This work involved the development of new perovskite oxides based on SmFeO3 and testing their performances as sensors for reducing gases (H2, CO & CH4) and as anode materials for dry methane oxidation in solid oxide fuel cells. The new perovskite oxide materials with formula Sm0.95Ce0.05Fe1-xMxO3-δ (M= Co, Ni & Cr) were synthesized by a sol gel method using citric acid as a complexing agent. The resulting materials were characterized by using a battery of techniques including XRD, XRF, XPS, SEM and electrochemical methods. Sensing experiments revealed that both cobalt doped and Cr doped materials can detect H2, CO and CH4 in air at different temperatures including room temperature. The Ni doped materials did not prove good candidates as sensors. However, their reduction treatment studies showed the formation of metallic nanoparticles on the surface which deeply influence their electrical conductivity as well as sensing ability. Consequently, this modification in surface structure and chemical composition enabled them to sense hydrogen gas at 300oC very effectively. The response of sensors based on these reduced materials was measurable and reversible. Some materials were also selected on the basis of their reduction stability and electrical properties, and their electrochemical performances were evaluated as SOFC anodes under dry methane and dry hydrogen fuels separately. The performance tests as SOFC anode revealed that the best anode material for the oxidation of dry hydrogen fuel is Sm0.95Ce0.05FeO3-δ. Furthermore, Sm0.95Ce0.05FeO3-δ proved to be coke resistant anode under dry methane fuel and exhibited reasonably low charge transfer resistance values at temperatures between 600-700oC. The doping of Co and Ni at the B-site of Sm0.95Ce0.05FeO3-δ found to be very effective in further improving its performance as SOFC anode towards oxidation of dry methane fuel at the lower temperatures.

This work involved the development of new perovskite oxides based on SmFeO3 and testing their performances as sensors for reducing gases (H2, CO & CH4) and as anode materials for dry methane oxidation in solid oxide fuel cells. The new perovskite oxide materials with formula Sm0.95Ce0.05Fe1-xMxO3-δ (M= Co, Ni & Cr) were synthesized by a sol gel method using citric acid as a complexing agent. The resulting materials were characterized by using a battery of techniques including XRD, XRF, XPS, SEM and electrochemical methods. Sensing experiments revealed that both cobalt doped and Cr doped materials can detect H2, CO and CH4 in air at different temperatures including room temperature. The Ni doped materials did not prove good candidates as sensors. However, their reduction treatment studies showed the formation of metallic nanoparticles on the surface which deeply influence their electrical conductivity as well as sensing ability. Consequently, this modification in surface structure and chemical composition enabled them to sense hydrogen gas at 300oC very effectively. The response of sensors based on these reduced materials was measurable and reversible. Some materials were also selected on the basis of their reduction stability and electrical properties, and their electrochemical performances were evaluated as SOFC anodes under dry methane and dry hydrogen fuels separately. The performance tests as SOFC anode revealed that the best anode material for the oxidation of dry hydrogen fuel is Sm0.95Ce0.05FeO3-δ. Furthermore, Sm0.95Ce0.05FeO3-δ proved to be coke resistant anode under dry methane fuel and exhibited reasonably low charge transfer resistance values at temperatures between 600-700oC. The doping of Co and Ni at the B-site of Sm0.95Ce0.05FeO3-δ found to be very effective in further improving its performance as SOFC anode towards oxidation of dry methane fuel at the lower temperatures.

This work involved the development of new perovskite oxides based on SmFeO3 and testing their performances as sensors for reducing gases (H2, CO & CH4) and as anode materials for dry methane oxidation in solid oxide fuel cells. The new perovskite oxide materials with formula Sm0.95Ce0.05Fe1-xMxO3-δ (M= Co, Ni & Cr) were synthesized by a sol gel method using citric acid as a complexing agent. The resulting materials were characterized by using a battery of techniques including XRD, XRF, XPS, SEM and electrochemical methods. Sensing experiments revealed that both cobalt doped and Cr doped materials can detect H2, CO and CH4 in air at different temperatures including room temperature. The Ni doped materials did not prove good candidates as sensors. However, their reduction treatment studies showed the formation of metallic nanoparticles on the surface which deeply influence their electrical conductivity as well as sensing ability. Consequently, this modification in surface structure and chemical composition enabled them to sense hydrogen gas at 300oC very effectively. The response of sensors based on these reduced materials was measurable and reversible. Some materials were also selected on the basis of their reduction stability and electrical properties, and their electrochemical performances were evaluated as SOFC anodes under dry methane and dry hydrogen fuels separately. The performance tests as SOFC anode revealed that the best anode material for the oxidation of dry hydrogen fuel is Sm0.95Ce0.05FeO3-δ. Furthermore, Sm0.95Ce0.05FeO3-δ proved to be coke resistant anode under dry methane fuel and exhibited reasonably low charge transfer resistance values at temperatures between 600-700oC. The doping of Co and Ni at the B-site of Sm0.95Ce0.05FeO3-δ found to be very effective in further improving its performance as SOFC anode towards oxidation of dry methane fuel at the lower temperatures.

Lithium-ion batteries(LIBs) have dominated the energy storage market in the past two decades. The high specific energy, low self-discharge, relatively high power and low maintenance of LIBs enabled the revolution of electronic devices and electric vehicle industry, changed the communication and transportation styles of the modern world. Although the specific energy of LIBs has increased significantly since first commercialized in 1991, it has reached a bottleneck with current electrode materials. To meet the increasing market demand, it is necessary to develop high capacity electrode materials.<div><br></div><div>Current commercial anode material for LIB is graphite which has a specific capacity of 372 mAh g-1. Other group IV elements (silicon (Si), germanium (Ge), tin (Sn)) have much higher capacities. However, group IV elements have large volume change during lithiation/delithiation, leading to pulverization of active materials and disconnection between electrode particles and current collector, resulting in fast capacity fading. To address this issue, it is essential to understand the microstructural evolution of Si, Ge and Sn during cycling.<br></div><div><br></div><div>This dissertation is mainly focused on the morphological and structural evolution of Sn and Ge based materials. In this dissertation, anin situ focused ion beam-scanning electron microscopy (FIB-SEM) method is developed to investigate the microstructuralevolution of a single electrode particle and correlate with its electrochemical performance. This method is applied toall projects. The first project is to investigate the microstructural evolution of a Sn particle during cycling. Surface structures of Sn particles are monitored and correlated with different states of charge. The second project is to investigate the morphological evolution of Ge particles at different conditions. Different structures (nanopores, cracks, intact surface) appear at different cycling rates. The third project is to study selenium doped Ge (GeSe) anodes. GeSe and Ge particles are tested at the same condition. Se doping forms Li-Ge-Se network, provides fast Li transport and buffers volume change. The fourth project is to study the reaction front of Ge particle during lithiation. Micron-sized Ge particles have two reaction fronts and a wedge shape reaction interface, which is different from the well-known core-shell mode. The fifth project is to investigate antimony (Sb)-coated porous Ge particles. The Sb coating suppresses electrolyte decomposition and porous structure alleviates volume change. The results in this dissertation reveal fundamental information about the reaction mechanism of Sn and Ge anode. The results also show the effects of doping, porous structuring and surface coating of anode materials.</div>

Afin d’améliorer les performances électrochimiques de cellules d’électrolyse de la vapeur d’eau à haute température (EVHT), de nouveaux matériaux d’électrode à oxygène de typeLn2NiO4+δ (Ln = La, Pr ou Nd), Pr4Ni3O10±δ et La0,6Sr0,4Fe0,8Co0,2O3-δ ont été étudiés. Ces composés ont été sélectionnés pour leurs propriétés de conduction mixte électronique et ionique. Après la caractérisation de leurs propriétés physico-chimiques, les matériaux ont été mis en forme au sein de demi-cellules symétriques, en intercalant une couche d’interface fine à base de cérine entre l’électrode et l’électrolyte de zircone yttriée. Cette architecture contribue à la diminution de la résistance de polarisation de l’électrode (RP <0,1 Ω.cm2 à 800°C) et de la surtension anodique. Un modèle électrochimique a été développé afin de décrire et d’analyser les courbes de polarisation expérimentales.L’électrode présentant les plus faibles surtensions, Pr2NiO4+δ, a été sélectionnée et caractérisée au sein de cellules complètes à cermet support. En fonctionnement EVHT à800°C, une densité de courant élevée a été obtenue, de l’ordre de i = -0,9 A.cm-2 pour une tension de cellule de 1,3V et un taux de conversion d’environ 60%. / In order to improve the electrochemical performances of cells for high temperature steam electrolysis (HTSE), innovative oxygen electrode materials have been studied. The compounds Ln2NiO4+δ (Ln = La, Pr or Nd), Pr4Ni3O10±δ and La0.6Sr0.4Fe0.8Co0.2O3-δ have been selected for their mixed electronic and ionic conductivity. First, their physical and chemical properties have been investigated. Then, the electrodes were shaped on symmetrical half cells,adding a thin ceria-based interlayer between the electrode and the yttria doped zirconia-based electrolyte. These architectured cells lead to low polarization resistances (RP< 0.1 Ω.cm2 at 800°C) as well as reduced anodic over potentials . An electrochemical model has been developed in order to describe and analyze the experimental polarization curves.The electrode with the lower overpotential, i.e. Pr2NiO4+δ, has been selected and characterized into complete cermet-supported cells. Under HTSE operation, at 800°C, a high current density was measured, close to i = -0.9 A.cm-2 for a cell voltage equals to 1.3 V, the conversion rate being about 60%.

The research work presented in this thesis reports for the first time the fabrication of Titanium Niobium complex oxide (TiNb2O7 (TNO)) thin films by employing pulsed laser deposition and their use as the anode material in Li-ion micro batteries. Chapter 1 provides a brief introduction to complex metal oxides as multifunctional materials. In the first section of this chapter, a brief introduction is given about the history of TNO complex oxide material. The complex structure and properties of TNO oxide are also discussed briefly. In the second section, the importance and need of thin film batteries in emerging applications is discussed. Finally, the specific objectives of the current research are outlined in the last section. Chapter 2 gives the details about various experimental methods and characterization tools used in this research. The first part gives a brief overview about the principles and the use of different experimental methods involved in the growth of TNO thin films using pulsed laser deposition. Details, including the laboratory setup designed for PLD growth, also described briefly. In the second part, the different state-of-the-art characterization tools used in this research are described in terms of their principles and their applications such as measuring structural, morphological, chemical and electrochemical properties. Chapter 3 describes the synthesis and characterization of TNO bulk targets prepared via solid state reaction. In the first part, the detailed descriptions of experimental conditions are given. In the second part, the study of as-prepared TNO targets by various characterization tools such as XRD, Raman, SEM and XPS for understanding its structure, morphology and chemical properties are discussed briefly. The emphasis is made on the preparation of a quality target by careful observations. Chapter 4 mainly describes the comprehensive studies carried out on the fabrication and characterization of TNO thin films using PLD. In the first part, the preliminary experimental conditions for the growth of TNO thin films on Pt (200)/TiO2/SiO2/ Si (100) substrates are explained briefly. The importance of primary understanding about target-laser interaction through the structural, morphology changes observed by various characterization tools is discussed. In the latter part of the chapter, the effects of systematic variation of deposition parameters on the properties of the grown TNO thin films are described extensively. Various advanced characterization tools are used to study the changes in as-grown TNO thin films in terms of their structural, morphological and chemical changes by various advanced characterization tools. Chapter 5 is an account of the state-of-the-art characterization tools that are used on the as-grown TNO thin films for determining structural, compositional and elemental information with nanometer spatial resolution. In the first part, the effects of various processing conditions used during FIB are discussed briefly, along with observed results. An attempt has been made to solve the experimental difficulties during FIB for cross sectional sample preparation for HRTEM analysis. Later, the imaging, diffraction and spectroscopic studies carried out on TNO thin films using HRTEM, STEM HAADF, and EDXS elemental mapping are discussed in detail. Finally, obtained results are correlated to the experimental conditions during PLD growth. Chapter 6 focuses on the usage of as-grown TNO thin films as a new anode material in rechargeable Li-ion micro batteries. The various experimental details, battery cell fabrication, etc are described in the first part of the chapter. Then the comprehensive studies are carried out for demonstrating TNO thin films as anode material in micro batteries. Besides this, the basic cyclic voltammogram and charge-discharge tests carried out on a TNO electrode are discussed in detail. The structural, morphological studies are done before and after the electrochemical cell reaction to understand the crystal stability of TNO as an anode electrode. The effects of important experimental parameters on their electrochemical properties are also described briefly. Finally, the observed results are compared with existing literature. Chapter 7 summarizes the present research reported in this thesis and discusses the future research that could give insight into the understanding and optimization of TNO thin films for better usage in battery applications.

Master of Science / Mechanical and Nuclear Engineering / Kevin B. Lease / Gurpreet Singh / Energy has always been one of the most important factors in any type of human or industrial endeavor. Clean energy and alternative energy sources are slowly but steadily replacing fossil fuels, the over-dependence on which have led to many environmental and economic troubles over the past century. The main challenge that needs to be addressed in switching to clean energy is storing it for use in the electrical grid and transportation systems. Lithium ion batteries are currently one of the most promising energy storage devices and tremendous amount of research is being done in high capacity anode and cathode materials, and better electrolytes and battery packs as well, leading to overall high efficiency and capacity energy storage systems. Polymer derived ceramics (PDCs) are a special class of ceramics, usually used in high temperature applications, but some silicon based PDCs have demonstrated good electrochemical properties in lithium ion batteries. The goal of this research is to explore a special hybrid ceramic of titanium dioxide (TiO₂) and silicon oxy carbide (SiOC) ceramic derived from 1,3,5,7 -- tetravinyl -- 1,3,5,7 -- tetramethylcyclotetrasiloxane (TTCS) polymer for use in lithium ion batteries and investigate the source of its properties which might make the ceramic particularly useful in some highly specialized energy storage applications.

Rechargeable lithium-ion batteries are now attracting great attention for applications in portable electronic devices and electrical vehicles, because of their high energy density, long cycle and great convenience. For new generations of rechargeable lithium-ion batteries, they applied not only to consumer electronics but also especially to clean energy storage and hybrid electric vehicles. Therefore, further breakthroughs in electrode materials that open up a new important avenue are essential. Graphite, the most commonly used commercial anode material, has a limited reversible lithium intercalation capacity (372 mAh g-1). In this regard, tremendous efforts have been made towards even further improving high capacity, excellent rate capability, and cycling stability by developing advanced anode materials. This work focuses on the lithium storage properties of nickel oxide (NiO) and germanium (Ge) nanomembranes anodes mainly fabricated by electron-beam evaporation. Specifically, NiO is selected for conversion-type material because of high theoretical specific capacity of 718 mAh g-1 and easily obtained material. The resultant curved NiO nanomembranes anodes exhibit ultrafast power rate of 50 C (1 C = 718 mA g-1) and good capacity retention (721 mAh g-1, 1400 cycles). Remarkably, multifunctional Ni/NiO hybrid nanomembranes were further fabricated and investigated. Benefiting from the advantages of the intrinsic architecture and the electrochemical catalysis of metallic nickel, the hybrid Ni/NiO anodes could be tested at an ultrahigh rate of ~115 C. With Ge as active alloying-type material (1624 mAh g-1), the effect of the incorporated oxygen to the lithium storage properties of amorphous Ge nanomembranes is well studied. The oxygen-enabled Ge (GeOx) nanomembranes exhibit improved electrochemical properties of highly reversible capacity (1200 mAh g-1), and robust cycling performance.

Le reformage catalytique du méthane en hydrogène, vecteur d'énergie pour les piles à combustibles de type Solid Oxide Fuel Cell (SOFC), a été étudié sur des matériaux d'anode à base de métaux supportés (NiO/CeO2, NiO-Y2O3-ZrO2) et également sur des catalyseurs de structure définie (La0,8Sr0,2TiO3+δ). La première famille de catalyseurs a été synthétisée par deux méthodes de préparation : la technique d'imprégnation en milieu aqueux et en milieu organique sur des supports du commerce CeO2 et Y2O3-ZrO2 ou préparés au laboratoire, et par le procédé sol-gel. Le titanate de lanthane dopé au strontium a été préparé par la méthode de co-précipitation et également par la méthode sol-gel. La méthode de préparation a un effet important sur les propriétés physico-chimiques des catalyseurs synthétisés et par conséquent affecte à la fois leur activité catalytique en reformage du méthane et leur résistance à l'empoisonnement par le dépôt de carbone. Les catalyseurs à base de nickel supporté sur cérine ont été par la suite dopés avec l'oxyde de magnésium (formation d'une solution solide MgO-NiO) ainsi qu'avec l'oxyde de lanthane (La2O3-NiO) en vue de limiter la formation de carbone sur la surface catalytique et augmenter ainsi la durée de vie des catalyseurs lors du reformage du méthane. Les résultats obtenus montrent que l'effet de promotion de la phase active NiO par MgO ou La2O3 diminue à la fois le dépôt de carbone mais également les performances catalytiques. Les propriétés physico-chimiques et les performances catalytiques de NiO-Y2O3-ZrO2 préparé par le procédé sol-gel ont été comparées à celles de matériaux commerciaux (Aldrich & Jülich) de même composition. Les résultats expérimentaux montrent que les matériaux synthétisés par la méthode sol-gel sont plus actifs en vaporeformage du méthane que ceux du commerce (dans le domaine de fonctionnement d'une pile SOFC) alors qu'ils présentent une activité similaire à ces derniers en reformage à sec du méthane. La quantité de carbone graphitique formée, quoique supérieure à celle observée dans le cas des catalyseurs commerciaux, demeure faible (< 2%). Ce dépôt de carbone ne provoque qu'une légère diminution des performances catalytiques en reformage à sec du méthane. Ceci est probablement lié à la diminution des sites actifs / The catalytic reforming of methane into hydrogen, for direct operation of Solid Oxide Fuel Cells (SOFCs) on methane, was studied on anode materials such as NiO/CeO2, NiO-Y2O3-ZrO2 and La0.8Sr0.2TiO3+δ. The first group of catalysts was synthesized by two methods: the impregnation technique both in aqueous and organic media (commercial and laboratory made CeO2 and Y2O3-ZrO2), and also using sol-gel process. Lanthanumtitanium oxide host structure doped with strontium was prepared both by co-precipitation and sol-gel process. The method of preparation has an important effect on the physico-chemical properties of the synthesized catalysts and affects consequently both their catalytic performances in methane reforming and their resistance to poisoning by carbon deposition. In order to limit carbon formation on the catalytic surface and to increase the lifetime of catalysts during the catalytic reforming of methane, ceria supported nickel based-catalysts were doped with magnesium oxide (forming MgO-NiO solid solution) as well as with lanthanum oxide (La2O3-NiO). The obtained results show that the effect of promotion of NiO active phase by MgO and La2O3 decreases carbon deposition but also the catalytic performances. Physico-chemical properties and catalytic performances of NiO-Y2O3-ZrO2 (Ni-YSZ) prepared by the sol-gel process were compared with those of commercial (Aldrich and Jülich) materials having the same composition. The experimental results showed that materials synthesized by the sol gel method are more active in methane steam reforming than commercial catalysts while sol gel and commercial samples show similar performances in methane dry reforming. Amounts of graphitic carbon, although being higher for sol gel samples compared to commercial ones, remain low (< 2%). This carbon deposit provokes only a slight decrease of catalytic performances of sol gel prepared materials in methane dry reforming, probably by decreasing the number of active sites

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