Dissertationen zum Thema „Co based oxides“

Le développement d'électrocatalyseurs efficaces pour la réaction de libération d'oxygène (OER) est important pour améliorer l'efficacité globale du processus d'électrolyse de l'eau. Les oxydes / hydroxydes de métaux de transition présentent une activité et une stabilité raisonnables lorsqu’utilisés dans un milieu alcalin. Ils ont le potentiel de remplacer les oxydes à base d'Ir et de Ru. Comprendre la réaction d’OER pour les oxydes / hydroxydes de métaux de transition dans les électrolytes alcalins aide à la conception d'électrocatalyseurs peu coûteux et très efficaces. Avec trois travaux différents sur les oxydes / hydroxydes à base de Co, cette thèse approfondit la compréhension des propriétés de surface des matériaux et des propriétés interfaciales sur la cinétique de la réaction d’OER. Tout d'abord, la substitution au fer régule par exemple la configuration des cations métalliques dans LaCoO3. Cela ajuste la covalence de la liaison oxygène 2p – métal 3d et améliore les performances. Deuxièmement, la substitution au Ni dans ZnCo2O4 modifie la position relative du centre de la bande O 2p et du centre de la bande métallique dans un environnement octahédrique MOh. Cela modifie la stabilité et la possibilité pour l'oxygène du réseau de participer à la réaction de dégagement d’oxygène. Enfin, en étudiant les séries La1-xSrxCoO3, CoOOH et CoOOH contenant Fe, l'impact de l'électrolyte sur les paramètres de la cinétique de réaction a été exploré. Avec une meilleure compréhension de la façon dont les propriétés des matériaux et l'environnement dynamique influencent l'activité et le mécanisme des OER, nous pouvons obtenir des catalyseurs de OER plus efficaces pour une meilleure infrastructure énergétique
The development of efficient electrocatalysts to lower the overpotential of oxygen evolution reaction (OER) is of fundamental importance in improving the overall efficiency of fuel production by water electrolysis. Among a plethora of catalysts being studied on, transition metal oxides / hydroxides that exhibit reasonable activity and stability in alkaline electrolyte have been identified as catalysts to potentially overpass the activity of expensive Ir- and Ru- based oxides. Understanding the OER for transition metal oxides / hydroxides in alkaline electrolytes paves the way for better design of low cost and highly efficient electrocatalysts. This dissertation, with three different work on Co-based oxides / hydroxides, studies and deepens the understanding of the bulk properties, surface properties of materials and interfacial properties on OER. Firstly, with Fe substitution, it addresses tuning the eg configuration of metal cations in LaCoO3 where adjusting the metal 3d oxygen 2p covalency can bring benefits to the OER performance. Secondly, with Ni substitution in ZnCo2O4, it demonstrates a change in relative position of O p-band and MOh d-band centre which induces a change in stability as well as the possibility for lattice oxygen to participate in the OER. Finally, with La1-xSrxCoO3 series, CoOOH and Fe-containing CoOOH as examples, the impact of the electrolyte has been explored by the study of reaction kinetics parameters. With a better understanding of how material properties and dynamic environment influence the OER activity and mechanism, we can obtain more efficient OER catalysts for better energy infrastructure

The catalytic oxidation of carbon monoxide is an important reaction in heterogeneous catalysis. Copper manganese mixed oxides in the form of Hopcalite, CuMn₂C₄, is used as a catalyst for the oxidation at ambient temperature and is important in respiratory protection, particularly in mining industries. These types of catalysts are prepared by a co-precipitation method variables in this preparation procedure are known to control catalytic activity. Previous work has shown that the addition of a cobalt dopant metal to the catalyst structure can have a positive effect on activity towards CO oxidation. This thesis furthers the work of dopant addition by studying the effects of zinc on the copper manganese catalyst. Catalyst testing for CO oxidation showed that the addition of the zinc dopant metal increases the stability of catalytic activity. Temperature Programmed Reduction studies show that the addition of zinc has an effect on the redox properties of the catalyst. Prepared copper manganese oxide catalysts were used as supports for gold catalysts. Gold supported CuMnOx was prepared by a deposition precipitation method. The addition of gold to these active materials leads to a marked increase in the catalytic activity. Scanning Electron Microscopy (SEM) showed that the morphology of the support used, played an important role in producing a highly active catalyst. Also, the ageing time of the catalyst precursor was shown to influence catalytic activity. The most effective catalyst for CO oxidation was found to be a 1 wt% Au supported catalyst. The presence of moisture in the gas feed is known to be detrimental to a Hopcalite catalyst for ambient temperature CO oxidation. The effect of moisture on the copper manganese mixed oxide catalysts highlighted the improvement in moisture tolerance with the addition of gold. The method of depositing gold onto an oxide support was shown to be applicable to a commercially available catalyst. The gold supported CuMnOx catalysts prepared were tested for oxidation reactions at higher temperatures. The reactions investigated were ethylene oxide oxidation and preferential oxidation (PROX) of carbon monoxide. Studies showed the addition of gold to the CuMnOx catalysts, improves activity compared to an undoped catalyst.

Co-Al-Ox mixed metal oxides partially modified with Cu or Mg, as well as Ag were successfully prepared, characterized and evaluated as potential catalysts for the N2O decomposition. The materials were characterized by the following techniques: X-Ray Diffraction, Thermogravimetric Analysis (TGA), N2 Physisorption, Hydrogen Temperature-Programmed Reduction (H2-TPR), and X-ray photoelectron spectroscopy (XPS). Ag-modified HT-derived mixed oxides showed enhanced activity compared to the undoped materials, the optimum composition was found for (1 wt.% Ag)CHT-Co3Al. The catalyst characterization studies suggested that the improved catalytic activity of Ag-promoted catalysts were mainly because of the altered redox properties of the materials.

Poor air quality has been projected to be the world’s top cause of environmental premature mortality by 2050 surpassing poor sanitation and dirty water (IGBP / IGAC press release, 2012 ). One of the major challenges of air quality management is how to adequately quantify both the spatial and temporal variations of pollutants for the purpose of implementing necessary mitigation measures. The work described in this thesis aims to address this problem using novel electrochemical based air quality (AQ) sensors. These instruments are shown to provide cost effective, portable, reliable, indicative measurements for urban air quality assessment as well as for personal exposure studies. Three principal pollutants CO, NO and NO2 are simultaneously measured in each unit of the AQ instrument including temperature / RH measurements as well as GPS (for time and position) and GPRS for data transmission. Laboratory studies showed that the electrochemical sensor nodes can be highly sensitive, showing linear response during calibration tests at ppb level (0-160 ppb). The instrumental detection limits were found to be < 4 ppb (CO and NO) and < 1 ppb for NO2 with fast response time equivalent to t90 < 20 s. Several field studies were carried out involving deployment of both the mobile and static electrochemical sensor nodes. Results from some short-term studies in four different cities including Cambridge (UK), London (UK), Valencia (Spain) and Lagos (Nigeria) are presented. The measurements in these cities represent snapshot of the pollution levels, the stark contrast between the pollution level especially CO (mean mixing ratio of 16 ppm over 3 hrs) in Lagos and the other three cities is a reflection of the poor air quality in that part of the world. Results from long-term AQ monitoring using network of 46 static AQ sensors were used to characterise pollution in different environments ranging from urban to semi-urban and rural locations. By coupling meteorological information (wind measurements) with pollution data, pollution sources, and phenomena like the street canyon effect can be studied. Results from the long-term study also revealed that siting of the current fixed monitoring stations can fail to represent the actual air quality distribution and may therefore be unrepresentative. This work has shown the capability of electrochemical based AQ sensors in complementing the existing fixed site monitors thus demonstrating an emerging measurement paradigm for air quality monitoring and regulation, source attribution and human exposure studies.

The present thesis focuses on studying structure/morphology/activity relationships in bimetallic Pt-Sn nanostructured electrodes for proton exchange membrane (PEM) fuel cells by adopting a rigorous surface science approach where: i) Model electrocatalysts are prepared in ultra-high-vacuum (UHV) conditions as ultrathin (UT) films (PtSnx/Pt(110) and SnOx/Pt(110)) to ensure a very reproducible control down to the atomic level; ii) Composition, morphology and structure of the UT nanostructured films are studied in situ by adopting state-of-the-art characterization tools; iii) Quantum mechanical calculations are carried out adopting the density functional theory (DFT) in order to determine the atomic structure of the UT films. A systematic search for possible Sn alloy or oxides on Pt(110) surface phases was carried out. Three surface alloys (including one already reported surface alloy) and two surface oxides on Pt(110) surface were identified. The two novel surface alloys: p(3×1)PtSn/Pt(110) and p(6×1) PtSn/Pt(110) can be prepared by means of UHV Sn deposition on Pt(110) at different thickness and by a subsequent annealing at proper temperature. Besides, two SnOx oxides surfaces, namely the c(2×4)SnOx/Pt(110) and the c(4×2) SnOx/Pt(110), were prepared by oxidizing the surface alloys. With optimization of the preparation conditions, a phase diagram for the surface alloys and surface oxides on Pt(110) was outlined. The two novel surface alloys were characterized by low energy electron diffraction (LEED), scanning tunnelling microscopy (STM) and synchrotron radiation photoemission spectroscopy (SRPES). STM images of the two surface alloys are characterized by a highly corrugated row structure whereas photoemission data indicate a complex intermixing between Pt and Sn which leads to the formation of extended near-surface alloys. Some models for the two surfaces were proposed on the basis of the experimental evidences. These models were then compared with DFT calculations and the simulated STM images of the models were used as final assessment of their validity. The reactivity of the surface alloys with CO was investigated both experimentally by thermal programmed desorption (TPD) and theoretically by DFT calculations. The results reveal a scarce reactivity towards CO on the two surfaces due the lower adsorption energy with respect to pure Pt(110) surface, indicating their use as highly CO tolerant catalysts. Based on the DFT results, the surfaces can have also an improved performance in CO oxidation reaction (COOR) on the basis of the calculated d-band centroid value. The two surface oxides (c(2×4)SnOx/Pt(110) and c(2×4)SnOx/Pt(110) ) were investigated by LEED, STM and SRPES. Some models for the two surfaces were proposed based on the experimental results, and investigated by DFT calculations. The good agreement between the simulated STM images with the experimental data suggests a good reliability of the proposed structures. The reactivity towards CO for the two oxidised phases was also investigated. The c(4×2) structure, constituted by a slightly oxidised Sn overlayer, demonstrated to be scarcely reactive, whereas the more oxidized c(2×4) phase proved to be able to efficiently oxidize CO. These results were also confirmed by DFT. The decomposition of methanol on c(2×4) surface was also investigated by TPD and SRPES, indicating that the methanol can be oxidised efficiently into CO2 and H2O. However the body of our experimental data points to a quite complex oxidation mechanism whose selectivity changes dynamically according to the experimental conditions. The fully oxidised c(2×4) can efficiently oxidise methanol to CO2 at low temperature, but this reaction path is progressively suppressed as soon as the phase is reduced. In this regime the methanol is oxidized to CO2 at higher temperature and less efficiently, the microscopic mechanism of the reaction implies the supply of oxygen by c(2×4) islands on reduced Pt or PtSn areas by spillover, where the actual reaction takes place. When the spillover is not anymore possible, because the methanol decomposition has removed most oxygen, methanol is simply oxidatively dehydrogenated to CO and H2, similarly to what happens on the clean Pt(110) surface but at a slightly lower temperature.
La presente tesi si concentra sullo studio della relazione struttura / morfologia / reattività in elettrodi bimetallici nanostrutturati Pt - Sn per celle a combustibile a membrana a scambio protonico (PEM), adottando un rigoroso approccio di scienza delle superfici sviluppato come segue: i) sistemi modello di elettrocatalizzatori sono stati preparati in condizioni di ultra - alto vuoto (UHV) depositando via epitassia da fasci molecolari (MBE) strati ultrasottili (UT) di PtSnx e SnOx su superfici di Pt monocristallino orientate (110), al fine di garantire un controllo fine e riproducibile su scala atomica; ii ) composizione, morfologia e struttura dei film nanostrutturati UT sono stati studiati in situ mediante l'adozione di strumenti di caratterizzazione in linea con le più avanzate tecniche offerte dallo stato dell’arte; iii ) calcoli quanto-meccanici basati sulla teoria del funzionale densità (DFT) sono quindi stati effettuati per determinare la struttura atomica dei film UT, in modo da razionalizzare e supportare i risultati sperimentali ottenuti al punto precedente. Una ricerca sistematica è stata effettuata allo scopo di identificare nuove possibili fasi di superficie di Sn o ossidi di Sn supportate su Pt (110). In questo modo, tre leghe di superficie (di cui una risulta già nota in letteratura) e due ossidi di superficie su Pt (110) sono stati identificati. Le due innovative leghe da film UT, la p(3 × 1) PtSn / Pt (110) e la p(6 × 1) PtSn / Pt (110) possono essere sintetizzate mediante deposizione di Sn su Pt (110), preparando spessori diversi e sottoponendo le superfici così ottenute a trattamenti termici effettuati a diverse temperature. Conseguentemente, l’ossidazione ad alta temperatura delle leghe superficiali ha permesso l’ottenimento di due nuove fasi ossidate di superficie, la (c(2 × 4) SnOx / Pt (110) e la c(4 × 2) SnOx / Pt (110). Infine, data l’elevata flessibilità delle tecniche di preparazione e caratterizzazione offerte dalla scienza delle superfici, è stato possibile delineare con grande accuratezza un diagramma di fase sia per le leghe che per gli ossidi di superficie sopra descritti. Le due nuove leghe superficiali sono state caratterizzate mediante diffrazione di elettroni a bassa energia cinetica (LEED), microscopia a scansione ad effetto tunnel (STM) e spettroscopia di fotoemissione da radiazione di sincrotrone (SRPES). Le immagini STM delle due leghe superficiali sono caratterizzate da una struttura a righe altamente corrugata; i dati di fotoemissione indicano inoltre un complesso intermixing tra Pt e Sn che porta alla formazione di leghe localizzate in prossimità della superficie. Alcuni modelli per le due superfici così ottenute sono state proposte sulla base delle evidenze sperimentali. Tali modelli sono stati poi confrontati con calcoli DFT; in particolare, sono state generate simulazioni di immagini STM che sono state quindi confrontate con i dati sperimentali ed usate come valutazione finale della validità dei modelli proposti. La reattività delle leghe di superficie rispetto al CO è stata studiata sia sperimentalmente, mediante desorbimento termico programmato (TPD), sia ricorrendo a calcoli DFT. I risultati rivelano una scarsa reattività delle due superfici nei confronti del CO a causa dell’energia di adsorbimento inferiore rispetto alla stessa superficie di Pt (110) presa come riferimento; tale fenomenologia indica pertanto il promettente impiego di tali sistemi come catalizzatori caratterizzati da elevata tolleranza al CO. Come già descritto per le leghe di superficie, i due ossidi superficiali (c(2 × 4) SnOx / Pt (110 ) e c(4 × 2) SnOx / Pt (110) ), sono stati studiati mediante LEED, STM e SRPES. Alcuni modelli per le due superfici sono stati proposti sulla base dei risultati sperimentali, la cui validità è stata supportata da calcoli DFT. Il buon accordo tra le immagini STM simulate e i dati sperimentali suggeriscono una buona affidabilità delle strutture proposte. La reattività verso il CO per le due fasi ossidate è stata inoltre indagata mediante TPD supportata da calcoli quantomeccanici. La struttura c(4 × 2), costituita da uno strato UT di SnOx sub-stechiometrico, ha dimostrato di essere poco reattiva, mentre la fase più ossidata c(2 × 4) ha dimostrato di essere in grado di ossidare efficacemente il CO. Lo studio della decomposizione del metanolo sulla fase c(2 × 4), effettuato mediante TPD e SRPES, indica come il metanolo possa essere ossidato in modo efficiente a CO2 e H2O. Tuttavia, i dati sperimentali indicano un meccanismo di ossidazione piuttosto complesso, la cui selettività cambia dinamicamente in base alle condizioni sperimentali. Ad ogni modo, la fase completamente ossidata c(2 × 4) può facilmente ossidare il metanolo a CO2 già a bassa temperatura, tuttavia tale reattività viene progressivamente soppressa non appena inizia la riduzione della fase con la perdita di ossigeno reticolare. In questo regime l’ossidazione del metanolo a CO2 richiede temperature più elevate; in particolare, il meccanismo microscopico della reazione implica la fornitura di ossigeno da parte della fase c(2 × 4) ad isole ridotte di Pt o PtSn, siti nei quali avviene effettivamente la reazione di ossidazione. Con il procedere della decomposizione del metanolo, il progressivo consumo di ossigeno porta ad una drastica soppressione della diffusione di superficie di quest’ultimo. In questo modo, il metanolo viene semplicemente deidrogenato a CO e H2 analogamente a quanto accade sulla superficie pulita di Pt (110), sebbene a temperature inferiori.

Les nanoparticules (NPs) bimétalliques Au-Pd ont été étudiées pour leur activité catalytique dans la réaction d'oxydation du CO. La technique de préparation, la taille et la composition des nanoparticules ont un grand impact sur le comportement catalytique du système. Ici, des nanoparticules de 3 et 5nm de diamètre Au1-xPdx (x = 0, 0.25, 0.5, 0.75, 1) ont été utilisées pour étudier l'effet de la taille et de la composition. Les échantillons ont été synthétisés par nano-lithographie à base de micelles, technique bien adaptée pour obtenir des particules ayant une distribution en taille étroite. Afin d’obtenir une répartition homogène des micelles chargées en ions métalliques sur des substrats de SiO2/Si(001), nous avons eu recours à la méthode de « spin-coating » et obtenu une organisation quasi-hexagonales des micelles observable en SEM. Un plasma d'oxygène ou d'hydrogène a été utilisé pour éliminer le polymère, réduire les ions métalliques et permettre la formation de nanoparticules. Nous avons entrepris une approche systématique pour étudier l'effet du plasma sur la structure et la morphologie des NPs à l'aide des techniques de diffusion des rayons X. L'oxydation et l'activité catalytique des NPs Au1-xPdx pour l'oxydation du CO ont été étudiées à 300 °C et 0.5 bar dans le réacteur à flux XCAT disponible sur la ligne de lumière SixS du Synchrotron SOLEIL, France. Les mesures de l'activité d'oxydation du CO ont montré que les NPs préparées en utilisant le plasma d'oxygène présentent un taux de conversion en CO2 plus élevé que les NPs préparées à l'aide de plasma d'hydrogène pour une composition donnée. Les nanoparticules de Pd préparées avec du plasma d'O2 se sont révélées être le catalyseur le plus actif : aucun effet synergique n'a été observé pour les nanoparticules bimétalliques pour la réaction d'oxydation du CO
Au-Pd bimetallic nanoparticles (NPs) have been studied for their catalytic activity in CO oxidation reaction. The preparation technique, size and composition of the nanoparticles have great impact on the catalytic behaviour of the system. Here, 3 and 5nm diameter Au1-xPdx (x = 0, 0.25, 0.5, 0.75, 1) nanoparticles were employed to study the effect of size and composition. The samples were synthesized by micelle nanolithography, a technique well adapted to yield narrow size distribution of nanoparticles. To achieve monodisperse metal-loaded micelles on SiO2/Si(001) substrates we employed spin-coating and observe quasi-hexagonal ordered micelles in SEM. Oxygen or hydrogen plasma were used to remove the polymer, reduce the metal ions and enable nanoparticle formation. We made a systematic approach to study the effect of plasma on the structure and morphology of the NPs by means of surface x-ray scattering techniques. The oxidation behavior and CO oxidation activity of the Au1-xPdx NPs were studied at 300°C and 0.5 bar in the flow reactor XCAT available at the SixS Beamline, Synchrotron SOLEIL, France. The CO oxidation activity measurements showed that the NPs prepared using the oxygen plasma present higher CO2 conversion rate than the NPs prepared using hydrogen plasma for a given composition. The Pd nanoparticles prepared using O2 plasma were found to be the most active catalyst: no synergetic effects were observed for bimetallic nanoparticles for the CO oxidation reaction

The Solid Oxide Fuel Cell (SOFC) is a promising technology for electricity generation. It converts the chemical energy of the fuel gas directly to electricity energy and therefore, very high electrical efficiencies can be achieved. The high operating temperature of the SOFC also provides excellent possibilities for cogeneration applications. In addition to producing power very efficiently, the SOFC has the potential to concentrate CO₂ with a minimum of an overall efficiency loss. Concentration of CO₂ is a desirable feature of a power generation process so that the CO₂ may be subsequently sequestered thus preventing its contribution to global warming. The primary purpose of this research project was to investigate the role of the SOFC technology in power generation processes and explore its potential for CO₂ capture in power plants.

This thesis introduces an AspenPlus^TM SOFC stack model based on the natural gas feed tubular internal reforming SOFC technology. It was developed utilizing existing AspenPlus^TM functions and unit operation models. This SOFC model is able to provide detailed thermodynamic and parametric analysis of the SOFC operation and can easily be extended to study the entire process consisting of the SOFC stack and balance of plant.

Various SOFC-based power generation cycles were studied in this thesis. Various options for concentrating CO₂ in these power generation systems were also investigated and discussed in detail. All the processes simulations were implemented in AspenPlus^TM extending from the developed natural gas feed tubular SOFC stack model. The study shows that the SOFC technology has a promising future not only in generating electricity in high efficiency but also in facilitating CO₂ concentration, but the cost of the proposed processes still need be reduced so SOFCs can become a technical as well as economic feasible solution for power generation.

Effects of urban air pollution on health and environment have lead researchers to find economic air quality monitoring regulations. Since tin dioxide (SnO2) was demonstrated as a gas sensing device in 1962, tin oxide based thin film sensors have been widely studied due to their high sensitivity and fast response. The main advantages of using tin oxide sensors are their low cost, small size and low power consumption for mobile system applications. But, in order SnO2 based sensors to meet low concentration of gases they should be highly upgraded in sensitivity, selectivity and stability. This study was focused on the capacity of dopants in the SnO2 layer to increase the sensitivity of the sensor in detecting carbon monoxide. 1 wt. % Pd promoted and 0.1 wt. % Na-1 % Pd promoted SnO2 multilayer thin films were produced by sol-gel technique followed by spin coating route on soda-lime glass substrates. The EDX and SEM studies showed the surface composition and the surface structure is homogeneous throughout the films. The film thickness was determined app. 450 nm from the SEM image of the cross-section, after coating 8 layers. The experiments conducted at several temperatures namely 150, 175 and 200oC, in oxygen free and 1% oxygen containing atmospheres showed that the responses at higher temperatures in the presence of oxygen were much sharper with respect to others. Besides, Na promoted test sensors showed larger responses with shorter response time in oxygen free atmospheres at relatively lower temperatures. The results showed that the sensor signal is not directly correlated with the carbon dioxide production in oxygen free atmospheres.

Noble metals notably platinum (Pt), is a major element of heterogeneous catalysts, excel in catalysing an extensive number of important catalytic reactions in chemical and automotive industries. Since the increased use of these metals is severely limited because of their high cost and scarcity’s, there is therefore an urgent need for the search of alternative base metal catalysts that are cheaper and more widely available. This can only be practical if the main drawbacks of base metals such as the agglomeration of particles under high temperatures operational conditions and irreversible sulphur poisoning can be overcome, and their activity enhanced, such that they can directly replace Pt on a weight-to-weight basis. However, most previous studies have been restricted to low temperature reaction conditions and have not compared their activity directly to that of Pt, whether in terms of active sites or on a weight-to-weight basis. Moreover, most researchers have not investigated extensively the long-term stability of their base metal catalysts, since the longest was at most around 200 hours and at relatively low temperatures, for example at room temperature. It is proposed that long term stability can be achieved by producing uniformly distributed nano-sized socketed and strained base metal particles via the exsolution method. The main objective of this thesis is to produce exsolved base metals catalyst systems rivalling Pt on a weight-to-weight basis in two base reactions; CO and NO oxidation. NO oxidation was also chosen as our model reaction in this research since most Pt in the automotive industry are used in the lean NOx trap (LNT) or a combination of LNT and selective catalytic reduction (SCR), which demand the high conversion of NO to NO2 at low temperatures to work effectively. Initial screening experiments were performed to evaluate the potential CO oxidation activities and long-term stability at 520 °C of two different exsolved metal pellet systems namely lanthanum-doped ceria nickel titanates to exsolve nickel (Ni) metal (La0.8Ce0.1Ni0.4Ti0.6O3) and lanthanum-doped strontium iron nickel titanates to exsolve iron-nickel (FeNi) alloy (La0.5Sr0.4Fe0.1Ni0.1Ti0.6O3). Exsolved FeNi pellet system gives high and stable turnover frequencies (TOFs) of 103 s-1 at 520 °C for almost 170 hours, which confirms the potential of these stable exsolved metal systems for CO oxidation. Sixty exsolved metal powder systems with various metal formulations were produced to enable direct activity comparison to Pt on a weight-to-weight basis. Most exsolved metal systems displayed increasing CO2 production rates with increasing CO partial pressures (PCO) and reversible sulphur poisoning with exsolved CoNi powder system showing remarkable stability at 200 °C for 655 hours (one month). This exsolved CoNi system also showed enhanced activity for CO oxidation upon exposure to CO-rich environment, as a result of the restructuring of particles iv into metal oxide nanocubes anchored onto nanosockets within the support surface. The CO2 production rates of the activated exsolved CoNi powder system at 200 and 520 °C were 0.13 x 10-4 and 1.5 x 10-4 mol s-1 g-1 compared to its initial rate of around 0 (below the detected limit of 0.007 x10-4 mol s-1 g-1) and 0.8 x 10-4 mol s-1 g-1 prior to activation. These active spinel (CoNi)3O4 cubic structures were seen planted at an angle of ~55°, at the edge of an empty socket with mediocre features for CO oxidation, such as rich in Co2+ with exposed (100) planes that had only 44 cubes μm-2 compared to its initial 144 particles μm-2 particle population. Above 450 °C, the main active sites for CO oxidation were thought to be close to or at the metal-support interface of the exsolved CoNi systems. Comparable NO2 production rates to those of commercial Pt catalyst was achieved with only ± 5 % of difference at each measured point within the temperature range used (100-440 °C) over exsolved CoNi system by exploiting the effect of having two particle size ranges (10 and 30 nm). These results confirm the dual functionality of the activated exsolved CoNi system and its huge potential to be commercialised as an alternative catalyst to Pt in two oxidation reactions; CO and NO oxidation. In general, a simple procedure that induces high, long-lasting activity in a base metal catalyst, rivalling platinum for CO and NO oxidation on a weight-to-weight basis was demonstrated. The nature of this activation by tracking individual nanoparticles was successfully elucidated to link their microstructural evolution to their catalytic and kinetic behaviour. This research also illustrates new strategies for enhancing and tailoring the catalytic activity of base metal systems towards replacing platinum.

Porphyrins consist of twenty-atom rings containing four nitrogen atoms and can be used as sensor to detect odours and gases.

This thesis investigates whether or not porphyrins can be used as functional materials on grid gate devices.  Drops of PVC embedded porphyrins were deposited on the surface of a grid gate which is a Metal Oxide Semiconductor (MOS) capacitor. In order to detect the gas sensing properties of the porphyrins a light addressable method called Scanning Light Pulse Technique (SLPT) has been used.

Drops of porphyrins were deposited with a stretched capillary tube (1 mm diameter).

The MOS capacitor has been exposed to nitrogen atmosphere as reference environment, while the target gases were carbon monoxide (100 ppm) and ammonia (500 ppm).

The result from the eight porphyrins is that one of them [Pt(II) TPP] has a response for both gases, ammonia induces a change in both the work function and surface resistance, while the carbon monoxide induces only a change in the surface resistance.

Kyoto University (京都大学)
0048
新制・課程博士
博士(工学)
甲第11580号
工博第2526号
新制||工||1343(附属図書館)
23223
UT51-2005-D329
京都大学大学院工学研究科物質ｴﾈﾙｷﾞｰ化学専攻
(主査)教授 江口 浩一, 教授 井上 正志, 教授 垣内 隆
学位規則第4条第1項該当

Made available in DSpace on 2014-10-09T12:34:46Z (GMT). No. of bitstreams: 0
Made available in DSpace on 2014-10-09T14:03:29Z (GMT). No. of bitstreams: 0
Dissertação (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

La société Nanoe en collaboration avec le Laboratoire de Chimie de la Matière Condensée de Paris (LCMCP) propose un procédé innovant pour la synthèse de NMC, un matériau communément utilisé en tant que matériau d’électrode positive pour accumulateur Li-ion. Ces matériaux sont actuellement synthétisés en solution par coprécipitation demandant de traiter des déchets de métaux dissous en solution aqueuse. La nouvelle méthode proposée est une synthèse par voie solide composée d’une étape de broyage à haute énergie des précurseurs, suivie d’une étape de séchage et de structuration par atomisation pour finir sur un traitement à haute température pour former la phase désirée. Cette voie possède les avantages de ne rejeter aucun déchet solide ou liquide mais également de compter moins d’étapes de synthèse et l’utilisation de matières premières moins coûteuses. Le but de ces travaux de thèse est d’optimiser ce procédé de synthèse pour la production de NMC de compositions de plus en plus riches en nickel. Les étapes du procédé ont été optimisées sur NMC333, un matériau largement étudié et commercialisé. La synthèse a ensuite été adaptée pour des compositions plus riches en nickel, à savoir NMC622 et 811. Il a été montré qu’enrichir la composition en nickel nécessitait de réduire la température de synthèse pour obtenir les meilleures propriétés structurales, morphologiques et électrochimiques. Les matériaux synthétisés sont ensuite comparés à leurs homologues commerciaux produits par coprécipitation et montrent, à un régime rapide de 1C, une capacité plus faible dans les premiers cycle mais une meilleure rétention de capacité leur permettant de dominer sur le long terme
The company Nanoe in collaboration with the Laboratoire de Chimie de la Matière Condensée de Paris (LCMCP) offers an innovative process for the synthesis of NMC, a positive electrode material for Li-ion batteries. These materials are currently synthesized in solution by coprecipitation, requiring retreating waste metals dissolved in aqueous solution. The new method proposed is a solid-state synthesis composed of a high-energy milling of the solid-state precursors in suspension, followed by a spray-drying structuration step and a final heat treatment.to form the NMC phase. This new route not only produces no solid or liquid waste, but also have fewer synthesis steps and the use of cheaper raw materials. The aim of this thesis work is to optimize this synthesis process to produce NMC by using nickel-rich compositions. The different process stages were first optimized on LiNi0.33Mn0.33Co0.33O2, a widely used and commercial material. The synthesis was then adapted for compositions richer in nickel, namely LiNi0.6Mn0.2Co0.2O2 and LiNi0.8Mn0.1Co0.1O2. It has been shown that enriching the nickel composition required reducing the synthesis temperature to obtain the best structural, morphological, and electrochemical properties. The synthesized materials are then compared to their commercial counterparts produced by a coprecipitation process and demonstrated, at 1C-rate, a lower capacity in the first cycles but a better capacity retention allowing them to dominate in long-term cycling

L'étude des mécanismes de nitruration du composé intermétallique Sm2 (Fe, Co)1#7 est effectuée sur des échantillons massifs à l'aide de la diffraction des rayons X et de la microscopie électronique à balayage. Nous avons utilisé deux modes de nitruration (lit fluidisé et flux gazeux) afin de comparer les processus mis en jeu lors du traitement. Des comportements différents interviennent au niveau de la distribution de l'azote dans les échantillons, des cinétiques de nitruration globale et de la couche de surface. Il apparaît que la diffusion de l'azote est principalement volumique dans le cas de la nitruration en lit fluidisé alors que les micro-fissures présentes dans les échantillons tiennent lieu de chemins de rapide diffusion pour la nitruration sous flux gazeux. L'étude des mécanismes d'oxydation du composé intermétallique Sm2 (Fe, Co)1#7 est effectuée sur des échantillons massifs et des poudres à l'aide de la diffraction des rayons X, des microscopies optique et électronique à balayage et d'une microsonde électronique. Les échantillons massifs sont oxydés à l'air tandis que les poudres sont traitées sous oxygène pur. Nous avons observé la formation de trois couches d'oxydes successives, différentes par leur aspect et leur composition. La cinétique d'oxydation est déterminée à partir de la croissance des couches sur les échantillons massifs et des mécanismes d'oxydation sont envisagés. La cinétique d'oxydation des poudres est étudiée par thermogravimétrie sur des courbes isothermes. Une loi empirique de cinétique d'oxydation globale est utilisée pour ajuster les courbes expérimentales.

Submitted by Rodrigo Martins Cruz (rodrigo.cruz@ufvjm.edu.br) on 2015-02-19T13:34:45Z No. of bitstreams: 5 fer.pdf: 3531496 bytes, checksum: da51c0e714843d62cd73ad67737d85b2 (MD5) license_url: 52 bytes, checksum: 3d480ae6c91e310daba2020f8787d6f9 (MD5) license_text: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) license_rdf: 23898 bytes, checksum: e363e809996cf46ada20da1accfcd9c7 (MD5) license.txt: 2110 bytes, checksum: b4c884761e4c6c296ab2179d378436d4 (MD5)
Approved for entry into archive by Rodrigo Martins Cruz (rodrigo.cruz@ufvjm.edu.br) on 2015-02-20T10:58:08Z (GMT) No. of bitstreams: 5 fer.pdf: 3531496 bytes, checksum: da51c0e714843d62cd73ad67737d85b2 (MD5) license_url: 52 bytes, checksum: 3d480ae6c91e310daba2020f8787d6f9 (MD5) license_text: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) license_rdf: 23898 bytes, checksum: e363e809996cf46ada20da1accfcd9c7 (MD5) license.txt: 2110 bytes, checksum: b4c884761e4c6c296ab2179d378436d4 (MD5)
Made available in DSpace on 2015-02-20T10:58:09Z (GMT). No. of bitstreams: 5 fer.pdf: 3531496 bytes, checksum: da51c0e714843d62cd73ad67737d85b2 (MD5) license_url: 52 bytes, checksum: 3d480ae6c91e310daba2020f8787d6f9 (MD5) license_text: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) license_rdf: 23898 bytes, checksum: e363e809996cf46ada20da1accfcd9c7 (MD5) license.txt: 2110 bytes, checksum: b4c884761e4c6c296ab2179d378436d4 (MD5) Previous issue date: 2013-02-20
L-Dopa ? convertida em dopamina no c?rebro e continua a ser a droga mais amplamente prescrita no tratamento da doen?a de Parkinson. Um sens?vel e seletivo sensor foi desenvolvido para a determina??o voltam?trica de L-Dopa em formula??es farmac?uticas usando um Eletrodo de Grafite Pirol?tico de Plano Basal (EGPPB) modificado com cloro(piridil)bis(dimetilglioximato) de cobalto (III) (Co(DMG)2ClPy), um modelo sint?tico da vitamina B12, adsorvido em Nanotubos de Carbono de Paredes M?ltiplas (NCPM), o qual foi denominado EGPPB/NCPM/Co(DMG)2ClPy. Microscopia Eletr?nica de Varredura e Espectroscopia no Infravermelho por Transformada de Fourier foram utilizadas para caracterizar os materiais. A oxida??o de L-Dopa utilizando o EGPPB/NCPM/Co(DMG)2ClPy foi investigada por Voltametria C?clica, Amperometria, Voltametria de Pulso Diferencial e Voltametria de Onda Quadrada. O eletrodo modificado apresentou uma excelente atividade catal?tica para a oxida??o de L-Dopa em 180 mV vs. Ag/AgCl. Os par?metros que influenciam a resposta do eletrodo foram investigados. As condi??es ?timas foram encontradas para o eletrodo modificado com 100 ?mol L-1 de Co(DMG)2ClPy, 2 mg mL-1 de NCPM, em solu??o tamp?o fosfato na concentra??o de 0,2 mol L-1 (pH 7,4). O n?mero de el?trons envolvidos na oxida??o de L-Dopa foi igual a dois. As correntes de pico voltam?tricas apresentaram uma resposta linear para a concentra??o de L-Dopa no intervalo de 3 a 100 ?mol L-1 para n = 12 (R = 0,9992), com sensibilidade, limite de detec??o e limite de quantifica??o iguais a 4,43 ?A cm-2/?mol L-1, 0,86 e 2,87 ?mol L-1, respectivamente. O Desvio Padr?o Relativo para 10 determina??es de solu??o 50 ?mol L-1 de L-Dopa foi de 1,63%. Os resultados obtidos para a determina??o de L-Dopa em formula??es farmac?uticas est?o de acordo com o m?todo de compara??o oficial. Estudos de adi??o e recupera??o do analito foram realizados para avaliar a exatid?o do m?todo e verificou-se que foi poss?vel uma porcentagem de recupera??o entre 99,4 e 101,5% para a L-Dopa. Portanto, o sensor desenvolvido pode ser aplicado com sucesso para a determina??o do referido f?rmaco em medicamentos.
Disserta??o (Mestrado) ? Programa de P?s-Gradua??o em Qu?mica, Universidade Federal dos Vales do Jequitinhonha e Mucuri, 2011.
ABSTRACT L-Dopa is converted to dopamine in the brain and remains the most widely prescribed drug in the treatment of Parkinson's disease. A sensitive and selective method was developed for the voltammetric determination of L-Dopa in pharmaceutical formulations using a Basal Plane Pyrolytic Graphite Electrode (BPPGE) modified with chloro(pyridil)bis(dimethylglyoximato)cobalt(III) (Co(DMG)2ClPy), synthetic model of vitamin B12, absorbed on Multi-walled Carbon Nanotube (MWCNT), denominated MWCNT/Co(DMG)2ClPy/BPPGE. Scanning Electron Microscopy and Fourier Transform Infrared Spectroscopy were used to characterize the materials. The oxidation of L-Dopa using the MWCNT/Co(DMG)2ClPy/BPPGE was investigated by Cyclic Voltammetry, Amperometry, Differential Pulse Voltammetry and Square Wave Voltammetry. The modified electrode showed an excellent catalytic activity for L-Dopa oxidation at 180 mV vs. Ag/AgCl. The parameters that influence on the electrode response were investigated. The optimum conditions were found to the modified electrode with 100 ?mol L-1 Co(DMG)2ClPy, 2 mg mL-1 MWCNT, in 0.2 mol L-1 phosphate buffer solution (pH 7.4). The number of electrons involved in L-Dopa oxidation was two. Voltammetric peak currents showed a linear response for L-Dopa concentration in the range from 3 up to 100 ?mol L-1 for n = 12 (R = 0.9992), with a sensitivity, detection limit and quantification limit of 4.43 ?A cm-2/?mol L-1, 0.86 and 2.87 ?mol L-1, respectively. The Relative Standard Deviation for 10 determinations of 50 ?mol L-1 L-Dopa was 1.63%. The results obtained for L-Dopa determination in pharmaceutical formulations was in accordance with the official method of comparison. Studies of addition and recovery of the analyte were carried out to evaluate the error of the method and was verified a recovery percentage between 99.4 and 101.5% for L-Dopa. Therefore the sensor developed can be applied successfully to the determination of this drug in pharmaceuticals formulations.

Three cobalt-based oxides operating at the Co(III)/Co(II) redox couple have been investigated as potential cathode materials for the intermediate-temperature solid oxide fuel cells (IT-SOFCs). X-ray absorption spectroscopy measurements confirmed that both the oxygen-deficient perovskite Sr[subscript 0.7]Y[subscript 0.3]CoO[subscript 2.65-delta] (SYCO) and the double-perovskite Ba₂[Co][Bi[subscript x]Sc[subscript 0.2]Co[subscript 1.8-x]][subscript O6-delta] (x = 0.1 and 0.2) (BBSC) contain high-spin Co(III) in the bulk at room temperature and thus avoid the thermally driven spin-state crossover of the Co(III) ions usually observed in other cobalt-containing perovskite oxides. Electrochemical characterizations demonstrated that both cobalt oxides operating on the Co(III)/Co(II) redox couple are equally catalytically active for the oxygen reduction reaction as those operating on the Co(IV)/Co(III) redox couple. With an LSGM electrolyte-supported single test cell and NiO+GDC as anode, the maximum power densities Pmax at 800 ºC reach 927 and 1180 mW·cm⁻² for SYCO and BBSC cathodes, respectively. The oxygen-deficient perovskites Sr[subscript 1-x]R[subscript x]CoO[subscript 3-delta] (R = Eu-Ho, Y, x [approximately equal] 0.3) are identified as a new class of cathode materials for IT-SOFCs in this dissertation. On the other hand, the layered Ba2Co9O14 (BCO) containing the low-spin Co(III) at room temperature undergoes a thermally driven spin-state crossover, which has prevented it from being evaluated as the cathode of IT-SOFCs. This problem was overcome by fabrication of a 50-50 wt.% BCO + SDC (Sm[subscript 0.2]Ce[subscript 0.8]O[subscript 1.9]) composite cathode. The addition of SDC not only improved the adhesion to the electrolyte, but also enhanced the electrocatalytic activity for the oxygen reduction reaction. The composite cathode delivers a nearly stable P[subscript max] of ~450 mW·cm-2 at 800 °C in an LSGM electrolyte-supported single test cell. In addition, the electrochemical lithium intercalation process in the monoclinic Nb12O29 was studied with a Li/Nb₁₂O₂₉ half-cell, and the results showed that it can reversibly incorporate a relatively large amount of Li-ions in the voltage window of 2.5-1.0 V at a slow discharge/charge rate while retaining structural integrity. Compared with that of the bare Nb₁₂O₂₉, samples with carbon coating show an improved rate capability. The lithium insertion mechanism into Nb₁₂O₂₉ has also been discussed in terms of sites available to the lithium ions
text

Research Doctorate - Doctor of Philosophy (PhD)
Ammonium nitrate remains a widely utilise ingredient in civil explosives, and fertilizers around the world. In civil explosive application, ammonium nitrate (AN) serves as a feedstock for making emulsion explosives as well as ammonium nitrate and fuel oil (ANFO) explosives, both commonly applied in open-cut mining operations. In recent years in Australia, demand for ammonium nitrate has increased significantly due to mining activities, the so called mining boom. However, the use of ammonium nitrate based explosives in civil applications may release orange clouds of nitrogen oxides under some condition of use and explosive formulations. Although AN-based explosives are formulated under stoichiometric compositions to produce only H₂O, CO₂, and N₂, in practice, CO, NO, and NO₂ gases are released when the formulation deviates from ideal conditions. Formation of carbon monoxide and nitrogen oxides poses risks to both people and the environment. In Australia, emissions of NOₓ (NO and NO₂) during blasting in mining operations have come under intense scrutiny by regulatory bodies and concerned citizens, as such emissions pose environmental and health risks; in particular, when orange clouds, characteristic of high levels of NO₂ and NO, do not dissipate rapidly and drift into populated areas surrounding the mines. Thus, there is a great interest in industries to find practical solutions to remedy the problems of NOₓ emissions from blasting of ammonium nitrate based explosives.

Thesis ( M.Sc)--University of the Witwatersrand, Faculty of Science, 2003
Initial investigations at Mintek, into the addition of gold to commercial hopcalite (CuxMnyOz), showed that it improved the activity of hopcalite. So this study was initially focused on investigating Aulhopcalite catalysts further. Also, since according to literature, MnxOy has catalytic potential, the study of AulMnxOy catalysts was included. Au/hopcalite and Aul/nxOy catalysts were made by means of deposition-precipitation, colloidal gold deposition and co-precipitation. Only one catalyst-type was highly active at room temperature - the co-precipitated Au/MnxOy catalysts. The optimised co-precipitated Au/MnxOy catalysts were more active than all the other catalysts by at least an order of magnitude. So the study focus changed, to make the optimisation of AulMnxOy catalysts a priority. Cerium is a well-known promoter on MnxOy catalysts, and so was also added to the co-precipitated Au/MnxOy catalysts. However, even small amounts of cerium had an adverse effect on the catalysts' activities. The compaction and crushing of a co-precipitated Au/MnxOy catalyst to obtain granules of larger particle size than the powders, was also carried out. The activities and surface areas of the catalysts were found to be comparable. This augers well for industrial purposes, since the use of powdered catalysts in industry is not viable.

碩士
國立臺北科技大學
材料科學與工程研究所
99
The IT-SOFC electrolytes, co-doped bismuth oxide based, were prepared by the solid state reaction. Due to the high oxide ionic conductivity of the bismuth oxide, it is a good material for application in SOFC electrolyte. The Bi0.76Y0.24-xGdxO1.5 (x=0.02~0.10), Bi0.76Y0.24-xNbxO1.5+δ (x=0.02~0.10), Bi0.76Y0.24-xScxO1.5 (x=0.02~0.10), Bi0.76Y0.24-xZr2xO1.5-δ (x=0.02~0.10) and Bi0.76Y0.24-xBa2xO1.5-δ (x=0.02~0.10) were prepared and sintered at 825oC~1025oC for 2 hours, respectively. The microstructure, crystal structure and ionic conductivity of the sintered specimens were analyzed by using SEM, XRD and DC resistance meters, respectively. The results show that most of the crystal structure of the sintered specimens are cubic.The best conductivity of these specimens is Bi0.76Y0.14Zrx0.10O1.5+δ with 1 S/cm at 800oC.

碩士
國立成功大學
微電子工程研究所
107
The increasing awareness of the environmental pollutions and industrial onsite safety demands have prompted the development of sensors in full thrust. The gas sensing properties of metal-oxide material are closely related to their composition, crystalline size, and surface morphology. Due to its small particle size and large surface area, the iron oxide nanoparticles greatly enhance the sensitivity of the sensor and has a high application value. In this experiment, the co-precipitation is utilized to synthesize two different types of iron oxide nanoparticles, namely, both magnetite (Fe3O4) and hematite (α-Fe2O3) are formulated for subsequent gas measurements and fundamental material characteristics evaluations by appropriately changing the relevant process parameters. The co-precipitation method is regarded as an economic way to synthesize iron oxide with the advantages of a low-cost, handling safety, and production in great quantity. The results show that the magnetite (Fe3O4) gas sensor annealed by muffle furnace has a high response to the detection of nitrogen dioxide, while the hematite (α-Fe2O3) gas sensor annealed by the same muffle furnace, on the other hand, has a high detecting selectivity towards ethanol. Consequently, comparatively better gas measurement results are obtained compared with those found using the rapid thermal annealing (RTA) furnace. For metal oxide semiconductor materials, the appropriate annealing method must be adopted to optimize the response of the gas sensor and also to choose the right material to perform the most effective detection of a particular gas.

碩士
國防醫學院
藥學研究所
104
Background and objectives. Nitric oxide (NO) is well known to regulate several important processes of physiology and pathology, and extensive research has been focused on treating diseases with therapeutic NO delivery. However the hyperreactivity and instability of NO makes it difficult to deliver. Previously, we have developed a convenient technique to produce NO-donating silica nanoparticles (S-NO-polysilsesquioxane platform) by a one-step nanoprecipitation approach with a single silica source, 3-mercaptopropyl trimethoxysilane (MPTMS). Furthermore, we have employed the same technique to prepare NO/doxorubicin (DOX)-co-delivering silica nanoparticles (namely, SNODOX). Interestingly, in the previous study we found that the fluorescence of SNODOX is photosensitive: the fluorescence intensity of SNODOX in solution increased upon visible-light exposure. Therefore, the major goal of the present study was to further explore the photophysicochemical properties of SNODOX and similar nanoparticles loading with various fluorescent comounds. Methods. First, the mechanism underlying light-mediated fluorescence enhancement of SNODOX particle dispersions were investigated by determining the following: DOX release, spectroscopic characteristics of DOX in molecular and particle solutions, the role of S-nitroso (SNO) linkage on DOX fluorescence, solvent accessibility upon light irradiation within particles, photobleaching effect, and the effect of light exposure on the cytotoxicity of SNODOX. Second, the same approach to prepare SNODOX was extended to encapsulate various fluorescenct drugs/theranostics, including mitoxantrone, pyrene, fluorescein and rhodamine 6G (R6G), and the photochemical properties of the resulting nanoparticles were evaluated. Third, the as-prepared SNOR6G particles were further studied for their potential photobiological application. Results. The present study reproduces our previous observations that fluorescence intensity of DOX in SNODOX aquesous dispersions increases under light irradiation. The fluorescence intensity increases maximally 10-fold after about 24 hr of light irradiation (13W, fluorescent lamp, irradiation distance 14 cm). The increase of fluorescence intensity was not due to the release of free DOX in solution; but it was correlated with light- and Hg2+-induced NO release. Moreover, after extensive light treatment to reach maximal fluorescence, the fluorescence intensity of SNODOX remained unchanged over time and showed no sign of photobleaching. Remarkably, light treatment of SNODOX led to more difficult extraction of entrapped DOX by organic solvents, suggesting that unknown intraparticle interactions has been altered by light. When R6G was entrapped in the SNO silica particles, the resulting SNOR6G nanoparticles showed remarkably higher photosensitivity, with a maximum fluorescence increase of 100-fold. Notably, the R6G molecules is stably entrapped in particles with only < 1 % release after 24 hr; and consistently SNOR6G showed significantly lower cytotoxicity than free R6G, which can be a suitable candidate for cell imaging. Conclusions. The S-NO-polysilsesquioxane platform can be utilized for preparing fluorescent nano-theranostics, with the advantages of ease of preparation, high molecular loading efficiency, and capable of post-synthesis fluorescence re-activation by light.

碩士
國立清華大學
化學工程學系
104
We report a systematic study of gas-phase controlled synthesis of copper oxides-based hybrid nanoparticles for catalytic CO oxidation. The complementary physical, spectroscopic and microscopic analyses were conducted to obtain a better understanding of the material properties, including particle size, crystallinity, elemental composition, and oxidation state. Results showed that the synthesized nanoparticles exhibited highly durable catalytic activity and stability, also the particle size, crystallite size, and chemical composition were tunable by choosing suitable chemical compositions of precursors and temperatures. The crystallite size of CuO influenced the reducibility of CuO by CO and the subsequent catalytic activity of CO oxidation. The hybridization process of CeO2 and CuO induces the formation of new active sites at the Cu-Ce-O interface, which enhances reproducibility of CuO and the catalytic activity. However, the reproducibility of CuO and catalytic activity were considerably decreased when CeO2 was replaced with the inert Al2O3. This work describes a prototype method to form highly pure and well-controlled hybrid nanocatalysts, which can be used to establish the correlation of material properties versus reducibility and subsequent catalytic activity for energy and environmental applications.

In recent times, as regulations and legislations for exhaust treatment have become more stringent, a major concern in the arena of environmental catalysis is to find new efficient and economical exhaust treatment catalysts. Chapter 1 is a review of the current status of various NOx abatement techniques and understanding the role of “auto-exhaust catalysts” involved therein. Chapter 2 presents the studies on synthesis of ionically substituted precious metal ions like Pd2+, Pt2+ and Rh3+ in CeO2 matrix and their comparative three-way catalytic performances for NO reduction by CO, as well as CO and hydrocarbon oxidation. Ce0.98Pd0.02O2- showed better catalytic activity than ionically dispersed Pt or Rh in CeO2. The study in Chapter 3 aims at synthesizing 1 atom% Pd2+ ion in TiO2 in the form of Ti0.99Pd0.01O2- with oxide ion vacancy. A bi-functional reaction mechanism for CO oxidation by O2 and NO reduction by CO was proposed. For NO reduction in presence of CO, the model based on competitive adsorption of NO and CO on Pd2+, NO chemisorption and dissociation on oxide ion vacancy fits the experimental data. The rate parameters obtained from the model indicates that the reactions are much faster over this catalyst compared to other catalysts reported in the literature. In Chapter 4 we present catalytic reduction of NO by H2 over precious metal substituted TiO2 (Ti0.99M0.01O2-, where M = Ru, Rh, Pd, Pt) catalysts. The rate of NO reduction by H2 depends on the reducibility of the catalysts. Chapter 5 presents the studies on reduction of NO by NH3 in presence of excess oxygen. 10 atom % of first row transition metal ions (Ti0.9M0.1O2-, where M = Cr, Mn, Fe, Co and Cu) were substituted in anatase TiO2 and TPD study showed that the Lewis and Bronsted acid sites are adsorption sites for NH3, whereas NO is found to dissociatively chemisorbed in oxide ion vacancies. The mechanism of the low temperature catalytic activity of the SCR and the selectivity of the products were studied to understand the mechanism by studying the by-reactions like ammonia oxidation by oxygen. A new catalyst Ti0.9Mn0.05Fe0.05O2- has shown low temperature activity with a broad SCR window from 200 to 400 °C and more selectivity than commercial vanadium-oxides catalysts. We attempted NO dissociation by a photochemical route with remarkable success. In Chapter 6 we report room temperature photocatalytic activity of Ti0.99Pd0.01O2- for NO reduction and CO oxidation by creating redox adsorption sites and utilizing oxide ion vacancy in the catalyst. The reduction of NO is carried out both in the presence and in the absence of CO. Despite competitive adsorption of NO and CO on the Pd2+ sites, the rate of reduction of NO is two orders of magnitude higher than unsubstituted TiO2. High rates of photo-oxidation of CO with O2 over Ti0.99Pd0.01O2- were observed at room temperature. In Chapter 7 the results are summarized and critical issues are addressed. Novel idea in this thesis was to see if both noble metal ions and base metal ions substituted in TiO2 and CeO2 reducible supports can act as better active sites than the corresponding metal atoms in their zero valent state.

In recent times, as regulations and legislations for exhaust treatment have become more stringent, a major concern in the arena of environmental catalysis is to find new efficient and economical exhaust treatment catalysts. Chapter 1 is a review of the current status of various NOx abatement techniques and understanding the role of “auto-exhaust catalysts” involved therein. Chapter 2 presents the studies on synthesis of ionically substituted precious metal ions like Pd2+, Pt2+ and Rh3+ in CeO2 matrix and their comparative three-way catalytic performances for NO reduction by CO, as well as CO and hydrocarbon oxidation. Ce0.98Pd0.02O2- showed better catalytic activity than ionically dispersed Pt or Rh in CeO2. The study in Chapter 3 aims at synthesizing 1 atom% Pd2+ ion in TiO2 in the form of Ti0.99Pd0.01O2- with oxide ion vacancy. A bi-functional reaction mechanism for CO oxidation by O2 and NO reduction by CO was proposed. For NO reduction in presence of CO, the model based on competitive adsorption of NO and CO on Pd2+, NO chemisorption and dissociation on oxide ion vacancy fits the experimental data. The rate parameters obtained from the model indicates that the reactions are much faster over this catalyst compared to other catalysts reported in the literature. In Chapter 4 we present catalytic reduction of NO by H2 over precious metal substituted TiO2 (Ti0.99M0.01O2-, where M = Ru, Rh, Pd, Pt) catalysts. The rate of NO reduction by H2 depends on the reducibility of the catalysts. Chapter 5 presents the studies on reduction of NO by NH3 in presence of excess oxygen. 10 atom % of first row transition metal ions (Ti0.9M0.1O2-, where M = Cr, Mn, Fe, Co and Cu) were substituted in anatase TiO2 and TPD study showed that the Lewis and Bronsted acid sites are adsorption sites for NH3, whereas NO is found to dissociatively chemisorbed in oxide ion vacancies. The mechanism of the low temperature catalytic activity of the SCR and the selectivity of the products were studied to understand the mechanism by studying the by-reactions like ammonia oxidation by oxygen. A new catalyst Ti0.9Mn0.05Fe0.05O2- has shown low temperature activity with a broad SCR window from 200 to 400 °C and more selectivity than commercial vanadium-oxides catalysts. We attempted NO dissociation by a photochemical route with remarkable success. In Chapter 6 we report room temperature photocatalytic activity of Ti0.99Pd0.01O2- for NO reduction and CO oxidation by creating redox adsorption sites and utilizing oxide ion vacancy in the catalyst. The reduction of NO is carried out both in the presence and in the absence of CO. Despite competitive adsorption of NO and CO on the Pd2+ sites, the rate of reduction of NO is two orders of magnitude higher than unsubstituted TiO2. High rates of photo-oxidation of CO with O2 over Ti0.99Pd0.01O2- were observed at room temperature. In Chapter 7 the results are summarized and critical issues are addressed. Novel idea in this thesis was to see if both noble metal ions and base metal ions substituted in TiO2 and CeO2 reducible supports can act as better active sites than the corresponding metal atoms in their zero valent state.

碩士
國立臺灣科技大學
機械工程系
89
In this paper, we study co-fire behavior and interaction between dielectric BaTiO3-based material and oxide electrode, LaxSr1-xMnO3, (LSMO). Through comparison of ferroelectric properties and characteristic capacitor, the availability will be estimated for oxide electrode replaced with metal electrode. Two BaTiO3 materials were used. One is commercial BaTiO3 powder (COM) and the other is Ba0.88Ca0.12Ti0.85Zr0.15O3,(BCTZ) prepared by a conventional oxide-mixing method. La0.7Sr0.3MnO3, (LSM73) and La0.5Sr0.5MnO3, (LSM55) were employed as the electrode material. Transformation behavior of materials was determined by differential scanning calorimeter (DSC). The firing profile was established utilizing a thermal mechanical analyzer (TMA). Finally, we fabricated electrode / dielectric / electrode tri-layer green samples, and then sintered them in the ambient atmosphere. Gain-phase analyzer, dc four-probe resistance tester and scanning electron microscopy (SEM) were used to measure the electric properties and morphology of specimens. Moreover, we analyzed the diffusion behavior of atomic species by energy dispersive x-ray spectroscopy (EDX), X-ray diffractometry and electron microprobe analysis (EMPA). Results of TMA and SEM analyses show that co-fired samples exhibit delamination or microcracks as a result of mismatch of firing profiles between BCTZ or COM and oxide electrode LSM55. Therefore, we fabricated the co-fired samples using LSM73. EPMA results and electric property measurements show that: (1)In the co-fired sample of BCTZ with LSM73 electrode, calcium and titanium atoms of BCTZ diffuse easily to LSM73 and form a new interphase. The interphase possesses a function that can resist interdiffusion between elements of BCTZ and LSM73, but the electric properties of specimens are poorer than those using the silver electrode. The elements of BCTZ diffuse toward LSM73 electrode in the experiments. (2)In the co-fired sample of COM with LSM73 electrode, the diffusion distance was farther than that of BCTZ with LSM73 electrode. The elements of COM and LSM73 diffused into each other, and the electric properties were the same as those using the silver electrode. In summary, fabricating multilayer ceramic capacitors (MLCCs) utilizing an oxide electrode works successfully; however, elemental diffusion between the dielectric material and the oxide electrode influence characteristics of the component seriously. This process was cheaper than those using the conventional Ag-Pd electrode and simpler than those using the nickel (base metal) electrode. In addition, MLCCs using oxide electrodes possess lower stress and higher adhesion strength between the interface of dielectrics and electrodes.

碩士
國立成功大學
化學工程學系碩博士班
101
In this study, we used PEDGE, DGEBA and D2000 by cross-linking to synthesis the copolymer –poly(ethylene oxide)-co-poly(propylene oxide) (P(EO-co-PO)). Immersing the polymer film into the organic electrolyte for 24 hours, then we got the gel polymer electrolyte (GPE). Took this GPE film to assemble batteries and test its performance. Compare the difference between GPE and the organic liquid electrolyte battery (LE) , find out the advantages of GPE. Compare to LE, the proposed GPE has higher ionic conductivity (3.8210-3 S cm-1 at 30 °C) and a wider electrochemical voltage range (5V). Besides, P(EO-co-PO) copolymer equipped better Lithium ion dissociation ability and higher transfer number (0.7). This high GPE transference number decreases electrode polarization caused by anion accumulation and suppresses the concentration gradient to facilitate lithium ion transport. That made the electrolyte-electrode surface of GPE more stable than LE with lower resistance. Therefore, the performance can be better at higher C-rate charge-discharge test and long-term stability. For battery performance test, we use LiFePO4-cathode and Graphite-anode to assemble the full-cell and compare the difference between GPE and LE. At lower C-rates, the discharge capacity is similar and the value is about 125mAh g-1. When discharge rate is higher than 10 C-rate, the performance decrease dramatically in LE full-cell, while GPE full-cell maintain the capacity even at 17C-rate. For long-term test, we conducted charge-discharge measurement at 1C-rate for 450 cycles. After 450 cycles the capacity retention maintained at ca. 77%. It’s better than the LE full-cell which kept only ca. 44%. Due to the bad performance at higher C-rates by using Graphite-anode, in this study, we also developed hydrothermal method to synthesis TiO2 nanotube. TiO2 is nontoxic, high chemical stability and low price. Moreover, the nanotube structure can help to catch the electrolyte into the tube, increase the electrolyte-electrode contact surface and decrease the distance of lithium ion diffusion. And then decrease the diffusion resistance, that resulted in a discharge capacity 70 mAh g-1 at 60C-rate.

博士
國立臺灣海洋大學
輪機工程學系
105
Solid oxide fuel cell (SOFC) converts chemical energy to electrical energy directly, it is different from Carnot cyclic internal combustion engine needing multiple mechanical processes. The SOFC components compose ceramic structures including electrolyte, cathode and anode. The efficiency of SOFC is about 55% larger than trandtional internal combustion engine. This dissertation is focused on investigating materials of intermediate-temperature solid oxide fuel cell (ITSOFC) which is operated among 500~800 oC. The oxygen ions conducting multiple elements doped ceria (LSBC) is utilized as electrolyte for cell support. The solid state oxides prepared electrolyte was densified by conventional high temprature sintering. The conductivity arrives to 0.01 S/cm at 650 oC in this study. The AC impedances of grains and grain boundaries (GB) in electrolyte and of metallic electrode indicate the most important impedance of grain boundaries. LSBC electrolyte has 95% relative density after 1400 oC sintering. The GB impedance almost disappears when the operation temperature higher than 550 oC. This approves the LSBC to be an electrolyte of intermediate temperature operation. The GB activation energy is higher than grain activation energy in various sintering conditions. The GB activation energy is hardly changed as 0.90 eV when the sintering temperature over 1400 oC. The gain activation energy is 0.84 eV. The activation energy of grain affects oxygen vacancies conducting behavior. The formation enthalpy (Ha) and migration enthalpy (Hm) of oxygen vacancy were calculated by Ln(T)-(1/T) data. The Ha in grains is about 0.90 V. The Hm in grains is about 0.62 V. Such enough low value of (Ha + Hm) promotes high oxygen ions conducting efficiency. Barium strontium ferrate (Ba0.5Sr0.5FeO3, BSF) cathode material is almost obtained pure pseudo-cubic phase while sintered at 1150 oC. The BSF material is sensivitive to moisture and carbon dioxide environment. It results in structure instability. The core-shell cathode of BSF-x mol%Ce prepared by semi-organic method can solve the above mentioned problems. Ce-coated BSF obtained stable Fe-O bonding. The FTIR analyses prove Ce-coating to avoid generation of hydrous iron oxides. When Ce-coating amount is over 10 mol%, the Ce-contained second phase will be segregated. The transition temperature (Tc ~ 510 C) measured in air atmosphere that represents the transition of electronic to ionic conduction shifts to high temperature with high Ce-coatings. The best DC conductivity is obtained by BSF-15 mol%Ce. The thermal expansion coefficient (TEC) of core-shell BSF over 15 mol% Ce-coatings matches with LSBC. When the Ce-coating is higher than 15 mol%, the interface impedance of BSF/LSBC and diffusion impedance in cathode can be reduced according to the AC-impedance analyses. For 1150 oC co-fired half-cell of BSF-20 mol%Ce/LSBC/Pt operated at 750 oC, the open circuit voltage of half-cell is about 0.8 V and the peak power densty is about 250 mW/cm2. The semi-organic method prepared core-shell structure of La0.3Sr0.7TiO3 (LST)-x mol%Ce (x=0.75, 1.5, 3, 6, 12) either sintered in oxidation or reduction atmosphere, the Ce component diffuses into the core lattice of LST. The more sintering temperature is higher, the more Ce diffuses. Also, high content of Ce in LST is obtained in reduction sintering. The core-shell anode sintered at 1300 C and 1500 C analyzed by Raman and XPS shows that the Ce valences in LST lattice are Ce4+ by air oxidation sintering and Ce3+ by activated carbon reduction sintering. The oxidation sintered LST-x mol%Ce core-shell structure exhibits crystallized CeO2 shell and crystallized LST core with two intimately core-shell interface. However, there are three regions in redcuction sintered core-shell LST-x mol%Ce structure including crystallized CeO2 layer, amorphous zone and crystallized LST core. The conductivity of core-shell anode increases whether oxidation sintering or reduction sintering. The lowest impedance is obtained for LST-3 mol%Ce after reduction treatment. The 1300 oC co-fired half-cell of LST-x mol%Ce/LSBC/Pt has 3.5 times higher peak power density than half-cell without core-shell anode. The best peak power density is achieved by BSF-20 mol%Ce/LSBC/LST-3 mol%Ce full ceramic cell. The cathode polarization impedance is more imprtant than anode contribution investigated by AC impedance analyses. The 500 m thick LSBC electrolyte suppoted cell with core-shell anode and cathode improves interface sintering mismatching, three phase boundary extension and gas diffusion reaction. LST-3 mol%Ce/LSBC/BSF-20 mol%Ce single cell achieves open circuit voltage of 0.8 V and peak power density of 355 mW/cm2 under operation temperature of 800 oC. Keywords: ceria-based electrolyte, BSF-Ce core-shell cathode, LST-Ce core-shell anode, intermediate-temperature solid oxide fuel cell (ITSOFC)

Synopsis of thesis entitled “Electrochemical and Photoelectrochemical Investigations of Co, Mn and Ir-based Catalysts for Water Splitting” by Ahamed Irshad M (SR No: 02-01-02-10-11-11-1-08823) under the supervision of Prof. N. Munichandraiah, Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore (India), for the Ph.D. degree of the Institute under the Faculty of Science. Hydrogen is considered as the fuel for future owing to its high gravimetric energy density and eco-friendly use. In addition, H2 is an important feedstock in Haber process for ammonia synthesis and petroleum refining. Although, it is the most abundant element in the universe, elemental hydrogen is not available in large quantities on the planet. Consequently, H2 must be produced from its various chemical compounds available on earth. Currently, H2 is produced in large scale from methane by a process called steam-methane reforming (SMR). This process releases huge amount of CO2 into atmosphere as the by-product causing serious environmental issues. The development of alternate clean methods to generate H2 is a key challenge for the realization of hydrogen economy. Production of H2 gas by water splitting using electricity or sunlight is known. Low cost, high natural abundance and carbon neutrality make water as the best source of hydrogen. Thermodynamically, splitting of H2O needs 237 kJ mol-1 of energy, which corresponds to 1.23 V according to the equation, ΔG = -nFE. However, commercial electrolyzers usually operate between 1.8 to 2.1 V, due to the need of large overvoltage. The high overvoltage and subsequent energy losses are mainly associated with the sluggish kinetics of oxygen evolution reaction (OER) at the anode and hydrogen evolution reaction (HER) at the cathode. The overvoltage can be considerably reduced using suitable catalysts. Hence, the design and development of stable, robust and highly active catalysts for OER and HER are essential to make water splitting efficient and economical. Attempts in the direction of preparing several novel OER and HER catalysts, physicochemical characterizations and their electrochemical or photoelectrochemical activity are described in the thesis. A comprehensive review of the literature on various types of catalysts, thermodynamics, kinetics and mechanisms of catalysis are provided in the Chapter 1 of the thesis. Chapter 2 furnishes a brief description on various experimental techniques and procedures adopted at different stages of the present studies. Chapter 3 explains the results of the studies on kinetics of deposition and stability of Nocera’s Co-phosphate (Co-Pi) catalyst using electrochemical quartz crystal microbalance (EQCM). The in-situ mass measurements during CV experiments on Au electrode confirm the deposition of Co-Pi at potential above 0.87 V vs. Ag/AgCl, 3 M KCl (Fig.1a and b). The catalyst is found to deposit via a nucleus mediated process at a rate of 1.8 ng s-1 from 0.5 mM Co2+ in 0.1 M neural phosphate solution at 1.0 V. Further studies on the potential and electrolyte dependent stability of the Co-Pi suggest that the catalyst undergoes severe corrosion at high overpotential and in non-buffer electrolytes. Current/ Fig.1 (a) Cyclic voltammograms and (b) mass variations vs. potential of Au-coated quartz crystal in 0.1 M potassium phosphate buffer solution (pH 7.0) containing 0.5 mM Co(NO3)2 Chapter 4 deals with the electrochemical deposition of a novel OER catalyst, namely, Co-acetate (Co-Ac) from a neutral acetate electrolyte containing Co2+ ions. Use of acetate solution instead of phosphate avoids the solubility limitations and helps to get thick layer of the catalyst in a short time from concentrated Co2+ solutions. In addition, the Co-Ac is found to be catalytically superior to Co-Pi (Fig. 2a). It is also observed that the Co-Ac catalyst undergoes ion exchange with electrolyte species during electrolysis in phosphate buffer solution, which results in the formation of a hybrid Co-Ac-Pi catalyst (Fig. 2b). The presence of both acetate and phosphate ions in the catalyst and their synergistic catalytic effect enhance the OER activity. Fig.2. (a) Linear sweep voltammograms of Co-Ac in (i) phosphate and (ii) acetate electrolytes, and that of Co-Pi in (iii) acetate and (iv) phosphate electrolytes. (b) SEM image showing the formation of two layers of the catalysts after electrolysis in phosphate solution. In Chapter 5, high OER activity of an electrodeposited amorphous Ir-phosphate (Ir-Pi) is investigated. The catalyst is prepared by the anodic polarization of a carbon paper electrode in neutral phosphate solution containing Ir3+ ions (Fig. 3). The Ir-Pi film deposited on the electrode has Ir and P in an approximate ratio of 1:2 with Ir in an oxidation state higher than +4. Phosphate ions play a major role for both the electrochemical deposition process and its catalytic activity towards OER. The Ir-Pi catalyst is superior to similarly deposited IrO2 and Co-Pi catalysts both in terms of onset potential and current density at any potential in the OER region. Tafel measurements and pH dependence studies identify the formation of a high energy intermediate during oxygen evolution. Fig.3. (a) Cyclic voltammograms during the Ir-Pi deposition and (b) SEM image of Ir-Pi on C. Chapter 6 is on the preparation of a composite of Mn-phosphate (MnOx-Pi) and reduced graphene oxide (rGO) and its utilization as an OER catalyst. The composite is prepared by the simultaneous electrochemical reduction of KMnO4 and graphene oxide (GO) in a phosphate solution (pH 7.0). Various analytical techniques such as TEM, XPS, Raman spectroscopy, etc. confirm the formation of a composite (Fig. 4) and electrochemical studies indicate the favourable role of rGO towards OER. Under identical conditions, MnOx-Pi-rGO gives 6.2 mA cm-2 at 2.05 V vs. RHE whereas it is only 2.9 mA cm-2 for MnOx-Pi alone. However, the catalyst is not very stable during OER which is ascribed to slow oxidation of Mn3+ in the catalyst. Fig.4. (a) Raman spectrum and (b) TEM image of MnOx-Pi-rGO. In Chapter 7, an amorphous Ni-Co-S film is prepared by a potentiodynamic deposition method using thiourea as the sulphur source. The electrodeposit is used as a catalyst for the HER in neutral phosphate solution. The composition of the catalyst and the HER activity are tuned by varying the ratio of concentrations of Ni2+ and Co2+. The bimetallic Ni-Co-S catalyst exhibits better HER activity than both Ni-S and Co-S (Fig. 5a). Under optimized deposition conditions, Ni-Co-S requires just 150 mV for the onset of HER and 10 mA cm-2 is obtained for 280 mV overpotential. The Ni-Co-S shows two different Tafel slopes, indicating two different potential dependent HER mechanisms (Fig. 5b). Presence of two different catalytic sites which contribute selectively in different potential regions is proposed. Fig.5. (a) Linear sweep voltammograms of HER at 1 mV s-1 in 1 M phosphate solutions (pH 7.4) using (i) Ni-S, (ii) Co-S and (c) Ni-Co-S. (b) Tafel plot of Ni-Co-S showing two Tafel slopes. Photoelectrochemical OER using ZnO photoanode and Co-acetate (Co-Ac) cocatalyst is studied in Chapter 8 of the thesis. Randomly oriented crystalline ZnO nanorods are prepared by the electrochemical deposition of Zn(OH)2 followed by heat treatment at 350 ºC in air. Co-Ac is then photochemically deposited onto ZnO nanorods by UV illumination in the presence of neutral acetate buffer solution containing Co2+ ions. The hybrid Co-Ac-ZnO shows higher photoactivity in comparison with bare ZnO towards PEC water oxidation (Fig. 6). Co-Ac acts as a cocatalyst and reduces the charge carrier recombination at the electrode/electrolyte interface. Fig.6. (a) Linear sweep voltammograms of ZnO under (i) dark and (ii) light conditions, and that of Co-Ac-ZnO in (iii) dark and (iv) light in 0.1 M phosphate (pH 7.0) electrolyte. Chapter 9 deals with PEC water oxidation using α-Fe2O3 photoanode and Ir-phosphate (Ir-Pi) cocatalyst. α-Fe2O3 is prepared by direct heating of Fe film in air which in turn is deposited by the electrochemical reduction of Fe2+. Thickness of the film as well as calcination temperature is carefully optimized. In order to further enhance the OER kinetics, Ir-Pi is electrochemically deposited onto α-Fe2O3. Under optimized conditions, Ir-Pi deposited α-Fe2O3 shows around 3 times higher photocurrent than that of bare α-Fe2O3 at 1.23 V vs. RHE (Fig. 7). Ir-Pi acts as a cocatalyst for OER and reduces the photogenerated charge carrier recombination. Fig.7. Photocurrent variation of α-Fe2O3 electrode at 1.23 V vs. RHE for (i) front and (ii) back side illuminations, against Ir-Pi deposition time. The thesis ends with a short summary and future prospectus of studies described in the thesis. The research work presented in the thesis is carried out by the candidate as the part of Ph.D. program. Some of the results have already been published in the literature and some manuscripts are under preparation. A list of publications is included at the end of the thesis. It is anticipated that the studies reported in the thesis will constitute a worthwhile contribution.

The primary objective of this research was to develop a new and efficient pathway for well-defined multicomponent homo/co/terpolymers of cyclic esters/ethers using an organocatalytic approach with an emphasis on the macromolecular engineering aspects of the overall synthesis. Macromolecular engineering (as discussed in the first chapter) of homo/copolymers refers to the specific tailoring of these materials for achieving an easy and reproducible synthesis that results in precise molecular characteristics, i.e. molecular weight and polydispersity, as well as specific structure and end?group choices. Precise control of these molecular characteristics will provide access to new materials that can be used for pre-targeted purposes such as biomedical applications. Among the most commonly used engineering materials are polyesters (biocompatible and biodegradable) and polyethers (biocompatible), either as homopolymers or when or copolymers with linear structures. The ability to create non-linear structures, for example stars, will open new horizons in the applications of these important polymeric materials. The second part of this thesis describes the synthesis of aliphatic polyesters, particularly polycaprolactone and polylactide, using a metal-free initiator/catalyst system. A phosphazene base (t?BuP2) was used as the catalyst for the ring-opening copolymerization of ?-aprolactone (??CL) and L,Lactide (LLA) at room temperature with a variety of protic initiators in different solvents. These studies provided important information for the design of a metal-free route toward the synthesis of polyester?based (bio) materials. The third part of the thesis describes a novel route for the one?pot synthesis of polyether-b polyester block copolymers with either a linear or a specific macromolecular architecture. Poly (styrene oxide)?b?poly(caprolactone)?b?poly(L,lactide) was prepared using this method with the goal of synthesizing poly(styrene oxide)-based materials since this styrene oxide (SO) monomer has been less investigated than other well-known epoxide monomers. The new one?pot synthesis of polyether?b?polyester block copolymers allowed a high degree of control with respect to the molecular weight and molecular weight distribution. It also eliminates the need for a multi-step process in which the first block must be isolated and purified prior to its subsequent use as a macroinitiator for the second block. It is also worth noting that this approach is based primarily on the use of organocatalyst because this class of block copolymers has greater potential in biomedical and pharmaceutical applications and because organocatalysts are believed to be less toxic than their metallic counterparts. The fourth part of the thesis describes the extension of the scope of the newly developed catalyst?switching approach in the synthesis of different macromolecular architectures, with a special focus on styrene oxide as a monomer, which had not previously been explored either as a linear copolymer with other monomers (except with EO) or with a macromolecular architecture such as block star or mikto arm star. The results detailed in Chapter 4 demonstrate the validity of extending the newly developed strategy to the synthesis of a variety of polymers with different macromolecular architectures. Since organic catalysts (phoshazene bases) have been utilized in this work for the synthesis of polyethers and polyesters with the aim of alleviating the toxic properties associated with metal-based catalysts, it was necessary to investigate the toxicity of this class of organocatalyst since, until now, no evidence has appeared of any attempt to address this issue. The objective of the work presented in the fifth part of this thesis was therefore to assess whether this class of organocatalysts are safe with respect to human health and whether their structure and concentration are dependent on an evaluation of the level of cytotoxicity or on other parameters. Both the pure catalyst and the polymers synthesized using this class of catalysts were tested using a CKK?8 assay, which is a very well?known protocol for measuring cytotoxicity.

Synopsis of thesis entitled “Electrochemical and Photoelectrochemical Investigations of Co, Mn and Ir-based Catalysts for Water Splitting” by Ahamed Irshad M (SR No: 02-01-02-10-11-11-1-08823) under the supervision of Prof. N. Munichandraiah, Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore (India), for the Ph.D. degree of the Institute under the Faculty of Science. Hydrogen is considered as the fuel for future owing to its high gravimetric energy density and eco-friendly use. In addition, H2 is an important feedstock in Haber process for ammonia synthesis and petroleum refining. Although, it is the most abundant element in the universe, elemental hydrogen is not available in large quantities on the planet. Consequently, H2 must be produced from its various chemical compounds available on earth. Currently, H2 is produced in large scale from methane by a process called steam-methane reforming (SMR). This process releases huge amount of CO2 into atmosphere as the by-product causing serious environmental issues. The development of alternate clean methods to generate H2 is a key challenge for the realization of hydrogen economy. Production of H2 gas by water splitting using electricity or sunlight is known. Low cost, high natural abundance and carbon neutrality make water as the best source of hydrogen. Thermodynamically, splitting of H2O needs 237 kJ mol-1 of energy, which corresponds to 1.23 V according to the equation, ΔG = -nFE. However, commercial electrolyzers usually operate between 1.8 to 2.1 V, due to the need of large overvoltage. The high overvoltage and subsequent energy losses are mainly associated with the sluggish kinetics of oxygen evolution reaction (OER) at the anode and hydrogen evolution reaction (HER) at the cathode. The overvoltage can be considerably reduced using suitable catalysts. Hence, the design and development of stable, robust and highly active catalysts for OER and HER are essential to make water splitting efficient and economical. Attempts in the direction of preparing several novel OER and HER catalysts, physicochemical characterizations and their electrochemical or photoelectrochemical activity are described in the thesis. A comprehensive review of the literature on various types of catalysts, thermodynamics, kinetics and mechanisms of catalysis are provided in the Chapter 1 of the thesis. Chapter 2 furnishes a brief description on various experimental techniques and procedures adopted at different stages of the present studies. Chapter 3 explains the results of the studies on kinetics of deposition and stability of Nocera’s Co-phosphate (Co-Pi) catalyst using electrochemical quartz crystal microbalance (EQCM). The in-situ mass measurements during CV experiments on Au electrode confirm the deposition of Co-Pi at potential above 0.87 V vs. Ag/AgCl, 3 M KCl (Fig.1a and b). The catalyst is found to deposit via a nucleus mediated process at a rate of 1.8 ng s-1 from 0.5 mM Co2+ in 0.1 M neural phosphate solution at 1.0 V. Further studies on the potential and electrolyte dependent stability of the Co-Pi suggest that the catalyst undergoes severe corrosion at high overpotential and in non-buffer electrolytes. Current/ Fig.1 (a) Cyclic voltammograms and (b) mass variations vs. potential of Au-coated quartz crystal in 0.1 M potassium phosphate buffer solution (pH 7.0) containing 0.5 mM Co(NO3)2 Chapter 4 deals with the electrochemical deposition of a novel OER catalyst, namely, Co-acetate (Co-Ac) from a neutral acetate electrolyte containing Co2+ ions. Use of acetate solution instead of phosphate avoids the solubility limitations and helps to get thick layer of the catalyst in a short time from concentrated Co2+ solutions. In addition, the Co-Ac is found to be catalytically superior to Co-Pi (Fig. 2a). It is also observed that the Co-Ac catalyst undergoes ion exchange with electrolyte species during electrolysis in phosphate buffer solution, which results in the formation of a hybrid Co-Ac-Pi catalyst (Fig. 2b). The presence of both acetate and phosphate ions in the catalyst and their synergistic catalytic effect enhance the OER activity. Fig.2. (a) Linear sweep voltammograms of Co-Ac in (i) phosphate and (ii) acetate electrolytes, and that of Co-Pi in (iii) acetate and (iv) phosphate electrolytes. (b) SEM image showing the formation of two layers of the catalysts after electrolysis in phosphate solution. In Chapter 5, high OER activity of an electrodeposited amorphous Ir-phosphate (Ir-Pi) is investigated. The catalyst is prepared by the anodic polarization of a carbon paper electrode in neutral phosphate solution containing Ir3+ ions (Fig. 3). The Ir-Pi film deposited on the electrode has Ir and P in an approximate ratio of 1:2 with Ir in an oxidation state higher than +4. Phosphate ions play a major role for both the electrochemical deposition process and its catalytic activity towards OER. The Ir-Pi catalyst is superior to similarly deposited IrO2 and Co-Pi catalysts both in terms of onset potential and current density at any potential in the OER region. Tafel measurements and pH dependence studies identify the formation of a high energy intermediate during oxygen evolution. Fig.3. (a) Cyclic voltammograms during the Ir-Pi deposition and (b) SEM image of Ir-Pi on C. Chapter 6 is on the preparation of a composite of Mn-phosphate (MnOx-Pi) and reduced graphene oxide (rGO) and its utilization as an OER catalyst. The composite is prepared by the simultaneous electrochemical reduction of KMnO4 and graphene oxide (GO) in a phosphate solution (pH 7.0). Various analytical techniques such as TEM, XPS, Raman spectroscopy, etc. confirm the formation of a composite (Fig. 4) and electrochemical studies indicate the favourable role of rGO towards OER. Under identical conditions, MnOx-Pi-rGO gives 6.2 mA cm-2 at 2.05 V vs. RHE whereas it is only 2.9 mA cm-2 for MnOx-Pi alone. However, the catalyst is not very stable during OER which is ascribed to slow oxidation of Mn3+ in the catalyst. Fig.4. (a) Raman spectrum and (b) TEM image of MnOx-Pi-rGO. In Chapter 7, an amorphous Ni-Co-S film is prepared by a potentiodynamic deposition method using thiourea as the sulphur source. The electrodeposit is used as a catalyst for the HER in neutral phosphate solution. The composition of the catalyst and the HER activity are tuned by varying the ratio of concentrations of Ni2+ and Co2+. The bimetallic Ni-Co-S catalyst exhibits better HER activity than both Ni-S and Co-S (Fig. 5a). Under optimized deposition conditions, Ni-Co-S requires just 150 mV for the onset of HER and 10 mA cm-2 is obtained for 280 mV overpotential. The Ni-Co-S shows two different Tafel slopes, indicating two different potential dependent HER mechanisms (Fig. 5b). Presence of two different catalytic sites which contribute selectively in different potential regions is proposed. Fig.5. (a) Linear sweep voltammograms of HER at 1 mV s-1 in 1 M phosphate solutions (pH 7.4) using (i) Ni-S, (ii) Co-S and (c) Ni-Co-S. (b) Tafel plot of Ni-Co-S showing two Tafel slopes. Photoelectrochemical OER using ZnO photoanode and Co-acetate (Co-Ac) cocatalyst is studied in Chapter 8 of the thesis. Randomly oriented crystalline ZnO nanorods are prepared by the electrochemical deposition of Zn(OH)2 followed by heat treatment at 350 ºC in air. Co-Ac is then photochemically deposited onto ZnO nanorods by UV illumination in the presence of neutral acetate buffer solution containing Co2+ ions. The hybrid Co-Ac-ZnO shows higher photoactivity in comparison with bare ZnO towards PEC water oxidation (Fig. 6). Co-Ac acts as a cocatalyst and reduces the charge carrier recombination at the electrode/electrolyte interface. Fig.6. (a) Linear sweep voltammograms of ZnO under (i) dark and (ii) light conditions, and that of Co-Ac-ZnO in (iii) dark and (iv) light in 0.1 M phosphate (pH 7.0) electrolyte. Chapter 9 deals with PEC water oxidation using α-Fe2O3 photoanode and Ir-phosphate (Ir-Pi) cocatalyst. α-Fe2O3 is prepared by direct heating of Fe film in air which in turn is deposited by the electrochemical reduction of Fe2+. Thickness of the film as well as calcination temperature is carefully optimized. In order to further enhance the OER kinetics, Ir-Pi is electrochemically deposited onto α-Fe2O3. Under optimized conditions, Ir-Pi deposited α-Fe2O3 shows around 3 times higher photocurrent than that of bare α-Fe2O3 at 1.23 V vs. RHE (Fig. 7). Ir-Pi acts as a cocatalyst for OER and reduces the photogenerated charge carrier recombination. Fig.7. Photocurrent variation of α-Fe2O3 electrode at 1.23 V vs. RHE for (i) front and (ii) back side illuminations, against Ir-Pi deposition time. The thesis ends with a short summary and future prospectus of studies described in the thesis. The research work presented in the thesis is carried out by the candidate as the part of Ph.D. program. Some of the results have already been published in the literature and some manuscripts are under preparation. A list of publications is included at the end of the thesis. It is anticipated that the studies reported in the thesis will constitute a worthwhile contribution.

碩士
國立中興大學
化學系所
105
A series of novel Nickel, Zinc and Cobalt acetate complexes (1-9) supported by NNO-tridentate Schiff-base ancillary ligands with variously electronic effect of substituents (L5H、L6H) or sterically bulky ligands (L9H) have been synthesized. All of complexes have been characterized by elemental analysis and UV-Vis as well as X-ray diffraction study indicate that complexes have a variety of geometry such as mononuclear four-coordinated nickel center, trinuclear six-coordinated metal center. Complexes 1-9 was applied to copolymerize carbon dioxide with cyclohexene oxide (CHO) to compare their activities. Experimental results demonstrate that Nickel complex 2 show efficient activity and highly alternating poly (cyclohexene carbonate) for CO2/CHO copolymerization. Complex 2 also illustrates “living” character with the molecular weight of polymers increased linearly with respect to the gradually enlarged portion of monomer. Zinc complex 5 and Cobalt complex 8 are also the active catalysts and highly cis-cyclic carbonate contents for the copolymerization of carbon dioxide with cyclohexene oxide on addition of co-catalyst (PPNCl).

碩士
國立中興大學
化學系所
105
A series of novel transition metal (Ni, Zn, Co) complexes bearing NNO-tridentate Schiff–base ligands have been synthesized and characterized as trinuclear complexes with respect to various electronic and steric effect. All of these complexes have been characterized by elemental analysis, LC/MS and UV-Vis spectroscopy. Experimental results demonstrate that nickel complexes (1)-(3) all show efficient activity for the copolymerization of cyclohexene oxide and carbon dioxide without co-catalysts giving copolymers with high molecular weight. Among them, complex (2) shows the highest catalytic ability and illustrates a living character with the molecular weight of polymer increases linearly with respect to the gradually enlarged portion of conversion. Zinc and cobalt complexes (4)-(9) are also show catalytical activity in the presence of co-catalyst PPNCl.

碩士
國立中興大學
化學系所
107
A series of novel transition metal (Ni, Co, Cu) complexes bearing S,N,O-tridentate Schiff–base ligands have been synthesized with respect to various electronic and steric effect. The results of one-pot CHO/CO2 reaction carried out with ligand precusors and transition metals infer the active species in the reaction. The composition of complexes has been characterized by elemental analysis, FT-IR and EPR spectroscopy. Their physical properties were investigated using the melting point analyzer and UV/Vis spectroscopy. X-ray diffraction studies of the complex (1) and (3) indicate that these are pentanuclear six-coordinated nickel complexes and the studies of the complex (7) indicate that it is a dinuclear six-coordinatrd cobalt complex. With Bu4NCl as a cocatalyst , all of the nickel complexes (1)-(3) and one-pot reaction with ligand precusors and nickel acetate show efficient activity and high selectivity in the reaction of cyclohexene oxide and carbon dioxide with similar conversion and selectivity. Moreover, comparison of the activity in the one-pot reaction with the activity of metal complexes indicates that the synthesized pentanuclear Ni complexes, pentanuclear Cu complexes and dinuclear Co complexes are the active species of their one-pot reactions.

Ionic conductivity of solid polymer electrolytes (SPEs) can be enhanced by the addition of fillers, while maintaining good chemical stability, and compatibility with popular cathode and anode materials. Additionally, polymer composite electrolytes can replace the flammable organic liquid in a lithium-ion battery design and are compatible with lithium metal. Compatibility with Li-metal is a key development towards a next-generation rechargeable Li-ion battery, as a Li-metal anode has a specific capacity an order of magnitude higher than LiC6 anodes used today in everyday devices. The addition of fillers is understood to suppress the crystalline fraction in the polymer phase, increasing the ionic conductivity, as Li-ion conduction is most mobile through the amorphous phase. A full model for a conduction mechanism has not yet constructed, as there is evidence that a semi-crystalline PEO-based electrolyte performs better than a fully amorphous electrolyte. Furthermore, it is not yet fully understood why the weight load of fillers in PCEs can range from 2.5%wt to 52.5%wt, in order to achieve high ionic conductivity (~10-4S/cm). This work seeks to investigate the conduction mechanism in the PCE through the use of doped-Li7La3Zr2O12 as a filler and analysis of the PCE microstructure. In this work, a solid-state electrolyte, doped-Li7La3Zr2O12 (LLZO) was synthesized via a sol-gel method, and characterized. The effect of doping and co-doping the Li, La and Zr sites in the LLZO garnet was investigated. A PEO-based polymer composite electrolyte (PCE) was prepared by adding bismuth doped LLZO (Li7-xLa3Zr2-xBixO12) as a filler. The bismuth molar ratio was changed in value to study the dopant role on the bulk PCE ionic conductivity, polymer phase crystallinity and microstructure. Results suggest that small variations in dopant can determine the optimal weight load of filler at which the maximum ionic conductivity is reached. By understanding the relationship between filler properties and electrochemical properties, higher performance can be achieved with minimal filler content, lowering manufacturing costs a solid-state rechargeable Li-ion battery.