Dissertations / Theses on the topic 'Pt-free'

Oxygen reduction reaction (ORR) catalysts are of crucial importance in developing low- and medium-temperature fuel cells, as PEMFCs (Polymer Electrolyte Membrane Fuel Cells), from which sizeable energy saving and reduction of greenhouse gas emission are expected in comparison with the use of coal and oil based fuels in thermal engines. The same electrochemical oxygen reduction reaction takes place in oxygen depolarized cathodes (ODC) in chlor-alkali electrolysis, replacing the conventional hydrogen evolving cathode, gaining about 30% energy consumption reduction in the overall process. At present carbon-supported Pt and Pt-rich alloys are best credited to the ORR purpose. However, Pt-based catalysts are not free from certain drawbacks, such as oxide formation and Pt particle coarsening through Ostwald ripening, that decrease the overall cell energy conversion efficiency. Furthermore, attendant problems concerning natural availability, geographic distribution and cost of platinum, render platinum supply strategic and fuel cells hardly scalable to mass production. At present, projections on platinum usage for PEMFCs are estimated at ~15 ton y-1 in addition to the current ones, at a cost of ~40 $ g-1. Therefore, non-precious metal catalysts are actively searched for, such as to meet already established operational benchmarks for conventional platinum PEMFC vehicular requirements (0.5 W cm-2; 5500 h durability) with the additional target of significant cost reduction. Several papers on non-precious ORR catalysts have been published after a first report by Jasinski in 1964 demonstrating the ORR activity of metal substitutes-phthalocyanines. Then, research on metal-nitrogen macrocycles significantly expanded, leading to the picture that ORR catalytic activity can be related to N4-Me and N2-Me moieties. However, for precursors cost and unsatisfactory lifetime performance, research was steered toward more simple nitrogen-containing reactants and preparation procedures. Significant steps in this direction were obtained by Dodelet et al. who demonstrated that ORR overpotentials almost linearly decrease with increasing nitrogen content in carbon. Positive results were obtained on a series of samples prepared by high temperature treatment of carbon precursors in NH3/H2/N2 mixtures; doping of these modified carbons with iron rather than cobalt salts was shown to be preferable for better efficiency in oxygen reduction, even though still lower than that of platinum. Further improvements both in terms of incipient ORR potentials and currents were obtained by Maruyama et al. using carbons from hemoglobin and adenine-glucose pyrolysis in the presence of added Fe(II) and Cu(II)/Fe(II) mixtures, respectively. The ORR promoting role of nitrogen in carbon was independently demonstrated both theoretically and experimentally. Indeed, it was found that substitutional nitrogen at a few, specific, peripheral positions of graphene layers in well-ordered carbon nanostructures is in itself able to promote ORR activity even in the absence of accompanying metal centers. Besides the above examined composition-dependent factors, catalyst activity also depends on structural and morphological carbon support features. In fact, many electrocatalytic reactions show faster kinetics on carbon edge planes compared with basal ones. This is related to the ability of the edges to more readily chemisorb O2 (this is the same reason why O2 combusts faster from edges and defects). On the other hand, an optimized porosity of carbon supports is beneficial for an easy access of the oxygen to the catalyst layer in contact with the proton exchange electrolyte membrane. Despite carbon materials of different textural morphology are widely used at an industrial level as supports for precious metal catalysts, in the PEMFC field, electrocatalysts are by far supported on the same VULCAN XC72 carbon. Given that improved catalytic activity of Pt-based catalysts has been achieved by the use of carbons with pore size centered in the mesoporous region, even developed with advanced synthesis, including template methods, such strategy should be pursued also for Pt-free catalytic systems. In this project a number of Pt-free N-doped C-based catalysts have been synthesized on the basis of different synthetic and templating strategies aiming to understand how compositional, morphological and textural aspects of the end material can affect the electrochemical behaviour of ORR. Materials have been characterized using different physico-chemical methods including a study of the kinetics and mechanism of the electrochemical oxygen reduction reaction. Electrochemical results were obtained by rotating disk electrode (RDE) and rotating ring disk electrode (RRDE). Surface and bulk analyses have been performed by BET technique, XPS and XRPD (sometimes data were recorded at synchrotron facilities). (HR) TEM, SEM (combined with FIB milling) imaging was also performed to characterize samples morphology. Many types of samples have been synthesized, starting with mesoporours N-, Fe- doped carbons obtained by heat treatment of a solution of precursors, using silica as a templating agent. Outstanding results in terms of ORR electroactivity in acidic and alkaline conditions have been recorded. Some samples, especially in alkaline media, catalyze ORR even better than commercial Pt-based catalysts. Then, attempting to prepare materials with a precise and defined order and trying to emphasize some of their properties such as surface area and conductivity, ordered carbonaceous nano- and microstructures were synthesized. By chemical vapor deposition N-, Fe- doped carbon nanotubes (N-CNTs) were prepared and some interesting aspects related to the aging of the Fe-doped MgO catalyst used to grow N-CNTs were evidenced. Then, a modified method, but very similar to that used in the synthesis of nanotubes, surprisingly allowed the synthesis of innovative N-doped hollow carbon nanocubes (N-CNCs). This is the great novelty of the work. Due to nanocubes endothermal transformation, happening at 37°C, as detected by DSC, and to the empty space available in the internal part of each cube, many applications can be thought for example involving cubes as nano-reactors that can be opened/close in correspondence of body’s temperature changes. This feature could be taken into considerations for medical applications, after testing and verifying the biocompatibility of nanocubes. Finally, a completely different technique, an ultraspray pyrolysis method (USP) was used to obtain N-, Fe- doped carbon microspheres. The inherent scalability of continuous flow methods such as USP represents a significant advantage compared to alternative synthetic strategies requiring batch processing or surface catalyzed deposition of nanostructured carbon materials (e.g. CVD growth), this feature might be useful in order to improve electrode packing and, consequently, mass transport electrocatalytic applications. The last results section, apparently diverging from the main goals of the present work, was thought to better understand the electronic C-surface behavior in charge transfer reactions. This is actually strongly connected to the oxygen reduction reaction, for which all the catalysts, hereby synthesized, were designed. However, instead of starting from complicated systems involving porous and doped-carbons, the choice was addressed to the simplest but closest material: annealed and non-annealed amorphous carbon thin films prepared by DC-magnetron sputtering technique. Part of the work described was carried out at Trinity College Dublin in the laboratory of Prof. Colavita as a part of an academic collaboration and 5 months exchange granted by the European LLP Erasmus Program.

NiSi and Ni(Pt)Si, and of the effects of dissociated ammonia on oxide reduction was carried out under controlled ultrahigh vacuum (UHV) conditions. X-ray photoelectron spectroscopy (XPS) has been used to characterize the evolution of surface composition. Vicinal surfaces on NiSi and Ni(Pt)Si were formed in UHV by a combination of Ar+ sputtering and thermal annealing. Oxidation of these surfaces in the presence of either O+O2 or pure O2 at room temperature results in the initial formation of a SiO2 layer ~ 7 Å thick. Subsequent exposure to O2 yields no further oxidation. Continued exposure to O+O2, however, results in rapid silicon consumption and, at higher exposures, the kinetically-driven oxidation of the transition metal(s), with oxides >35Ǻ thick formed on all samples, without passivation. The addition of Pt retards but does not eliminate oxide growth or Ni oxidation. At higher exposures, in Ni(Pt)Si surface the kinetically-limited oxidation of Pt results in Pt silicate formation. Substrate dopant type has almost no effect on oxidation rate. Reduction of the silicon oxide/metal silicate is carried out by reacting with dissociated NH3 at room temperature. The reduction from dissociated ammonia (NHx+H) on silicon oxide/ metal silicate layer shows selective reduction of the metal oxide/silicate layer, but does not react with SiO2 at ambient temperature.

Ce travail propose l’utilisation d’un nouveau matériau, appelé PMN-PT, qui continue aider la miniaturisation des systèmes complexes, utilisés dans des différentes technologies. Le travail est présenté dans le cadre de collaboration entre deux projets, MIOP et ADMAN. Les besoins tient compte que les actionneurs soient capables de délivrer de haute déplacement tout en conservant la simplicité et la fiabilité du système. L’accent est mis sur la polyvalence de ce matériau piézo-électrique, PMN-PT, en raison de ses propriétés électro-mécanique. Le travail comprend un aperçu sur quoi influence les propriétés électro-mécaniques du PMN-PT. L’accent est mis sur deux différentes, mais très puissants coupes: anisotrope [011] et longitudinale [001], choisi pour grand déplacement et haute dynamique avec un volume petit. Pour le PMN-PT[001], une structure de type poutre a été étudié, avec un modèle amélioré pour prendre en compte les spécificités de matériel. Les déplacements et forces ont été trouvés d’ être supérieur `a un actionneur en PZT, similairement dimensionnée, tandis que avoir des non-linéarités réduites. Ceci est illustré avec une micro pince avec 6DDL. L’étude de PMN-PT [001] coupé longitudinal suit. Cette étude a été fait en utilisant PMNPT comme un actionneur avec une structure simple, facile à intégrer. Les résultats démontrent les améliorations PMN-PT peut apporter à micro-spectrométrie et la correction d’image avec des micromiroirmobiles. Un micro actionneur PMN-PT a été intégré dans une structure compatible avec des MOEMS et présenté
This work proposes the use of a novel material, called PMN-PT, that futher aids the miniaturizationof complex systems used in different technologies. The work is presented within the collaborativeframework of two projects, MIOP and ADMAN. The end-needs account for actuators capable ofdelivering high displacement, while maintaining system simplicity and reliability. The focus is onthe versatility of the PMN-PT piezoelectric material, due to its electro-mechanical properties. Thework includes an overview on what influences the electro-mechanical properties focusing on twodifferent, though very potent cuts: anisotropic [011] and longitudinal [001]. They were chosen forgenerating large displacement and high dynamics with small volume. For PMN-PT[001] a cantileverstructure was studied, for which the model was improved taking into account the material specificities.Displacements and forces were found to be superior to a similarly dimensioned PZT actuator, whilsthaving reduced non-linearities. This is exemplified with a 6 DoF capable microgripper. The PMNPT[001] longitudinal cut based actuator study follows. This is done by using PMN-PT as a simple,easy to integrate, bulk actuator. The findings demonstrate the improvements PMN-PT can bringto micro-spectrometry and image correction with micro-mirror displacement. A bulk PMN-PT microactuator was integrated into a MOEMS compatible structure and presented

NiSi is an attractive material in the production of CMOS devices. The problem with the utilization of NiSi, is that there is no proper method of cleaning the oxide on the surface. Sputtering is the most common method used for the cleaning, but it has its own complications. Dry cleaning methods include the reactions with radicals and these processes are not well understood and are the focus of the project. Dissociated NF3 and NH3 were used as an alternative and XPS is the technique to analyze the reactions of atomic fluorine and nitrogen with the oxide on the surface. A thermal cracker was used to dissociate the NF3 and NH3 into NFx+F and NHx+H. There was a formation of a NiF2 layer on top of the oxide and there was no evidence of nitrogen on the surface indicating that the fluorine and hydrogen are the reacting species. XPS spectra, however, indicate that the substrate SiO2 layer is not removed by the dissociated NF3 and NiF2 growth process. The NiF2 over layer can be reduced to metallic Ni by reacting with dissociated NH3 at room temperature. The atomic hydrogen from dissociated ammonia reduces the NiF2 but it was determined that the atomic hydrogen from the ammonia does not react with SiO2.

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A partir das relações de poder que se estabelecem entre o campo político e a instância comunicativa midiática, a dissertação tem como ponto de partida o conceito de campanha permanente, definido como o uso dos recursos disponíveis no trabalho por parte dos atores políticos (governos, partidos, congressistas ou líderes), a fim de construir e manter o apoio popular. A pesquisa desenvolve um estudo sobre a construção da imagem de Dilma Rousseff, do partido dos trabalhadores (PT), em três instâncias: pronunciamentos em rede de TV, Horário Gratuito de Propaganda Eleitoral (HGPE) e jornal Folha de S. Paulo. Busca-se verificar como foi trabalhada a campanha, permanente, na função de Presidente da República, eleita em 2010 e de candidata à reeleição em 2014. Como corpus de análise, são analisados, primeiramente, os espaços institucionais ocupados como presidente da República, tomando como recorte os pronunciamentos em Cadeia Nacional de Rádio e TV (CNRT), durante seu primeiro mandato. Secundariamente, procura-se verificar se a imprensa, por meio da cobertura dos pronunciamentos, projetou uma imagem negativa, positiva ou neutra de Dilma Rousseff na posição de presidente, tomando como recorte as notícias publicadas pelo jornal Folha de S. Paulo. Como terceira dimensão de análise, são investigados os HGPEs de 2014. Como estratégia metodológica, recorreu-se à Análise de Conteúdo de Bardin (1977), a fim de analisar separadamente os objetos e depois identificar os pontos de confluência e os aspectos dissonantes. Identificam-se dois momentos no governo Dilma: o de alta popularidade até as manifestações de junho de 2013, e a fase posterior, com queda da aprovação e uma disputa acirrada na eleição de 2014, quando saiu vitoriosa com um percentual muito reduzido de votos em relação ao candidato Aécio Neves do Partido Social da Democracia Brasileira (PSDB). Houve mais pontos de confluências no primeiro momento entre o discurso da petista e a cobertura da imprensa. O segundo período foi conturbado e houve uma cobertura mais negativa e crítica por parte da mídia. A comunicação eleitoral foi uma forma de buscar resgatar as ações do governo, havendo uma intensa propaganda negativa de ataques entres os adversários.
From the power relations that are establish between political field and the media communication system, this dissertation has as a key concept ‘the permanent campaign’, defined as the implementation of the any available resources for the political actors during their work (government, political parties, congressman or leaders) aiming to obtain and keep popular support. This research develops a study about the making of the image of Dilma Rousseff (PT) in three situations: pronouncement in TV network, HGPE and Folha de S. Paulo newspaper. This paper tries to verify how the permanent campaign has been undertaken as president of the Brazilian Republic, elected in 2010, and as a candidate running for reelection in 2014. As empirical data, firstly are analysed the institutionalized spaces occupied as president of the Brazilian Republic, defining as analytical material the pronouncements in National Network of Radio and Television (CNTR, in portuguese) during her fist mandate. Secondly, it tries to verify if the press, through its pronouncements coverage, created a negative, positive or neutral image of Dilma Rousseff in her position as president, taken as empirical data the news published by Folha de S. Paulo newspaper. As third material data, it will be analysed the programs of Free Political Advertising Time (HGPE, in portuguese) in 2014. As methodological strategy, we recurred to the Content Analysis (Bardin, 1977) with the goal of analysing separately the objects and then identify the convergence and dissonant aspects. We can identify two different moments in Dilma’s government: high popularity until june 2013 manifestations and the subsequent period with fall of approval and fierce competition on the 2014 election, when she won the elections with a minor percentage of votes in relation to the candidate Aécio Neves (PSDB). There were more confluence aspects in the first period between the president’s pronouncements and the media coverage. The second moment was troubled and there was a more negative and critical coverage by the media. The electoral communication was an attempt to retrieve the governments’ actions and there was an intense negative propaganda of attacks between the candidates.

博士
國立臺灣大學
化學工程學研究所
103
This dissertation aimed to systematically develop Pt-free counter electrodes (CEs) and to design a novel iodide-free electrolyte for the dye-sensitized solar cells (DSSCs) with low-costs and highly cell efficiencies (η’s). This dissertation is divided into two parts: (1) Pt-free CEs (Chapter 3~Chapter 7) and (2) iodide-free electrolyte (Chapter 8). In the case of Pt-free CEs, we aim to reduce the costs of the DSSCs using various electro-catalysts for completely replacing the expensive Pt via the simple, non-vacuum, and low-cost fabrication processes. Accordingly, three types of Pt-free composite films were studied using a standard iodide electrolyte. (I) Transition metallic compound-type CEs, including the composite film of TiS2/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (TiS2/PEDOT:PSS) in Chapter 3, the composite films of Si3N4/PEDOT:PSS, SiO2/PEDOT:PSS, SiS2/PEDOT:PSS, SiSe2/PEDOT:PSS in Chapter 4, and the composite films of Zn3N2/PEDOT:PSS, ZnO/PEDOT:PSS, ZnS/PEDOT:PSS, ZnSe/PEDOT:PSS in Chapter 5, were indivitually investigated. In a composite film, the transition metallic compound nanoparticles were separately used to provide attractive electro-catalytic abilities and large active areas for I3- reduction; among those NPs, TiS2, Si3N4, SiS2, SiSe2, Zn3N2 and ZnSe were applied in DSSCs for the first time. Among them, the cell with Zn3N2/PEDOT:PSS CE reached a higher η than that of Pt-based cell. (II) Carbonaceous-type CEs, i.e., the composite films of nano-porous carbon black nanoparticles/ sulfonated-poly(thiophene-3-[2-(2-methoxyethoxy)-ethoxy]-2,5-diyl) (CB NPs/s-PT), were investigated in Chapter 6 to provide large surface area, fast eletrolyte penetratoin, and rapid reaction rate for I3– reduction. When a composite film contains 5 wt% CB NPs, the pertinent DSSC reached best η of 9.02%, which is even higher than that of Pt-based DSSC. The s-PT is introduced as a novel thiophene-based water-soluable conducting polymer for CE in DSSC for the very first time. Under weak sunlight, the cell with CB NPs/s-PT composite CE still maintains good performance, indicating its good compatibility at both outdoor or indoor electronics. (III) Conducting polymer type CEs, including poly(3,4-ethylenedioxythiophene) (PEDOT) and six different ionic-liquid-doped PEDOT films were systematically investigated in Chapter 7. Six different ionic liquids containing three imidazolium cations with different alkyl chains (–C2H5, –C6H13, –C10H21) and four anions (BF4−, PF6−, SO3CF3−, TFSI−) were used as the chemical dopants to increase the surface area of PEDOT films and to ehance the conjugation of the PEDOT films, respectively. Among them, the cell with HMIPF6-doped PEDOT and HMITFSI-doped PEDOT CEs reached higher η’s than that of Pt-based DSSC. In brief, this dissertation explores four Pt-free composite films of Zn3N2/PEDOT:PSS, HMIPF6-doped PEDOT, HMITFSI-doped PEDOT, and CB NPs/s-PT are a promising substitutions of Pt due to their outstanding properties, i.e., good electro-catalytic ability for I3– reduction, low-cost, simple preparation process, and easy for large-scale production. In the case of iodide-free electrolyte, we designed a novel dual-channel ionic liquid compound (Chapter 8), 1-butyl-3-{2-oxo-2-[(2,2,6,6-tetramethylpiperidin-4-yl)amino]ethyl}-1H-imidazol-3 -ium selenocyanate (ITSeCN), to further improve the cell effiency of DSSCs. ITSeCN is designed to contain dual redox channels of imidazolium-functionalized TEMPO (cationic redox mediator) and selenocyanate (anionic mediator). Thereby, the ITSeCN shows the favorable redox natures, which gave more positive standard potential, larger diffusivity, and better kinetic heterogeneous rate constant than those of iodide. To further investigate a suitable electro-catalytic material for triggering the redox of ITSeCN mediator, several materials were used: (1) Pt (metal type), (2) PEDOT (conducting polymer type), (3) CoSe (transition metallic compound type), and (4) carbon black (carbonaceous type) films were chosen to represent four types of electro-catalytic materials in DSSCs. Finally, the DSSCs with PEDOT and CoSe CEs achieved better performance than that of the Pt-based DSSC. Therefore, it can be infered that the transition metallic compound type CEs would be more suitable for our new synthesized-ITSeCN mediator than the others.

博士
國立臺灣大學
化學工程學研究所
107
This dissertation aimed to systematically study Pt-free and TCO-free counter electrodes (CEs) with low-costs and highly cell efficiencies (η’s). This dissertation is divided into two parts: (1) Pt-free CEs (Chapter 3 and Chapter 4) and (2) Pt-free and TCO-free CEs (Chapter 5 and Chapter 6). In the case of Pt-free CEs, we aim to reduce the costs of the DSSCs using various electro-catalysts for completely replacing the expensive Pt via the simple, non-vacuum, and low-cost fabrication processes. Accordingly, three types of Pt-free composite films were studied using a standard iodide electrolyte. (I) Transition metallic compound-type CEs, i.e. CoSe2/CoSeO3 with nanocube (NC), nanorod (NR), and nanoparticle (NP) structures in Chapter 3, the composite films of CoSe2/CoSeO3 with hierarchical urchin-like structure in Chapter 4, were indivitually investigated. In the composite film, the different nanostructures were separately used to provide attractive electro-catalytic abilities and large active areas for I3- reduction. (II) Transition metallic and conducting polymer type CEs, i.e. MoSe2 NS/PEDOT:PSS in Chapter 5, were investigated to provide large surface area, fast eletrolyte penetration, well adhesion, and rapid reaction rate for I3- reduction. (III) Carbonaceous-type CEs, i.e. pristine monolithic carbon aerogel (CA-O, CA-Q, CA-F, CA-C, and CA-G) in Chapter 6, were investigated by controlled resorcinol (R)/formaldehyde (F) and resorcinol (R)/sodium carbonate (C) molar ratios. In the case of Pt-free and TCO-free CEs. In the case of Pt-free and TCO-free CEs, the classic TCO substrate is replaced by Ti foil and carbon aerogel for low-cost, simple preparation process, and large-scale production. (I) Ti foil substrate collocate with MoSe2 NS/PEDOT:PSS, which presents a higher η of 8.51 ± 0.05%, as compared to a lower η of 8.21 ± 0.02% using the Pt-coated Ti foil CE. (II) Carbon aerogel replace traditional CEs based on the Pt/FTO/glass in DSSCs. The DSSCs using the as-prepared CA-C CE gave the best η of 9.08 ± 0.01%, among all the CA CEs. In brief, this dissertation explores three Pt-free composite films of CoSe2/CoSeO3, MoSe2 NS/PEDOT:PSS, and CA are a promising substitutions of Pt due to their outstanding properties, i.e., good electro-catalytic ability for I3– reduction, low-cost, simple preparation process, and easy for large-scale production.

Pt-aluminide (PtAl) coatings form an integral part of thermal barrier coating (TBC) systems that are applied on Ni-based superalloy components operating in the hot sections of gas turbine engines. These coatings serve as a bond coat between the superalloy substrate and the ceramic yttrium stabilized zirconia (YSZ) coating in the TBC system and provide oxidation resistance to the superalloy component during service at high temperatures. The PtAl coatings are formed by the diffusion aluminizing process and form an integral part of the superalloy substrate. The microstructure of the PtAl coatings is heavily graded in composition as well as phase constitution. The matrix phase of the coating is constituted of the B2-NiAl phase. Pt, in the coating, is present as a separate PtAl2 phase as well as in solid solution in B2-NiAl. The oxidation resistance of the PtAl bond coat is derived from the B2-NiAl phase. At high temperatures, Al from the B2-NiAl phase forms a regenerative layer of alumina on the coating surface which, thereby, lowers the overall oxidation rate of the superalloy substrate. The presence of Pt is beneficial in improving the adherence of the alumina scale to the surface and thereby enhancing the oxidation resistance of the coating. However, despite its excellent oxidation resistance, the B2-NiAl being an intermetallic phase, renders the PtAl coating brittle and imparts it with a high brittle-to-ductile-transition-temperature (BDTT). The PtAl coating, therefore, remains prone to cracking during service. The penetration of these cracks into the substrate is known to degrade the strain tolerance of the components. Evaluation of the mechanical behavior of these coatings, therefore, becomes important from the point of views of scientific understanding as well as application of these coatings in gas turbine engine components. Studies on the mechanical behavior of coatings have been mostly carried on coated bulk superalloy specimens. However, since the coating is brittle and the superalloy substrate more ductile when compared to the coating, the results obtained from these studies may not be representative of the coating. Therefore, it is imperative that the mechanical behavior of the coating in stand-alone condition, i.e. the free-standing coating specimen without any substrate attached to it, be evaluated for ascertaining the true mechanical response of the coating. Study of stand-alone bond coats involves complex specimen preparation techniques and challenging testing procedures. Therefore, reports on the evaluation of mechanical properties of stand-alone coatings are limited in open literature. Further, no systematic effort has so far been made to examine important aspects such as the effect of temperature and strain rate on the tensile behavior of these coatings. The deformation mechanisms associated with these bond coats have also not been reported in the literature. In light of the above, the present research study aims at evaluating the tensile behavior of free-standing PtAl coatings by the micro-tensile testing technique. The micro-tensile testing method was chosen for property evaluation because of its inherent ability to generate uniform strain in the specimen while testing, which makes the results easy to interpret. Further, since the technique offers the feasibility to test the entire graded PtAl coating in-situ, the results remain representative of the coating. Using the above testing technique, the tensile behavior of the PtAl coating has been evaluated at various temperatures and strain rates. The effect of strain rate on the BDTT of the coating has been ascertained. Further, the effect of Pt content on the tensile behavior of these coatings has also been evaluated. Attempts have been made to identify the mechanisms associated with tensile deformation and fracture in these coatings. The thesis is divided into nine chapters. Chapter 1 presents a brief introduction on the operating environment in gas turbine engines and the materials that are used in the hot sections of gas turbine engines. The degradation mechanisms taking place in the superalloy in gas turbine environments and the need for application of coatings has also been highlighted. The basic architecture of a typical thermal barrier coating (TBC) system applied on gas turbine engine components has been presented. The constituents of the TBC system, i.e. the ceramic YSZ coating, MCrAlY overlay as well as diffusion aluminide bond coats and, the various techniques adopted for the deposition of these coatings have been described in brief. Chapter 2 presents an overview of the literature relevant to this study. This chapter is divided into four sub-chapters. The formation of diffusion aluminide coatings on Ni-based superalloys has been described in the first sub-chapter. Emphasis has been laid on pack cementation process for the formation of the coatings. The fundamentals of pack aluminizing process, including the thermodynamic and kinetic aspects, have been mentioned in brief. The microstructural aspects of high activity and low activity plain aluminide and Pt-aluminide coatings have also been illustrated. The techniques applied for the mechanical testing of bond coats have been discussed in the second sub-chapter. The macro-scale testing techniques have been mentioned in brief. The small scale testing methods such as indentation, bend tests and micro-tensile testing have also been discussed in the context of evaluation of mechanical properties of bond coats. Since the matrix in the aluminide bond coats is constituted of the B2-NiAl phase, a description of the crystal structure and deformation characteristics of this phase including the flow behavior, ductility and fracture behavior has been mentioned in the third sub-chapter. In the fourth sub-chapter, reported literature on the tensile behavior and brittle-to-ductile-transition-temperature (BDTT) of diffusion aluminide bond coats has been discussed. In Chapter 3, details on experiments carried out for the formation of various coatings used in the present study and, their microstructural characterization, are provided. The method for extraction of stand-alone coating specimens and their testing is discussed. The microstructure and composition of the various coatings used in the present study are discussed in detail in Chapter 4. Unlike in case of bulk tensile testing, for which standards on the design of specimens exist, there are no standards available for the design of micro-tensile specimens. Therefore, as part of the present research work, a finite element method (FEM)-based study was carried out for ascertaining the dimensions of the specimens. The simulation studies predicted that failure of the specimens within the gage length can be ensured only when certain correlations between the dimensional parameters are satisfied. Further, the predictions from the simulation study were validated experimentally by carrying out actual testing of specimens of various dimensions. Details on the above mentioned aspects of specimen design are provided in Chapter 5. The PtAl coatings undergo brittle fracture at lower temperatures while ductile fracture occurs at higher temperatures. Further, the coatings exhibit a scatter in the yielding behavior at temperatures in the vicinity of BDTT. Therefore, the BDTT, determined as the temperature at which yielding is first observed in the stress-strain curves, may not be representative of the PtAl coatings. In Chapter 6, a method for the precise determination of BDTT of aluminide bond coats, based on the variation in the plastic strain to fracture with temperature, has been demonstrated. The BDTT determined by the above method correlated well with the variation in fracture surface features of the coating and was found representative of these coatings. In Chapter 7, the effect of temperature and strain rate on the tensile properties of a PtAl bond coat has been evaluated. The temperature and strain rate was varied between room temperature (RT)-1100°C and 10-5 s-1-10-1 s-1, respectively. The effect of strain rate on the BDTT of the PtAl bond coat has been examined. Further, the variation in fracture surface features and mechanism of fracture with temperature and strain rate are illustrated. The micro-mechanisms of deformation and fracture in the coating at different temperature regimes have also been discussed. The coating exhibited brittle-to-ductile transition with increase in temperature at all strain rates. The BDTT was strain rate sensitive and increased significantly at higher strain rates. Above BDTT, YS and UTS of the coating decreased and its ductility increased with increase in the test temperature at all strain rates. Brittle behavior occurring in the coating at temperatures below the BDTT has been attributed to the lack of operative slip systems in the B2-NiAl phase of the coating. The onset of ductility in the coating in the vicinity of BDTT has been ascribed to generation of additional slip systems caused by climb of dislocations onto high index planes. The coating exhibited two distinct mechanisms for plastic deformation as the temperature was increased from BDTT to 1100°C. For temperatures in the range BDTT to about 100°C above it, deformation was controlled by dislocations overcoming the Peierls-Nabarro barrier. Above this temperature range, non-conservative motion of jogs by jog dragging mechanism controlled the deformation. The transition temperature for change of deformation mechanism also increased with increase in strain rate. For all strain rates, fracture in the coating at test temperatures below the BDTT, occurred by initiation of cracks in the intermediate single phase B2-NiAl layer of the coating and subsequent inside-out propagation of the cracks across the coating thickness. Ductile fracture in the coating above the BDTT was associated with micro-void formation throughout the coating. The effect of Pt content on the tensile behavior of PtAl coating, evaluated at various temperatures ranging from room temperature (RT) to 1100°C and at a nominal strain rate of 10-3 s-1, is presented in Chapter 8. Irrespective of Pt content in the coating, the variation in tensile behavior of the coating with temperature remained similar. At temperatures below BDTT, the coatings exhibited linear stress-strain response (brittle behavior) while yielding (ductile behavior) was observed at temperatures above BDTT. At any given temperature, the elastic modulus decreased while the strength increased with increase in Pt content in the coating. On the other hand, the ductility of the coating remained unaffected with Pt content. The BDTT of the coating also increased with increase in Pt content in the coating. Addition of Pt did not affect the fracture mechanism in the coating. Fracture at temperatures below BDTT was caused by nucleation of cracks at the intermediate layer and their subsequent inside-out propagation. At high temperatures, fracture occurred in a ductile manner comprising void formation, void linkage and subsequent joining with cracks. The deformation sub-structure of the coating did not get affected with Pt incorporation. Short straight dislocations were observed at temperatures below BDTT, while, curved dislocations marked by jog formation were observed at temperatures above BDTT. The factors controlling fracture stress and strength in the PtAl coatings at various temperatures have also been assessed. The overall summary of the present research study and recommendations for future studies are presented in the last chapter, i.e. Chapter 9.

碩士
東海大學
物理學系
103
Photoelectrochemical dye-sensitized solar cells (DSCs) have attracted much interest in the field of sustainable green energy. However, their counter electrodes (CEs) usually fabricated by the noble metal Pt. To obtain the alternative Pt-Free CEs for DSCs is desirable for the wide deployment of DSCs. Buckypapers (BPs) are prepared in the random and highly interpenetrative configuration of multi-walled carbon nanotubes (MWCNTs), and it has high porosity and conductivity. In this study, BPs are unitized as the CEs for DSCs. From the results of electrochemical impedance spectroscopy (EIS) analysis, the charge transfer rate (fct) of BP-DSC (9357 Hz) is greater than that of Pt-DSC (698 Hz) and the recombination rate (frec) of BP-DSC (1.1 Hz) is lower than that of Pt-DSC (1.7 Hz), indicating the BP-CE provides an efficient reduction and suppresses the recombination in DSC. For the results of cyclic voltammetry (CV), the reduction current [I(Red1)] of BP electrode (-0.956 mA) is greater than that of Pt electrode (-0.083 mA). The results of EIS and CV measurement reveal that the reduction reaction of BP electrode is improved because of its extreme electroactive surface area, and this improvement suppresses the recombination rate in DSCs. Accordingly, BP-DSCs show a high open-circuit voltage (Voc) and fill factor (FF) in power-dependent J-V characterization. As the results, BP-DSCs exhibit a higher enhancement in PCE than that of Pt-DSCs and show the PCE comparable to Pt-DSCs under 100 mW/cm2 illumination.

碩士
大同大學
化學工程學系(所)
102
In this study, we first utilize the high temperature reflux mode to well mix the CNT and PP and followed by thermal compression to prepare the CNT/PP thin plates as a Pt-free and TCO-free CE for DSSCs. After that, to further carry out the test of materials characterizations and electrochemical activity. Although the cell efficiency of DSSCs using CNT/PP based CEs was still much lower than that of DSSC with Pt/FTO CE, it is showed the excellent sheet resistance and flexibleness. Therefore, we used the CNT/PP to replace the FTO glass as a substrate. In order to enhance the photovoltaic performance, we further deposited PEDOT thin film on flexible CNT/PP plates via electropolymerization method as a PEDOT-CNT/PP CE. From a series of results and discussion, the composites of PEDOT-CNT/PP exhibited excellent electrocatalytic activity and low charge transfer resistance. On the other hand, after the optimization of flexible test, the CNT/PP plate prepared in the ratio of CNT/PP with 43% possessed the highest bending ability. However, the power conversion efficiency of the PEDOT coated on CNT/PP with 43% is 6.09%, which is lower than Pt/FTO CE (6.69%). In the bending characteristics, the composites of PEDOT-CNT/PP showed the excellent potential as a low-cost and flexible composites CE in DSSCs.

碩士
國立交通大學
材料科學與工程系所
92
The fully Cu metallization InP heterojunction bipolar transistor (HBT) using Platinum (Pt) as diffusion barrier has been successfully fabricated and demonstrated in this study. The InP HBT uses Ti/Pt/Cu for n-type, Pt/Ti/Pt/Cu for p-type ohmic contacts metals and Ti/Pt/Cu for interconnect metals with Pt as the diffusion barrier. Both the n+-InGaAs/Ti/Pt/Cu/Cr multilayer structure and GaAs/SiNx/Ti/Pt/Cu/Cr structure were stable up to 350oC 30 min annealing as judged from data of AES, XRD, and AFM and from the measurement of the sheet resistance. Current accelerated stress test was conducted on the device with current density (JC) of 80 kA/cm2 for 24 hours, the current gain showed no degradation after the high current stress. The devices were also thermally annealed at 200oC for 1 and 3 hours and showed no dramatic changes. Overall, we have successfully demonstrated that fully Cu metallization InP HBT can be achieved by using Pt as the diffusion barrier and Ti/Pt/Cu and Pt/Ti/Pt/Cu as the ohmic contacts.

碩士
國立中央大學
化學研究所
99
Dye-Sensitized Solar Cells (DSSCs) are attractive the third generation thin film solar cells due to their low cost, light weight, colorful, fabricated easily and flexible. Generally, platinum is employed as a catalyst for the cathode in DSSC to catalyze the reduction reaction (I3- to 3I-) of the electrolyte. However, platinum is one of the most expensive materials on the earth. The preparation of Pt counter electrode at high temperature also increases the cost and difficulty in fabricating large-size device. Therefore, extensive studies have been carried out for developing other cheaper materials to replace Pt in DSSC. In this study, we investigated the performance of DSSCs using polyaniline (PANI) or poly(3,4-ethylenedioxythiophene) (PEDOT) as a catalyst on the counter electrode. We found that HFIP (Hexafluoroisopropanol) is a very good solvent for PANI and PEDOT powder. PANI and PEDOT counter electrode with large surface area and good conductivity can be made from PANI/HFIP and PEDOT/HFIP solution simply by spin coating at room pemperature, and the heating process is unnecessary. DSSC uses PANI/ FTO as a counter electrode exhibits an efficiency of 7.77 % with CYC-B11 as a sensitizer ( Pt：8.83 % ). Nevertheless, the efficiency of DSSC used PANI-SO4-HFIP CE (made from the H2SO4-Doped PANI/HFIP solution by spin coating the film on FTO) as counter elctrode achieves the highest efficiency of 8.76 %，which is comparable to that (8.83 %) of Pt-based DSSC under the same fabrication and measurement conditions. Furthermore, dispersing of PEDOT powder in HFIP was also used to prepare PEDOT counter electrode (PEDOT CE) by spin coating. The efficiency of PEDOT CE-based DSSC with CYC-B11 as sensitizer is 8.98 % ( Pt：8.74 % ). The results proved that conjugated polymers are good materials for replacing Pt as a counter electrode catalyst for DSSC.

碩士
國立臺灣科技大學
化學工程系
105
Fuel cells have been considered as a potential candidate for alternative energy generation system. Unfortunately, the use of high cost precious Pt catalyst limits its wide spread application. In this study, CNT supported Ni-Ru bimetallic catalyst was successfully synthesized by using hydrothermal method and the catalyst loading can be well controlled about 22-25% as well as good reproducibility, which is applied to hydrogen oxidation reaction (HOR) and hydrogen gas precipitation reaction (HER) under alkaline conditions. The size of the catalyst was observed from 2 to 3 nm by TEM, and the nanocatalyst are well dispered on CNT. The results of X-ray absorption spectra indicate that the catalyst has a high alloy extent after ammonia heat treatment, nickel-nitride bonding is confirmed by XPS. The electrochemical test for alkaline HOR and HER shows that the Ni-Ru/C catalyst after ammonia heat treatment at 4500C an possesses activity comparable to Pt/C and much better than Ni/C and Ru/C catalysts while the cost of Ni-Ru/C is much lower than Pt/C. Due to the excellent activity of alkaline HOR and HER for as-prepared Ni-Ru/C catalyst which is well-matched to Pt/C catalyst, the bi-functional property may be included in the catalyst. In the further discussion of the stability test, the stability of the test using the constant voltage test, after 12 hours of testing time, after ammonia heat treatment catalyst, the HOR and HER, 4%(Pt/C 23%) and 11% (Pt/C 5.5%) decay, respectively, has a very high stability.

The introductory chapter reviews the current state of mechanistic understanding of the hexadehydro-Diels-Alder (HDDA) reaction. With the rapid development of the HDDA reaction from its first discovery in 1997, the question of whether a concerted or stepwise mechanism better describes the thermally activated formation of ortho-benzyne from a diyne and a diynophile has been debated. Mechanistic and kinetic investigations were able to show that this is not a black or white situation, as minor changes can tip the balance. In chapter 2 of this thesis, the catalytic process leading from 1,11-bis(p-tolyl)undeca-1,3,8,10-tetrayne to fully-substituted naphthalene and azulene derivatives, by two different platinum-catalyzed dimerization pathways, was investigated. In chapter 3, the cannibalistic self-trapping reaction of an ortho-benzyne derivative generated from 1,11-bis(p-tolyl)undeca-1,3,8,10-tetrayne in an HDDA reaction was investigated. Without adding any specific trapping agent, the highly reactive benzyne is trapped by another bisdiyne molecule in at least three different modes. In chapter 4 direct UV/VIS spectroscopic evidence for the existence of an o-benzyne in solution is reported, and the dynamics of its formation in a photo-induced reaction are established. For this purpose, 1,11-bis(p-tolyl)undeca-1,3,8,10-tetrayne was investigated, using femtosecond transient absorption spectroscopy in the ultraviolet/visible region. In chapter 5, following the isolation and characterization of the reaction products discussed in chapter 3, further species resulting from reactions of the highly reactive ortho-benzyne derivative were identified
Das einleitende Kapitel gibt einen Überblick über den aktuellen Stand des mechanistischen Verständnisses der Hexadehydro-Diels-Alder (HDDA)-Reaktion. Mit der rasanten Entwicklung der HDDA-Reaktion seit ihrer ersten Entdeckung im Jahr 1997 wurde die Frage diskutiert, ob ein konzertierter oder ein schrittweiser Mechanismus die thermisch aktivierte Bildung von ortho-Benzin aus einem Diin und einem Diinophil besser beschreibt. Mechanistische und kinetische Untersuchungen konnten zeigen, dass es sich hierbei nicht um eine Schwarz-Weiß-Situation handelt, da schon kleine Änderungen das Gleichgewicht verändern können. In Kapitel 2 dieser Arbeit wurde der katalytische Prozess, der von 1,11-Bis(p-tolyl)undeca-1,3,8,10-tetrain zu vollständig substituierten Naphthalin- und Azulen-Derivaten führt, über zwei verschiedene platinkatalysierte Dimerisierungspfade untersucht. In Kapitel 3 wurde die kannibalistische Selbsteinfangreaktion eines ortho-Benzin-Derivats untersucht, das aus 1,11-Bis(p-tolyl)undeca-1,3,8,10-tetrain in einer HDDA-Reaktion erzeugt wurde. Ohne Zugabe eines spezifischen Einfangmittels wird das hochreaktive Benzin von einem anderen Bisdiin-Molekül in mindestens drei verschiedenen Modi eingefangen. In Kapitel 4 wird der direkte UV/VIS-spektroskopische Nachweis für die Existenz eines o-Benzins in Lösung berichtet und die Dynamik seiner Bildung in einer photoinduzierten Reaktion aufgezeigt. Zu diesem Zweck wurde 1,11-Bis(p-tolyl)undeca-1,3,8,10-tetrayne mittels Femtosekunden-Transienter-Absorptionsspektroskopie im ultravioletten/sichtbaren Bereich untersucht. In Kapitel 5 wurden nach der Isolierung und Charakterisierung der in Kapitel 3 diskutierten Reaktionsprodukte weitere Spezies identifiziert, die aus Reaktionen des hochreaktiven ortho-Benzin-Derivats resultieren

Thesis (Ph. D.)--University of Notre Dame, 2007.
Thesis directed by E. E. Wolf for the Department of Chemical and Biomolecular Engineering. "December 2007." Includes bibliographical references (leaves 196-214).

博士
國立臺灣大學
高分子科學與工程學研究所
97
The main purpose of this thesis is to investigate the behaviors of new approaches in electrodes (working and counter), sensitizers and gel polymer electrolytes for dye-sensitized solar cells (DSSCs) and discussing the influences on the cell performance and stability of DSSCs. In the first part of this thesis (Chapter 2 and 3), the optimization of solar energy conversion efficiency of DSSCs was investigated by the tuning of TiO2 photoelectrode’s morphology. Double-layered TiO2 photoelectrodes were designed by the coating of TiO2 suspension incorporated with low and high molecular weight poly(ethylene glycol) as a binder. Among four types of TiO2 electrodes, the P2P1 showed the highest efficiency under the conditions of identical film thickness and constant irradiation. This can be explained by the larger pore size and higher surface area of P2P1 TiO2 electrode than the other materials and these two factors assist for the facile transport of I3-/I- ion couple through the TiO2 matrix. The best efficiency (h) of 9.04% for a solar cell was obtained by introducing the light scattering particles to the TiO2 electrode measured under AM 1.5G. As for the part of low-temperature fabricated DSSC, the TiO2 film with the TTIP/TiO2 molar ratio of 0.08 has the best conduction. Meanwhile, the charge transport resistance at the TiO2/dye/electrolyte interface increased as a function of the MWCNT concentration, ranged from 0.1 to 0.5 wt%, due to a decrease in the surface area for dye adsorption. The DSSC with the TiO2 containing 0.1 wt% of MWCNT resulted in a JSC of 9.08 mA/cm2 and a cell conversion efficiency of 5.02 %. On the other hand, TiO2 film prepared by using binder-free TiO2 paste which developed by Prof. Miyasaka’s group was also used in plastic DSSC to optimal the SJW-E1 dye which synthesized by Prof. Wu’s group. The effects of TiOx buffer layer and co-adsorbents as well as long-term stability of plastic DSSCs were investigated. The TiOx buffer layer not only benefited the adhesion between TiO2 thin film and ITO/PEN substrate but also reduced the electron recombination, resulting in the improvement of the FF and conversion efficiency of cells. The optimized solar cell based on SJW-E1 showed a high efficiency of 6.31 % at 100 mW/cm2 (AM 1.5G), and SJW-E1 based solar cell showed a better stability than that of N719 based after 500 h light soaking test. In the second part of this thesis (Chapter 4), the co-sensitization of dyes for the complementary in the spectral characteristics in plastic DSSCs was investigated. Two co-sensitization systems for the plastic DSSCs, including N719/FL and black dye/FL showed enhanced photovoltaic performances compared with that of each dye individually. The optimal conversion efficiencies of N719/FL and black dye/FL DSSCs reached 5.10 % and 3.78 %, respectively, which were higher than that of individual sensitizers. However, for the system co-sensitized with FL and Chl-e6, the cell performances only lay in between that of each dye. From the EIS analysis, the characteristic frequencies (C.F.) at TiO2/dye/electrolyte interface for N719/FL and black dye/FL are kept the same or lower than that of individual dyes. While for the FL /Chl-e6 co-sensitized DSSCs, the C.F. were higher than that based on only FL, indicating that they had shorter electron lifetime in the TiO2 electrode after co-sensitization. In the third part of this thesis (Chapter 5), two kinds of gel polymer electrolytes were developed and used in DSSCs. At the beginning, it was found that the donor number of solvent in electrolyte is the one of the key factors that effect the photovoltaic performance of DSSC. Meanwhile, the quasi-solid state DSSCs were fabricated with polyvinyidene fluoride-co-hexafluoro propylene (PVDF-HFP) in methoxy propionitrile (MPN) as gel polymer electrolyte (GPE), tetrabutylammonium iodide/iodine as redox couple, 4-TBP as additive and nano-silica as fillers. The energy conversion efficiency of the cell with 5 wt% PVDF-HFP is comparable to that one obtained in liquid electrolyte system. Solar cell containing PVDF-HFP with 0.8 M of TBAI and 0.12 M of I2 shows maximum photocurrent. Moreover, the addition of 1wt% nano-silica is found to improve the at-rest durability and the performance of the solar cell. A photocurrent of 14.04 mA/cm2, a VOC of 0.71 V and an overall conversion efficiency of 5.97 % under 100 mW/cm2 irradiation was observed for the best performance of a solar cell in this work. On the other hand, the ionic conductivities and performances of DSSCs of GPEs prepared by in situ polymerization with different cross-linkers were investigated. The poly(imidazole-co-butylmethacrylate)-based GPE containing the B4Br cross-linker showed a higher ionic conductivity, due to the formation of micro-phase separation that resulted in an increase of ion transport paths in the GPE. Moreover, a co-adsorbent, (4-pyridylthio) acetic acid, co-adsorbed with N3 dye on the TiO2 electrode not only reduced dye aggregation, but also reacted with the cross-linkers in the GPE at the TiO2/GPE interface after gelling, thus the value of JSC significantly increased from 7.72 to 10.00 mA/cm2. In addition, in order to reduce the ionic diffusion resistance within the TiO2 electrode, incorporation of monodispersed PMMA in the TiO2 paste was considered. With the optimal volume ratio of PMMA/TiO2 (v/v = 3.75), the micro-porous TiO2 electrode exhibited larger pores (ca. 350 nm) uniformly distributed after sintering, and the ionic diffusion resistance within the TiO2 film could significantly be reduced. The cell conversion efficiency increased from 3.61 to 5.81% under illumination of 100 mW/cm2, an improvement of ca. 55 %. In the fourth part of this thesis (Chapter 6), a series of poly(3,4-alkylenedioxythiophene) counter electrodes prepared by electrochemical polymerization on the fluorine-doped tin oxide (FTO) glass substrate were incorporated in the platinum-free DSSCs. Cells fabricated with a PProDOT-Et2 counter electrode showed a higher conversion efficiency of 7.88 % compared to cells fabricated with PEDOT (3.93 %), PProDOT (7.08 %), and sputtered-Pt (7.77 %) electrodes. The FF was strongly dependent on the deposition charge capacity of the PProDOT-Et2 layer, but the aggregation of PProDOT-Et2 in higher deposition capacities (> 80 mC/cm2) resulted in decreases in JSC and the cell conversion efficiency. Incorporating the best ProDOT-Et2 film (40 mC/cm2) as the counter electrode in plastic DSSC was compared and showed similar tendency as mentioned above. The cell fabricated with a PProDOT-Et2 counter electrode showed a higher conversion efficiency of 5.20 % compared with that fabricated with sputtered-Pt (5.11%) electrodes under the illumination of 100 mW/cm2 (AM 1.5G).