Rozprawy doktorskie na temat „TERNARY FUEL”

Understanding the behaviour of actinide species is of importance when removing and processing all nuclear waste. Examples include the safe clean-up of contaminated waste ponds and aspects of the TALSPEAK (Trivalent Actinide-Lanthanide Separation by Phosphorus Reagent Extraction from Aqueous Komplexes) process. The chemistry of the ponds and the TALSPEAK process has been studied by probing the aqueous solution behaviour of Ln(III), Am(III), Cm(III) and Th(IV) ions in the presence of organic (EDTA4- (ethylenediamine tetraacetate), DTPA5- (diethylenetriamine pentaacetate) and lactate) and inorganic (CO32- (carbonate) and OH- (hydroxide)) ligands by a variety of techniques including Nuclear Magnetic Resonance (NMR), Ultra Violet-Visible (UV-Vis) and luminescence spectroscopies, as well as potentiometry. Various ternary complexes have been shown to exist, including [M(EDTA)(CO3)]3-(aq), (where M = LnIII, AmIII or CmIII) and [Th(EDTA)(CO3)2]4-(aq), which form approximately over the pH range 8 to 11, and also [M(EDTA)(lactate)]2-(aq) (where M = Ln(III) or Am(III)) and [Th(EDTA)(lactate)]-(aq), which predominantly occur over the pH range 4 to 6. The nature of lactate interaction with [M(DTPA)]2-(aq) complexes (where M = Ln(III) or Am(III)) is unclear, as it may be possible that lactate can coordinate directly to the metal ion or to the acetate groups of DTPA5- (via a H-bonding interaction). The knowledge gained in this research has given a deeper insight into the nature of lanthanide and actinide coordination chemistry in mixed-ligand environments. For example, the increasing solubility of actinide metal ions in the contaminated waste ponds is probably due to the ability of organic ligands present in the ponds to solubilise metal ions at high pH, and also under TALSPEAK conditions of pH 3.5, there is likely to be minimal interaction of lactate with the [Ln(DTPA)]2-(aq) complexes. The determination of metal ion speciation using a combination of NMR, UV-Vis and luminescence spectroscopies, coupled with potentiometry, could be applied to new characterisation challenges faced in the future of the nuclear industry.

Thesis (Ph.D)--Chemical Engineering, Georgia Institute of Technology, 2010.
Committee Chair: Dr. David S. Sholl; Committee Member: Dr. Andrei G. Fedorov; Committee Member: Dr. Ronald R. Chance; Committee Member: Dr. Victor Breedveld; Committee Member: Dr. William Koros. Part of the SMARTech Electronic Thesis and Dissertation Collection.

The MgO:TiO2 :ZrO2 ternary system was investigated as a possible novel anode material in a solid oxide fuel cell. Titanium-substituted yttria-stabilised zirconias have the necessary electrical conductivity properties for a ZrO2 -based fluorite electrode but problems have been encountered such as a decrease in unit-cell size upon reduction leading to mechanical failure. By incorporating magnesium into the titanium-stabilised zirconia structure, it was thought that the cubic-fluorite structure might be stabilised. A phase diagram study was made of the MgO:TiO2 : ZrO2 ternary system at 1500°C. Upon researching the literature phase diagram of the MgO:TiO2 :ZrO2 system, it was found that the authors had not studied the single-phase region in the ZrO2 -rich area extensively and did not use a consistent temperature for their analysis of samples. This has meant that the phase diagram has had to be reinvestigated. The results obtained at 1500°C are in disagreement with the previously published phase diagram. A large area bounded by single-phase cubic-fluorite was detected; however the central region of this domain contained both tetragonal and cubic-fluorite domains. This implies that for the central region of this phase area that the cubic- fluorite phase is not stable at 1500°C. Selected stabilised cubic-fluorite samples with ~ 10 atom% Mg were annealed at l000°C after preparation at 1500°C and it was found that due to the presence of other phases present at 1000°C, that the cubic-fluorite phase is thermodynamically unstable at lower temperatures. DTA analysis revealed that as the titanium content in the cubic-fluorite solid-solution increased, the phase transition from tetragonal phase (+ MgO) to cubic-fluorite phase decreased. These results were used to provide a basis for a temperature phase diagram showing the likely phase transitions that occur at a particular temperature range. The activation energy for conduction increased and ionic conductivity decreased with increasing titanium content in the solid solution, due to the effects of local distortions created by the smaller ionic radius of titanium when compared to zirconium.

Les isotopes de l’Américium sont les principaux contributeurs à la radioactivité des déchets nucléaires. Parmi les scénarios pour diminuer la toxicité des déchets, la transmutation dans les réacteurs à neutrons rapides utilisant des pastilles d’oxyde mixte (U,Am)O2 est une voie prometteuse. Dans ce cadre, la connaissance des propriétés thermodynamiques du système U-Am-O est essentielle pour prédire le comportement des pastilles (U,Am)O2 en conditions nominale et accidentelle. Cette thèse est dédiée à l’étude expérimentale d’oxydes mixtes (U,Am)O2 dans une large gamme de composition (7,5 % at. ≤ Am/(Am+U) ≤ 70 % at.). L’objectif est d’acquérir des données pour développer un modèle thermodynamique avec la méthode semi-empirique CALPHAD. Les résultats peuvent être classés en trois catégories : données structurales, données de diagramme de phase et données thermodynamiques. Pour la modélisation thermodynamique d’un système ternaire, l’optimisation des sous-systèmes binaires est nécessaire. Comme des questions restaient en suspens sur le système Am-O, le diagramme de phase Am-O a tout d’abord été étudié par diffraction des rayons X à haute température. L’existence d’un domaine de composition de la phase bcc AmO1.61 a été mis en évidence et la lacune de miscibilité dans la phase fluorite, proposée dans la littérature, n’a pas été confirmée. Grâce à ces nouveaux résultats, le modèle CALPHAD de Gotcu et al a été modifié. Dans une deuxième étape, des analyses structurales des dioxydes (U,Am)O2±x ont été effectuées par DRX, XAS et spectroscopie RAMAN. La DRX a permis de confirmer que tous les échantillons sont constitués d’une seule phase de structure fluorite. Le rapport O/M (avec M=U+Am) mesuré à température ambiante est inférieur à 2 ; la stabilité de l’Américium trivalent Am3+ a été mise en évidence. Celle-ci induit l’oxydation partielle de l’U4+ en U5+. Cette distribution de charge s’accompagne par la formation de défauts de l’oxygène complexes dans la structure fluorite. Lors de l’étude par DRX HT des oxydes mixtes sous air, il a été montré que la présence d’Am3+ stabilise la phase fluorite par rapport aux oxydes plus riches en oxygène (U4O9, U3O8). De nouvelles données de diagramme de phase ont été obtenues : des conodes dans les domaines biphasés M4O9-M3O8 and MO2+x-M3O8 et la solubilité de l’Américium dans les oxydes M4O9 et M3O8. L’étude du diagramme de phase U-Am-O a été poursuivie par la détermination des températures de solidus/liquidus des oxydes mixtes par une technique de chauffage laser, sous argon et sous air, et par la caractérisation des échantillons après fusion par SEM et XAS. La température de fusion des oxydes mixtes diminue avec une teneur croissante d’Américium (Am/(Am+U)) et d’oxygène (O/(Am+U)). Finalement, les propriétés thermodynamiques des oxydes (U,Am)O2±x ont été mesurées : les incréments enthalpiques par calorimétrie de chute et les pressions partielles des espèces gazeuses par Spectrométrie de Masse couplée à une cellule de Knudsen (KEMS). Une contribution d’excès de la capacité calorifique a été observée à haute température, attribuée à la réduction des oxydes (avec formation de lacunes d’oxygène). Les résultats de KEMS ont permis de déterminer une composition congruente de vaporisation à 2300 K, pour un rapport Am/(Am+U) de 0,6 et un rapport O/(U+Am) inférieur à 1,9. Finalement, la modélisation thermodynamique du système U-Am-O par la méthode CALPHAD a été abordée par la description de la phase fluorite. Un bon accord est obtenu entre le modèle et les données de potentiel d’oxygène pour l’oxyde (U0.5Am0.5)O2±x et de distribution des cations. De plus, le modèle permet de reproduire de façon satisfaisante les données de KEMS. En perspective de ce travail, la modélisation thermodynamique du ternaire sera étendue à la description des équilibres de phase mettant en jeu les oxydes M4O9, M3O8 et la phase liquide
Americium isotopes are the main contributors to the long-term radiotoxicity of the nuclear wastes, after the plutonium extraction. Among the reprocessing scenarios, the transmutation in fast neutron reactors using uranium-americium mixed oxide (U,Am)O2±x pellets seems promising. In this frame, the knowledge of the thermodynamics of the U-Am-O ternary system is of essential for the prediction of the behavior of (U,Am)O2 pellets and their possible interaction with the cladding, under normal and accidental conditions. This thesis is dedicated to the experimental investigation of U-Am mixed oxides on a wide range of Am contents (7.5 at.% ≤ Am/(Am+U) ≤ 70 at.%), with the aim to collect data for developing a thermodynamic model based on the semi-empirical CALPHAD method. The obtained results can be classified in three categories: structural, phase diagram and thermodynamic data. For the thermodynamic modeling of the ternary system, the assessment of the binary sub-systems is first required. As open questions still existed on the Am-O system, a first part of the work was dedicated to the study of the Am-O phase diagram by high-temperature (HT) XRD. The existence of a composition range of the bcc AmO1.61 phase was highlighted and the miscibility gap in the fluorite phase, proposed in the literature, was not found. Thanks to the new experimental data, the existing CALPHAD model of Gotcu et al. was modified. In a second step, structural investigations were performed on synthesized (U,Am)O2±x dioxides by coupling XRD, XAS and Raman spectroscopy. For all the compositions, the XRD confirmed the formation of a single fluorite structure. The O/M ratio (with M=U+Am) at room temperature was determined to be lower than 2; the stability of trivalent americium Am3+ in the dioxide solid solution was highlighted, which induces a partial oxidation of uranium from U4+ to U5+. This charge distribution, peculiar for a dioxide, is accompanied by the formation of complex oxygen defects in the fluorite structure. By a HT-XRD investigation of the mixed oxides under air combined with XAS characterization of the oxidized samples, it was shown that the presence of Am3+ leads to a stabilization of the dioxide fluorite phase toward the formation of oxides richer in oxygen, in comparison to the U-O system. New phase diagram data were obtained in the oxygen rich region at 1470 K: tie-lines in the M4O9-M3O8 and MO2+x-M3O8 domains were determined and the solubility of americium in the M4O9 and M3O8 oxides was estimated. The investigation of the U-Am-O phase diagram continued at higher temperature with the study of the solidus/liquidus transitions using a laser-heating technique, under argon and air, and post-melting characterizations conducted by SEM and XAS. The melting temperature of Am-U dioxides decreases with the increase of both the Am/(Am+U) and O/M ratios. Finally, thermodynamic properties of the U1-yAmyO2±x oxides were measured: enthalpy increments using drop calorimetry, partial vapor pressures by Knudsen cell effusion mass spectrometry (KEMS). An excess contribution to the heat capacity at high temperature was observed and this was attributed to the reduction of the dioxides at high temperature (formation of oxygen vacancies). The KEMS results lead to determine the congruent vaporization composition at 2300 K, for a Am/(Am+U) ratio of 0.6 and an O/M ratio lower than 1.9. Finally, the CALPHAD thermodynamic assessment of the U-Am-O system was started, by focusing the attention on the modelling of the fluorite phase. A good agreement between the model and the oxygen potential data for (U0.5Am0.5O2±x) and the cation distribution was achieved. Furthermore, the model is able to satisfactorily reproduce the KEMS data and hence the equilibrium between the dioxide and gas phase. For the perspectives of this work, the optimization of the thermodynamic model should be extended to describe the phase equilibria involving the M4O9, M3O8 oxides and the liquid phase

>Magister Scientiae - MSc
This study explores the use of UV-assisted reduction method to synthesise the catalysts, aiming at reducing synthesis time. The Pd and Au catalyst loading is kept at 5 wt% in order to reduce the cost associated with high loading (20 wt%) of platinum group metals. The synthesised catalysts have SnO2 incorporated in them for two purposes, one being to activate the chemical reaction by absorbing UV-light and the second one is to serve as a promoter for binary and ternary catalysts. All the synthesised electrocatalysts in this study were denoted as Au/10wt%SnO2-C, Au/15wt%SnO2-C, Au/20wt%SnO2-C, Au/40wt%SnO2-C, Au/60wt%SnO2-C, Pd/10wt%SnO2-C, Pd/15wt%SnO2-C, Pd/20wt%SnO2-C, Pd/40wt%SnO2-C, Pd/60wt%SnO2-C and PdAu/10wt%SnO2-C respectively. The UV-assisted reduction method was proved to be effective with the obtained results from TEM, SEM, XRD and electrochemical studies. TEM micrographs revealed nanoparticles of Pd, Au and SnO2 which were proved by the measured d-spacing values corresponding to the element’s structures. The measured average particle size ranged from 3.05 to 14.97 nm for the electrocatalysts. The XRD profiles confirmed the face centred cubic of Pd, Au and tetragonal structures of SnO2. These electrocatalysts showed varied activity towards the oxidation of alcohols namely, methanol, ethanol, ethylene glycol and glycerol in alkaline electrolyte The cyclic voltammetry results showed improved performance towards the oxidation of glycerol on Au-based electrocatalysts, highest current density of 22.08 mA cm-2 than on Pd-based electrocatalysts. Pd-based electrocatalysts were more active towards the oxidation of ethanol than Au-based electrocatalysts with the highest current density of 19.96 mA cm-2. The co-reduced PdAu on 10wt%SnO2-C electrocatalysts showed the lowest current density of 6.88 mA cm-2 for ethanol oxidation when compared to Pd/10wt%SnO2-C and Au/10wt%SnO2-C. Linear sweep voltammograms showed more negative onset potentials on Pd-based electrocatalysts than Au-based electrocatalysts. The more negative onset potential obtained on Pd-based electrocatalysts was observed for ethanol oxidation. These results correspond to the trend observed in literature for ethanol oxidation being more favoured on Pd-based electrocatalysts whereas the polyalcohol oxidation is more favoured on Au-based electrocatalysts. The best performing and most stable electrocatalyst among the Au-based electrocatalysts is Au/10wt%SnO2-C and Pd/10wt%SnO2-C for the Pd-based electrocatalysts.

Masters of Science
The electrochemical oxidation of ammonia has attracted much attention as an efficient green method for application in direct ammonia fuel cells (DAFCs) and the production of high purity hydrogen. However, the insufficient performance and high costs of platinum has hindered the large scale application of ammonia (NH₃) electro-oxidation technologies. Therefore, there is a need for the fabrication of efficient electrocatalysts for NH₃ electrooxidation with improved activity and lower Pt loading. Owing to their unique catalytic properties, nanoalloys of platinum group metals (PGMs) are being designated as possible electrocatalysts for NH₃ oxidation. This study presents for the first time a chemical synthesis of unsupported ternary PGM based nanoalloys such as Cu@Pt@Ir with multi-shell structures and Cu-Pt-Ir mixed nanoalloys for electro-catalysis of NH3 oxidation. The nanoalloys were stabilised with polyvinylpyrrolidone (PVP) as the capping agent. The structural properties of the nanoalloys were studied using ultraviolet-visible (UV-Vis) and fourier transform infra-red (FTIR) spectroscopic techniques. The elemental composition, average particle size and morphology of the materials were evaluated by high resolution transmission electron microscopy (HRTEM) coupled to energy dispersive X-ray (EDX) spectroscopy. High resolution scanning electron microscopy (HRSEM) was used for morphological characterisation. Additionally, scanning auger nanoprobe microscopy (NanoSAM) was employed to provide high performance auger (AES) spectral analysis and auger imaging of complex multi-layered Cu@Pt@Ir nanoalloy surface. X-ray diffraction (XRD) spectroscopy was used to investigate the crystallinity of the nanoalloys. The electrochemistry of the nanoalloy materials was interrogated with cyclic voltammetry (CV) and square wave voltammetry (SWV). The electrocatalytic activity of novel Cu-Pt-Ir trimetallic nanoalloys for the oxidation of ammonia was tested using CV. UV-Vis spectroscopy confirmed the complete reduction of the metal precursors to the respective nanoparticles. FTIR spectroscopy confirmed the presence of the PVP polymer as well as formation of a bond between the polymer (PVP) chains and the metal surface for all nanoparticles (NPs). Furthermore, HRTEM confirmed that the small irregular interconnected PVP stabilised Cu@Pt@Ir NPs were about 5 nm in size. The elemental composition of the alloy nanoparticles measured using EDX also confirmed the presence of Cu, Pt and Ir. Cyclic voltammetry indicated that both the GCE|Cu-Pt-Ir NPs and GCE|Cu@Pt@Ir NPs are active electrocatalysts for NH3 oxidation as witnessed by the formation of a well-defined anodic peak around -0.298 V (vs. Ag/AgCl). Thus the GCE|Cu-Pt-Ir NPs was found to be a suitable electrocatalyst that enhances the kinetics of oxidation of ammonia at reduced overpotential and high peak current in comparison with GCE|Cu@Pt@Ir NPs, GCE|Pt NPs, GCE|Ir NPs and GCE|Cu NPs electrocatalysts. The presence of the crystalline phases in each sample was confirmed by XRD analysis. The surface analysis of Cu@Pt@Ir nanoalloy with AES surveys revealed the presence of Pt, Ir and Cu elements in all probed spots suggesting some mixing between the layers of the nanoalloy. Yet, analysis of nanoalloys by CV and XRD confirmed the presence of Cu-Pt and Pt-Ir solid solutions in the Cu-Pt-Ir and Cu@Pt@Ir nanoalloys respectively.

Among the obstacles for the commercialization of the MoltenCarbonate Fuel Cell (MCFC), the dissolution of thestate-of-the-art lithiated NiO cathode is considered as aprimary lifetime limiting constraint. Development ofalternative cathode materials is considered as a main strategyfor solving the cathode dissolution problem. LiFeO₂and LiCoO₂had earlier been reported as the most promisingalternative materials; however, they could not satisfactorilysubstitute the lithiated NiO. On the other hand, ternarycompositions of LiFeO₂, LiCoO₂and NiO are expected to combine some desirableproperties of each component. The aim of this work was todevelop alternative cathode materials for MCFC in the LiFeO₂-LiCoO₂-NiO ternary system. It was carried out byinvestigating electronic conductivity of the materials, firstin the form of bulk pellets and then in ex-situ sinteredporous-gas-diffusion cathodes, and evaluating theirelectrochemical performance by short-time laboratory-scale celloperations.

Materials in the LiFeO₂-NiO binary system and five ternary sub-systems,each with a constant molar ratio of LiFeO₂:NiO while varying LiCoO₂content, were studied. Powders withcharacteristics appropriate for MCFC cathode fabrication couldbe obtained by the Pechini method. The particle size of LiFeO₂-LiCoO₂-NiO powders considerably depends on thecalcination temperature and the material composition. Theelectrical conductivity study reveals the ability of preparingLiFeO₂-LiCoO₂-NiO materials with adequate electricalconductivity for MCFC cathode application.

A bimodal pore structure, appropriate for the MCFC cathode,could be achieved in sintered cathodes prepared usingporeformers and sub-micron size powder. Further, this studyindicates the nature of the compromise to be made between theelectrical conductivity, phase purity, pore structure andporosity in optimization of cathodes for MCFC application. Cellperformance comparable to that expected for the cathode in acommercial MCFC could be achieved with cathodes prepared from20 mole% LiFeO₂- 20 mole% LiCoO₂- 60 mole% NiO ternary composition. It shows aniR-corrected polarization of 62 mV and a iR-drop of 46 mV at acurrent density of 160 mAcm^-2at 650 °C. Altogether, this study revealsthe possibility of preparing LiFeO₂-LiCoO₂-NiO cathode materials suitable for MCFCapplication.

Keywords: molten carbonate fuel cell (MCFC), MCFC cathode,LiFeO₂-LiCoO₂-NiO ternary compositions, electrical conductivity,porous gas diffusion electrodes, polarization, electrochemicalperformance, post-cell characterization.

En raison de leurs propriétés chimiques et physiques, les oxydes mixtes d'uranium et de plutonium sont considérés comme combustibles pour les réacteurs nucléaires de quatrième génération. Dans ce cadre, des études expérimentales complémentaires sont nécessaire, notamment pour mieux comprendre les phénomènes mis en jeu lors de la fabrication ou sous irradiation. L'objet de ce travail est d'étudier le diagramme de phase U-Pu-O dans une large gamme de composition et de températures afin d'améliorer notre connaissance de ce système. La plupart des expériences ont été réalisées par diffraction des rayons X en fonction de la température. La contrôle in situ de la pression partielle en oxygène a permis de faire varier la stœchiométrie en oxygène dans le matériau. L'approche expérimentale a été couplée avec la modélisation thermodynamique par la méthode CALPHAD afin de mieux dimensionner les expériences et interpréter les résultats. Cette méthodologie a permis d'améliorer notre connaissance des équilibres de phase dans le système U-Pu-O
Due to their physical and chemical properties, mixed uranium-plutonium oxides are considered for fuel in 4th generation nuclear reactors. In this frame, complementary experimental studies are necessary to develop a better understanding of the phenomena that take place during fabrication and operation in the reactor. The focus of this work was to study the U Pu–O phase diagram in a wide range of compositions and temperatures to ameliorate our knowledge of the phase equilibria in this system. Most of experiments were done using in situ X-ray diffraction at elevated temperatures. The control of the oxygen partial pressure during the treatments made it possible to change the oxygen stoichiometry of the sample, which gave us an opportunity to study rapidly different compositions and the processes involved. The experimental approach was coupled with thermodynamic modeling using the CALPHAD method, to precisely plan the experiments and interpret the obtained results. This approach enabled us to enhance the knowledge of phase equilibria in the U–Pu–O system

Over the past decade studies into the application of radiometrics for soil and regolith mapping have met with mixed response. While the use of radiometric data for regolith mapping has been generally well received, radiometric methods have not commonly been adopted to assist and improve soil mapping. This thesis contributes to the development of radiometric techniques as soil and regolith mapping tools by examining soil characteristics and radiometric response using non-standard radiometric methods. This is accomplished through the development of new data processing methodologies, which extracts additional information from standard radiometric data that is unattainable using standard processing methods, and development of a new interpretation approach to soil and regolith mapping employing the multispectral processed radiometric data. The new multispectral processing methodology resolves seven gamma ray peaks from standard 256-channel NaI radiometric data to produce new radiometric uranium ternary, thorium ternary and uranium ratio imagery. Changes in the gamma ray relationships, identified through the new imagery, identify changes in soil and/or environmental conditions that are absent or difficult to identify in the standard radiometric imagery. With the isolation of non-standard thorium channels 228 [superscript] Ac (900 keV) and 228 [superscript] Ac (1600 keV), case studies in this thesis demonstrate how the difference of 1.9 years (half-life) between thorium 228 [superscript] Ac and 232 [superscript] Th decay daughter products can be mapped through the interpretation of thorium energy using ternary imagery [red: 208 [superscript] Tl (1764 keV), green: 228 [superscript] Ac (900 keV), blue: 228 [superscript] Ac (1600 keV)]. Energy peak differences may be be linked to local variations in soil chemistry, soil movement, and water movement.
Additionally, through the isolation of non-standard uranium channels 214 [superscript] Bi (1120 keV) and 214 [superscript] Bi (1253 keV), preferential attenuation of lower energy gamma-rays from 214 [superscript] Bi decay events are exploited to map variations in soil density and/or porosity. These variations are illustrated through the interpretation of uranium energy using ternary imagery [red: 214 [superscript] Bi (1764 keV), green: 214 [superscript] Bi (1120 keV), blue: 214 [superscript] Bi (1253 keV)] and uranium peak energy ratio [214 [superscript] Bi 1120 keV / 214 [superscript] Bi 1764 keV] pseudo colour imagery. Case studies examined in this thesis explore the characteristics of 256-channel radiometric spectrum from different resolution datasets from different Western Australian soil types, provide recommendations for acquiring radiometric data for soil mapping in different agricultural environments, demonstrate how high resolution 256-channel radiometric data can be used to model soil properties in three-dimensions, and illustrate how three-dimension soil models can be used to separate surface waterlogging influences from rising groundwater induced waterlogging.

The equilibrium phase behaviour of ternary mixtures of water, oil and surfactants is examined using both a lattice-gas model and a Ginzburg-Landau model. The lattice model is based on the Blume-Capel model with additional orientational degrees of freedom for surfactants, and the Ginzburg-Landau model is based on two local scalar fields. When the concentrations of water and oil are equal the following phases are observed: a water and oil rich phase, a lamellar phase, and a disordered phase which is divided into an ordinary disordered fluid and a microemulsion region. In the lattice model, a square phase is also observed. The effects of fluctuations on the lattice model is studied via Monte-Carlo simulations and by the Langevin approach in the Ginzburg-Landau model. In both cases, we found that in the vicinity of the water/oil coexistence region, the lamellar phase becomes unstable against the microemulsion.
Furthermore, we have studied the effects of surfactants on the dynamics of phase separation of two immiscible fluids, and found a drastic alteration in the kinetics. In particular, we found that surfactants slow down the growth to a non-algebraic one leading eventually to a microphase separation.

A biosorbent prepared from Ascophyllum nodosum seaweed biomass, designated as FCAN2, was examined for its sorption capacity. Equilibrium batch sorption studies were performed using two-metal systems respectively comprised of (Cd + Cu), (Cd + Zn), (Cu + Zn) and a three-metal system comprised of (Cd + Cu + Zn). In the evaluation of the two-metal sorption system performance, simple sorption isotherm curves had to be replaced by three-dimensional sorption isotherm surfaces. In order to describe the isotherm surfaces mathematically, three Langmuir-type models were evaluated. The apparent one-parameter Langmuir constant was used to quantify FCAN2 'affinity' for one metal in the presence of another one. In order to represent the equilibrium data of the ternary system, a multicomponent Langmuir model was adopted and triangular equilibrium diagrams were used. Mathematical models for the two- and three-metal sorption systems enabled quantitative estimation of one metal sorption inhibition due to the influence of the other metal(s). For biosorption on FCAN2 at pH 4.5, the inhibition dominance observed in the two- and three-metal systems was Cu $>$ Cd $>$ Zn.

A partially purified chlorophyllase, obtained from alga Phaeodactylum tricornutum, was assayed for its hydrolytic activity towards the pheophytin in ternary micellar systems of hexane/Tris-HCl/surfactant. A wide range of surfactants, sorbitans (Span 20, 40, 60, 80 and 85) and polysorbates (Tween 20, 40, 60, 80 and 85), was used. The use of either 50 $ mu$M of Span 85 or 1 $ mu$M of Tween 80 increased the hydrolytic activity of chlorophyllase by 110 and 23%, respectively. The optimum values of pH, enzyme content, incubation time and temperature for the hydrolytic activity of chlorophyllase were determined as 8.25, 8 $ mu$g protein/ml, 60 min and 27.5$ sp circ$C, respectively. The enzyme was assayed for its hydrolytic activity in the most appropriate ternary system containing Span 85 with purified pheophytin, as well as chlorophyll derivatives, as substrates. Moreover, the values of $V sb{ rm max}/K sb{ rm m}$ ratio for chlorophyllase, using the partially purified pheophytin as substrate, in ternary systems with Span 85 and Tween 80 as surfactants, were 0.15 and 0.08, respectively; however, the value of $V sb{ rm max}/K sb{ rm m}$ ratio for the enzyme, in the ternary system with Span 85, using purified pheophytin as substrate was 0.07. The addition of optimized amounts of individual membrane lipids, L-$ alpha$-phosphatidylcholine, L-$ alpha$-phosphatidyl-DL-glycerol and $ beta$-carotene increased the hydrolytic activity of chlorophyllase, using partially purified pheophytin as substrate, by 50, 36 and 10%, respectively, for Span 85, and 30, 48 and 15%, respectively, for Tween 80; in addition, these lipids increased the enzyme activity by 6, 23 and 31%, respectively, in the Span 85 media, using purified pheophytin as substrate. Phytol showed a competitive inhibitory effect on chlorophyllase activity in both Span and Tween systems containing partially purified pheophytin substrate; however, phytol had an uncompetitive inhibitory effect on the enzyme activity in the S

In the present study, dilute alloys in the Mg-rich corner of the Mg-Ce-In ternary system in the composition range 0 to 3% In and 0 to 1.5% Ce were synthesized. Cooling curve analysis was used to determine the liquidus points in order to construct the liquidus surface of the ternary phase diagram in the Mg corner. Energy dispersive spectroscopy (EDS), wavelength dispersive spectroscopy (WDS), and x-ray diffraction (XRD) techniques were used to examine phases present at the compositions studied. A thermal arrest presumed to represent a eutectic transformation was discovered at 580°C. Two new intermetallic compounds, designated tau and theta, were found. Trace silicon present in the alloys was found to concentrate in one of the intermetallic compounds.
To further investigate these compounds, an induction furnace was used to synthesize alloys containing the concentrations of Ce and In seen in electron probe micro-analysis (EPMA) examinations of these compounds. The alloys were examined using the cooling curve technique and XRD, and proved to contain the compounds already observed with some variation in dissolved indium content. In addition, differential scanning calorimetry (DSC) was used to confirm the liquidus and solidus values determined using cooling curve analysis.
A diffusion couple with terminal compositions of pure Ce and a Mg-In alloy was prepared in order to determine the equilibrium phases present in the system between these two compositions at 390°C. EPMA was used to identify the zones obtained, and confirmed the presence of several Mg-Ce compounds with 1 at% dissolved indium, as well as a ternary compound corresponding to the theta compound found in the dilute alloys.
Finally, literature values and experimental data were used to calculate a preliminary ternary phase diagram using FACTSage, in collaboration with the CTRC at Ecole Polytechnique, in order to affirm the validity of the experimentally determined values as well as to project the diagram beyond the studied composition range.

The ternary Mg-Mn-Ce phase diagram was experimentally studied and thermodynamically calculated at the Mg-rich corner. More than twenty binary and ternary alloys were synthesized and heat-treated at both ambient and elevated temperatures. The microstructures and lattice parameters of the samples were studied via XRD, SEM/EDS and EPMA to determine phase equilibria. The ternary phase diagram was also calculated via thermodynamic calculation software FactSage. The results from both experiment and the assessment were compared and discussed. The binary phase diagrams were re-examined, especially the Mg-Ce system. In order to investigate the composition range of the intermetallic compounds Mg12Ce and Mg41Ce5, and to clarify data in the existing phase diagram, both the solid-liquid diffusion couple method and alloys synthesized with target phases were analyzed. The binary phase diagram study was also extended to the Ce-rich side of Mg-Ce system. A modified phase diagram was suggested to accommodate the stoichiometry of Mg11Ce, Mg39Ce5, and Mg3Ce. The experimental study on the ternary phase diagram was conducted on three isopleths: 0.6, 1.8 and 2.5wt% Mn, respectively, and Ce varied between 0 and 25wt%. Finally, the phase diagram calculation with FactSage program was conducted and the small disagreement between the modeling results and present experimental data were found.
Le diagramme de phase ternaire Mg-Mn-Ce a été étudié expérimentalement et calculé thermodynamiquement à son extrémité riche en magnésium. Plus de 20 alliages binaires et ternaires ont été synthétisés et traités thermiquement à température pièce et températures élevées. La microstructure et les paramètres de maille des échantillons ont été étudiés via XRD, SEM/EDS et EPMA pour déterminer les phases à l'équilibre. Le diagramme de phase ternaire a aussi été calculé à l'aide du logiciel de calcul thermodynamique Factsage. Les résultats provenant des expériences ainsi que de l'évaluation thermodynamique ont été comparés et discutés. Les diagrammes de phase binaires ont été re-examinés, spécialement pour le système Mg-Ce. Dans le but d'évaluer l'étendue de composition des composés intermétalliques Mg12Ce et Mg41Ce5, ainsi que de clarifier les données des diagrammes de phase existants, les méthodes de couple de diffusion solide-liquide et de synthèse d'alliages aux phases ciblées ont été utilisés. L'étude du diagramme de phase binaire a été prolongée à l'extrémité riche en Ce du système Mg-Ce. L'étude expérimentale du diagramme de phase ternaire a été conduite sur trois isoplèthes: 0.6, 1.8 et 2.5wt% Mn, respectivement, et Ce a été varié entre 0 et 25wt%. Finalement, les calculs de diagramme de phase provenant du logiciel FactSage ont été fait et de petites divergences entre les résultats modélisés et ceux expérimentaux ont été observées.

A review of immiscibility data in 62 silicate, borate and germanate binaries permits identification of four groups of cations displaying different immiscibility behaviour. The first group consists of network-modifier cations which have ionic radii ≳ 87.2 pm and coordination numbers equal to, or higher than, 5 (e.g. Ca2+, La3+, U4+). The second group involves cations with ionic radii ≲ 87.2 pm. They have at least two coordination numbers: the first one is always 4 and the second is ≥5; for this reason they are called amphoterics (e.g. Li1+, Mg2+, Al3+). The third group contains cations with variable crystal field stabilization energies (e.g. Fe2+, Ni2+, Cr3+), and the fourth group includes cations with a lone pair of electrons (e.g. Pb 2+, Bi3+, Te4+).
Immiscibility data suggest that the origin of phase separation is associated with coulombic repulsions between poorly screened cations. The larger the ionic potential of a cation, the greater the repulsions with its neighbours, and the larger the size of its immiscibility field. However, amphoterics do not obey this rule because network-formers like SiO2 exert a structural control upon immiscibility which creates a selective solution mechanism that affects cations with radii ≲ 87.2 pm. Such small cations appear to be capable of fitting in pentagonal-like cages where they adopt a 4-fold coordination. In tetrahedral coordination, the bonds have a greater covalent character and the oxygens are more polarized towards the amphoterics which efficiently shield their positive charges, reducing coulombic repulsions and thus immiscibility.
Experiments performed in the system CaO-MgO-SiO2 at 1.0 GPa show that pressure has little effect on miscibility gaps associated to network-modifiers such as Ca2+ and "weak" amphoterics like Mg 2+. However, it is shown that amphoterics with substantial fractions of cations in 4-fold coordination and cations with variable crystal field stabilization energies capable of high spin to low spin transitions are expected to enlarge their immiscibility fields at high pressure. Magmas rich in these cations are potential candidates to develop phase separation at depth.
Experiments were also performed in the systems CaO-SiO2 and MgO-SiO2 at 1.0 GPa and results were combined with all the currently available phase equilibria and thermodynamic data at 1 bar in the same systems to critically optimize the thermodynamic properties of the liquid phase at low and high pressures. Assessments were made with the modified quasi-chemical model of Blander & Pelton using a computer program that simultaneously optimized all reliable data to give a small set of excess Gibbs free energy parameters. Pressure was found to have little effect on the topology of the CaO-SiO2 system but a pronounced one on the MgO-SiO2 binary. These contrasting behaviours from two homovalent and isochemical cations are linked to the polymorphic transition of the magnesium metasilicate. The amphoteric nature of the Mg2+ cation in the liquid phase makes MgO-SiO2 melts compressible but this effect appears to be small.

Dans la section UO2-PuO2-Pu2O3, les équilibres de phases décrivent un domaine monophasé (U1-y,Puy)O2-x stable pour y<0,20 à 25°C et jusqu'à l'équilibre solide-liquide. Aux teneurs Pu supérieures, ils sont plus complexes avec l'apparition d'une démixtion et la précipitation de phase(s) additionnelle(s). L'objectif de la thèse a consisté à améliorer la représentation du système pour 0,15≤y≤0,65 et 25≤T(°C)≤1500.A 25°C, une lacune de miscibilité composée de deux phases (U1-y,Puy)O2-X a été observée pour y<0,45, dont l'une est de rapport Oxygène/Métal proche de la stœchiométrie et une autre très réduite. Pour la première fois, un domaine triphasé a été caractérisé à teneurs Pu supérieures avec deux phases (U1-y,Puy)O2-X de teneurs proches de y=0,45, et une phase (U1-y,Puy)2O3 comprenant une faible proportion d'uranium solubilisée.L'étude en fonction de la température a démontré que la température de démixtion augmente avec la teneur Pu. Plusieurs représentations ont été établies. A 200°C, les limites d'existence du domaine multiphasé évoluent peu par rapport à 25°C. A 400°C, la démixtion survient à une teneur Pu proche de 0,35, largement inférieure à celle suggérée par la littérature. A 600°C, les résultats précisent les équilibres de phases jusqu'alors très méconnus avec une démixtion apparaissant à partir de y=0,60.L'analyse microstructurale des échantillons a clairement démontré l'impact significatif de la démixtion sur le matériau se traduisant par des fissures au sein des échantillons, d'autant plus nombreuses que la teneur en Pu est élevée
In the UO2-PuO2-Pu2O3 section, a monophasic (U1-y,Puy)O2-x domain is stable for y<0,20 at 25°C and up to solid-liquid equilibrium. At higher Pu content, phase equilibria are more unclear with a phase separation process. The main objective of this work consisted in upgrading the representation of this system for 0,15≤y≤0,65 and 25≤T(°C)≤1500.At 25°C, a miscibility gap composed by two different (U1-y,Puy)O2-X phases has been observed for y<0,45, with one very closed to stoichiometric state (Oxygen/Metal=2) and one other very reduced. For the first time, a triphasic domain has been characterized at higher Pu contents, with two (U1-y,Puy)O2-X phases near y=0,45 and one (U1-y,Puy)2O3 phase with a low U content inside. Concerning the study in function of temperature, we have demonstrated that phase separation temperature increase when Pu content grows. Several representations have been established. At 200°C, the representation is closed to that at 25°C. At 400°C, the phase separation have been specified at a lower Pu content than that of literature : y=0,35. At 600°C, our results have clarified the section, until then very unclear, with a phase separation appearing at y=0,60.The microstructural analysis has clearly demonstrated the significant impact of the phase separation on the material. Indeed many cracks have been observed in our samples, and quantity of these defects increases when Pu content grows

碩士
元智大學
機械工程學系
97
This study provides the standard operation procedures of impregnation method and thermal decomposition of a polymeric precursor (DPP) method for the preparations of Pt-based catalysts as the electrode catalysts in unitized regenerative fuel cell (URFC). PtRu and PtIr have been widely used as the electrode catalysts in URFC because Ru can prevent the CO poison and Ir can provide better reversibility both at the water electrolysis mode and at the fuel cell mode. In addition, introduction of W has also been fund to increase specific surface area and resist CO poison. In order to decrease particle size and cost of the catalysts used in URFC, this study combines Pt, Ir, and Ru or W to form the ternary catalysts. This study used impregnation method to prepare Pt, PtIr, and PtRuIr; thermal decomposition of a polymeric precursor (DPP) method and microwave heating method to prepare PtWIr. For, impregnation and microwave heating method, three different pH values were selected for preparation. For DPP method, the chosen parameter was the heat treatment temperature. And some add Carbon nanotubes to prepare and compare. Carbon nanotubes material the use of commercial carbon nanotubes, respectively, as well as the oxidation of commercial carbon nanotubes. And other synthetic catalyst / carbon nanotubes, analysis of their physical properties and electrochemical properties. In this study, the use of impregnation catalyst synthesized with 60% -80% good recovery rate, by XRD can also be found to have a good crystalline structure, with an average particle size can also be controlled at below 5 nm. And found that when combining carbon nanotubes with the business when the Pt / CNT and PtWIr / CNT have good electrochemical surface area. And PtRuIr / CBT and PtIr / CBT by the cyclic voltammetry graph we can see that although both have a good reversibility, but its activity compared with Pt / CNT and PtWIr / CNT many poor in terms of performance. The experiment found that the use of DPP synthesis PtWIr / CNT could be synthesized than impregnation Pt / CNT higher activity, so the next choice PtWIr / CNT and may further improve the manufacturing process in terms of the URFC has the potential to be more than a new choice. This experiment also established a synthesis of the use of Pt catalyst impregnation with a high recovery rate and good lattice structure and the electrochemical activity of the synthetic method.

Large fluctuatuons in the price of a barrel of crude oil and awareness of the finite nature of fossil fules have strongly built the general interest for biofuels. The replacement of some traditional fuels with products from biomass meets a triple challenge : economic (self-generation of evergy), environmental (emissions effect) and legislative (Gpvernment mandates/standards). Compared to the spark ignition engine, the diesel engine has the advantage of having a high efficiency owing to its higher compression ratio. In recent years, not so notable improvements in the diesel engine have been made and it is very difficult to meet pollutant emission standards.

碩士
國立臺灣師範大學
化學系
98
We developed the morphological control of ternary alloy nanocystal (FePtCo and FePtNi) through the polyol reduction in high-boiling solvent. The metallic precursors were reacted with different surfactant combination, including, oleicacid/oleylamine (OLA/OA) and oleylamine/alkyl-phosphonic acid (OLA/TDPA or OLA/ODPA). The uniform polyhedron was synthesized in the OA/OLA = 4 mL/4 mL. The formation of uniform polyhedron was reasonably explained by the classical nucleation theory. Moreover, the nanowire was synthesized in the excess amount of OLA (12 mL) and the absence of OA. The growth mechanism was suggested that the soft template of OLA was formatted due to the achievement of critical micelle concentration (CMC). On the other hand, the nanocubes were synthesized in the presence of OLA/TDPA and/or OLA/ODPA. The two-step growth mechanism was observed because of the difference between the kinetic and thermodynamic growth trend on {111} and {100} facets of cuboctahedral seed. Also, several experimental parameters, including reaction time and concentrations of reducing agent were also considered as the key factor in the morphological. 　　Finally, we used FePtCo and FePtNi with different shapes (polyhedron, nanocube and nanowire) as catalysts. The results in methanol oxidation reaction (MOR) showed the onset potential of all samples were more negative than that of PtRu-JM. However, the measurements in oxygen reduction reaction (ORR) showed that mass activity of FePtCo were 2-fold higher than that of Pt-JM. Further, the ORR efficacy was in the sequence: nanocube > polyhedron > nanowire. The results showed that the difference in structural facets differentiated the ORR activity. We also demonstrated that FePtCo exhibited lower O2 adsorption energy and Co and Fe atoms significantly transferred electrons into Pt atoms through the computation of density functional theory (DFT). According to the results, the catalytic activity of FePtCo nanocrystal outperformed that of FePtNi in ORR.

碩士
國立臺灣科技大學
材料科學與工程系
104
Energy supply is an urgent need for society in this 21st century due the crisis of fossil fuels. Therefore, development new feasible energy, such as fuel cells, has drawn research interest. Low temperature fuel cells, such as direct methanol fuel cell are suitable for transportation and portable application because of their high energy density, low operation temperature and low pollution emissions. To improve the electrocatalytic activity of mono-Pd catalyst, most of the work has addressed to the modification of Pd environment by alloying with other elements. In this study, XC72 was used as carbon support and Pd(acac)2 as Pd metal precursor. For preparing the electrocalysts, emulsion method was used as experimental procedure. Benzyl alcohol was used as solution and oleylamine and oleic acid was used as reducing agent and surfactant. In this study, effect of experimental parameter was studied. Volume ration between reducing agent and total volume 0.5, 0.3, 0.1; and reduction temperature 110, 130, and 150 oC was considered for improving the catalytic activity. Another factor would affect the catalytic activity was alloying elements. There were Fe, Co, and Ni that used as alloying elements. The results showed that the volume ratio 0.1 and reduction temperature 150 oC was the best experimental parameter for synthesized Pd-based ternary alloy. It shows has large ECSA at 0.573 cm2 and high current density at 16.32 mA cm-2. PdFeCo/C was ternary alloy that had the best catalytic activity with high current density at 21.84 mA cm-2 and good stability toward MOR with current density after 3600 s at 0.69 mA cm-2.

Το Η2 είναι το ελαφρύτερο και πλέον άφθονο στοιχείο στη φύση. Βρίσκεται παντού στη γη, στο νερό, στα ορυκτά καύσιμα και σε όλα τα έμβια όντα. Αν το Η2 αξιοποιηθεί κατάλληλα και χρησιμοποιηθεί για τροφοδοσία των κελιών καυσίμου, θα ελαχιστοποιηθεί η εξάρτηση του σύγχρονου πολιτισμού από τα ορυκτά καύσιμα, με συνεπακόλουθο τη μείωση των εκπομπών βλαβερών αερίων στην ατμόσφαιρα. Η χαμηλή θερμοκρασία λειτουργίας των κελιών καυσίμου πολυμερούς ηλεκτρολύτη (PEMFCs) προσφέρει πολλά πλεονεκτήματα και σε συνδυασμό με την υψηλή πυκνότητα ισχύος που αποδίδουν, τα καθιστά κύριους υποψήφιους για εφαρμογή στην αυτοκίνηση. Ωστόσο, η χαμηλή θερμοκρασία εγείρει και σημαντικά προβλήματα, όπως η χρήση ευγενών μετάλλων για την επιτάχυνση των αντιδράσεων και η ευαισθησία σε φαινόμενα δηλητηρίασης. Το κυριότερο δηλητήριο είναι το CO, βασικό παραπροϊόν των διεργασιών παραγωγής H2 από τους υδρογονάνθρακες, οι οποίοι προς το παρόν αποτελούν την κύρια πηγή του. Στην παρούσα διδακτορική διατριβή εξετάστηκαν τα φαινόμενα δηλητηρίασης από το CO της ανόδου του PEMFC. Καθώς το CO δεσμεύεται ισχυρότερα στην επιφάνεια του Pt από το καύσιμο Η2, η παρουσία του στην τροφοδοσία ακόμα και σε ίχνη απενεργοποιεί δραματικά τη λειτουργία της ανόδου. Έτσι, μελετήθηκαν διμεταλλικά και τριμεταλλικά καταλυτικά συστήματα, βασισμένα στο Pt, για την πιθανή αντιμετώπιση του προβλήματος, διαμέσου εξασθένισης του δεσμού Pt-CO ή ενίσχυσης της ηλεκτροχημικής οξείδωσής του από το Η2Ο, που είναι άφθονο στο περιβάλλον ενός PEMFC. Στο κεφάλαιο 1 περιγράφονται οι βιβλιογραφικές πληροφορίες για την τεχνολογία του Η2, όπως μέθοδοι παραγωγής του, καθαρισμού του και αποθήκευσης/μεταφοράς του. Στο κεφάλαιο 2 αναφέρονται οι βασικές αρχές λειτουργίας των κελιών καυσίμου, όσον αφορά στη θερμοδυναμική και στην κινητική, στα είδη τους και στις πιθανές εφαρμογές τους. Στο κεφάλαιο 3 γίνεται εκτενής περιγραφή των δομικών στοιχείων που απαρτίζουν ένα PEMFC, και βιβλιογραφική ανασκόπηση των καταλυτικών συστημάτων που έχουν μελετηθεί για τις βασικές αντιδράσεις. Στο κεφάλαιο 4 περιγράφονται συνοπτικά οι μέθοδοι χαρακτηρισμού και ανάλυσης καθώς και οι πειραματικές διατάξεις που χρησιμοποιήθηκαν. Στο κεφάλαιο 5 εξετάστηκε η επίδραση του υποστρώματος TiO2 στα χαρακτηριστικά του Pt, όσον αφορά την αλληλεπίδρασή του με το CO, σε διάταξη μονής κυψέλης καυσίμου. Παρουσιάστηκε αυξημένη ενεργότητα για την ηλεκτροοοξείδωση του CO και ασθενέστερη αλληλεπίδρασή του με την επιφάνεια του Pt, συντελώντας σε ενεργοποιημένη ρόφηση. Στο κεφάλαιο 6 με φασματοσκοπία υπερύθρου μελετήθηκαν τα χαρακτηριστικά της ρόφησης/εκρόφησης του CO σε μια σειρά καταλυτών Pt-Mo σε υπόστρωμα TiO2. Παρουσία των οξειδίων του Mo η θερμοκρασία εκρόφησης του CO ήταν σημαντικά μειωμένη σε σχέση με μονομεταλλικό Pt, υποδεικνύοντας ασθενέστερο δεσμό του CO με την καταλυτική επιφάνεια. Ωστόσο, παρουσία H2 ο δεσμός ισχυροποιείται, με αποτέλεσμα η εκρόφηση να πραγματοποιείται σε υψηλότερη θερμοκρασία. Αυτό εξηγήθηκε με βάση την ανταγωνιστική αντίδραση του H2 με τις οξειδικές ομάδες, τόσο του υποστρώματος TiO2, όσο και των οξειδίων του Mo. Στο κεφάλαιο 7 εξετάστηκε η οξείδωση του CO σε καταλύτη Pt4Mo/C, δεδομένου του αποσταθεροποιητικού ρόλου του Mo στα χαρακτηριστικά της αλληλεπίδρασης με το CO. Έτσι, αναγνωρίστηκε η ικανότητα των οξειδίων του Mo να διασπούν το Η2Ο σε δυναμικά που συμπίπτουν με τη λειτουργία της ανόδου ενός PEMFC, ενώ παρουσίασαν ενεργότητα για την οξείδωση του CO σε συνθήκες ανοιχτού κυκλώματος διαμέσου της αντίδρασης μετατόπισης με ατμό σε χαμηλή θερμοκρασία μέχρι και 60οC. Ωστόσο, η παραπάνω ιδιότητες δεν ήταν κατανεμημένες ομοιόμορφα στην καταλυτική επιφάνεια, παρά μόνο στη διεπιφάνεια Pt/MoOx, ενώ οι θέσεις μονομεταλλικού Pt παρουσίασαν έντονα φαινόμενα δηλητηρίασης. Επιπλέον, το Mo παρουσιάστηκε ευαίσθητο σε φαινόμενα διάλυσης στο όξινο υδατικό περιβάλλον του PEMFC για δυναμικά μεγαλύτερα από 0.2 V. Στο κεφάλαιο 8 μελετήθηκε η αλληλεπίδραση του CO με τριμεταλλικό καταλύτη Pt-Ru-Co σε σύγκριση με εμπορικό PtRu/C. Ο τριμεταλλικός καταλύτης παρουσιάστηκε ενεργότερος, με χαμηλότερη φαινόμενη ενέργεια ενεργοποίησης για την οξείδωση ροφημένου CO, εμφανίζοντας ισχυρότερη εξάρτηση από το εφαρμοζόμενο δυναμικό.
Hydrogen is the lighter and more abundant element in nature. It is everywhere in earth, water, fossil fuels and in all the living creatures. If H2 can be properly extracted and utilized as a fuel in fuel cells, the dependence of the global economy on fossil fuels will be minimized, resulting in significant attenuation of the greenhouse gases emissions in the atmosphere. The low operation temperature of the polymer electrolyte membrane fuel cells (PEMFCs) offers a lot of advantages. In combination with the high power density yielded by the PEMFCs renders them as the main candidates for application in automotive industry. However, the low temperature raises significant problems, such as the use of noble metals for the acceleration of the basic reactions and the susceptibility in poisoning phenomena. The basic poison is carbon monoxide (CO), one of the main side-products of H2 production from fossil fuels, which for the moment is the main source of H2. In this thesis, the poisoning phenomena of the PEMFCs anode electrocatalysts from CO were investigated. Since CO is bounded on the surface of Pt stronger than the H2 fuel, its presence in the fuel feed in ppm levels deactivates the anode electrocatalyst. In order to eliminate this problem, bimetallic and ternary catalytic systems, based on Pt, were studied with the aim to reduce the Pt-CO bond strength or to promote the electrocatalytic oxidation of CO by water, which is abundant in the PEMFC environment. In chapter 1 is reported the literature information about H2 technology, such as H2 production and cleaning methods and the transport and storage infrastructure. In chapter 2, the basic thermodynamic and kinetic rules of fuel cells operation are referred together with the types of fuel cells and the possible applications. In chapter 3 the structural characteristics of the PEMFCs are outlined and the basic catalytic systems that have been studied for the fuel cell reactions are reviewed. The catalysts’ characterization methods, as well as the experimental procedures utilized in this thesis, are briefly described in chapter 4. In chapter 5 the effect of TiO2 support on the CO chemisorption’s and oxidative properties of Pt was investigated in a single PEMFC configuration. The activity of the CO electrooxidation reaction was enhanced and the Pt-CO bond was destabilized comparing to a commercial Pt/C catalyst. In chapter 6 the CO adsorption/desorption properties were studied by Infrared Spectroscopy, on a series of Pt-Mo catalysts supported on anatase TiO2. The presence of Mo oxides on the catalyst surface reduces significantly the CO desorption temperature in comparison to monometallic TiO2 supported Pt, suggesting the weak CO bonding on the catalytic surface. However, in the presence of H2, the Pt-CO bond strengthens, resulting in higher CO desorption temperature for all the catalysts tested. This was explained on the basis of competitive reaction of H2 with the oxidic surface species, originating from the TiO2 support and the surface Mo oxides. The CO electrooxidation activity of a Pt4Mo/C catalyst is described in chapter 7, considering the destabilizing effect of Mo on the Pt-CO bond. The surface Mo oxide species were able to dissociate H2O at potential values that coincide with the potential window of the PEMFC anode operation. This catalyst oxidized CO under open circuit conditions through the water gas shift reaction and at temperature as low as 60oC. However, the catalytic activity was not homogeneously distributed on the entire catalyst surface, but it was located at the Pt/MoOx interface, with the monometallic Pt sites to be strongly susceptible to CO poisoning. Furthermore, Mo was sensitive to dissolution phenomena in the hydrous acidic environment of the PEMFC for potentials higher than 0.2 V vs. rhe. Finally, in chapter 8 is described the interaction of CO with a ternary Pt-Ru-Co catalyst surface, in comparison to a commercial PtRu/C catalyst. The ternary catalyst was more active for the adsorbed CO electrooxidation, with a lower apparent activation energy than the bimetallic commercial one. The ternary catalyst exhibited zero reaction order with respect to CO partial pressure, while the PtRu/C showed negative reaction order due to competitive adsorption of CO and oxidic species for the same catalytic sites. The kinetic rate constant of the CO electrooxidation reaction for the ternary catalyst showed stronger dependence on the applied potential.

碩士
國立臺灣科技大學
化學工程系
105
In this work, nanoflower-like ternary CuxSnSy (CTS) semiconductor were synthesized by a novel solvothermal approach. Based on the point of view of Cu-Sn-S phase diagram, atomic ratio and crystal strcture can be changed by tuning sulfur molar ratio of CTS during the procedure of synthesis. In order to ensure that CTS can be applied on carbon dioxide reduction reaction, the nanoflower-like CTS powder will be identified by some optical analysis to define its band gap and band edge. On the other hands, from the results of composition, crystal structure and other analysis can found that in the case of low sulfur condition is easier to produce secondary phase copper(I) sulfide (Cu2S) which can enhance CTS system to produce C1 product: methanol (CH3OH). Moreover, sulfonic group (SO3H) can appear in someparameter, which can be a proton donor and proton hoppingto help acetaldehyde (CH3CHO) to convert to ethanol (C2H5OH). In optimization ofthis study, it was found that CTS215(Cu:Sn:S = 2:1:5) after 300oC annealing treatment have the most suitable size of the nanoflower-like structure, it can produce three different products including methanol, acetaldehyde and ethanol, its quantum efficiency also can achieve 0.0471%. In the future, followed by the annealing treatment, surface area control, crystal orientation control of CTS photocatalyst might be a good way for further development of carbon dioxide reduction.