-LUMO gap are more reliable, as the low ionization potential of the 2x-1 series generally implies low HOMO-LUMO gap and suggests that the 2x-1 cluster series more likely prefer to remain as cations. To further confirm this, we examine the density of states of Ti3O5 and Ti3O6 which show a larger HOMO- HOMO-1 gap in case of Ti3O5, indicating that the cluster would like to lose an electron for enhancing electronic stability.

Les matériaux à base de dioxyde de titane (TiO2) sont des candidats prometteurs pour remplacer le graphite utilisé actuellement dans les électrodes négatives des batteries lithium-ion (LIB), du fait de leur sécurité élevée, de leur capacité volumétrique supérieure et de leurs excellentes performances à hautepuissance.Dans cette thèse, différentes approches de synthèse à bas coût sont évaluées pour préparer du TiO2 nanostructuré avec différentes compositions de phase et des morphologies variées. L'influence de ces paramètres sur la capacité de TiO2 à insérer réversiblement le lithium est étudiée par des mesures électrochimiques. À cet égard nous avons également étudié l'effet du dopage aliovalent et de la morphologie poreuse sur les propriétés d'insertion du TiO2, révélant des résultats encourageants avec notamment un transfert de charge amélioré, principale limitation des matériaux à base d'oxyde de titane. Afin de comprendre le processus de stockage du lithium des deux phases de TiO2 synthétisées, des méthodes de diffraction et de caractérisation spectroscopique ont été utilisées dans des conditions opérando.Nous montrons qu'indépendamment de leur similitude de composition chimique, les deux phases révèlent des mécanismes d'insertion du lithium très différents, menant à des propriétés électrochimiques de charge/décharge très différentes.Nous avons également amélioré les performances électrochimiques en travaillant sur la formulation d'électrodes à base de TiO2 nanostructuré, en optimisant le choix des composants (additif carboné, liant, électrolyte) et le processus de préparation. De nombreuses réactions parasites électrode-électrolyte ont été mises en évidence à travers cette étude, phénomènes très peu décrits dans la littérature à ce jour. / Titania based electrode materials are promising candidates to replace widely used graphite as negative electrode material in lithium ion batteries (LIB), due to their increased safety, volumetric capacity, and high rate performance.In this thesis different low-cost synthesis approaches are evaluated to prepare nanostructured TiO2 with various phase composition and morphology. The influence of these parameters on its ability to reversibly insert lithium are studied in electrochemical measurements. In this regard we also investigated the effect of aliovalent doping and porous structures on the insertion properties of two main polymorphs of TiO2, Anatase and TiO2(b), revealing encouraging results in overcoming the low charge transfer, which is the main drawback of titanium oxide based materials.In order to understand the mechanism of lithium storage process of the two synthesized TiO2 phases, diffraction and spectroscopic characterization methods were carried out under operando conditions. We show that, regardless of their chemical similarity, both phases reveal very different lithium insertion processes, leading to distinct electrochemical cycling properties.Another field of interest is the adaptation of electrode components to the nanostructured TiO2 active insertion material. The choice of binder, carbon additive, and electrolyte components can have significant impacts on the performance. Especially the origin and prevention of parasitic side reactions were in the focus of our work, as these pose an under estimated hindrance in the application of titania based electrode materials in LIB.

This work investigates the use of the novel electric field assisted chemical vapour deposition (EACVD) process in the production of titanium dioxide thin films for photocatalytic applications on glass substrate. This work looks into the interaction of applied electric fields with the precursor species during the aerosol assisted chemical vapour deposition (AACVD) and atmospheric pressure chemical vapour deposition (APCVD) reaction of Titanium isopropoxide (TTIP) and Titanium (IV) Chloride (TiCl4) with different solvents. The electric field was generated by applying a potential difference between two fluorine-doped tin oxide glass sheets. The electric field was varied between 0 – 3000 Vm-1. The deposited films were analysed and characterized using scanning electron microscopy, X-ray diffraction, Raman spectroscopy, atomic force microscopy, UV-vis spectroscopy, water-contact angles and resazurin photcatalytic testing. It was observed that the application of electric fields produced changes in the morphology, particle size, growth rate, crystal orientation and crystal phases. Generally, films produced under the influence of the electric fields showed higher photo-activity than films produced in absence of electric fields. The deposited films produced from the electric field assisted aerosol chemical vapour deposition (EAACVD) showed higher photo-activity with applied AC electric fields than with applied DC electric fields. Likewise, they showed higher photo-activity than the deposited films produced from the electric field assisted atmospheric pressure chemical vapour deposition (EAAPCVD) with applied AC electric fields. The results obtained were explained by the interaction mechanisms between the electric fields and the precursor species, which differ depending on the CVD technique used. Although titanium dioxide photo-activity is comprised by a combination of factors, it was observed that an optimum can be obtained by varying both experimental conditions and field strength. In particular, optimum results were obtained for deposited films which showed long-shaped particles, reduced particle size and high preferential orientation in the anatase (004) plane. Electric field assisted chemical vapour deposition (EACVD) shows a great potential for the improvement of commercial products available in the market such as self-cleaning and antibacterial surfaces.

The work in this thesis examines the effects of the application of oxide coatings on the performance of the single crystalline silicon photovoltaic solar cells. A variety of potential oxide materials for solar cells performance enhancement are investigated. These films are silicon oxide, titanium oxide and rare earth ion-doped gadolinium oxysulfide phosphor. This study compares the electrical characteristics, optical properties and surface chemical composition of mono-crystalline silicon cells before and after coating. The first study investigates the potential for using single and double layers of silicon oxide films produced by low-temperature Plasma Enhanced Chemical Vapour Deposition (PECVD) using tetramethylsilane as a silicon precursor and potassium permanganate oxidising agent for efficiency enhancement of solar cells at low manufacturing cost. Deposition of the films contributes to the increase of the conversion energy of the solar cells on one hand while the variety of colours obtained in this study can be of great importance for building-integrated photovoltaic application on the other hand. The obtained results demonstrated a relative enhancement of 3% in the conversion efficiency of the crystalline silicon solar cell. In the second study, the effects of using a single layer of titanium oxide and a stack of silicon oxide and titanium oxide on the performance of solar cell are demonstrated. Moreover, this study shows the use of different sputtering configurations and oxidation methods. The experimental results showed a relative enhancement of 1.6% for solar cells coated with a stack of silicon oxide/titanium oxide. In the third study, silicon cells were coated with a luminescent layer consisting of down-converting phosphor, gadolinium oxysulfide doped with erbium and terbium, and a polymeric binder of EVA using doctor-blade screen printing technique. A relative enhancement of 4.45% in the energy conversion efficiency of PV solar cell was achieved. Also, the effects of combining silicon oxide layers together with the luminescent composite are also presented in this study.

The main objective of this Thesis is the synthesis, characterization and application in the PROX reaction of several series of catalysts synthesized using different methods, in order to find efficient materials with high catalytic activity. This work has been divided in six chapters. Chapter I presents an introduction about current energy problems and hydrogen (energy carrier) as a solution, with its limitations and advances on its use: storage, transport and security. Finally, its use as a fuel in PEMFC (Proton Exchange Membrane Fuel Cells) and the advantages comparing other existent fuel cells has been discussed. A brief summary was done about the catalytic systems studied in literature for PROX reaction and their characteristics. Following, Chapter 2 describes all the characterization techniques which were used to study the properties of the synthesized supports and catalysts, together with the experimental system employed for the catalytic tests. Most of these equipments belong to SSTTI of University of Alicante or are hand-made systems in the LMA group. DRIFTs and DTP were done at TUDelft, Catalysis Engineering Section. Next chapters contain the most important results obtained during the complete research work; they have been divided in two parts. On one hand, Chapter 3 describes the synthesis of pure TiO2 using five different methods, and its use as platinum support for PROX catalysts. On the other hand, taking into account the obtained results, three synthesis methods were chosen, and the study was centered in the addition of CeO2 to TiO2. Chapter 4 discusses the TixCe(1-x)O2 series synthesized using the sol-gel method. In Chapter 5 a solvothermal procedure was employed for the synthesis of supports with similar composition and, finally, impregnation of cerium over commercial P25 titania was compared in Chapter 6. Each chapter contains a complete study of characterization of both supports and catalysts. Synthesis parameters, pretreatment and reaction conditions were also modified for the best catalyst of the three series. Analyzing the catalysts’ behavior, a reaction mechanism was proposed. Finally, general conclusions summarize the most relevant results obtained in each chapter.

In this work, a series of simple, rapid and effective photoelectrochemical methodologies have been developed and successfully applied to the study of kinetic and thermodynamic characteristics of photocatalytic oxidation processes at TiO2 nanoparticulate films. As an application of the systematic studies of photocatalytic processes by photoelectrochemical techniques, a rapid, direct, absolute, environmental-friendly and accurate COD analysis method was successfully developed. In this work, the TiO2 nanoparticles colloid was prepared by the sol-gel method. The TiO2 nanoparticles were immobilized onto ITO conducting glass slides by dip-coating method. Thermal treatment was carried out to obtain nanoporous TiO2 films of different structures. At low calcination temperature (below 600°C), nanoporous TiO2 films of pure anatase phase were prepared. At high calcination temperature (above 600°C), nanoporous TiO2 films of mixed anatase and rutile phases were obtained. At these film electrodes, the work was carried out. By employing steady state photocurrent method and choosing phthalic acid as the model compound, the photocatalytic activity of the TiO2 nanoporous films calcined at various temperatures and for different lengths of time was evaluated. It was found that the films with mixed anatase and rutile phases calcined at high temperature exhibited high photocatalytic activity. Based on semiconductor band theory, a model was proposed, which explained well this finding. By employing linear sweep voltammetry (under illumination) and choosing glucose (an effective photohole scavenger) as a model compound, the characteristics of the photocatalytic processes at nanoparticulate semiconductor electrodes were investigated. Characteristics of the nanoporous semiconductor electrodes markedly different from bulk semiconductor electrodes were observed. That is, within a large range of electrode potentials above the flat band potential the electrodes behaved as a pure resistance instead of exhibiting variable resistance expected for bulk semiconductor electrodes. The magnitude of the resistance was dependent on the properties of the electrodes and the maximum photocatalytic oxidation rate at TiO2 surface determined by the light intensity and substrate concentration. A model was proposed, which explained well the special characteristics of particulate semiconductor electrodes (nanoporous semiconductor electrodes). This is the first clear description of the overall photocatalytic process at nanoparticulate semiconductor electrodes. The investigation set a theoretical foundation for employing photoelectrochemical techniques to study photocatalytic processes. By using the transient technique (illumination step method analogous to potential step method in conventional electrochemistry), the adsorption of a number of strong adsorbates on both low temperature and high temperature calcined TiO2 nanoporous films was investigated. Similar adsorption characteristics for different adsorbates on different films were observed. In all the cases, three different surface bound complexes were identified, which was attributed to the heterogeneity of TiO2 surface. The photocatalytic degradation kinetics of the pre-adsorbed organic compounds of different chemical nature was also studied by processing the photocurrent-time profiles. Two different photocatalytic processes, exhibiting different rate characteristics, were observed. This was, again, attributed to the heterogeneity of the TiO2 surface corresponding to heterogeneous adsorption characteristics. The catalytic first order rate constants of both fast and slow processes were obtained for different organic compounds. It was found that for different adsorbates of different chemical nature the magnitudes of rate constant for the slow kinetic process were very similar, while the magnitudes of rate constant for the fast process were significantly affected by the photohole demand characteristics of different adsorbates. Photohole demand distribution that depends on the size and structure of the adsorbed molecules was believed to be responsible for the difference. By employing steady state photocurrent method, the photocatalytic degradation kinetic characteristics of both strong adsorbates and weak adsorbates of different chemical structures were compared at pure anatase TiO2 nanoporous TiO2 films as well as at anatase/rutile mixed phase TiO2 nanoporous film electrodes. At the former electrodes for all the different organic compounds studied, the photocatalytic reaction rate increased linearly with concentration at low concentrations. Under such conditions, it was demonstrated that the overall photocatalytic process was controlled by diffusion and was independent of the chemical nature of organic compounds. However, the linear concentration range and the maximum photocatalytic reaction rate at high concentrations were significantly dependent on the chemical nature of the substrates. This was explained by the difference in the interaction of different organic compounds with TiO2 surface, the difference in their photohole demand distributions at the TiO2 surface and the difference in their nature of intermediates formed during their photocatalytic mineralization. In contrast, at the latter electrodes for the photocatalytic oxidation of different organic compounds the linear ranges (diffusion control concentration range) and the maximum reaction rates at high concentration were much larger than at the former electrodes and much less dependent on the chemical nature of the organic compounds. The spatial separation of photoelectrons and photoholes (due to the coexistence of rutile phase and anatase phase) and the increase in the lifetime of photoelectrons and photoholes are responsible for the excellent photocatalytic activity of the electrodes. By employing the thin-layer photoelectrochemical technique (analogous to the thin-layer exhaustive electrolytic technique), the photocatalytic oxidation of different organic compounds at the mixed phase TiO2 nanoporous electrodes were investigated in a thin layer photoelectrochemical cell. It was found that the charge derived from exhaustive oxidation agreed well with theoretical charge expected for the mineralisation of a specific organic compound. This finding was true for all the compounds investigated and was also true for mixtures of different organic compounds. The photocatalytic degradation kinetics of different organic compounds of different chemical identities in the thin layer cell was also investigated by the photoelectrochemical method. Two kinetic processes of different decay time constants were identified, which were attributed to the degradation of preadsorbed compounds and the degradation of compounds in solution. For the degradation of compounds in solution, a change in the overall control step from substrate diffusion to heterogeneous surface reaction was observed. For different organic compounds, the variation of the rate constant was determined by the photohole demand rather than by the chemical identities of substrates. The kinetics of the fast kinetic process, on the other hand, was greatly affected by the adsorption properties of the substrates. For the strong adsorbates, the rate was much larger than for weak adsorbates. However, the rate constant of the process was independent of the chemical identities of the substrates and the variation of the constant was also determined by the photohole demand. Based on the principles of exhaustive photoelectrocatalytic degradation of organic matter in a thin layer cell, a novel, rapid, direct, environmental-friendly and absolute COD analysis method was developed. The method was tested on synthetic samples as well as real wastewater samples from a variety of industries. For synthetic samples with given compositions the COD values measured by my method agree very well with theoretical COD value. For real samples and synthetic samples the COD values measured by my method correlated very well with those measured by standard dichromate COD analysis method.

In the industry of metal cutting tools the conditions are extreme; the temperature can vary thousand degrees rapidly and the pressure can be tremendously high. To survive this kind of stress the cutting tool must be both hard and tough. In order to obtain these properties different coatings are used on a base of cemented carbide, WC-Co. Common coatings are hard ceramics like titanium nitride and titanium carbon-nitride with an outer layer of aluminium oxide. In this thesis the possibility of using titanium dioxide as an interlayer between titanium carbon-nitride and aluminium oxide to control the morphology and phase of aluminium oxide is investigated. Of the different aluminium oxide phases only the alpha-Al2O3 is stable. The titanium carbon-nitride coatings are made by CVD (chemical vapour deposition); also the alumina is deposited by CVD. The titanium dioxide was deposited by atomic layer deposition (ALD) which is a sequential CVD technique that allows a lower deposition temperature and better control of the film growth than CVD. The obtained thin films were analyzed using XRD, Raman spectroscopy, ESCA and SEM. To test the adhesion of the coatings the samples were sand blasted. A thin interlayer of titanium dioxide causes the aluminium oxide to grow as alpha-Al2O3, thinner TiO2 gave better adhesion.

Abstract Recently, titanium dioxide¡]TiO2¡^ is one of the most extensively studied transition-metal oxides because of its remarkable photocatalyst efficiency and electronic properties. In this paper, thin films ware obtained by dual ion beam sputtering. By different processes, these samples can be classified into three categories. Firstly, thin films, deposited on 200 mash copper grids for 15 minutes, were investigated that many TiO grains is about 5 nm in size by transmission electron microscopy¡]TEM¡^. Next, TiO2 thin films, sputtered on si wafers and glass for 180 minutes in an O2 environment by using titanium target, were initially identified by X ray diffraction instrument¡]XRD¡^. The result shows that some thin films have good orientations. By TEM, TiO2 grains on bottom of films are about 20 nm. By scanning electron microscopy¡]SEM¡^, TiO2 grains on the surface are about 1~2 £gm in size and are oblong in shape. The last, TiO thin films were directly deposited on si wafer for 180 minutes in no O2 environment by using titanium target and then annealed to transform from TiO to TiO2. By XRD, the thin film, annealed at 600¢J for 1hr, has good orientation. By TEM, TiO2 grains, annealed at 1000¢J for 24hr, grow up to 1-2 £gm in size and are oblong in shap.

The potential use of 3D aluminium nanorod structures as current collectors and negative electrodes for 3D Li-ion micro-batteries was studied based on the use of relatively simple and cost-effective electrochemical and sol-gel deposition techniques. Aluminium rod structures were synthesised by galvanostatic electrodeposition using commercial porous membranes as templates. It was shown that the use of a short (i.e., 50 ms long) potential pulse (i.e., -0.9 V vs. Al3+/Al) applied prior to a pulsed current electrochemical deposition gave rise to homogeneous deposits with more even rod heights.  Electrophoretic and sol-gel deposition of TiO2 on the same substrates were also studied. The use of the sol-gel technique successfully resulted in a thin coating of amorphous TiO2 on the Al nanorod current collector, but with relatively small discharge capacities due to the amorphous character of the deposits. Electrophoretic deposition was, however, successful only on 2D substrates. Anodisation of titanium was used to prepare 3D TiO2 nanotube electrodes, with a nanotube length of 9 um and wall thickness of 50 nm. The electrodes displayed high and stable discharge capacities of 460 µAh/cm2 at a 0.1 C rate upon prolonged cycling with good rate capability. The 3D aluminium nanorod structures were tested as negative electrodes for Li-ion cells and the observed capacity fading was assigned to trapping of LiAl alloy inside the aluminium electrode caused by the diffusion of lithium into the electrode, rather than to pulverisation of the aluminium rods. The capacity fading effect could, however, be eliminated by decreasing the oxidation potential limit from 3.0 to 1.0 V vs. Li+/Li. A model for the alloying and dealloying of lithium with aluminium was also proposed. Finally, a proof-of-concept for a full 3D Li-ion micro-battery with electrodes of different geometries was demonstrated. The cell comprised a positive electrode, based on LiFePO4 deposited on a carbon foam current collector, with an area gain factor an order of magnitude larger than that for the Al nanorod negative electrode. This concept facilitates the balancing of 3D Li-ion cells as the positive electrode materials generally have significant lower specific energy densities than the negative electrodes.