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The experimental work described in this thesis is aimed primarily towards elucidation of the speciation of zinc-cyanide systems at elevated pH. In this study the formation and stability of H+-eN-, binary Zn2+-eN- and ternary Zn2+-CN--QH- complexes were studied by glass electrode potentiometry in aqueous solutions at 25.0°0 and in a medium of ionic strength of 0.1 mol dm-3. The solution pH was varied to cover the range 4 to 11. The study was undertaken with a view to establishing whether and under what conditions soluble binary zinc-cyanide complexes and ternary zinc-cyanide-hydroxide complexes form, and to determine formation constants for any such species that are found. This information would be useful in defining more precisely the speciation of solutions containing zinc and cyanide ions at elevated pH values. A titration method was used, in which hydrogen ion concentration was monitored by means of a glass indicating electrode. The cell was calibrated to allow measurements of hydrogen ion concentration rather than hydrogen ion activity. Owing to precipitation difficulties, the reagents were used at sub-millimolar concentration levels. The potentiometric data was interpreted with the aid of various formation function plots together with the use of various computer programs, such as HALTAFALL and ESTA. The results show that the ternary complex Zn(ON)3(OH)2- is formed in significant amounts in solutions of pH > 8.5. Some evidence was also obtained for the existence of the five coordinated species Zn(CN)3(OH)~- and Zn(CN)~- in these solutions, but existence of the latter two species cannot yet be regarded as firmly established. No polynuclear complexes were detected at the sub-millimolar concentrations used. Formation constants are reported for H+-eN- and both binary Zn2+-eN- and ternary Zn2+-eN--QH- species. / Thesis (M.Sc.)-University of Natal, Durban, 1990.

L'intérêt porté sur la miniaturisation des systèmes par la communauté scientifique est grand, que ce soit pour des raisons de mobilité, d'économie d'énergie ou d'innovation technologique. L'objectif de cette thèse est de déterminer les caractéristiques physiques et structurales des couches minces et des nanofils d'oxydes métalliques synthétisés par la méthode électrochimique. La première partie de cette thèse est consacrée à l'oxyde de bismuth en phase delta. Les couches minces élaborés par électrochimie sont de très bonne qualité cristalline, et seul la phase delta- Bi2O3 est présente. Le caractère nano structuré des couches minces est mis en évidence par les expériences de microscopie électronique en transmission (MET) et participe à la stabilisation de cette phase à température ambiante. Les mesures de conductivité réalisées par spectroscopie d'impédance complexe montrent un comportement différent selon la nature du substrat utilisé. Nous observons une excellente conductivité électrique des dépôts réalisés sur les substrats en argent doré (4*10-3 S*cm-1), alors que les dépôts obtenus sur l'inox montre un comportement très résistif (10-7 S*cm-1). La seconde partie de cette étude concerne l'oxyde de zinc. Les conditions d'élaboration par électrochimie influence les propriétés structurales et physiques des couches minces obtenues. Les différents traitements thermiques réalisés sur les couches minces de ZnO ont permis d'améliorer la qualité optique des couches et de modifier la structure du ZnO par incorporation d'azote lors de recuit dans l'ammoniaque. La dernière partie est consacrée à la synthèse et à la caractérisation de nanofils de ZnO élaborés par la méthode " template ". Cette méthode nous a permis de confiner la croissance par électrochimie dans des pores de différents diamètres. Les observations réalisés par MET et MET en Haute Résolution montrent que les nanofils obtenus sont monocristallins et de bonne qualité. Les propriétés d'émission observées en PL sont très proches des propriétés d'émission des couches minces

Women are four to eight times more likely to injure their anterior cruciate ligament (ACL) compared to men. It is most commonly injured through a non-contact mechanism during game time situations. During landings, women display valgus collapse, where a less active gluteus medius muscle (GMed) may be unable to control the internal rotation of the thigh, causing an increase in knee joint abduction angle, augmenting the risk of ACL injury. This study’s purpose was to determine the difference between 12 male and 12 female athletes in muscle activity, specifically the GMed, and the 3D kinematics and kinetics of the lower-limb during drop jump landings from three heights; maximum vertical jump height, tibial length, and a commonly used height of 40cm. Results showed that females had greater hip adduction and knee abduction angles compared to men. The GMed activity showed no significant differences between sexes at each drop jump height.

Monitoring bio-electric events is a common procedure, which provides medical data required in clinical and research applications. Electrophysiological measurements are applied in diagnosis as well as evaluation of the performance of different body organs and systems, e. g. the heart, muscles and the nervous system. Furthermore, it is staple feature in operation rooms and extensive care units. The performance of the recording system is affected by the tools and instrumentation used and the bio-electrode is a key-player in electrophysiology, hence, the improvements in the electrode recording technique will be directly reflected in the system?s performance in terms of the signal quality, recording duration as well as patient comfort. In this thesis, a design methodology for micro-spike array dry bio-electrodes is introduced. <br /><br /> The purpose of this methodology is to meet the design specifications for portable long-term EEG recording and optimize the electrical performance of the electrodes by maximizing the electrode-skin contact surface area, while fulfilling design constraints including mechanical, physiological and economical limitations. This was followed by proposing a low cost fabrication technique to implement the electrodes. The proposed electrode design has a potential impact in enhancing the performance of the current recording systems, and also suits portable monitoring and long term recording devices. The design process was aided by using a software design and optimization tool, which was specifically created for this application. <br /><br /> The application conditions added challenges to the electrode design in order to meet the required performance requirements. On the other hand, the required design specifications are not fulfilled in the current electrode technologies which are designed and customized only for short term clinical recordings. <br /><br /> The electrode theory of application was verified using an experimental setup for an electrochemical cell, but the overall performance including measuring the electrode impedance is awaiting a clinical trial.

Recent advances in third generation photovoltaics, particularly the rapid increase in perovskite power conversion efficiencies, may provide a cheap alternative to silicon solar cells in the near future. A key component to these devices is the transparent front electrode, and in the case of Dye Sensitized Solar Cells, it is the most expensive part. A lightweight, cost-effective, robust, and easy-to-fabricate new generation TCE is required to enable competition with silicon. Indium Tin Oxide, commonly used in touchscreen devices, Organic Light Emitting Diodes (OLEDs), and thin film photovoltaics, is widely used and commonly referred to as the industry standard. As the global supply of indium decreases and the demand for this TCE increases, a similar alternative TCE is required to accompany the next generation solar cells that promise energy with lighter and significantly cheaper modules. This alternative TCE needs to provide similar sheet resistance and optical transmittance to ITO, while also being mechanically and chemically robust. The work in this thesis begins with an exploration of several synthesized ITO replacement materials, such as copper nanowires, conductive polymer PEDOT:PSS, zinc oxide thin films, reduced graphene oxide and combinations of the above. A guiding philosophy to this work was prioritizing cheap, easy deposition methods and overall scalability. Shortcomings of these TCEs were investigated and different materials were hybridized to take advantage of each layers strengths for development of an ideal ITO replacement. For CuNW-based composite electrodes, ~85% optical transmittance and ~25 Ω/sq were observed and characterized to understand the underlying mechanisms for optimization. The second half of this work is an examination of many different perovskite synthesis methods first to achieve highest performance, and then to integrate compatible methods with our CuNW TCEs. Several literature methods investigated were irreproducible, and those that were successful posed difficulties integrating with CuNW-based TCEs. Those shortcomings are discussed, and how future work might skirt the issues revealed here to produce a very low cost, high performance perovskite solar cell.

Approved for public release; distribution is unlimited / The aim of this study was to fabricate tin/carbon (Sn/C) battery anodes using a novel approach, reduction expansion synthesis (RES), and test their performance as electrodes in lithium or sodium batteries. A second preparation route, the Aerosol-Through-Plasma (ATP) method, was also employed for comparison. The specimens generated were characterized, before and after cycling, using techniques such as X-ray diffraction, scanning, and transmission electron microscopy. The RES technique was successful in creating remarkably small (ca. <5 nm) nano-scale particles of tin dispersed on the carbon support. The use of the electrodes as part of coin cell batteries resulted in capacitance values of 320 mAh/g and 110 mAh/g for lithium-ion and sodium-ion batteries, respectively. Nano-sized Sn particles were found before and after cycling. It is believed that bonds between metal atoms and dangling carbon produced via the reduction of the carbon surface during RES were responsible for the materials' ability to withstand stresses during lithiation, avoid volumetric expansion, and prevent disintegration after hundreds of cycles. When tin loading in Sn/C was increased from 10% to 20%, an increase of capacitance from 280 mAh/g to 320mAh/g was observed; thus, increased tin loading is recommended for future studies. Tin/carbon produced using ATP presented morphology consistent with stable electrodes, although battery testing was not completed because of the difficulty of producing the material in sufficient quantity. / Military Expert 5, Republic of Singapore Navy

Submitted in the fulfillment of the requirements for the Master of Engineering, Durban University of Technology, Durban, South Africa. 2016. / The effectiveness of using a low cost non - platinum (Pt) material for the catalyst layer of a polymer electrolyte fuel cell (PEMFC) was investigated. A test cell and station was developed. Two commercial Pt loaded membrane electrode assemblies (MEA) and one custom MEA were purchased from the Fuelcelletc store. Hydrogen and oxygen were applied to either side of the custom MEA which resulted in an additional sample tested. An aluminium flow field plate with a hole type design was manufactured for the reactants to reach the reaction sites. End plates made from perspex where used to enclose the MEA, flow field plates, and also to provide reactant inlet and outlet connection points. The developed test station consisted of hydrogen and oxygen sources, pressure regulators, mass flow controllers, heating plate, and humidification units. A number of experimental tests were carried out to determine the performance of the test cells. These tests monitored the performance of the test cell under no-load and loaded conditions. The tests were done at 25 °C and 35 °C at a pressure of 0.5 bar and varying hydrogen and oxygen volume flow rates. The no-load test showed that the MEA’s performed best at high reactant flow rates of 95 ml/min for hydrogen and 38 ml/min for oxygen. MEA 1, 2, 3, and 4 achieved an open circuit voltage (OVC) of 0.936, 0.855, 0.486 and 0.34 V respectively. The maximum current density achieved for the MEAs were 0.3816, 0.284, 15x10-6, and 50x10-6 A/cm2. Under loaded conditions the maximum power densities achieved at 25 °C for MEA’s 1, 2, 3, and 4 were 0.05, 0.038, 2.3x10-6, 1.99x10-6 W/cm2 respectively. Increasing the temperature by 10°C for MEA 1, 2, 3, 4 resulted in a 16.6, 22.1, 1.79, 10.47 % increase in the maximum power density. It was found that increasing platinum loading, flow rates, and temperature improved the fuel cell performance. It was also found that the catalytic, stability and adsorption characteristics of silver did not improve when combining it with iridium (Ir) and ruthenium oxide (RuOx) which resulted in low current generation. The low maximum power density thus achieved at a reduced cost is not feasible. Thus further investigation into improving the catalytic requirements of non Pt based catalyst material combinations is required to achieve results comparable to that of a Pt based PEMFC. / M

Clean and affordable energy, especially solar energy, is becoming more and more important as our annual total energy consumption keeps rising. However, to make solar energy more affordable and accessible, the cost for fabrication, transportation and assembly of all components need to be reduced. As a crucial component for solar cells, transparent conductive electrode (TCE) can determine the cost and performance. A light weight, easy-to-fabricate and cost-effective new generation TCE is thus needed. While indium-doped tin oxide (ITO) has been the most widely used material for commercial applications as TCEs, its cost has gone up due to the limited global supply of indium. This is not only due to the scarcity of the element itself, but also the massive production of various opto-electronic devices such as TVs, smartphones and tablets. In order to reduce the cost for fabricating large area solar cells, substitute materials for ITO should be developed. These materials should have similar optical transmittance in the visible wavelength range, as well as similar electrical conductivity (sheet resistance) to ITO. This work starts with synthesizing ITO-replacing nano-materials, such as copper nanowires (CuNWs), derivative zinc oxide (ZnO) thin films, reduced graphene oxide (rGO) and so on. Further, we applied various deposition techniques, including spin-coating, spray-coating, Mayer-rod coating, filtration and transferring, to coat transparent substrates with these materials in order to fabricate TCEs. We characterize these materials and analyze their electrical/optical properties as TCEs. Additionally, these fabricated single-material-based TCEs were tested in various lab conditions, and their shortcomings (instability, rigidity, etc.) were highlighted. In order to address these issues, we hybridized the different materials to combine their strengths and compared the properties to single-material based TCEs. The multiple hybridized TCEs have comparable optical/electrical metrics to ITO. The doped-ZnO TCEs exhibit high optical transmittance over 90% in the visible range and low sheet resistance under 200Ω/sq. For CuNW-based composite electrodes, ~ 85% optical transmittance and ~ 25Ω/sq were observed. Meanwhile, the hybridization of materials adds additional features such as flexibility or resistance to corrosion. Finally, as a proof of concept, the CuNW-based composite TCEs were tested in dye-sensitized solar cells (DSSCs), showing similar performance to ITO based samples.

L’efficacité énergétique d’un électrolyseur alcalin est liée aux surtensions de réactions aux électrodes. Dans le but d’améliorer cette efficacité, nous avons développé de nouvelles électrodes composites polymère/particules maximisant la surface active des meilleurs catalyseurs, les propriétés de conductivité électrique et de transport des espèces en choisissant le polymère-liant le plus avantageux pour la cinétique réactionnelle. Les notions théoriques et l’état de l’art des principaux matériaux d’anodes et de cathodes et des différents paramètres régissant le fonctionnement d’un électrolyseur alcalin sont présentés afin de faire une synthèse des nombreux travaux réalisés. Des méthodes de fabrication d’électrodes au laboratoire ou lors d’essais préindustriels ont été explorées et comparées. Les performances électrochimiques des cathodes et anodes composites développées pour les réactions de l’évolution d’hydrogène et d’oxygène en milieu alcalin concentré sont étudiées par voltammétrie cyclique, polarisation linéaire et spectroscopie d’impédance électrochimique. Ce travail donne lieu à la description des différents paramètres clés du fonctionnement des électrodes composites polymère/particules. Différentes formulations de cathodes et d’anodes ont donc été étudiées afin d’établir des corrélations entre les propriétés physico-chimiques des polymères liants et des particules sur le comportement électrochimique des électrodes réalisées. Ces résultats sont discutés en termes de surtension de réactions, de cinétique électrochimique et de densités de sites actifs. Enfin, les résultats de la mise à l’échelle des cathodes composites et de leur procédé de fabrication pour une application industrielle sont rapportés avec l’objectif d’intégrer celles qui ont démontré des performances supérieures à celles de l’état de l’art dans un dispositif prototype industriel d’électrolyse. La démarche de la mise à l’échelle, les moyens expérimentaux développés, et une partie des résultats des essais y sont présentés. / The electrolyzer efficiency is directly related to the electrode reaction overpotentials. To improve this efficiency, new composite electrodes with selected binders and electrocatalysts showing large active area have been formulated to enhance the electrochemical kinetics. First, a state of the art of electrode materials and electrolysis parameters have been reported in a relevant literature survey about different topics developed in the thesis manuscript. Then, a few laboratory and preindustrial electrode fabrication processes were explored and compared on both technical and economical aspects. Moreover, the electrochemical performances of composite cathodes and anodes for hydrogen and oxygen evolution reactions have been studied by cyclic voltammetry, linear polarization and electrochemical impedance spectroscopy. This comprehensive study leads to a precise description of the interfacial phenomena at the microscopic scale during gas production and the evaluation of key parameters for the formulation of advanced electrodes. Many electrode formulations were studied for the correlation of physicochemical properties of components and corresponding electrochemical behaviors. These results are discussed in terms of overpotentials, electrochemical kinetics and active site density. Finally, scale-up of composite cathode is reported. The aim of this work is to integrate the best formulated composite electrodes in a real scale prototype. The scale-up process, experimental devices developed and some electrochemical results are presented.