Des couches minces d'oxyde de vanadium, V2O5, ont été déposées à température ambiante sur substrat ITO/verre en utilisant trois conditions de dépôt différentes, à savoir la pulvérisation cathodique par magnétron haute fréquence (RFMS) avec cible métallique en V (métal V2O5RF) et cible d’oxyde de V2O5 (oxyde V2O5RF) et la pulvérisation cathodique par magnétron en régime d’impulsions de haute puissance (HiPIMS) avec cible métallique (V2O5HiPIMS), respectivement. L’optimisation des différents paramètres de dépôt conduit à une modulation de la structure et morphologie des films, d’amorphes à cristallisés et de denses à poreux. Le cyclage en milieu lithié ou sodé montre un multichromisme associé à un changement réversible de coloration impliquant 4 couleurs, orange, vert, bleu et gris, en fonction des états de réduction et d’oxydation. Un cyclage prolongé sur 1000 CV, indique une différence de stabilité en fonction de la méthode de dépôt. Les films denses déposés par HiPIMS présentent une grande stabilité tandis qu’une dégradation très rapide est observée pour les films amorphes (oxyde V2O5RF) et qu’une augmentation de capacité est observée pour les films (métal V2O5RF). Ces différences de comportement sont attribuables à des différences de morphologie faisant apparaitre des films fissurés et fragiles dans un cas et denses sans grande évolution dans l’autre cas. Par ailleurs, le cyclage longue durée entraine une amorphisation des films. La caractérisation par un grand nombre de techniques (GIXRD, XPS, TOF-SIMS, AES et RBS / NRA) des différents comportements au cours du processus électrochrome a mis en évidence que le mécanisme ne peut être simplement décrit par une unique réaction d’insertion/désinsertion. Les propriétés électrochromes prometteuses des couches unitaires de V2O5 (métal V2O5RF) ont permis leur intégration dans des dispositifs complets à base d’électrolyte transparent ou opaque. Ainsi, des dispositifs WO3/V2O5 et V2O5/V2O5 ont été caractérisés pour des applications vitrage et afficheur. / Vanadium oxide thin films were deposited on ITO coated glass substrate at room temperature using three different deposition conditions, namely radio frequency magnetron sputtering (RFMS) with V metallic target (V2O5RF-metal) or V2O5 oxide target (V2O5RF-oxide) and High Power Impulse Magnetron Sputtering (HiPIMS) with V metallic target (V2O5HiPIMS), respectively. Significant difference in structure and morphologies are reported. V2O5RF-metal films are crystalline and dense with a disturbed surface which is thickness dependent, while V2O5RF-oxide and V2O5HiPIMS films are amorphous and porous or dense respectively. V2O5 thin films show reversible electrochromism with 4 colors, which are orange, green, blue and gray, in reduction/oxidation states when cycled in Li and Na based electrolytes. However, depending on the deposition method, V2O5 films show different cycling stability, recorded up to 1000 cycles, that is attributed to a modification of the morphology (i.e. increase of the surface area due to cracks and increase porosity, as well as a progressive amorphization particularly in lithium electrolyte. The different behaviors during the electrochromic process were investigated with GIXRD, XPS, TOF-SIMS, AES and RBS/NRA indicating a mechanism more complex than a simple insertion/deinsertion. Finally, two types of ECDs using either transparent electrolyte membrane or opaque are fabricated coupling V2O5 thin films to WO3 or to V2O5 in a symmetrical device aiming at application in smart windows and displays, respectively.

Electrochemical capacitors, now often termed supercapacitors, are high power electrochemical energy storage devices that complement or replace high power batteries in applications ranging from wind turbines to hybrid engines to uninterruptable power supplies to electronic devices. My dissertation explores the applications of relatively uncommon techniques for both supercapacitor material syntheses and gaining better mechanistic understanding of factors impacting electrochemical performance of supercapacitors. From fundamental ion electroadsorption studies made possible by using small angle neutron scattering (SANS), to the systematic investigations of coating thickness and microstructure in metal oxide / carbon nanocomposite electrodes realized through the novel use of the atomic layer deposition (ALD) technique, new avenues of material characterization and fabrication have been studied. In this dissertation I first present the motivation to expand the knowledge of supercapacitor science and technology, and follow with an in-depth literature review of the state of the art. The literature review covers different types of supercapacitors, the materials used in the construction of commercial and exploratory devices, an exploration of the numerous factors which affect supercapacitor performance, and an overview of relevant materials synthesis and characterization techniques The technical objectives for the work performed in this dissertation are then presented, followed by the contributions that I made in this field in my two primary research thrusts: advances to the understanding of ion electroadsorption theory in both aqueous and organic electrolytes through the development of a SANS-based methodology, and advances to metal-oxide carbon nanocomposites as electrodes through the use of ALD. The understanding of ion electro-adsorption on the surface of microporous (pores < 2 nm) solids is largely hindered by the lack of experimental techniques capable of identifying the sites of ion adsorption and the concentration of ions at the nanoscale. In the first research thrust of my dissertation, I harness the high penetrating power and sensitivity of neutron scattering to isotope substitution to directly observe changes in the ion concentration as a function of the applied potential and the pore size. I have conducted initial studies in selected aqueous and organic electrolytes and outlined the guidelines for conducting such experiments for the broad range of electrode-ions-solvent combinations. I unambiguously demonstrate that depending on the solvent properties and the solvent-pore wall interactions, either enhanced or reduced ion electro-adsorption may take place in sub-nanometer pores. More importantly, for the first time I demonstrate the route to identify the critical pore size below which either enhanced or reduced electrosorption of ions takes place. My studies experimentally demonstrate that poor electrolyte wetting in the smallest pores may indeed limit device performance. The proposed methodology opens new avenues for systematic in-situ studies of complex structure-property relationships governing adsorption of ions under applied potential, critical for rational optimization of device performance. In addition to enhancing our understanding of ion sorption, there is a critical need to develop novel supercapacitor electrode materials with improved high-energy and high-power characteristics. The formation of carbon-transition metal oxide nanocomposites may offer unique benefits for such applications. Broadly available transition metal oxides, such as vanadium oxide, offer high ion storage capabilities due to the broad range of their oxidation states, but suffer from high resistivities. Carbon nanomaterials, such as carbon nanotubes (CNT), in contrast are not capable to store high ion content, but offer high and readily accessible surface area and high electrical conductivity. In the second research thrust of my thesis, by exploiting the ability of atomic layer deposition (ALD) to produce uniform coatings of metal oxides on CNT electrodes, I demonstrated an effective way to produce high power supercapacitor electrodes with ultra-high energy capability. The electrodes I developed showed stable performance with excellent capacitance retention at high current densities and sweep rates. Electrochemical performance of the oxide layers were found to strongly depend on the coating thickness. Decreasing the vanadium oxide coating thickness to ~10 nm resulted in some of the highest values of capacitance reported to date (~1550 F·g⁻¹VOx at 1 A·g⁻¹ current density). Similar methodology was utilized for the deposition of thin vanadium oxide coatings on other substrates, such as aluminum (Al) nanowires. In this case the VOₓ coated Al nanowire electrodes with 30-50% of the pore volume available for electrolyte access show volumetric capacitance of 1390-1950 F cc⁻¹, which exceeds the volumetric capacitance of porous carbons and many carbon-metal oxide composites by more than an order of magnitude. These results indicated the importance of electrode uniformity and precise control over conformity and thickness for the optimization of supercapacitor electrodes.

Thesis (Ph. D.)--State University of New York at Binghamton, Department of Chemistry, 2004. / Includes bibliographical references.

Abstract In this thesis work, crystal and phase structure, chemical composition and gas sensing properties of pulsed laser deposited vanadium oxide thin films were studied. Pulsed laser deposition was used to manufacture vanadium oxide thin films with various crystal structures, film morphologies and phase compositions. Both the well-known vanadium pentoxide V2O5, and a totally new stable phase in a solid-state thin-film form, V7O16, was produced. The existence of these phases was proven by several different characterization methods such as, X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy. The resistive gas sensing measurements of the films with pure V2O5 composition, and mixed phase compositions of V2O5 and V7O16, showed that behaviour of the electrical response to different gases at various measurement temperatures was dependent on the phase composition of the thin films. It was proved that in certain conditions the mixed phase films show p-type semiconducting gas sensing behaviour, instead of the pure n-type behaviour of V2O5. Both types of film compositions were shown to be highly sensitive to ammonia gas, down to 40 ppb-level. The mixed phase composition showed a higher response to ammonia compared to the pure V2O5 phase; however the pure V2O5 showed better long-term stability. Both sensing layer types also showed high selectivity to ammonia in comparison to NO and CO gases. Nanostructured pure V2O5 layers were successfully deposited on commercial microheater platforms and then used as a gas sensor. The V2O5 nanostructures were proven to be very promising candidates as gas sensor material to control the Selective Catalytic Reduction process used in the reduction of NOx gas emissions. The surface valence states of the thin film structures with various phase compositions were studied spectroscopically, and a clear connection between the valence states of the film surfaces and gas sensing properties was found. It was concluded that the pure V2O5 films also had some V4+ ions in the surface, and in the mixed phase thin films, the amount V4+ ions was already quite high, indicating a higher amount of oxygen vacancies in the thin film surface – another proof of the existence of V7O16 phase in the film composition. It is also suggested that the particular quantity of oxygen vacancies is one of the reasons for the high gas-sensing response of the thin films. / Tiivistelmä Tässä työssä tutkittiin pulssilaserkasvatettujen vanadiinioksidiohutkalvojen kide- ja faasirakenteita sekä ominaisuuksia kaasuantureina. Vanadiinioksidiohutkalvoja, jotka omaavat erilaiset kide- ja faasirakenteet, sekä erilaiset morfologiat valmistettiin pulssilaserkasvatuksella. Tunnetun V2O5 -faasin lisäksi myös V7O16 -faasi onnistuttiin valmistamaan ensimmäistä kertaa kiinteän aineen epäorgaanisena faasina ohutkalvorakenteeseen. Näiden erilaisten faasirakenteiden olemassaolo todistettiin käyttämällä useita menetelmiä kuten röntgendiffraktiota, Raman spektroskopiaa ja röntgenfotoelektronispektroskopiaa. Sekä ainoastaan V2O5 -faasia sisältäviä ohutkalvoja, että V2O5 ja V7O16 sekafaasirakenteen omaavia ohutkalvoja tutkittiin kaasuanturina, ja mittaustulokset osoittivat erilaisten kalvojen sähköisten kaasuanturivasteiden ominaisuuksien voimakkaan riippuvuuden kalvojen faasirakenteesta. Havaittiin myös, että sekafaasirakenne omaa tietyissä olosuhteissa p-tyyppisen puolijohteen sähkönjohtavuusmekanismin, toisin kuin puhdas V2O5-rakenne, joka on täysin n-tyyppinen. Molemmat ohutkalvotyypit todennettiin olevan erityisen herkkiä ammoniakki (NH3) kaasulle, jopa 40 miljardisosatasolle. Kalvo, jossa oli sekafaasirakenne, omasi korkeamman sähköisen kaasuvasteen kuin puhtaasta V2O5 faasista koostuva ohutkalvo, joka taas toisaalta omasi paremman stabiiliuden pidemmällä aikavälillä. Molemmat kaasuanturimateriaalit havaittiin selektiiviseksi NH3 -kaasulle verrattuna NO- ja CO-kaasuihin. Puhdas V2O5 nanorakenne onnistuttiin myös kasvattamaan kaupalliselle anturialustalle, ja käyttämään menestyksekkäästi herkkänä NH3- kaasuanturina. Lisäksi puhtaan V2O5 nanorakenteen todennettiin olevan erittäin lupaava kaasuanturimateriaali hyödynnettäväksi NOx-kaasupäästöjen vähentämiseen käytettävän SCR-katalyysiprosessin (Selective Catalytic Reduction) ohjauksessa. Ohutkalvotyyppien pinnan sähköistä rakennetta tutkittiin röntgenspektroskopiamenetelmillä, ja selvä yhteys materiaalien pintojen valenssitilojen ja kaasuanturiominaisuuksien välillä havaittiin. Huomattiin, että myös puhdas V2O5 ohutkalvo omaa pinnallaan pienen määrän V4+ -ioneja, ja että ohutkalvossa, jossa on sekafaasirakenne, V4+ -ionien määrä on suuri, ollen yksi todiste lisää V7O16 faasin olemassaoloon kalvon rakenteessa. Tästä johtuva happivakanssien olemassaolo on yksi syy näiden ohutkalvojen korkeaan kaasuherkkyyteen.

No description available.

<p>Nanomaterials have attracted great interest in recent years, and are now also being considered for battery applications. Reducing the particle size of some electrode materials can increase battery performance considerably, especially with regard to capacity, power and rate capability. This thesis presents a study focused on the performance of such a material, vanadium oxide nanotubes, as cathode material for rechargeable lithium batteries.</p><p>These nanotubes were synthesized by a sol-gel process followed by hydrothermal treatment. They consist of vanadium oxide layers separated by structure-directing agents, normally amines or metal ions, e.g., Na⁺, Ca²⁺, Mn²⁺ and Cu²⁺. The layers are arranged in a scroll-like manner, allowing the interlayer structure to expand and contract, depending on the size of the embedded guest. This tubular form of vanadium oxide was able to insert lithium ions reversibly, making it a candidate cathode material. The structural and electrochemical response to lithium ion insertion was carefully studied to define optimal performance criteria and probe the lithium insertion mechanism. This was done using several characterization techniques, including X-ray diffraction, a variety of spectroscopic methods and electrochemical testing. Galvanostatic measurements show that the material can be charged and discharged reversibly for >100 cycles with a capacity of 150-200 mAh/g. The electrochemical performance is, however, dependent on the electrode film preparation technique, the choice of salt in the electrolyte and the nature of the embedded guest. Results from photoelectron spectroscopy, and soft X-ray emission and absorption spectroscopy confirm that vanadium is reduced during lithium insertion and that three oxidation states (V⁵⁺, V⁴⁺and V³⁺) co-exist at potentials below 2.0 V. <i>In situ</i> X-ray diffraction, performed during potential stepping, identifies two separate processes during lithium insertion: a fast decrease of the interlayer distance followed by a slow two-dimensional relaxation of the vanadium oxide layers. </p>

Nanomaterials have attracted great interest in recent years, and are now also being considered for battery applications. Reducing the particle size of some electrode materials can increase battery performance considerably, especially with regard to capacity, power and rate capability. This thesis presents a study focused on the performance of such a material, vanadium oxide nanotubes, as cathode material for rechargeable lithium batteries. These nanotubes were synthesized by a sol-gel process followed by hydrothermal treatment. They consist of vanadium oxide layers separated by structure-directing agents, normally amines or metal ions, e.g., Na+, Ca2+, Mn2+ and Cu2+. The layers are arranged in a scroll-like manner, allowing the interlayer structure to expand and contract, depending on the size of the embedded guest. This tubular form of vanadium oxide was able to insert lithium ions reversibly, making it a candidate cathode material. The structural and electrochemical response to lithium ion insertion was carefully studied to define optimal performance criteria and probe the lithium insertion mechanism. This was done using several characterization techniques, including X-ray diffraction, a variety of spectroscopic methods and electrochemical testing. Galvanostatic measurements show that the material can be charged and discharged reversibly for &gt;100 cycles with a capacity of 150-200 mAh/g. The electrochemical performance is, however, dependent on the electrode film preparation technique, the choice of salt in the electrolyte and the nature of the embedded guest. Results from photoelectron spectroscopy, and soft X-ray emission and absorption spectroscopy confirm that vanadium is reduced during lithium insertion and that three oxidation states (V5+, V4+ and V3+) co-exist at potentials below 2.0 V. In situ X-ray diffraction, performed during potential stepping, identifies two separate processes during lithium insertion: a fast decrease of the interlayer distance followed by a slow two-dimensional relaxation of the vanadium oxide layers.

Infrared detector technologies have been developing each day. Thermal detectors take great attention in commercial applications due to their low power consumption and low costs. The active material selection and the deposition of the material are highly important performance effective factors for microbolometer detector applications. In that sense, developing vanadium oxide (VOx) microbolometer active material by sol-gel method might be feasible approach to achieve good performance microbolometer detectors. In this study, vanadium oxide thin films are prepared by sol-gel method is deposited on silicon or silicon nitride wafers as active material by spin coating. The films are annealed under different hydrogen concentration of H2/N2 environments at 410

<p>In the present work, the thermodynamic activities of chromium and vanadium oxide in CaO-SiO2-MgO-Al2O3 slags were measured using gas-slag equilibration technique. The slag was equilibrated with a gas mixture of CO, CO2 and Ar gases enabling well-defined oxygen partial pressures in the gas mixture (PO2=10-3,10-4,10-5 Pa) at temperatures 1803, 1823K, 1873, 1923 K. The slags were kept in Pt crucibles during the equilibration and the duration of which was 20 h. From a knowledge of the thermodynamic activity of chromium and vanadium in Cr or V in Pt alloy, obtained from literature, and the oxygen partial pressure in the gas stream calculated by Thermo Calc software, the thermodynamic activity of chromium, vanadium oxide in the slags could be observed.An assessment of the experimental studies in earlier works reveal that, the activities of chromium at low chromium contents and vanadium in their respective alloys in platinum exhibits a strong negative deviation from ideality, the logarithms of activity coefficient of these elements were found to increase with increasing mole fractions of these metals in the Pt-alloys.Regarding the slag phase, all the chromium in the slags was assumed to be present in the divalent state in view of the low Cr contents and the low oxygen potentials employed in the present studies. Analogously, vanadium in the slag was assumed to be in the trivalent state in view of the low vanadium contents in the slag and the low oxygen partial pressure in the gas phase. Activity of chromium oxide, CrO decreases with increasing temperature and decreasing content of chromium oxide in slag and oxygen partial pressure in the gas phase. Activity of vanadium oxide, VO1.5 in slag phase shows a negative deviation from ideality. Activity coefficient of vanadium oxide shows a decrease with basicity of slag and the “break point” occurs at about slag basicity of 1 under the oxygen partial pressure of 10-3 Pa and temperature of 1873 K.A relationship for estimating the actual content of chromium, vanadium in slag as a function of activities of chromium or vanadium, temperature, oxygen partial pressure and slag basicity were developed from the present results, the agreement between the estimated and experimental values is satisfactory, especially at lower oxygen partial pressure.</p>

Orientador: Diogo Paschoalini Volanti / Resumo: O avanço na ciência e tecnologia de sensores de compostos orgânicos voláteis (VOCs) é importante para o desenvolvimento sustentável de materiais funcionais. A dissertação de mestrado refere-se à avaliação do uso de óxido de grafeno (GO, sigla em inglês) em óxido metálicos (OM) tipo-n (V2O5) e tipo-p (Co3O4) para melhorar a sensibilidade, a seletividade e o tempo de resposta dos sensores. O GO teve uma modificação sendo submetido a um processo oxidativo. Os OMs nano ou microestrurados foram preparados a partir de seus sais ou por processos de ressolubilização dos óxidos. Por fim, os compósitos GO-OM foram preparados após os percursores ficarem em suspensão com o GO por 24 horas. O GO aumentou a adsorção gasosa dos compostos resultando em maior seletividade e sensibilidade. Por outro lado, os principais benefícios das estruturas nano e microestrutruradas dos OMs seriam a maior área superficial do material resultando em melhores propriedades gasosas, resultando em mais sítios ativos para adsorção do oxigênio e das moléculas do gás analito. As respostas sensoras foram avaliadas na presença de diferentes concentrações (nas faixas de ppm e ppb) de VOCs (ex.: acetona, acetaldeído, etanol, metanol, benzeno, xileno e tolueno) em atmosfera seca. / Abstract: The advancement in science and technology of volatile organic compounds (VOCs) sensors is essential for the sustainable development of functional materials. The master's thesis refers to the evaluation of the use of graphene oxide (GO) in metallic oxides (OM) type-n (V2O5) and type-p (Co3O4) to improve sensitivity, selectivity and the response time of the sensors. The GO had a modification being subjected to an oxidative process. The nano or microstructured OMs were prepared from its precursors. Finally, the GO-OM composites were prepared after the precursors were in suspension with the GO for 24 hours. The GO increased the gaseous adsorption of the compounds resulting in greater selectivity and sensitivity. On the other hand, the main benefits of the nanostructured and micro-structured structures of OMs would be the greater surface area of the material resulting in better gaseous properties, resulting in more active sites for adsorption of oxygen and analyte gas molecules. The sensory responses were evaluated in the presence of different concentrations (in the ppm and ppb ranges) of VOCs (e.g., acetone, acetaldehyde, ethanol, methanol, benzene, xylene and toluene) in a dry atmosphere. / Mestre