Dissertations / Theses on the topic 'Fundamentals of electrochemistry'

Graphene is reported to possess a range of unique and highly desired properties and consequently has potential to revolutionise the field of electrochemistry if diligently employed as a new-generation electrode material. Graphene potentially represents the world’s thinnest electrode material, but there are experimental parameters to be overcome: the first problem is how to electrically wire/connect to the graphene sample(s) as to obtain the reported benefits; the second issue is how to reduce aggregation of graphene sheets back to their lowest energy conformation, that is, graphite, due to the strong π–π interactions between the graphene sheets; the third and final limitation is that various fabrication routes produce graphene to differing qualities, a factor that must be considered when exploring its fundamental electrochemical properties and electroanalytical implementation. This thesis reports on the fundamental electrochemical characterisation and resultant electroanalytical applicability of utilising graphene as a novel electrode material. The thesis consists of four key contributions, each developing on the knowledge gained from the previous. Chapters 1 through to 3 give an overview of the relevant fundamental electrochemical concepts with which this thesis is concerned. Chapter 4 provides a ‘snap-shot’ of the state of the graphene literature from 2010 (upon the commencement of this work), from which successive chapters follow the chronological development and investigation of graphene as produced through a variety of synthesis methods, gradually building a complete picture and understanding of the electrochemistry of graphene and the implications of its properties towards the fabrication and implementation of graphene as an electroanalytical sensor substrate. IV | P a g e Chapter 5 details the relevant experimental information and the full physicochemical characterisation of the various graphene materials utilised within this work. Chapters 6 and 7 utilise graphenes that are fabricated via a ‘top-down’ approach, which is most commonly employed in the literature, where in order to ‘connect to’ the graphene a liquid suspension is immobilised onto a suitable electrode surface. Chapter 6 uses surfactant-modified graphene and investigates, for the first time, the influence that such surfactants have on the observed electrochemistry. Chapter 7 uses pristine graphene in solution and considers; the aspects of various ‘coverages’ of graphene, the supporting electrode substrate, and how the formation of few and multiple layered graphene structures can influence the observed response. These parameters are overlooked within the current literature. Chapter 8 utilises graphene that is fabricated via a ‘bottom-up’ Chemical Vapour Deposition approach, which gives rise to high quality single layer graphene domains that, once efficiently ‘housed’ in order to connect to the graphene, allow the electrochemical exploration of monolayer graphene to be realised and be compared to quasi-graphene and defect abundant graphene structures for the first time. This approach allows the structure of graphene to be correlated with that of the electrochemical response for the first time. Critically, this work unambiguously demonstrates that the electrochemical response is edge plane like defect dependent. The final part of this thesis (Chapter 9) utilises a range of modified graphenes including novel three-dimensional (3D) structures (a graphene foam and graphene paste) and functionalised graphene (graphene/graphitic oxide), with the effects of said modifications explored towards the fundamental electrochemical and electroanalytical properties obtained. The first part of this chapter reports the electrochemistry of a novel freestanding 3D graphene V | P a g e foam and, for the first time, critically compares this to a freestanding 3D carbon foam alternative. It is demonstrated that the graphene foam gives rise to beneficial voltammetric responses in non-aqueous media, namely ionic liquids. This chapter also explores the use of a graphene paste electrode and demonstrates that the voltammetric response is no better than that of a graphite based paste electrode. Last, the use of graphene/graphitic oxide as an electrode material is explored and shown to give rise to unique voltammetric signatures, which are coverage dependant and can be utilised as a means of characterising the successful production of graphene through the reduction of graphene/graphitic oxide (as commonly utilised within the current electrochemical literature). Furthermore, it is shown that the unique voltammetry observed at graphene/graphitic oxide modified electrodes can be used beneficially for electrocatalytic processes. This thesis demonstrates that, within the graphene electrochemical literature, control experiments are often an overlooked comparison, which are needed for the electrochemical response of graphene to be understood and before the benefits of graphene can be claimed in such instances where superiority is ‘demonstrated’.

Boron doped diamond (BDD), due to its exceptional electrochemical response (extended solvent window and low background current) and thermal properties (large thermal diffusivity and extreme resistance to thermal ablation), is investigated as the electrode material for thermoelectrochemical studies. A pulsed infrared (IR) laser technique is used to heat the electrode from the back (nonsolution) side. The non-isothermal pulsed technique enables mass transport to be more readily controlled as opposed to isothermal heating approaches such as a water bath. The effect of temperature on fundamental electrochemical processes, such as mass transport, electron transfer (ET) kinetics and thermodynamics of both outer sphere and inner sphere redox mediators is investigated on both BDD macro- and micro- electrodes. The effective temperature increase at electrode surface can be determined both experimentally and theoretically using finite element models. Enhanced mass transport and ET process at elevated temperatures, in addition to the temperature coefficient of the redox mediators, play a crucial role in the temperature dependent electrochemical response. Thermoelectrochemical studies are extended to an electroactive species which forms a solid structure after electrolysis. In particular, the cathodic electrodeposition of lead/lead oxide (Pb/PbO) under non-isothermal heating conditions in nitrate containing solutions is investigated. The effect of deposition potential, time, dissolved oxygen content and temperature are explored to understand the mechanism for the synthesis of crystalline PbO “plate” structures, and the role of electrodeposited Pb. Further work explores the effect of temperature on an electroactive species which upon electrolysis forms a solid product which fouls the electrode surface. Using a BDD microelectrode it is possible to show how temperature can be used to minimise the effect of surface blocking after the oxidation of a neurotransmitter, dopamine, which is known to lead to electrode fouling. Finally, proof of concept studies are undertaken to assess the suitability of a thermoelectrochemical approach to the detection of single nucleotide polymorphism (SNP) in deoxyribonucleic acid (DNA). Initial studies investigate immobilisation strategies for both (in separate experiments) electrochemically active self-assembled monolayers (SAM) and redox-labelled double stranded DNA on gold and BDD electrodes.

Intermittent renewable energy sources, such as solar and wind, will only be viable if the electrical energy can be stored efficiently. It is possible to store electrical energy cleanly by splitting the water into oxygen (a clean byproduct) and hydrogen (an energy dense fuel) via water electrolysis. The efficiency of hydrogen production is limited, in part, by the high kinetic overpotential of the oxygen evolution reaction (OER). OER catalysts have been extensively studied for the last several decades. However, no new highly active catalyst has been developed in decades. One reason that breakthroughs in this research are limited is because there have been many conflicting activity trends. Without a clear understanding of intrinsic catalyst activity it is difficult to identify what makes catalysts active and design accordingly. To find commercially viable catalysts it is imperative that electrochemical activity studies consider and define the catalyst’s morphology, loading, conductivity, composition, and structure. The research goal of this dissertation is twofold and encompasses 1) fundamentally understanding how catalysis is occurring and 2) designing and developing a highly active, abundant, and stable OER catalyst to increase the efficiency of the OER. Specifically, this dissertation focuses on developing methods to compare catalyst materials (Chapter II), understanding the structure-compositional relationships that make Co-Fe (oxy)hydroxide materials active (Chapter III), re-defining activity trends of first row transition metal (oxy)hydroxide materials (Chapter IV), and studying the role of local geometric structure on active sites in Ni-Fe (oxy)hydroxides (Chapter V). As part of a collaboration with Proton OnSite, the catalysts studied are to be integrated into an anion exchange membrane water electrolyzer in the future. This dissertation includes previously published and unpublished co-authored material.
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Understanding the characteristics of special nuclear materials in LiCl-KCl eutectic salt is extremely important in terms of effective system operation and material accountability for safeguarding pyroprocessing technology. By considering that uranium (U) is the most abundant and important element in the used nuclear fuel, measurements and analyses of U properties were performed in LiCl-KCl eutectic salt. Therefore, the electrochemical techniques such as cyclic voltammetry (CV), open circuit potential (OCP), Tafel, linear polarization (LP), and electrochemical impedance spectroscopy (EIS) were conducted under different experimental conditions to explore the electrochemical, thermodynamic, and kinetic properties of U in LiCl-KCl eutectic. The ultimate goal of this study was to develop proper methodologies for measuring and analyzing the exchange current density (i0) of U3+/U reaction, which has not been fully studied and understood in literature. In the preliminary study, cerium (Ce) was selected as a surrogate material for uranium and its behavior was being explored with the developments of experimental methods. CV was performed to evaluate Ce properties such as the diffusion coefficients (D), apparent standard reduction potential (E0*), Gibbs free energy (DG), and activity coefficient (g). In addition, EIS methods were adapted and specific experimental procedures were established for the proper i0 measurements providing repeatable and reproducible data sets. The i0 values for Ce3+/Ce pair were ranging from 0.0076 A cm-2 to 0.016 A cm-2, depending on the experimental conditions. These preliminary results give insight in developing the experimental setups and methods to evaluate the properties of U in LiCl-KCl. Plus, Ce is one of the lanthanide (Ln) fission products in electrorefiner (ER) system; therefore, the resulting data values yield useful information of the fundamental behaviors of Ln elements in the system. Based on these developed methodologies, the experimental designs and routines were established to explore the main properties (e.g., D, E0*, etc.) of UCl3 in LiCl-KCl eutectic salt under different concentrations (0.5 wt% to 4 wt% UCl3) and temperatures (723 K to 798 K). Specially, the i0 values of U3+/U were evaluated via EIS, LP, Tafel, and CV methods. All i0 values had linear trends with the change of concentration and temperature; however, these values measured by LP, Tafel, and CV methods were greatly influenced by the change in electrode surface area. Overall, the i0 values agreed within 33% relative error range with the EIS method being the most consistent and accurate in comparison to reported literature values. The measured values of i0 were ranging from 0.0054 A cm-2 to 0.102 A cm-2. Therefore, an extremely reliable database for i0 was provided and it is feasible to anticipate the i0 kinetics in other experimental conditions by using the provided equation models. Furthermore, GdCl3 was added to the LiCl-KCl-UCl3 system to explore the effects of other elements on the U properties such as the diffusion coefficients, thermodynamic properties, and i0 kinetics. The diffusion coefficient was generally decreased by 12 ~ 35% with addition of GdCl3 in LiCl-KCl-UCl3; however, the apparent standard potentials and exchange current density follow the same trends with data obtained without GdCl3 additions. Hence, the results indicate that the thermodynamic and kinetic values for U3+/U reaction in LiCl-KCl eutectic salt are not greatly influenced by the presence of GdCl3.

In recent years, Polymer Electrolyte Membrane Fuel Cells (PEMFC) have attracted much attention due to their potential as a clean power source for many applications, including automotive, portable and stationary devices. This resulted in a tremendous technological progress, such as the development of new membranes and electro-catalysts or the improvement of electrode structures. However, in order to compete within the most attractive markets, the PEMFC technologies did not reach all the required characteristics yet, in particular in terms of cost and durability.Because of the strong coupling between different physicochemical phenomena, the interpretation of experimental observations is difficult, and analysis through modeling becomes crucial to elucidate the degradation and failure mechanisms, andto help improving both PEMFC electrochemical performance and durability.The development of a theoretical tool is essential for industrials and the scientific community to evaluate the PEMFC degradation and to predict itsperformance and durability in function of the materials properties and in a diversity of operating conditions. This manuscript summarizes my scientific research efforts in this exciting topic during the last 9 years in France, including my invention of the MEMEPhys multiscale simulation package,developed on the basis of my childhood passion for the New Technologies for Energyin Argentina. My perspectives of adapting this approach to other electrochemical systems such as water electrolyzers and batteries are also discussed.

This thesis aims to provide insight into the fundamental electrochemical processes taking place when cycling SnO2 in lithium-ion batteries (LIBs). Special attention was paid to the partial reversibility of the tin oxide conversion reaction and how to enhance its reversibility. Another main effort was to pinpoint which limitations play a role in tin based electrodes besides the well-known volume change effect in order to develop new strategies for their improvement. In this aspect, Li+ mass transport within the electrode particles and the large first cycle charge transfer resistance were studied. Li+ diffusion was proven to be an important issue regarding the electrochemical cycling of SnO2. It was also shown that it is the Li+ transport inside the SnO2 particles which represents the largest limitation. In addition, the overlap between the potential regions of the tin oxide conversion and the alloying reaction was investigated with photoelectron spectroscopy (PES) to better understand if and how the reactions influence each other`s reversibility. The fundamental insights described above were subsequently used to develop strategies for the improvement of the performance and the cycle life for SnO2 electrodes in LIBs. For instance, elevated temperature cycling at 60 oC was employed to alleviate the Li+ diffusion limitation effects and, thus, significantly improved capacities could be obtained. Furthermore, an ionic liquid electrolyte was tested as an alternative electrolyte to cycle at higher temperatures than 60 oC which is the thermal stability limit for the conventional LP40 electrolyte. In addition, cycled SnO2 nanoparticles were characterized with transmission electron microscopy (TEM) to determine the effects of long term high temperature cycling. Also, the effect of vinylene carbonate (VC) as an electrolyte additive on the cycling behavior of SnO2 nanoparticles was studied in an effort to improve the capacity retention. In this context, a recently introduced intermittent current interruption (ICI) technique was employed to measure and compare the development of internal cell resistances with and without VC additive.

L’électrochimiluminescence (ECL) est un phénomène d’émission de lumière obtenue suite à la génération d’espèces très réactives à l’électrode. Ces dernières vont subir une série de réactions de transfert d’électrons qui conduisent à la formation d’un état excité qui mène à l’émission finale de photons. La première partie de mon travail de thèse a porté sur l’étude de deux systèmes supramoléculaires. Les performances ECL d’un dérivé du spirofluorène et de trois composés modifiés avec un truxène comme partie centrale sont examinées. L’étude d’un deuxième système supramoléculaire, [18]-C-6bispyréne, a permis de démontrer une nouvelle propriété de l’ECL, maintenant capable de distinguer entre deux énantiomères, grâce à la détection du niveau de polarisation de l’émission ECL résultante. La combinaison entre ECL et systèmes confinés est présentée dans la deuxième partie de ma thèse. L’amplification du signal ECL par annihilation a été possible grâce à l’emploi d’un dispositif comprenant deux électrodes séparées par une distance de 100 nm. De plus, l’imagerie ECL a été utilisée pour mettre en évidence l’amélioration des performances de l’ECL bipolaire en utilisant une configuration comprenant un micropore planaire de 20 µm de long. Enfin, une nouvelle microscopie basée sur l’ECL a été développée. En perméabilisant la membrane cellulaire, l’ensemble de la cellule est visualisé par ECL. De plus, en se basant sur la distribution de l’émission ECL dans différents plans focaux, nous avons pu démontrer qu’une des caractéristiques fondamentales de cette nouvelle microscopie ECL est d’être confinée à la surface de l’électrode du fait des temps de vie limités des radicaux électro-générés. L’utilisation d’électrodes transparentes de nanotubes de carbone imprimés sur une lamelle de microscope a permis de réaliser l’imagerie ECL de cellules marquées aussi bien en réflexion qu’en transmission
Electrogenerated chemiluminescence (ECL) is a light emission phenomenon initiated by electrochemically generated radical species, which then undergo a series of electron transfer reactions. It leads to the final generation of an excited state that radiatively decays to the ground state. In this work, my goal was to develop fundamental aspects of ECL as well as analytical applications at different scales. In the first part, two supramolecular systems are studied. The ECL performances of spirofluorene derivatives based on trigonal truxene-core structure are investigated, focusing on the role of the different functional groups on the ECL properties. Then a bispyrene scaffold mounted on a constrained polyether macrocycle displaying intense excimer fluorescence has been selected to study the circularly polarized ECL. We show for the first time that ECL can discriminate enantiomers. In the second part of the thesis, annihilation ECL is enhanced by exploiting nanogap amplification. Furthermore, ECL imaging experiments enabled to demonstrate the increase in the performances of a bipolar electrochemistry system by employing a solid-state micropore configuration. Finally, the first steps in the development of a new ECL-based microscopy are presented. Using a unique ECL mechanism, which involves short-lifetime electrogenerated radicals, surface-confinement of ECL microscopy was demonstrated by cellular membranes’ imaging. ECL microscopy applied to cells imaging was further improved by adding a permeabilization step during cells labeling procedure. Disposable transparent carbon nanotube-based electrodes inkjet-printed on classic microscope glass coverslips, were used to image cells in both reflection and transmission configurations

Após uma abordagem crítica a respeito do impacto da poluição sobre o meio ambiente, decorrente do uso indiscriminado dos recursos naturais, a presente Tese discute o papel do ozônio na remediação da carga de poluentes emitida ao meio ambiente por diferentes efluentes urbanos e industriais. Diferentes tecnologias disponíveis para a produção de ozônio em pequena e grande escala são apresentadas e discutidas, dando especial enfoque para a produção eletroquímica de ozônio, PEO, a qual é o assunto abordado na parte experimental da Tese. Os experimentos efetuados foram separados em estudos fundamentais, os quais consistiram no estudo da PEO em eletrodos de PbO2 e de IrO2+Ta2O5, em diferentes condições da temperatura e da composição do eletrólito, e aplicados, onde foi projetado e caracterizado um reator para a PEO com capacidade de até 100 A. Na parte fundamental foi proposto uma nova metodologia eletroquímica para a caracterização de eletrodos rugosos/porosos, a qual é baseada na análise combinada de parâmetros superficiais extensivos e intensivos. A partir dos dados obtidos no estudo cinético foi proposto um mecanismo representativo da produção simultânea de oxigênio e ozônio, o qual possibilita uma análise da eficiência da corrente para a PEO com base na cobertura superficial dos intermediários oxigenados. Os estudos de caracterização do reator protótipo #1, o qual foi construído empregando-se um eletrodos planar perfurado de PbO2 como ânodo e um eletrólito polimérico sólido (Nafion 117) como separador dos compartimentos catódico e anódico, revelaram que a PEO é uma promissora alternativa ao processo corona convencional empregado para a geração de ozônio na fase gasosa.
After a critical discussion about the environmental pollution resulted from the continuous consumption of the natural energy sources, is discussed in the Thesis the role of the ozone on reduction of the pollution burden released in the environment by different urban and industrial effluents. Different technologies available for the ozone production in the low and large scale are presented and discussed, given a special attention for the electrochemical ozone production, EOP, which is the issue under investigation in the experimental section of the Thesis. The experiments were separated in fundamentals, which comprises the investigation of EOP at PbO2 and IrO2+Ta2O5 electrodes, in different conditions of the temperature and composition of the electrolyte, and applied studies, where is proposed and characterised a reactor for EOP having a capacity of up to 100 A. In the fundamental section one proposed a new electrochemical methodology for characterisation of porous/rugged electrodes, which is based on a combined analysis of the intensive and extensive surface parameters. From the kinetic data it was proposed a electrode mechanism representative of the simultaneous production of oxygen and ozone, which makes possible to analyse the EOP current efficiency considering the surface coverage by the oxygenated reaction intermediates. The characterisation of the electrochemical reactor (prototype #1), which was constructed using a planar perforated PbO2 as anode and a solid polymer electrolyte (Nafion 117) as separator of the cathodic and anodic compartments, revealed that EOP is a promising alternative technology to the conventional corona process used in the ozone generation in the gaseous phase. P.S. For more details about the present Thesis in a English version see references extracted from this contribution already cited as a header in the main chapters.

Orientador: Prof. Dr. Hugo Barbosa Suffredini
Dissertação (mestrado) - Universidade Federal do ABC. Programa de Pós-Graduação em Ciência e Tecnologia/Química, 2015.
O presente trabalho é referente à utilização de técnicas eletroanalíticas diretamente na interface formada entre dois líquidos imiscíveis. Esta nova metodologia de trabalho está em pleno desenvolvimento em nosso grupo de pesquisa, apresentando resultados promissores em diversas vertentes. De maneira específica neste projeto, os estudos foram realizados em fase aquosa, constituída ora por uma solução de NaCl 1x10-3 mol L-1, ora por água do mar, bem como em fase oleosa, aqui representada pelo petróleo bruto. Utilizou-se o eletrodo impresso de carbono como ferramenta de trabalho, aplicando-se técnicas eletroanalíticas, tais como a voltametria cíclica e a voltametria de onda quadrada. Contaminou-se artificialmente o petróleo com algumas moléculas-modelo, em particular o fenol e o cicloexano. Para iniciar os experimentos, verificou-se a possibilidade de obtenção das respostas de oxidação ou redução das moléculas a partir da técnica de voltametria cíclica, utilizando nesta etapa o NaCl 1x10-3 mol L-1 como eletrólito suporte. Em seguida, estudaram-se os mesmos sistemas por voltametria de onda quadrada, técnica esta mais sensível e adequada para fins analíticos. Resultados obtidos mostraram ser possível realizar a caracterização de moléculas introduzidas artificialmente à fase petróleo. Foram satisfatórios nos experimentos realizados neste trabalho a obtenção de dados que permitiram se obter voltamogramas para melhor análise e compreensão dos fenômenos de oxidação e redução das moléculas estudadas. Para tanto, foi utilizando como ferramenta principal as técnicas eletroanalíticas. Ainda, houve a possibilidade de se determinar o tempo de saturação do eletrodo impresso de carbono, na área interfacial petróleo/água. Deste trabalho qualitativo, foi possível concluir que todas as moléculas propostas neste projeto foram detectadas com êxito, ou seja, a técnica proposta em interfaces foi eficiente para a finalidade proposta. Trabalhos futuros serão necessários para refinar a metodologia e aplicar o sistema em amostras reais.
This work describes the use of a new electrochemical technique applied directly at the interface between two immiscible liquids. This new methodology is now been developed in our group and promising results were found in different research lines. More specifically, the studies in this project were carried out in aqueous support electrolyte solution constituted by a home-made 1 x 10-3 NaCl solution and also constituted by natural sea salt water. The organic phase was constituted by crude oil. A carbon screen-printed electrode was used as the main tool in this work. Cyclic Voltammetry (CV) and Square Wave Voltammetry (SWV) were used as electrochemical techniques. Portions of crude oil were contaminated with model molecules, as phenol and cyclohexane. Firstly, the CV was used to determine the possibility of detection. Following these preliminary studies, SWV studies were carried out since that technique is more adequate to promote analytical studies. Results indicates that was possible to characterize molecules artificially introduced to oil phase. Furthermore, it was possible to determine the time of saturation of the printed-screen carbon electrode at the interfacial Oil / water region. It was possible to conclude from this qualitative work that all molecules were successfully detected directly at the crude oil/water interface. On the other hand, future works will be necessary to improve this kind of methodology.

A análise da concentração de metabólitos no sangue pode refletir o comportamento metabólico durante o exercício físico. O presente estudo teve por objetivo analisar o comportamento eletroquímico e do distúrbio ácido-básico de praticantes de Parkour, durante a realização de um percurso que utilizou movimentos fundamentais desta modalidade. Foram avaliados 23 praticantes de Parkour do sexo masculino, com idade média de 21,4±2,7 anos, com no mínimo dois anos de experiência na modalidade. Foram realizadas cinco coletas de sangue capilar da polpa digital dos dedos da mão, em diferentes momentos: (1) repouso, (2) após aquecimento, (3) logo após o esforço, (4) após cinco minutos e (5) após dez minutos. Foi realizado um percurso usando movimentos fundamentais da modalidade para caracterizar o esforço. A amostra foi analisada utilizando o aparelho de gasometria GEM Premier 3000, utilizando os parâmetros pH, Na+, K+, pH, lactato e HCO3−. Os valores de pH, lactato e HCO3− apresentaram diferença significativa (p<0,05) na maioria dos momentos analisados. Os valores de Ca2+, Na+, K+ apresentaram diferença significativa após o esforço, e uma rápida recuperação após cinco e dez minutos, quando comparados com os valores de referência. Os resultados obtidos demonstraram uma adaptação fisiológica dos eletrólitos, com rápida recuperação aos valores de referência. As alterações dos valores do pH, lactato e HCO3− identificam a utilização de vias anaeróbias para a produção de energia, assim como uma evidente acidose metabólica após o esforço. Os valores obtidos são similares a atletas de alto rendimento, principalmente de modalidades de força e velocidade. O presente estudo contribuiu para o entendimento do comportamento eletroquímico e do equilíbrio ácido-básico da modalidade Parkour, preenchendo assim uma lacuna na literatura.
The analysis of the blood metabolites can show the metabolic behavior during physical exercises. This study aimed to analyze the electrochemical and acid base disorders behavior in Parkour athlets, during an exercise routine that used basic movements of this particular sport. Twenty three male athletes (average of 21,4±2,7 years old) with a minimum of two years of experience in Parkour were evaluated. The capillary blood was collected through the fingers in five diferent moments: (1) rest, (2) after warm-up, (3) after exercise, (4) five minutes later and (5) ten minutes later. A course using basic Parkour movements was used as reference. The samples were analyzed by the gasometric equipment GEM Premier 3000. The variables pH, sodium (Na+), potassium (K+), calcium (Ca2+), lactate and bicarbonate (HCO3−) were used. The pH, lactate and HCO3− showed significant variation (p<0,05) in most of the analyzed moments. Ca2+, Na+ and K+ values showed significant difference right after the exercise and a fast recovery after five and ten minutes when compared to the reference values. Results showed a physiological adaptation of electrolytes with a fast recovery back to the reference values. The values of pH, lactate e HCO3− present an anaerobic system usage, as well as a clear metabolic acidosis post exercise. The values obtained in this study are similar to high performance athletes values, mostly in strength and speed modalities. This study contributes to the understanding of the eletrochemical and acid-basic disorders behavior of Parkour athletes, filling a gap in the literature.

Notre dépendance croissante vis-à-vis des batteries lithium-ion pour le stockage d’énergie exige une amélioration de leurs électrodes positives, qui fonctionnent encore grâce au redox cationique des métaux de transition. L’émergence du redox anionique – une approche transformationnelle qui double la capacité des électrodes positives « Li-riches » – a récemment suscité de grands espoirs mondialement. Toutefois, des questions subsistent sur les origines fondamentales du redox anionique et sur son potentiel dans les applications pratiques. Cette thèse vise à répondre précisément à ces questions, en utilisant les connaissances de la chimie des solides, de l’électrochimie, de la spectroscopie des rayons X, et de la thermochimie. Pour ce faire, nous fournissons d’abord un compte rendu historique, un cadre théorique, les règles de conception de nouveaux matériaux, ainsi qu’un résumé des techniques de caractérisation propres au redox anionique. Ensuite, à travers des études expérimentales menées à la fois sur un matériau « modèle » (à base de métal 4d) et sur un matériau « pratique » (à base de métal 3d), nous montrons comment l’interaction fondamentale entre les processus de redox cationique et anionique régit les propriétés pratiques de ces matériaux (c’est-à-dire hystérésis de tension, performance de vitesse, chute de tension, et production de chaleur). Enfin, en utilisant ces résultats, nous décrivons les approches possibles pour améliorer ces matériaux et en concevoir de nouveaux. Nous résumons également leurs chances d’implantation sur le marché face aux cathodes lamellaires à base de nickel qui prévalent aujourd’hui
Our increasing dependence on lithium-ion batteries for energy storage applications calls for continual performance improvements of their positive electrodes, which have so far relied solely on cationic redox of transition-metal ions for driving the electrochemical reactions. Great hope has recently been placed on the emergence of anionic redox – a transformational approach for designing Li-rich positive electrodes as it leads to a near-doubling of capacity – hence generating worldwide research interest. However, questions have been raised on the fundamental origins of anionic redox and whether its full potential can be realised in applications. This is exactly what this thesis aims to answer by using the knowledge from the fields of solid-state chemistry, electrochemistry, X-ray spectroscopy, and thermochemistry. We first provide a comprehensive historical account, a theoretical framework, some materials’ design rules, and a survey of characterization techniques specific to anionic redox. Then, through comprehensive experimental studies that were performed in parallel on one ‘model’ (4d metal based) and one ‘practical’ (3d metal based) material, we highlight how the fundamental interplay between cationic and anionic redox processes governs the application-wise important properties of these promising battery materials (i.e. voltage hysteresis, rate performance, voltage decay, and heat generation,). Finally, using these results, we outline possible approaches for improving such materials and for designing novel ones. We also summarize their chances for market implementation in face of the competing nickel-based layered cathodes that are prevalent today

Previous research indicates compositional variation of pentlandite [(Fe,Ni)9S8] and the effect this variation may have on the electrochemical behaviour of pentlandite is poorly understood. Pentlandite is the primary source of nickel and an important base metal sulfide (BMS) in the platinum industry. It hosts significant amounts of PGEs especially palladium and rhodium when compared to chalcopyrite and pyrrhotite. The aim of the project was to investigate the possible compositional variations of natural pentlandite and the effect of these variations on the electrochemical behavior thereof. To study possible compositional variations, single pentlandite particles - in the order of 100μm in size from flotation concentrates (PGM deposits) and massive samples (massive ore bodies) - from various sources were employed. Electron microprobe analysis indicated a compositional variation of the pentlandite particles hand-picked from the flotation concentrate samples. Variation was observed in the cobalt, iron and nickel content and this was independent of the deposit. A slight compositional variation was observed from the massive pentlandite samples. The effect the compositional variation may have on the electrochemical reactivity of pentlandite was investigated using electrochemical techniques, i.e. measurement of the polarisation resistance and mixed potential as well as performing linear anodic voltammetry, current density–transients and electrochemical impedance spectroscopy (i.e. capacitance). Poor electrochemical response of the pentlandite microelectrodes was observed. Pre–existing pores, deep pores, cracks and the brittle nature of pentlandite microelectrodes may have contributed to the poor electrochemical response of natural pentlandite particles hand-picked from the flotation concentrate. Slight compositional variations of the massive pentlandite sample influenced the electrochemical behaviour. In aerated solutions, iron enriched pentlandites were less reactive after progressive oxidation. The lower reactivity of the electrodes was a result of thick oxide films formed. This was illustrated by polarisation resistance and capacitance measurements. The lower reactivity of the electrodes was also related to the mechanism of the reduction of oxygen at oxidised passive electrode surfaces. It is however difficult to distinguish if the differences in the reactivity was a result of the Fe/Ni ratio or the influence of cobalt. Current density transients confirmed that the reactivity of a pentlandite electrode to be time dependent. The reactivity of the electrode decreased during oxidation. A variation in the electronic properties of the formed oxide film was observed. Slight compositional variation of pentlandite did not have a significant effect on the rest potential values as do changes in the type of sulfides (e.g. pyrite vs. pentlandite). This was confirmed by similar rest potential values of various pentlandite electrodes. The oxidation of synthetic pentlandite may be influenced by the chemical composition. In de-aerated solutions, anodic oxidation (as indicated by the linear anodic voltammogram) of synthetic pentlandite started at a potential lower than of the natural electrodes. In aerated solutions, the synthetic pentlandite was less reactive and formed thicker oxide films. Copyright
Dissertation (MEng)--University of Pretoria, 2010.
Materials Science and Metallurgical Engineering
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