Hochleistungsfähige Lithium-Ionen-Batterien sind insbesondere von der hohen spezifischen Kapazität ihrer Elektrodenmaterialien abhängig. Intermetallische Phasen sind vielversprechende Kandidaten für alternative Anodenmaterialien mit verbesserten spezifischen Kapazitäten (LiAl: 993 Ah/kg; Li22Si5: 4191 Ah/kg) gegenüber den derzeit vielfach verwendeten Kohlenstoff-Materialien (LiC6: 372 Ah/kg). Nachteilig ist jedoch, dass die kristallinen Phasenumwandlungen während der Lade-Entlade-Prozesse Volumenänderungen von 100-300% verursachen. Durch die Sprödigkeit der intermetallischen Phasen führt dies zum Zerbrechen des Elektrodenmaterials und damit zum Kontaktverlust. Um Lithiierungs- und Delithiierunsprozesse ohne kristalline Phasenumwandlungen zu realisieren und somit große Volumenänderungen zu vermeiden, wurden amorphe Al-Legierungen untersucht. In amorphe, mittels Schmelzspinnen hergestellte Legierungen (Al86Ni8La6 und Al86Ni8Y6) kann beim galvanostatischen Zyklieren nur sehr wenig Li eingelagert werden. Da kristalline Phasenumwandlungen im amorphen Zustand nicht möglich sind, wird für die Diffusion und Einlagerung von Li-Ionen ein ausreichendes freies Volumen im amorphen Atomgerüst benötigt. Die Dichtemessung der Legierungen zeigt, dass dieses freie Volumen für eine signifikante Lithiierung nicht ausreichend ist. Wird Li bereits in die amorphe Ausgangslegierung integriert, können Li-Ionen auf elektrochemischem Wege aus ihr entfernt und auch wieder eingebaut werden. Die neuartige Legierung Al43Li43Ni8Y6, die Li bereits im Ausgangszustand enthält, konnte mittels Hochenergiemahlung als amorphes Pulver hergestellt werden. Verglichen mit den Li-freien amorphen Legierungen Al86Ni8La6 bzw. Al86Ni8Y6 und ihren kristallisierten Pendants zeigt diese neu entwickelte, amorphe Legierung eine signifikant höhere Lithiierungsfähigkeit und erreicht damit eine spezifische Kapazität von ca. 800 Ah/kg bezogen auf den Al-Anteil. Durch den Abrieb des Stahlmahlbechers enthält das Pulver Al43Li43Ni8Y6 einen Fe-Anteil von ca. 15 Masse%. Dieses mit Fe verunreinigte Material zeigt besonders bei niedrigen Laderaten eine bessere Zyklenstabilität als ein im abriebfesten Siliziumnitrid-Becher gemahlenes Pulver der gleichen Zusammensetzung. Mittels Mössbauerspektroskopie wurde nachgewiesen, dass das Pulver z.T. oxidisches Fe enthält. Dieses kann über Konversionsmechanismen einen Beitrag zur spezifischen Kapazität leisten. / High-energy Li-ion batteries exceedingly depend on the high specific capacity of electrode materials. Intermetallic alloys are promising candidates to be alternative anode materials with enhanced specific capacities (LiAl: 993 Ah/kg; Li22Si5: 4191 Ah/kg) in contrast to state-of-the-art techniques, dominated by carbon materials (LiC6: 372 Ah/kg). Disadvantageously the phase transitions during the charge-discharge processes, induced by the lithiation process, cause volume changes of 100-300 %. Due to the brittleness of intermetallic phases, the fracturing of the electrode material leads to the loss of the electrical contact. In order to overcome the huge volume changes amorphous Al-based alloys were investigated with the intension to realize the lithiation process without a phase transformation. Amorphous powders (Al86Ni8La6 and Al86Ni8Y6) produced via melt spinning and subsequent ball milling only show a minor lithiation during the electrochemical cycling process. This is mainly caused by the insufficient free volume, which is necessary to transfer and store Li-ions, since phase transitions are impossible in the amorphous state. If Li is already integrated into the amorphous alloy, Li-ions can easily be removed and inserted electrochemically. The new alloy Al43Li43Ni8Y6 contains Li already in its initial state and could be prepared by high energy milling as an amorphous powder. Compared with the Li-free amorphous alloys Al86Ni8La6 or Al86Ni8Y6 and their crystalline counterparts, this newly developed amorphous alloy achieves a significantly higher lithiation and therefore reaches a specific capacity of 800 Ah/kg, based on the Al-content. By the abrasion of the steel milling vials the powder contains a wear debris of 15 mass% Fe. This contaminated material shows a better cycling stability than a powder of the same composition, milled in a non-abrasive silicon nitride vial. By means of Mössbauer spectroscopy has been shown that the wear debris contains Fe oxides. This may contribute to the enhancement of the specific capacity about conversion mechanisms.

Porous carbons are promising anode materials for next generation lithium batteries due to their large lithium storage capacities. However, their highsloping capacity during lithiation and delithiation as well as capacity fading due to intense formation of solid electrolyte interphase (SEI) limit their gravimetric and volumetric energy densities. Herein we compare a microporous carbide derived carbon material (MPC) as promising future anode for all solid state batteries with a commercial high performance hard carbon anode. The MPC obtains high and reversible lithiation capacities of 1000 mAh g 1 carbon in half cells exhibiting an extended plateau region near 0 V vs. Li/Liþ preferable for full cell application. The well defined microporosity of the MPC with a specific surface area of >1500 m2 g 1 combines well with the argyrodite type electrolyte (Li6PS5Cl) suppressing extensive SEI formation to deliver high coulombic efficiencies. Preliminary full cell measurements vs. nickel rich NMC cathodes (LiNi0.9Co0.05Mn0.05O2) provide a considerably improved average potential of 3.76 V leading to a projected energy density as high as 449 Wh kg 1 and reversible cycling for more than 60 cycles. 7Li Nuclear Magnetic Resonance spectroscopy was combined with ex situ Small Angle X ray Scattering to elucidate the storage mechanism of lithium inside the carbon matrix. The formation of extended quasi metallic lithium clusters after electrochemical lithiation was revealed.

No description available.

Constructing dual-ion energy storage devices using anion-intercalation graphite cathodes offers the unique opportunity to simultaneously achieve high energy density and output power density. However, a critical challenge remains in the lack of proper anodes that match with graphite cathodes, particularly in sustainable electrolyte systems using abundant potassium. Here, a surface grafting approach utilizing multifunctional azobenzene sulfonic acid is reported, which transforms V2C MXene into a high-kinetics K+-intercalation anode (denoted ASA-V2C) for dual-ion energy storage devices. Importantly, the grafted azobenzene sulfonic acid offers extra K+-storage centers and fast K+-hopping sites, while concurrently acting as a buffer between V2C layers to mitigate the structural distortion during K+ intercalation/de-intercalation. These functionalities enable the V2C electrode with significantly enhanced specific capacity (173.9 mAh g−1 vs 121.5 mAh g−1 at 0.05 A g−1), rate capability (43.1% vs 12.0% at 20 A g−1), and cycling stability (80.3% vs 45.2% after 900 cycles at 0.05 A g−1). When coupled with an anion-intercalation graphite cathode, the ASA-V2C anode demonstrates its potential in a dual-ion energy storage device. Notably, the device depicts a maximum energy density of 175 Wh kg−1 and a supercapacitor-comparable power density of 6.5 kW kg−1, outperforming recently reported Li+-, Na+-, and K+-based dual-ion devices.

The research presented in this thesis is a collection of many different, yet connected, parts that stemmed from the development of a new alternative material intended to be utilised as anode material in solid oxide fuel cells. The main part is the research conducted in the development and characterisation of the novel A-site deficient La₀.2₂Sr₀.₇₋ₓCaₓTiO₃. Calcium introduction resulted in reducing this perovskite unit cell volume which, at the beginning, enhanced its electrical conductivity in reducing conditions. However, the ideal cubic symmetry coud not be maintained, as in the starting material LA₀.₂Sr₀.₇TiO₃, as a result of the increased A-site ionic radius mismatch and two lower symmetries were observed at room temperature. These were the tetragonal I4/mcm for 0.1 ≤ x ≤ 0.35 and orthorhombic Pbnm for 0.4 ≤ x ≤ 0.7. Higher temperature NPD data showed that the orthorhombic samples transformed into higher symmetries with Pbnm → I4/mcm → Pm3-m phase transitions. Detailed crystallographic analysis is discussed; where the different unit cells showed changes to the tilts of the BO₆ octahedra, along with distortions to these octahedra. DC conductivity measurements showed a high electrical conductivity of 27.5 S/cm for a pre-reduced composition La₀.₂Sr₀.₂₅Ca₀.₄₅TiO₃ at 900°C and pO₂ = 10⁻¹⁹ atm. This material showed very encouraging features; which makes it a very promising anode material for SOFCs. A study was also done which explores the best renewable energy options for the United Arab Emirates given its local climate and other aspects. The reliance on seawater desalination is argued to by unsustainable for different reasons. Thus, water security should be a main element in the planning process for adopting renewable energy technologies. A system that combines different technologies; with a focus on fuel cells technology; is outlined which is thought of to be a very promising basis for a broader system that will secure power and water in a very environment friendly way. Different compositions of the system La₀.₂Sr₀.₇₋ₓCaₓTiO₃ were also studied using AC impedance spectroscopy in order to establish whether or not this system can show a ferroelectric behaviour. Results showed a variation in the dielectric constant of different samples with temperature; however, no Curie point was observed. Nonetheless, the results did show that the different compositions were very homogeneous when fully oxygenated and there were some indications of possible symmetry changes at sub-ambient temperatures. The final part of this thesis outlined the work done towards the development of a new analytical instrument. An existing TGA instrument was altered in order to provide a simultaneous thermogravimetric analysis and DC conductivity measurement for solid solutions at controlled temperature and oxygen partial pressure. Results were obtained for different samples of the system La₀.₂Sr₀.₇₋ₓCaₓTiO₃ which showed a great dependence of the electrical conductivity on the oxygen stoichiometry in these oxides. Also, a direct method is possible with this instrument to estimate the oxygen chemical diffusion coefficient using the electrical conductivity relaxation method. This new setup will be very useful for different electrochemical and thermal studies which can broaden the understanding of the different mechanisms that affect the performance of different solid state materials.

<p align="justify">Plusieurs métaux de notre vie courante sont obtenus industriellement au moyen de procédés électrolytiques. Un des procédés les plus communs est l’électro-obtention de cuivre, dans lequel le métal est déposé à la cathode tandis que l'oxygène se dégage à l'anode. Généralement, en usine, plusieurs anodes et cathodes, ayant une surface de 1 m2 et séparées par plus ou moins 10 cm sont alternées dans une cellule contenant une solution d'acide sulfurique riche en sulfate de cuivre. En fonction des conditions d'utilisation, les cathodes sont remplacées, après un certain temps, par des nouvelles de façon à récupérer le cuivre déposé. De ce fait, les anodes doivent être capables de résister sans se corroder, se déformer ou perdre leurs propriétés électrocatalytiques pendant de longues périodes. Au début, des alliages en Pb (pb-Ag, Pb-Ca-Sn,...) ont été utilisés comme anodes. Malheureusement, malgré leur faible prix, ces anodes présentent des surtensions élevées et une faible résistance à la corrosion et au fluage. Par conséquent, une alternative aux anodes traditionnelles en 1 développée. Ce nouveau type d'anode, connu sous le nom d’anode dimensionnellement stable (DSA) est fabriquée à partir d'une tôle en Ti recouverte par un mélange d'oxydes de métaux nobles catalysant la réaction de dégagement d'oxygène. Différentes techniques peuvent être utilisées pour préparer la couche d'oxyde. La technique la plus souvent employée consiste à décomposer thermiquement une solution de chlorures contenant un ou plusieurs nobles. Malheureusement, ce type d'anode est cher et a tendance à perdre son activité électrocatalytique avec le temps.</p> <p align="justify">Dans le but de produire une DSA à faible prix, pouvant résister de longues périodes sans se passiver, un nouveau type de DSA a été développé dans le présent travail. Cette anode est produite par électrodépôt d'un métal noble dans les pores d'un substrat microporeux en Ti/TiO2.</p> <p align="justify">Ce travail a permis de démontrer qu'une DSA avec une concentration en métal noble peut être obtenue par la voie proposée. Il a été montré que les propriétés électriques et électrochimiques de ces DSAs sont directement liées aux caractéristiques morphologiques et structurales du en Ti/TiO2. Lorsque la couche barrière existant au fond des pores est suffisamment fine et que le film présente des défauts, la résistance me l'interface Ti/métal noble est faible. Ceci abouti à des DSAs possédant d'excellentes propriétés électrocatalytiques. Les DSAs optimales sont capables de résister à des conditions similaires à celles employées en industrie avec des surtensions de ~ 0.4 V, ce qui représente un gain de 50% par rapport aux surtensions normalement atteintes par les anodes traditionnelles en Pb.</p>

Three-dimensional macroporous structures (‘opals’ and ‘inverse opals’) can be produced by colloidal crystal templating, one of the most intensively studied areas in materials science today. There are several potential advantages of lithium-ion battery electrodes based on inverse opal structures. High electrode surface, easier electrolyte access to the bulk of electrode and reduced lithium diffusion lengths allow higher discharge rates. Highly open structures provide for better mechanical stability to volume swings during cycling. Silicon is one of the most promising anode materials for lithium-ion batteries. Its theoretical capacity exceeds capacities of all other materials besides metallic lithium. Silicon is abundant, cheap, and its use would allow for incorporation of microbattery production into the semiconductor manufacturing. Performance of silicon is restricted mainly by large volume changes during cycling. The objective of this work was to investigate how the inverse opal structures influence the performance of silicon electrodes. Several types of silicon-based inverse opal films were synthesised, and their electrochemical performance was studied. Amorphous silicon inverse opals were fabricated via chemical vapour deposition and characterised by various techniques. Galvanostatic cycling of these materials confirmed the feasibility of the approach taken, since the electrodes demonstrated high capacities and decent capacity retentions. The rate performance of amorphous silicon inverse opals was unsatisfactory due to low conductivity of silicon. The conductivity of silicon inverse opals was improved by crystallisation. Nanocrystalline silicon inverse opals demonstrated much better rate capabilities, but the capacities faded to zero after several cycles. Silicon-carbon composite inverse opal materials were synthesised by depositing a thin layer of carbon via pyrolysis of a sucrose-based precursor onto the silicon inverse opals in an attempt to further increase conductivity and achieve mechanical stabilisation of the structures. The amount of carbon deposited proved to be insufficient to stabilise the structures, and silicon-carbon composites demonstrated unsatisfactory electrochemical behaviour. Carbon inverse opals were coated with amorphous silicon producing another type of macroporous composites. These electrodes demonstrated significant improvement both in capacity retentions and in rate capabilities. The inner carbon matrix not only increased the material conductivity, but also resulted in lower silicon pulverisation during cycling.

Poisoning of the catalyst seems to be one of the most serious problems preventing a widespread commercialization of fuel cell technology. This thesis focuses on the effect of CO poisoning and hydrogen dilution by nitrogen on performance of fuel cells with low platinum content. Catalysts were deposited by magnetron sputtering directly on membrane etched by plasma. Alloys with different platinum-ruthenium ratio were used to mitigate the CO poisoning. We found that presence of nitrogen has almost negligible effect on the fuel cell performance. On the other hand, CO, even in small concentrations, caused a significant drop in power density. PtRu with atomic ratio 2:1 and 1:1 showed the best CO tolerance.

Este trabalho investigou a oxidação eletroquímica do ácido tânico em eletrodos do tipo Ânodo Dimensionalmente Estáveis (ADE) a base de SnO2 e IrO2 e eletrodos de Diamante Dopado com Boro (BDD). As eletrólises foram feitas em modo galvanostático em função de parâmetros como densidade de corrente e concentração de cloreto. A oxidação eletroquímica do ácido tânico foi capaz de promover a diminuição da concentração de fenóis totais, Carbono Orgânico Total (COT) e Demanda Química de oxigênio (DQO). Para os ADE os melhores resultados de remoção de Carbono Orgânico Total (COT) foram nas condições em que se utilizou 300 mg L-1 de cloreto e densidade de corrente de 25 mA cm-2. No entanto houve a formação de compostos organoclorados que não foram degradados com maiores tempo de reação. Para os eletrodos de BDD, obteve-se a remoção de aproximadamente 98% de COT após 10 horas de reação à 75 mA cm-2, na ausência de cloreto. Maiores remoções de COT são obtidas com o aumento da densidade de corrente. Eletrólises na presença de cloreto removeram quase 100% do COT em tempos menores de reação. Análises de compostos organohalogenados (AOX) mostraram que não houve a formação de compostos organoclorados. Menores densidades de corrente apresentaram maiores Eficiência de Corrente (EC) e menor Consumo de Energia (CE). As eletrólises na presença de cloro apresentaram melhores resultados de EC que na ausência do mesmo. A oxidação fotoeletroquímia do ácido tânico em eletrodos do tipo ADE de composição nominal Ti/ Sn0,7 Ir0,3 O2 também foi investigada nesse trabalho. O tratamento fotoeletroquímico foi realizado utilizando uma lâmpada de vapor de mercúrio de alta pressão de 125 W como fonte de irradiação. A variação da corrente não mostrou diferença significativa na oxidação do ácido tânico. A variação da concentração de cloreto no eletrólito suporte influenciou de forma acentuada a oxidação do ácido tânico. O tratamento fotoeletroquímico se mostrou mais eficiente na remoção de COT que os tratamentos eletroquímico e fotoquímico. No tratamento fotoeletroquímico ocorreu a formação de AOX no início da reação, no entanto com o passar do tempo esses compostos foram degradados. / This study investigated the electrochemical oxidation of tannic acid on electrodes of the Dimensionally Stable Anode (DSA) type based on SnO2 and IrO2 as well as on boron doped diamond (BDD) electrodes. The electrolyses were performed in the galvanostatic mode, as a function of such parameters as current density and chloride concentration. The electrochemical oxidation of tannic acid was able to promote the reduction of the concentration of total phenolics, total organic carbon (TOC), and chemical oxygen demand (COD). For the DSA the best results of Total Organic Carbon (TOC) removal were achieved at 300 ppm chloride and current density of 25 mA cm-2. However, organochlorine compounds were formed and were not degraded with increased reaction times. For the BDD electrodes, the removal of approximately 98% TOC was obtained after 10 hours of reaction at 75 mA cm-2, in the absence of chloride. Major TOC removals were obtained with increasing current density. Electrolyses in the presence of chloride removed almost 100% TOC in shorter reaction times. Analysis of organohalogen compounds (AOX) showed no formation of organochlorine compounds. Lower current densities led to higher current efficiency (CE) and lower Energy Consumption (EC). The electrolyses in the presence of chlorine produced better CE results than those performed in the absence of chlorine. The photoelectrochemical oxidation of tannic acid in ADE-type electrodes of nominal composition Ti / Sn0.9 Ir0.3 O2 was also investigated in this work. The photoelectrochemical treatment was performed using a high pressure mercury vapor lamp 125 W as the source of irradiation. The variation in current revealed no significant difference in the oxidation of tannic acid. The variation in chloride concentration in the electrolyte markedly influenced the oxidation of tannic acid. The photoelectrochemical treatment was more efficient for TOC removal than the electrochemical and photochemical treatments. Formation of AOX occurred at the beginning of the photoelectrochemical treatment, but over time these compounds were degraded.

<div>Potassium-ion batteries (PIBs) recently emerged as a next-generation energy storage technology, utilizing abundant and inexpensive potassium as the charge carrier cation. PIBs operate by an analogous mechanism to lithium-ion batteries (LIBs), with reversible potassium intercalation in anode and cathode through an inorganic salt - organic solvent electrolyte medium. Despite its larger size, potassium exhibits several electrochemical advantages over sodium, including a higher affinity for intercalation into graphitic (carbonaceous) anodes, forming a stage-one KC₈ structure in graphite for a specific capacity of 279 mAh g^-1. This thesis aims to provide a thorough foundation for PIB carbon anodes, through a comprehensive experimental approach combining electrode synthesis, advanced material characterization and electrochemical-analytical techniques.</div><div><br></div><div>Safety concerns have consistently plagued LIBs despite almost three decades of widespread commercialization. Thermal runaway of LIBs can initiate as early as 80°C from exothermic breakdown of the solid electrolyte interphase (SEI) layer that covers the carbon anode surface. The subsequent reaction of lithiated carbon with electrolyte solvent leads to cathode decomposition and oxygen release for cell gassing and combustion. This thesis investigates the thermal runaway behavior of graphite anode for PIBs via differential scanning calorimetry analysis, determining the effect of electrode material, state-of-charge, and cycling history on heat generation. Notably, the PIB system emits significantly less heat overall than for LIBs, albeit an earlier and more intense onset reaction at 100°C raises safety concerns. Strategies to mitigate this exothermic reaction are presented, including electrode binder manipulation to improve graphite particle coverage and enhance SEI layer stability.</div><div><br></div><div>To further evaluate the practicality of PIBs, the electrochemical behavior of graphite anode was investigated from 0 - 40°C operating temperature, in comparison to standard LIBs. The poor rate capability of potassium is attributed to sluggish solid-state diffusion and augmented cell impedance, where 3-electrode studies revealed dramatic polarization of the potassium metal counter electrode at low temperatures. Accelerated cell aging at elevated temperatures is attributed to SEI layer growth induced by the 61% volumetric expansion of graphite during potassiation, as well as the extreme reactivity of potassium metal. A full-cell system with a Prussian blue nanoparticle cathode and graphite anode showed enhanced rate performance at low temperatures by removing potassium metal counter electrode. These results provide valuable mechanistic insight for potassium intercalation in graphite and offer a practical evaluation of temperature dependent electrochemical performance for PIBs.</div><div><br></div><div>Supplementary research includes the exploration of carbon nanofibers electrospun from polyacrylonitrile precursor with subsequent pyrolysis as PIB anode. The design of an amorphous, low density carbon with a nanoscale one dimensional morphology enables mitigation of the 61% volumetric expansion of graphite during potassiation. Remarkable stability (2000 charge-discharge cycles) is thus achieved by preventing electrode pulverization, SEI layer growth, and impedance rise during cycling. Electrochemical analysis revealed a pseudo-capacitance mechanism, enabling rapid charging through surface storage of potassium that could be enhanced by surface functionalization via plasma oxidation treatment. Moreover, two dimensional MXene transition carbonitride sheets were explored as PIB anode with X-ray diffraction and X-ray photoelectron spectroscopy used to study structural changes during potassium insertion.</div><div><br></div><div>Finally, the effect of particle morphology was investigated for LIB carbon anodes, wherein commercial graphite is compared with synthesized spherical and spiky carbons. Intercalation dynamics, side reaction rates (e.g. SEI growth), self-heating, and thermal runaway behavior were studied through a combination of electrochemical analysis and modeling by a finite volume method. Spherical particles outperform irregular commercial graphite by eliminating unstructured inhomogeneities that lead to non-uniform current distributions. Interestingly, spiky particles offer a nontrivial response, where the ordered irregularities enhance intercalation dynamics to prevent degradation at extreme operating conditions. These findings emphasize the importance of tailoring particle morphology and structure in promoting desired LIB behavior and suppressing unwanted problems.</div>