Dissertations / Theses on the topic 'Alkaline metal oxides'

Dans cette thèse, des simulations DFT-MD couplées à des techniques inno-vantes de métadynamique, sont appliquées pour acquérir une compréhensionglobale des interfaces aqueuses d'oxyde de cobalt Co3O4 et CoO(OH) dansla catalyse de la réaction d'évolution de l'oxygène (OER), et ainsi éventuellement aider à la conception de nouveaux catalyseurs basés sur des matériaux non précieux, un domaine clé de la recherche scientifique et technologique, particulièrement important pour l'économie de l'hydrogène, pour les technologies vertes dans une période de temps avec une demande toujours plus croissanteen énergie verte. Dans cette thèse, nous révélons étape par étape les mécanismes de l'OER sur les électrocatalyseurs aqueux d'oxyde de cobalt Co3O4 etCoO(OH) via de nouvelles techniques de métadynamique.Jusqu'à présent, la littérature n'a jamais pris en compte les modificationsau niveau atomique de la structure des électrodes ainsi que de l'eau interfaciale dans leur modélisation des processus OER. Ce manque de connaissances représente clairement un obstacle important au développement de catalyseurs améliorés, qui pourrait être surmonté en utilisant des méthodes capables de suivre les caractéristiques catalytiques de l'OER à l'échelle atomique. Pour la première fois, nous montrons combien il est important de prendre en considération la présence de l'environnement aqueux dans la caractérisation structurale des surfaces du catalyseur, c'est-à-dire (110)-Co3O4 et (0001)-CoO(OH) dans ce travail. Une caractérisation détaillée des propriétés chimiques et physiques des interfaces aqueuses est fournie (la structure, la dynamique, la spectroscopie, le champ électrique), pour les surfaces (110)-Co3O4 et (0001)-CoO(OH) en contact avec l'eau liquide.Une étude détaillée de l'OER est présentée non seulement du point de vue descatalyseurs, mais aussi en abordant le rôle de l'environnement de l'eau dans leprocessus catalytique, ce qui n'a pas été fait auparavant dans la littérature. En conséquence, l'OER en phase gazeuse et en phase liquide sont étudiés ici auxinterfaces aqueuses (110)-Co3O4 et (0001)-CoO(OH) en adoptant une nouvelleapproche de métadynamique d'échantillonnage amélioré, capable d'identifieret caractériser les mécanismes de réaction chimique et d'intégrer pleinement lerôle des degrés de liberté du solvant, permettant ainsi de dévoiler des réactivités chimiques d'une complexité remarquable. L'énergétique, la cinétique et la thermodynamique derrière l'OER sont donc trouvées à ces surfaces d'oxyde de cobalt à l'interface avec l'eau
In this thesis, DFT-MD simulations, coupled with state-of-the-art metadynamics techniques, are applied to gain a global understanding of Co3O4 and CoO(OH) cobalt oxide aqueous interfaces in catalyzing the oxygen evolution reaction (OER), and hence possibly help in the design of novel catalysts basedon non-precious materials, a current key field of research in science and technology, especially of importance for the hydrogen economy, for green technology in a period of time with an ever more growing demand in green-energy. In this thesis, we step-by-step reveal the OER mechanisms on spinel Co3O4 andCoO(OH) cobalt aqueous electrocatalysts carefully and rationally via novelmetadynamics techniques.Up to now, the literature has never taken into account the atomistic modifications on the electrode structure as well as on the interfacial water into their modeling of OER processes. Such lack of knowledge clearly represents a significant hurdle toward the development of improved catalysts, which couldbe overcome by employing methods able to track the catalytic features of theOER at the atomistic scale. For the first time, we show how important itis to take into consideration the presence of the liquid water environment inthe structural characterization of catalyst surfaces, i.e. for (110)-Co3O4 and(0001)-CoO(OH) in this work. A detailed characterization of chemical andphysical properties of the aqueous interfaces is provided (i.e. structure, dynamics, spectroscopy, electric field), for the (110)-Co3O4 and (0001)-CoO(OH)aqueous surfaces.A study of the OER is presented not only by looking at the catalysts, butalso by addressing the role of the water environment in the catalytic process,not done before in literature. Accordingly, both gas-phase and liquid-phaseOER are here investigated at the (110)-Co3O4 and (0001)-CoO(OH) adoptinga novel enhanced sampling metadynamics approach able to address a widerange of chemical reaction mechanisms and to fully include the role of thesolvent degrees of freedom, allowing to unveil reaction networks of remarkablecomplexity. The energetics, kinetics and thermodynamics behind the OER aretherefore found at these cobalt oxide surfaces

Oxides of ABO3 composition (A = alkali, alkaline earth or rare earth metal in general, B = transition metal) constitute a large family of metal oxides of current interest to solid state and materials chemistry. Among the several structure types exhibited by ABO3 oxides (ilmenite, LiNbO3, perovskite, YAIO3/YMnO3, KSbO3, pyrochlore, among others), the perovskite structure is probably the most well known and widely investigated. The ideal perovskite structure consists of a three-dimensional (3D) framework of corner-sharing BO6 octahedra in which the A cation resides in the dodecahedral site surrounded by twelve oxide ions. The ideal cubic structure occurs when the Gold Schmidt’s tolerance factor, t = (rA + ro)/{V2 (rB + ro)}, adopts a value of unity and the A-O and B-O bond distances are perfectly matched. The flexibility of the perovskite structure towards a wide variety of substitutions at both A and B sites gives rise to a very large number (several hundreds) of perovskite derivatives with subtle variations in structure. The perovskite structure can also tolerate vacancies at both the A and O sites giving ordered superstructures. Members of y4BO3 oxides have numerous properties that find technological application, such as nonlinear optical response (LiNbO3), Ferro electricity (BaTiO3), piezoelectricity (PbZn_xTixO3), magneto ferroelectricity (YMnO3), superconductivity (Bai_xKxBi03)5 colossal magnetoresistance (La^xCaxMnO3) and ionic conductivity [(Lil_a)TiO3] Ordering of cations at the A and B sites of the perovskite structure is an important phenomenon. Ordering of B site cations in double (/42BB'O6) and multiple (/43BB'2Og) perovskites gives rise to newer and interesting materials properties For example, 1*1 ordered Sr2FeMoO6 and Sr2FeReO6 are half-metallic ferrimagnets; Pb3MgNb2O9 is a relaxor ferroelectric; Ba3ZnTa2O9 is a low loss dielectric used in telecommunication and, last but not least, Ba3CoNb2O9 is a visible light driven photocatalyst. Realization of these properties in these materials depends crucially on the ordering/or otherwise of the B site cat ions in the perovskite structure. Furthermore, ordering of not only the metal atoms but also the oxygen/oxygen vacancies in the perovskite structure is equally important for the occurrence of superconductivity in the cuprate superconductor, YBa2Cu3O7. The ideal perovskite structure gives way to hexagonal YMnO3/YAIO3 structure for smaller A cations (tolerance factor, t < 1). Oxides of this structure are attracting current attention for the realization of multiple magnetoferroic properties. On the other hand, for larger A cations (tolerance factor, t > 1), various perovskite polytypic structures are formed. For example, BaNiO3 forms a 2H polytypic structure, SrMnO3 and BaRuO3 adopts a 4H and 9R structures respectively, where the SO6 octahedra share faces or faces and corners. Besides the foregoing 3D perovskites, a number of layered variants of the perovskite structure are also known. The most common layered perovskites are the Aurivillius phases, (Bi2O2)[A»-iBnO3n+iL the Ruddlesden-Popper phases, /4'2|7ln_iBnO3n+1], and the Dion-Jacobson phases, A[An^BnOzn+-\]' The two-dimensional (2D) perovskite unit, [^n-iBnOsn+i], which could be visualized as formed by slicing the 3D perovskite structure along <001>p is common for all the three layered perovskite series. The perovskite slabs are stacked alternately with various charge-balancing units, for example, with [Bi2O2]2+ in the Aurivillius phases and two alkali/alkaline earth cations (A+JA2+) in the Ruddlesden-Popper phases etc. Members of the layered perovskites are also important from the point of view of materials properties. For example, 2D magnetism (K2NiF4), superconductivity (La2-xSrxCuO4), ion exchange, Bronsted acidity, intercalation, exfoliation (K2La2Ti3Oio and CsCa2Nb3O10), photo catalysis (Rb2La2Ti30io) are some of the important materials properties found in layered perovskites. The high Tc-superconductors, Bi2Sr2CaCu2O8+XJ TI2Ba2Ca2Cu3Oi0, TIBa2Ca2Cu3O9 and HgBa2Ca2Cu3O8+x, also belong to the family of layered perovskites where the defective perovskite cuprate sheets are interleaved by other 2D entities like (Bi2O2), (TI2O2), (TIO) or (HgOx). In addition, Aurivillius phases, such as Bi2SrTa209 and Bi325Lao75Ti3Oi2, in thin film geometry are candidate materials for non-volatile ferroelectric memory devices. Synthesis plays a key role in realizing new structures and materials properties for ABO3 oxides. The conventional synthetic methods (ceramic method) involve mixing and heating of solid reactants at elevated temperatures. Although this approach continues to be employed to synthesize new materials, it is often limited by the fact that it yields thermodynamically stable phases. Since many of the perovskite oxides showing useful materials properties are metastable in nature and are required in the form of fine particles (free-standing / monodisperse / submicron or nanometer dimensions) for application, the ceramic methods are of no avail for this purpose. Therefore, materials chemists constantly endeavor to develop alternate synthetic routes that enable them to synthesize novel oxides under mild conditions. Typical examples of metastable perovskites are: the super conducting cuprates (e.g. TlosPbosS^CaC^Og) and perovskite based lithium ion conductors (La2/3-xLi3XDi/3-2xTiO3). Also the control of oxidation states in double perovskites, such as Sr2FeMoO6 and Sr2FeRe06 and pyrochlores such as Pb2MnReC>6, cannot be achieved by conventional means. Therefore, the synthesis of such metastable phases requires special synthetic strategies that involve soft chemistry (chimie douce) methods where mild reactions/reaction conditions are employed to access metastable phases. The present thesis is mainly devoted to an investigation of perovskite related oxides towards developing new synthetic strategies and materials as well as exploring hydrogen insertion - a novel materials property - in certain members of this family. Solid-state metathesis (SSM) reactions provide a convenient route for the synthesis of a wide variety of non-oxide ceramic materials such as, bondes, carbides, silicides, pnictides and chalcogenides. A typical metathesis reaction, for example, M0CI5 + 5/2 Na2S -» MoS2 + 5 NaCI + 1/2 S (1) involves exchange of atoms/ions between the reactants and is accompanied by a large enthalpy change (AHm = - 890 kJ mol"1) and high adiabatic reaction temperature (Tm = 1413 °C). The reactions are often self-propagating and believed to be driven by the formation of stable salt byproducts such as alkali halides with high lattice energy. In our laboratory we have developed a different kind of metathesis reaction for the synthesis of perovskite related oxides, a typical example being, K2La2Ti30io + 2 BiOCI -* [Bi2O2]La2Ti3O10 + 2 KCI. A major difference between metathesis reactions (1) and (2) is that unlike (1), reaction (2) is not self-propagating, requiring longer duration. In this study, we have investigated metathesis reactions of the second kind at some length for the synthesis of perovskite related oxides. We found that rocksalt oxides such as UMO2 (M = Mn, Co) and Li2TiO3 constitute convenient precursors for the formation of v4BO3 perovskite oxides in metathesis reactions with appropriate reaction partners such as halides, oxyhalides or sulphates, LiCoO2 + LaOCl -» LaCoO3 + LiCt (3) LiMnO2 + LaOCl + x/2 O2 -> LaMnO3+x + LiCI (4) Li2TiO3 + PbSO4 -» PbTiO3 + Li2SO4. (5) We could synthesize not only well known ABO3 oxides but also functional perovskites such as PbZr0 4sTio 52O3 (PZT), La2/3Cai/3MnO3 as well as superconducting BaPbo75Bio2s03 by this method. We could also synthesize La2CuO4 and its superconducting analogues, La185^oi5Cu04 (A = Sr, Ba), by the same method using Li2CuO2 and LaOCl. For the synthesis of double perovskites A2BB%OQ by this method however, appropriate lithium containing rocksalt precursor oxides are not known in the literature. Therefore, we first synthesized rocksalt precursor oxides of the general formula Li4MWO6 (M = Mg, Mn, Fe, Ni) and established their identity. Using these precursor oxides, we could synthesize the double perovskite oxides Sr2MWO6 (M = Mg, Mn, Fe, Ni) in the metathesis reaction Li4MWO6 + 2 SrCI2 -» Sr2MWO6 + 4 LiC Significantly, the double perovskites are formed with an ordered structure at relatively low temperatures (750 - 800 °C) as compared to the high temperatures (up to 1400 °C) usually employed for the synthesis of these materials by conventional ceramic approach. Next, we investigated ABO$ compositions corresponding to the formula for 6 = Cu and Ni, where we could obtain a YAIO3 superstructure consisting of triangular Cu clusters for 6 = Cu, whereas a perovskite phase for B = Ni. Moreover, the Cu-phase appears to be a unique line phase formed around LasCi^VOg composition, whereas a continuous series of GdFeO3-like perovskite oxides are formed for LaNii»xVxO3 (0 < x < 1/3)forS = Ni. Considering the current interest in bringing different transition metal ions (d°/dn electronic configuration) in the same perovskite related structure towards developing multiferroic materials, we investigated the substitution of aliovalent cations in a typical Aurivillius phase, Bi2Sr2Nb2TiOi2. We have characterized new aliovalent cation substituted Aurivillius phases, Bi2SrNaNb2TaOi2, Bi2Sr2Nb2Zr012J Bi2Sr2Nb2 5Feo50i2 and Bi2Sr2Nb2 ezZno 33O12. Lastly, we investigated the interaction of hydrogen with perovskite oxides, /\MnO3 (A = Ca, Sr, Ba) in an attempt to characterize possible existence of hydrogen-inserted oxide materials. An oxide-hydride of the formula LaSrCoO3H07 has recently been reported in the literature. Conventionally, the interaction of hydrogen with perovskite related oxides is known to result in either anion deficient phases (e.g. CaMnO3 -> Ca2Mn205), or hydrogen inserted materials, 'hydrogen bronzes', (e. g. HXWO3, HxBaRuO3), where hydrogen acts as an electron donor (H -^ H+ + e). We have characterized a new mode of hydrogen incorporation in Pt dispersed BaMnO3 and SrMnO3. Detailed investigation of the hydrogen sorption behaviour of 1 atom % Pt dispersed materials showed that about 1.25 mass % of hydrogen is inserted per mole of BaMnO3/Pt, corresponding to an insertion of - 3 hydrogen atoms giving 'BaMnOsHs'. While the exact nature of inserted hydrogen is yet to be established unambiguously, our results suggest that the inserted hydrogen is unlikely to be protonic (H+) in the hydrogen insertion product, BaMnO3H3. The results of these investigations are presented in the thesis consisting of seven chapters. Chapter 1 gives an overview of perovskite related oxides - structure, properties and synthesis. Chapter 2 presents metathesis as a general route for the synthesis of ABO3 oxides and illustrates the method by transforming several rocksalt oxides such as LiCoO2, Li2Mn03 and Li2Ti03 to corresponding ABO3 oxides, LaCoO3, /\MnO3 and ATiO3 (A = Ca, Sr, Ba). Uniformly in all the cases, the perovskite oxides are obtained in the form of loosely connected submicron sized particles at considerably lower temperatures than those usually employed for their synthesis by ceramic methods. Thermodynamic calculations have also been carried out to probe into the driving force of metathesis reactions involved in the synthesis. Chapter 3 describes an extension of the metathesis route for the synthesis of double perovskites, Sr2MWO6 (M = Mg, Mn, Fe, Ni). For this purpose, first we synthesized new rocksalt oxides of the general formula, Li4MWO6 (M = Mg, Mn, Fe, Ni). The oxides adopt rocksalt superstructures related to Li4MgReO6 (for M = Mg, Mn, Ni) and U4WO5 (for M = Fe). Metathesis reaction between Li4MWO6 and SrCi2 at 750 - 800 °C yields the corresponding double perovskites where the octahedral site M and W are ordered in the long range. Formation of ordered perovskite oxides at relatively low temperatures (750 - 800 °C) by the metathesis route is a significant result, considering that synthesis of these oxides by conventional ceramic method requires much higher temperatures (1300 - 1400 °C) and prolonged annealing. Synthesis of La2CuO4, Nd2CuO4 and super conducting La-j 85>4oi5Cu04 (A = Sr, Ba) by the metathesis route is described in Chapter 4. Chapter 5 deals with synthesis, structure and magnetic properties of mixed-metal oxides of ABO3 composition in the La-6-V-O (6 = Ni, Cu) systems. While the B = Ni oxides adopt GdFeO3-like perovskite structure containing disordered nickel and vanadium at the octahedral B site, La3Cu2VO9 crystallizes in a YAIO3-type structure. A detailed investigation of the superstructure of nominal La3Cu2VO9 by WDS analysis and Rietveld refinement of powder XRD data reveals that the likely composition of the phase is Lai3Cu9V4O38 5, where the Cu and V atoms are ordered in a Vi3ah (ah = hexagonal a parameter of YAlCMike subcell) superstructure. Magnetic susceptibility data support the proposed superstructure consisting of triangular Cu3 clusters. The present work reveals the contrasting behaviour of La-Cu-V-O and La-Ni-V-0 systems, while a unique line-phase related to YAIO3 structure is formed around La3Cu2VO9 composition in the copper system, a continuous series of perovskite-GdFeO3 solid solutions, LaNi1.0CVxO3 for 0 < x < 1/3 seems to obtain in the nickel system. The chapter also describes the formation of a new transparent Cu(l) oxide, Lai4V6CuO365, and its characterization. This oxide was obtained during attempts to grow single crystals of LasC^VOg. Single crystal structure determination of Lai4V6CuO36 5 showed that the structure contains isolated VO43" tetrahedra and [OCuO]3" sticks dispersed in a lanthanum oxide network. Films of Lai4V6CuO36 5 were grown on R-plane sapphire by using pulsed laser deposition. Rutherford backscattering spectroscopic and X-ray diffraction analyses of the films showed oriented growth of the title phase, with an optical band gap of -~ 5 eV and n-type conductivity Chapter 6 presents the work on the flexibility of the Aurivillius structures for substitution of aliovalent/isovalent cations at both A and 6 sites of the perovskite slabs. For example, in a typical n = 3 member, Bi2Sr2Nb2TiOi2, substitution of both Sr and Na at the A site and Ta at the B site has enabled us to synthesize a new n = 3 member, Bi2SrNaNb2Ta0i2, where we see a preference of Nb for the terminal octahedral sheets. Similarly, aliovalent substitution only at the B site of the perovskite slabs of Bi2Sr2Nb2TiOi2 has yielded new members for specific compositions, Bi2Sr2Nb2ZrOi2, Bi2Sr2Nb2 5Feo50i2 and Bi2Sr2Nb2 67Zno33012 that tend to be oxygen-stoichiometric. The latter phases again show a preference of Nb for the terminal octahedral sites that are strongly distorted as compared to the middle octahedral site. This chapter also describes substitution of La3+ for Bi3+ in the perovskite slabs of Bi4Nb30i5 stabilizing a new series of n = 1/ n = 2 intergrowth Aurivillius phases of the formulas, Bi4LnNb3Oi5 (Ln = La, Pr, Nd) and Bi4LaTa30i5. The present work suggests that replacement of Bi3+: 6s2 lone pair ion by non-6s2 cations such as Sr2"* and La3+ in the perovskite slabs of Aurivillius phases tends to render the structure Centro symmetric and the materials lose NLOSHG response. Chapter 7 describes our investigation of the interaction of hydrogen with alkaline earth manganites (IV) >AMnO3 (>A = Ca, Sr, Ba) dispersed with 1 atom % Pt. The result shows an unprecedented uptake of hydrogen by BaMnO3/Pt to the extent of - 1.25 mass % at moderate temperatures (190 - 260 °C) and ambient pressure. Gravimetric sorption isotherms and mass spectrometric analysis of the desorption products indicate that approximately three hydrogen atoms per mole of BaMnCVPt is inserted reversibly. The nature of hydrogen in the insertion product, BaMnO3H3, is discussed in the light of the structure of BaMnC>3. The work presented in the thesis is carried out by the candidate as a part of the Ph. D. training programme and most of it has been published in the literature. He hopes that the studies reported here will constitute a worthwhile contribution to the materials chemistry of ABO3 oxides in general.

Atmospheric CO2 concentrations are at their highest level on record. Scientific evidence has demonstrated a direct correlation between the rise of CO2 levels and an increase of the global median temperature (~1°C higher than compared to the pre-industrial revolution times) due to the greenhouse gas effect. The change in climate due to this rapid increase of CO2 levels is already negatively affecting our ecosystem and lives, with unpredictable consequences in the future. The main source of anthropogenic CO2 emissions is attributed to the combustion of fossil fuels for energy production and transportation. Global indicators signal that carbon-intensive fuels will continue to be utilized as a main energy source despite the rising implementation of renewable energy sources. In order to curb CO2 emissions, several carbon dioxide capture, utilization and sequestration (CCUS) technologies have been suggested. The current state-of-the-art CO2 capture technology utilizes toxic and corrosive aqueous amine solutions that capture CO2 at room temperature but require heating above the water boiling point temperatures to separate CO2 from the amine solution; the latter of which is to be recycled. Once the CO2 is purified, it is necessary to transport it to its sequestration site or an upgrading processing plant. These are complicated schemes that involve many energy-intensive and costly processes. To address the shortcomings of these technologies, we propose a Dual Function Material (DFM) that both captures CO2 and catalytically converts it to methane in-situ. The DFM consists of a catalytic metal intimately in contact with an alkaline metal oxide supported on a high surface area carrier. The process operates within the flue gas at 320°C for both CO2 capture and methane generation upon the addition of renewable H2. The catalyst is required to methanate the adsorbed CO2 after the capture step is carried out in an O2 and steam-containing flue gas. Ruthenium, rhodium, and nickel are known CO2 methanation catalysts, provided they are in the reduced state. All three were compared for performance under DFM flue gas conditions. Ni is a preferred methanation catalyst based on price and activity; however, its inability to be reduced to its active state after experiencing O2-containing flue gas during the capture step was an outcome determined in this thesis. The performance of a variety of alkaline adsorbents (“Na2O”, CaO, “K2O” and MgO) and carriers (Al2O3, CeO2, CeO2/ZrO2 (CZO), Na-Zeolite-X (Na-X-Z), H-Mordenite Zeolite (H-M-Z), SiC, SiO2 and ZrO2-Y) were also studied. Selection of the best materials was based on CO2 capture capacity, net methane production and hydrogenation rates that were evaluated with thermogravimetric analysis and in fixed bed reactor tests. Rh and Ru DFMs were effective methanation catalysts with Ru being superior based on capture capacity, hydrogenation rate and price. Ru remained active towards methanation even after exposure to O2 and steam-containing simulated flue gas. Alkaline adsorbents, in combination with reduced Ru, were tested for adsorption and methanation. Ru – “Na2O”/Al2O3 DFMs showed the highest rates for methanation although CaO is also a reasonable candidate with slightly lower methanation kinetics. To date, we have demonstrated that -Al2O3 is the most suitable carrier for DFM application relative to other materials studied. The Ni-containing DFM, pre-reduced at 650°C, was highly active for CO2 methanation. However, the hydrogenation with 15% H2/N2 is completely inactive after exposure to O2 and steam, in a flue gas simulation, during the CO2 capture step at 320oC. This thesis reports that small amounts of precious metal (≤ 1% Pt, Pd or Ru) enhance the reduction (at 320°C) and activation of Ni-containing DFM towards methanation even after O2 exposure in a flue gas. While ruthenium is most effective, Pt and Pd all enhance reduction of oxidized Ni. Another objective of this thesis was to investigate whether a portion of the Ru, at its current loading of 5%, could be replaced with less expensive Ni while maintaining its performance. The findings show that the main advantage of the presence of Ni is a small increase in CO2 adsorption and increase in methane produced, at the expense of a lower methanation rate. Extended cyclic aging studies corroborate the stable performance of 1% Ru, 10% Ni, 6.1% “Na2O”/Al2O3. Characterization methods were used to monitor physical and chemical changes that may have occurred during aging studies. Measurements of the BET surface area, H2 chemisorption, XRD pattern, TEM images and STEM-EDS mapping were utilized to study and compare the structural and chemical changes between fresh and aged Ru doped Ni DFM samples. While similar BET surface areas were observed for the fresh and aged samples, some redispersion of the Ru and Ni sites was confirmed via H2 uptake and the observed decreases in Ru and Ni cluster size in the aged sample in comparison to the fresh. XRD patterns confirm an almost complete disappearance of the NiOx and RuOx species and the appearance of catalytically active Ru0 and Ni0 peaks on the aged sample compared to the fresh one. Further details of these methods, findings and conclusions are described in this thesis.

碩士
淡江大學
物理學系
91
The aspect of this thesis is to study the alkaline-earth doping in the parent compound WO3.We observed this series sample.In the In-situ measurement,an oxygen concentration dependent metal-nonmetal transition was observed.The electric behavior woule be changed from metal (the room temperature resistivity was smaller than 10-3Ω-cm) into nonmetal(the room temperature resistivity was greater than 10-3Ω-cm) by increasing the concentration of the oxygen.In the sintering process,it was found that the resistivity of the sample suddenly rose from 8.8×10-4Ω-cm to 1.66×10-3Ω-cm at temperature of 940oC.We took the RbxAuyWOz series as the principal things in studying magnetic properties.After sintering,we found that the sample(RbxAu0.05WOδ x=0.22、0.17、0.12)produced antiferromagetic several days later.

碩士
國立成功大學
尖端材料國際碩士學位學程
105
Through the years, the demand for renewable sources of energy increases significantly as we are facing serious problems with safety hazards, air and land pollution, global warming and many other ecological complications. Biodiesel is an alternative diesel fuel derived from animal fats or vegetable oils. It is purely biodegradable, non-toxic and sustainable. Biodiesel is made from the process called transesterification wherein animal fats or vegetable oils (triglyceride) are mixed with alcohol, and with an aid of a catalyst, will produce biodiesel and glycerol. For this study, we focused our research on the catalyst, a heterogeneous basic catalyst to be specific. One of the drawbacks of using basic catalyst is the low biodiesel yield due to soap formation and lack of reusability due to serious problems of leaching. The goal was to develop a catalyst that will hinder soap formation and leaching during transesterification. We also wanted to determine the effects of single-phase versus two-phase oxides using CaxSr1-xO system. In this study, we performed three various methods for catalyst synthesis – Co-Precipitation (CP), Solid State Sintering (SSS) and Polymer Complex Method (PCM). It was found out that PCM is the best method for synthesizing a high purity and homogeneous sample due to atoms mixed atomistically rather than just surface reactions for solid state sintering. PCM offers more purity than co-precipitation since the chelating agent catches the cations, which ensures random mixing and homogeneity. Single phase Ca0.2Sr0.8O, exhibited the highest yield amongst all the catalysts. However, the two-phase system has stabilized the yield within its range. Leaching was also decreased within the two-phase region, as well as the particle size of the catalysts. It was also found out that Sr(OH)2 contributes significantly to the biodiesel conversion.

碩士
國立東華大學
光電工程學系
105
In this study, different alkali metal-doped cuprous oxide was prepared on ITO substrates by electrochemical deposition. The electrolyte for electrochemical deposition was prepared with different alkali metal hydroxides and the deposition voltage was -0.4 V at 60 °C for the growth of different morphology of the p-type copper oxide films. And according to Faraday's law of electrolysis, it is known that the amount of electrochemical reaction is proportional to the coulomb number in deposition process. Therefore, the thickness of p-type copper oxide films is controlled by changing the different coulomb numbers in this experiment. First, the thickness of the deposited film was fixed at 0.67 C/cm2. And the alkali metal electrolytes at different pH values were compared with the maximum photocurrent in photoelectrochemical reaction. Then, the photocurrent values of different coulomb numbers in each system were compared. The maximum photocurrent values of lithium hydroxide and potassium hydroxide electrolytes can be obtained at 0.67 C/cm2.And the photoocurrent values are 2.35,1.9,1.62 mA/cm2.There are decreasing between the photocurrents was found, so the difference between the systems was be discussed at 0.67C/cm2. The analysis of material was done first. Difference of the morphology of the material was observed by field emission scanning electron microscopy (FE-SEM). Next, the crystal structure was analyzed by X-ray diffraction (XRD). Then, Raman was used to study the lattice and molecular vibration modes of the material. At last, X-ray photoelectron spectroscopy (XPS) was used to analyze the composition of p-type copper oxide films. The optical and electrical characteristics of p-type copper oxide films also be study. First, the energy gap was analyzed by absorption spectroscopy (ABS). Then, the defects in the structure were detected by photoluminescence (PL). Next, througth Mott-Schottky analysis, measuring the flat band and carrier concentration of them. Calculating photoelectric conversion efficiency with incident photon-to-current efficiency (IPCE) at last. Througth above the analysis, we understand the difference between the three systems, and know that if we want to get the best conversion in photoelectrochemical what should be required. This experiment will be our foundation to study p-type cuprous oxide doped with alkali metal ions for photoelectrochemical hydrogen production in the future.

碩士
國立東華大學
光電工程學系
107
In this study, p–n homojunction cuprous oxide thin film solar cells were grown on indium-doped tin-oxide (ITO) substrates by using the electrochemical deposition method. The electrolyte for depositing a p-type cuprous oxide thin film is prepared by using three different alkali metal hydroxides of lithium hydroxide, sodium hydroxide and potassium hydroxide. Desirable to improve the conductivity of the p-type cuprous oxide thin film by alkali metal ions doped. Further improve the efficiency of p–n homojunction cuprous oxide thin film solar cells. The p-type cuprous oxide thin film deposited by lithium hydroxide has lower lattice distortion and less lattice defects. Benefit from the improvement of the crystal structure of p-type cuprous oxide thin film, the p–n homojunction cuprous oxide thin film solar cells grown with lithium hydroxide has an optimum fill-factor of 0.34 and efficiency of 0.43%. Proof from experimental results, lithium ion doping can effectively improve the crystal structure of p-type cuprous oxide thin film, and improve the efficiency of p–n homojunction cuprous oxide thin film solar cells.

Alkali metal chloride melts are used to refine refractory metals and as a heat carrier for promising nuclear reactors. The oxygen content is a critical parameter for such systems. It determines technological process and the quality of obtained products. The work is devoted to the development of methods for the determination of oxygen in chloride melts. HORIBA EMGA-620W/C gas analyzer was used. The paper presents information on the choice of methods for determining oxygen in various oxygen-containing compounds of tungsten and molybdenum. An inert chamber has been developed and combined with a gas analyzer. This allowed to determine low oxygen contents in volatile matrices with high affinity for oxygen.
Системы хлоридных расплавов щелочных металлов применяются для рафинирования ряда тугоплавких металлов и в качестве теплоносителя в перспективных реакторах нового типа. Содержание кислорода в таких системах является критическим параметром, обуславливающим правильный ход технологического процесса и качество получаемой продукции. Работа посвящена разработки методики определения кислорода в хлоридных расплавах. Для измерений использовали газоанализатор HORIBA EMGA-620W/C. В работе представлены сведения о выборе способов определения кислорода в различных кислородсодержащих соединениях вольфрама и молибдена. Разработана и совмещена с газоанализатором инертная камера, позволяющая проводить определения низких содержаний кислорода в относительно летучих матрицах, в том числе с макрокомпонентами, имеющими высокое сродство к кислороду. Выбраны оптимальные условия проведения измерений.