This thesis concerns several advances in electroanalytical chemistry which are separated into four parts: the electrochemical investigation of diffusional behaviour, the mechanistic and kinetic study of electrochemistry with room temperature ionic liquids (RTILs), the study of weakly-supported electrochemistry and a comparison of the Butler-Volmer and Marcus-Hush kinetic theories of electron transfer. A study of the diffusional behaviour of electroactive species is essential for further studies, especially in the case when electrochemistry is complicated through ion-pairing interactions between the electroactive species and other electrolytes. In Part II of this thesis, the possibility of the ferricenium ion-paired with perchlorate and hexauorophosphate in acetonitrile was discussed firstly employing chronoamperometric technique. Afterwards, the hexaammineruthenium III/II couple supported by chloride, nitrate and sulfate respectively was studied by a similar method. In order to avoid unwanted ion-pairing effects, room temperature ionic liquids can be applied as solvent, which provide high conductivity by their own ionic nature so that experiments can be conducted without adding additional supporting ions. Because of RTILs have distinctive properties, for example, high viscosity, high conductivity and ionic nature, electrochemistry could be greatly changed compared to those in conventional solvents. Part III of this thesis gives a detailed description of this topic. First, a study of the reduction of 1,4-benzonquinone in 1-ethyl-3-methylimidazolium bis(triuoromethanesulfonyl)imide is presented to show the new mechanistic insight into comproportionation in a electrochemical process. Second, a discussion of the oxidation of hydroquinone in the same RTIL is introduced to suggest a possible ECE scheme which was never reported before. The interest of weakly supported electrochemistry is also well-established, which not only provides another alternative strategy to avert ion-pairings but also offers more physical insights into electrochemical processes. Quantitative methods analysing voltammetries without an excess amount of supporting electrolyte are developed by introducing a migration term into the mass transport equation. In Part IV, new mechanistic insights into the reduction of 2-nitrobromobenzene and the dimerisation of 2,6-diphenylpyrylium in acetonitrile were provide by using weakly-supported cyclic voltammetry. Also, pulse techniques was also adopted to investigate the reduction of cobaltocenium and cobalt(III) sepulchrate, giving an alternative way for electrochemical analysis. A major application of electroanalytical chemistry is investigating electrochemical kinetics. Two kinetic models mostly concerned by electrochemists are Butler-Volmer and Marcus-Hush formalisms. The classic phenomenological model, Butler-Volmer formalism successfully describes most common electron transfer kinetics but shows little reference with nature of the involved species, solution and electrode material, while a more physically insightful theory, the Marcus-Hush formalism, takes species natural properties, for instance, a change of distances or geometry in the solvation or coordination shells of the redox, into account although it requires more complex formulations. Comparative studies of these two theories are presented in Part V in order to improve our understanding of the electron transfer kinetics under different circumstances. First, comparison of cyclic voltammograms of the reduction of europium(III) and 2-methyl-2-nitropropane at mercury microhemispherical electrodes was carried out. Second, square wave and differential pulse voltammetric techniques were also employed to further discriminate the two kinetic models. These studies all find that the symetric Marcus-Hush theory assuming the reactants and products have identical force constant dose not satisfactorily agree with the experimental results. Hence, the introduction of asymmetric Marcus-Hush theory was presented considering different oxidative and reductive reorganization energies, which gives reasonable agreement with experiments and makes this theory more insightful.

M. Tech. (Engineering, Electrical, Department Applied Electronics and Electronic Communication, Faculty of Engineering and Technology) -- Vaal University of Technology / This dissertation presents the design and development of a remote monitoring system (RMS) for polymer electrolyte membrane fuel cells (PEMFC) to facilitate their efficient operation. The RMS consists of a data acquisition system built around the PIC 16F874 microcontroller that communicates with a personal computer (PC) by use of the RS232 serial communication standard, using a simple wired connection between the two. The design also consists of a human machine interface (HMI) developed in Visual Basic 6.0 to provide a platform for display of the monitored parameters in real time. The first objective was to establish performance variables and past studies on PEM fuel cells revealed that variables that affect the system's performance include: fuel and oxidant input pressure and mass flow rates as well as operation temperature and stack hydration. The next objective was to design and develop a data acquisition system (DAS) that could accurately measure the performance variables and convey the data to a PC. This consisted of sensors whose outputs were input into two microcontrollers that were programmed to process the data received and transfer it to the PC. A HMI was developed that provided graphical display of the data as well as options for storage and reviewing the data. The developed system was then tested on a 150Watt PEM fuel cell stack and the data acquisition system was found to reliably capture the fuel cell variables. The HMI provided a real-time display of the data, with alarms indicating when set minimums were exceeded and all data acquired was saved as a Microsoft Excel file. Some recommendations for improved system performance are suggested. / Vaal University of Technology -- National Research Foundations

Lithium-ion batteries are today finding use in automobiles aiming at reducing fuel consumption and emissions within transportation. The requirements on batteries used in vehicles are high regarding performance and lifetime, and a better understanding of the interior processes that dictate energy and power capabilities is a key to strategic development. This thesis concerns aging in lithium-ion cells using electrochemical tools to characterize electrode and electrolyte properties that affect performance and performance loss in the cells.   A central difficulty regarding battery aging is to manage the coupled effects of temperature and cycling conditions on the various degradation processes that determine the lifetime of a cell. In this thesis, post-mortem analyses on harvested electrode samples from small pouch cells and larger cylindrical cells aged under different conditions form the basis of aging evaluation. The characterization is focused on electrochemical impedance spectroscopy (EIS) measurements and physics-based EIS modeling supported by several material characterization techniques to investigate degradation in terms of properties that directly affect performance. The results suggest that increased temperature alter electrode degradation and limitations relate in several cases to electrolyte transport. Variations in electrode properties sampled from different locations in the cylindrical cells show that temperature and current distributions from cycling cause uneven material utilization and aging, in several dimensions. The correlation between cell performance and localized utilization/degradation is an important aspect in meeting the challenges of battery aging in vehicle applications.   The use of in-situ nuclear magnetic resonance (NMR) imaging to directly capture the development of concentration gradients in a battery electrolyte during operation is successfully demonstrated. The salt diffusion coefficient and transport number for a sample electrolyte are obtained from Li+ concentration profiles using a physics-based mass-transport model. The method allows visualization of performance limitations and can be a useful tool in the study of electrochemical systems. / <p>QC 20140512</p>

A temperatura de operação de células a combustível de óxido sólido (SOFCs) que utilizam zirconia estabilizada com itria (YSZ) como eletrólito é 1000 oC. Essa alta temperatura gera graves problemas relativos a materiais e vida util da célula. Por isso, condutores iônicos que possuem alta condutividade em temperaturas inferiores são pesquisados atualmente. Estudos mostraram que La10Si6O27 tipo apatita possui alta condutividade iônica de oxigenio, que é comparativamente maior que a de YSZ, a 500 oC, sendo, portanto, um potencial candidato como eletrólito para SOFC. O objetivo do presente trabalho é o desenvolvimento de técnicas de síntese de silicato de lantânio tipo apatita. Rotas inéditas de solgel modificada para sintetizar La9,33Si6O26 são propostas. Volumes estequiométricos de soluções de Na2SiO3 e LaCl3 foram misturados para a formação de gel de Si. Em seguida este gel foi calcinado a 900 °C, lavado, filtrado e tratado novamente a 900 °C. Em outra rota, volumes estequiométricos de soluções de Si (Na2SiO3 ou TEOS) e de La (LaCl3) foram utilizados para obtenção de gel de Si. Em seguida, hidróxido de La foi precipitado pela adição de uma base (NaOH ou NH4OH) ao gel. O material resultante foi calcinado a 900 °C, lavado, filtrado e tratado novamente a 900 °C. Pós de aglomerados fracos e alta sinterabilidade foram obtidos. DRX dos pós mostrou a estrutura de apatita monofásica a 900 oC. Morfologia de ceramica densa foi observada em imagens de MEV da superfície das pastilhas sinterizadas a 1200,1300 e 1400 oC por 4 h. Estas temperaturas e tempo de sinterização são significativas, pois no método convencional temperaturas superiores a 1700oC e tempos muito maiores são necessários para obtenção de tais cerâmicas. Densidades relativas superiores a 90% foram obtidas através dos métodos propostos. Uma conclusão importante é que TEOS, o reagente usual de alto custo, pode ser substituído por Na2SiO3, de preço muito mais baixo, para obter La9,33Si6O26 tipo apatita. / Solid oxide fuel cell (SOFCs) operating temperature that uses yttria stabilized zirconia (YSZ) as the electrolyte is 1000ºC. This high temperature causes serious problems concerning cell life and materials. Therefore, the ionic conductors which have high conductivity at lower temperature are currently researched. Studies have shown that the composition of La10Si6O27 apatite type has high oxygen ionic conductivity, which is comparably higher than that of YSZ, at 500 oC, it is therefore a potential candidate as for SOFC electrolyte. The objective of the present work is the development of lanthanum silicate with apatite type synthesis techniques. Novel modified solgel routes to synthesize La9.33Si6O26 are proposed. Stoichiometric volumes of Na2SiO3 and LaCl3 solutions were mixed for the formation of Si gel. This gel was calcined at 900 °C, washed, filtered and again thermally treated at 900 °C. In the other route, stoichiometric volumes of Si (Na2SiO3 or TEOS) and La (LaCl3) solutions were used for obtaining Si gel. Then, La hydroxide was precipitated by adding of a base (NaOH or NH4OH) to gel. Then the material was calcined at 900 °C, washed, filtered and again treated at 900 °C. Highly sinterable weakly agglomerated powders have been obtained. XRD patterns of the powders showed the single-phase apatite structure at 900 oC. Dense ceramic morphology was observed from the SEM images of surface of the pellets sintered at 1200, 1300 and 1400oC for 4h. This low temperature sintering and time of sintering are significant because the conventional method requires superior temperatures of 1700 oC to obtain the same dense ceramics. High relative densities higher than 90% was obtained via proposed methods. An Important conclusion is the TEOS, the usual high cost reagent, may be substituted by a cheap price Na2SiO3, to obtain apatite type La9.33Si6O26.

As células eletroquímicas emissoras de luz são dispositivos eletroluminescentes cuja camada ativa é uma mistura de um material eletroluminescente e um eletrólito sólido a base de sais de metais alcalinos, geralmente lítio. A presença dos íons na camada ativa modificam o mecanismo de funcionamento das células quando comparadas ao diodos emissores de luz. Nas células, a concentração de íons nas interfaces eletródicas forma uma dupla camada elétrica que auxilia a injeção de cargas na camada ativa, por sua vez e na presença dos íons, o material eletroluminescente sofre dopagem se tornando condutor, os portadores injetados irão se encontrar numa região da camada ativa recombinando-se e emitindo luz. Compreender as interações dos diversos materiais que formam a camada ativa é fundamental para otimizar o desempenho do dispositivo. Neste trabalho estudamos a interação do ADS108GE, um polímero luminescente, e um eletrólito sólido a base de poli (óxido de etileno) (PEO) e LiCF3SO3 ou LiB(C2O4)2. O LiB(C2O4)2 foi sintetizado neste trabalho para estudar a viabilidade de se substituir o LiCF3SO3 que é o sal tipicamente utilizado nas células. Foram utilizadas técnicas de Análise Dinâmico-Mecânica (DMA), Espectroscopia Vibracional no Infravermelho (FTIR), Microscopia de Força Atômica (AFM), Difração de Raios-X (DRX), Microscopia Óptica de Varredura no Campo Próximo (IR-SNOM), Impedância Elétrica e Voltametria Cíclica. Os resultados de DMA em conjunto com DRX e AFM, permitiram estabelecer que o aumento da concentração de sal contribui para mudanças morfológicas que se relacionam com o aumento da fração de fase amorfa e independem do ânion, demonstrando que estes efeitos estão ligados à interação PEO-Lítio. Por outro lado, os espectros de FTIR e resultados de impedância elétrica mostram que o aumento da concentração de LiCF3SO3 gera agregação do sal diminuindo a condutividade, a mobilidade iônica e o número de portadores efetivos, enquanto para o LiB(C2O4)2 não se observa tal efeito. O IR-SNOM permitiu identificar nas misturas utilizadas como camada ativa que o ADS108GE forma estruturas globulares embebidas numa matriz de PEO. Do ponto de vista operacional, as células a base de LiB(C2O4)2 possuem uma eficiência maior do que as a base LiCF3SO3 e maior estabilidade. / Light-emitting electrochemical cells are electroluminescent devices whose active layer is a mixture of an electroluminescent material and a solid electrolyte based on alkaline salts, usually a lithium salt. The ions within thea ctive layer change the devices working mechanism when compared to light emitting diodes. In the cells, there is an ion build up at electrodic interfaces creating an electric double layer allowing charge injection in the active layer. The electroluminescent material is doped by these injected charges becoming conductive. These injected charges recombine emitting light. In order to optimize devices performance, it is fundamental to study materials interactions when mixed as an active layer. In this work, we studied the interactions between ADS108GE, a luminescent polymer, and a solid electrolyte based on polyethylene oxide and LiCF3SO3 or LiB(C2O4)2. LiB(C2O4)2 was prepared in this work to assess its feasibility as LiCF3SO3 substitution which is the typical choice. We used the following techniques in this work: Dynamical Mechanical Analysis (DMA), Infrared Vibration Spectroscopy (FTIR), Atomic Force Microscopy AFM), X-Ray Diffraction (XRD), Infrared Scanning Near-Field Optical Microscopy (IRSNOM), Electrical Impedance and Cyclic Voltammetry. From DMA, XRD and AFM results, it is possible to conclude that as we increase salt concentration, the active layer has morphological changes related to an increasing fraction of an amorphous phase. These effects are anion independent showing that PEO-Li interactions are the responsible ones. On the other hand, FITR and electrical impedance experiments show that increasing LiCF3SO3 concentration leads to salt aggregation decreasing conductivity, ionic mobility and the effective number of carriers, moreover, we do not see this effect with LiB(C2O4)2. IR-SNOM identified that ADS108GE were organized as globular structures embedded in a PEO matrix. The cells made with LiB(C2O4)2 were more efficient than those based on LiCF3SO3 and were even more stable.

Os eletrólitos poliméricos formados com base de poli(óxido de etileno) POE e um sal alcalino, vem sendo motivo de grande interesse científico devido ao seu potencial de aplicações em dispositivos eletroquímicos. A condutividade iônica nestes sistemas resulta do fato que a macromolecula atua como solvente para o sal, deixando-o parcialmente dissociado. Neste trabalho, foi utilizada a técnica de Ressonância Magnética Nuclear (RMN) para caracterizar as dinâmicas do spin nuclear do 1H e do 7Li findando investigar os mecanismos de transporte iônico dos compósitos de eletrólitos poliméricos baseados no POE8:LiC104 e partículas de &3945; e &#947;-alumina. Foram feitas medidas da forma da linha de ressonância e da relaxação spin-rede nas frequências de 36 MHz (1H) e 155,4 MHz (7Li) em função da temperatura no intervalo de 170-350 K. Caracterizações fisicas das partículas foram realizadas através das medidas de tamanho de partícula, porosidade e área superficial. Nos compósitos foram feitas medidas de análise témica por DSC e de condutividade elétrica ac por impedância complexa. Os resultados de RMN do 1H mostraram uma maior mobilidade das cadeias poliméricas para o compósito preparado com a dispersão de 20% de &#945;-Al203 em massa, em relação ao eletrólito polimérico sem partículas. Nenhuma alteração foi observada nas medidas de largura de linha e relaxação spin-rede para os compósitos preparado com 5% de &#945; ou &#947;-alumina. A mobilidade dos íons Li+ apresenta um aumento quando é disperso 20% de &#945;-alumina no complexo polimérico. Em contrapartida, a adição de 20% de &#947;-alumina não altera os valores da taxa de relaxação (1/T1), porém um estreitamento da linha de ressonância em baixas temperaturas, em relação ao complexo polimérico, é observado. Os resultados serão discutido com base nas interações de ácido-base de Lewis / Polymeric electrolytes based on poly(ethylene oxide) (PEO) and alkaline salts has been subject of scientific and technological interest due to its potential applications as solid electrolytes in electrochemical devices. The ionic conductivity of such electrolytes results from the fact that the macromolecule acts as a solvent for the salt, leaving it partially dissociated. Nuclear magnetic resonance (NMR) techniques were used to characterize the 1H and 7Li nuclear spin dynamics in order to investigate the transport properties associated to the ionic conduction mechanisms of polymeric composites based on PEO8:LiC1O4 and particles of &#945; and &#947;-alumina. NMR lineshapes and spin-lattice relaxation were measured at 36 MHz (1 H) and 155.4 MHz (7Li) as a function of temperature in the range of 170-350 K. Physical characterization of the particles was realized by measuring the particle size distribution, porosity and superficial area. Differential scanning calorimetry (DSC) and ac electric conductivity of the composites were measured. 1H NMR results show that the polymeric chains of the composite prepared with 20 wt.% of &#945;-alumina has a greater mobility if compared with the unfilled polymeric material. No changes in linewidth and relaxation rates were observed following the addition of 5 wt.% of &#945; or &#947;-alumina. The 7Li mobility increases when 20 wt.% of &3945;-alumina is added to the starting polymeric material. On the other hand, addition of 20 wt.% of &#947;-alumina do not alter the relaxation rates but produces a small change in linewidth. Results are discussed in accordance with the Lewis acid-base interaction

O sucesso da conclusão de um poço por perfuração e o custo do projeto estão relacionados às propriedades dos fluidos de perfuração. O estudo experimental foi realizado a partir da determinação e análise das curvas de tensão de cisalhamento versus taxa de deformação de suspensões aquosas de bentonita e carboximetilcelulose com diferentes concentrações de NaCl. Investigou-se, inicialmente, o comportamento reológico de suspensões de carboximetilcelulose 0,5% (em massa) com concentrações de sal, NaCl de 0 a 4% (em massa), para temperaturas variando de 14 a 26ºC. Os resultados experimentais possibilitam a caracterização reológica destas soluções como fluidos pseudoplásticos e indicam que a adição de NaCl em soluções com CMC alteram significativamente o comportamento reológico desse tipo de solução. Numa segunda etapa, estudou-se o comportamento reológico de suspensões de bentonita e carboximetilcelulose em diferentes concentrações de sal, NaCl. Empregaram-se soluções contendo 4,8 % de bentonita, 0,5 % de carboximetilcelulose e concentrações de 0 a 4% de NaCl. Constata-se o comportamento tixotrópico destas suspensões e a forte dependência com a concentração de sal. O estudo foi complementado com uma análise comparativa dos resultados do comportamento reológico obtidos por reômetro de cilindros coaxiais modelo Brookfield e o viscosímetro FANN 35 A, usualmente empregado na análise de fluidos de perfuração. O equacionamento do escoamento do fluido nos aparelhos permitiu uma interpretação mais detalhada dos valores descritos na norma, obtendo-se uma equivalência dos valores medidos em campo com os obtidos no reômetro Brookfield apesar de as faixas de operação de taxas de deformação serem distintas. / The properties of drilling fluids have a very significant effect on the successful of a well completion and the project costs. The experimental study was conducted based on the determination and analysis of the curves of shear stress and shear rate of aqueous suspensions composed of bentonite and carboxymetil cellulose at different concentrations of NaCl. The rheological behaviour of carboxymetil cellulose suspensions 0.5% w/w at NaCl concentrations in the range of 0 to 4% w/w from 14 to 26°C was studied. The experimental results allow the rheological characterization of these solutions as pseudoplastic fluid. It was observed that the addition of NaCl to CMC solutions changes its rheological behaviour significantly. In addition, the rheological behaviour of 4,8% bentonite suspensions with 0,5% carboxymethyl cellulose at different concentrations of NaCl in the range of 0 to 4% was studied. The characterization of these solutions showed thixotropic behaviour and a strong dependence on the salt concentration. The study was complemented with a comparative analysis of the results obtained by using a coaxial cylinders rheometer model Brookfield and the FANN Model 35 A viscometer, usually employed in drilling fluids analysis. The analytical solutions allowed a more detailed interpretation of the values described in the standard resulting in an equivalence between the measured values obtained in the field and in the Brookfield rheometer despite the differents shear rate ranges.

Fast oxide-ion and proton conductors are the subject of considerable research due to their technological applications in sensors, ceramic membranes and solid oxide fuel cells (SOFCs). This thesis describes the use of computer modelling techniques to study point defects, dopants and clustering effects in fluorite-and perovskitetype ion conductors with potential SOFC applications. Bi2O3 related phases are being developed with the objective of high oxide-ion conductivities at lower operating temperatures than 1000°C, as in current generation SOFC electrolytes. Doped Bi2O3 phases have shown promise as materials capable of accomplishing this goal. First, the Y-doped phase, Bi3YO6, has been investigated including the ordering of intrinsic vacancies. The defect and dopant characteristics of Bi3YO6 have been examined and show that a highly mobile oxygen sub-lattice exists in this material. A preliminary structural modelling study of a new Re-doped Bi2O3 phase was also undertaken. A comprehensive investigation of the proton-conducting perovskites BaZrO3, BaPrO3 and BaThO3 is then presented. Our results suggest that intrinsic atomic disorder in BaZrO3 and BaThO3 is unlikely, but reduction of Pr4+ in BaPrO3 is favourable. The water incorporation energy is found to be less exothermic for BaZrO3 than for BaPrO3 and BaThO3, but in all cases the results suggest that the proton concentration would decrease with increasing temperature, in accord with experimental data. The high binding energies for all the dopant-OH pair clusters in BaPrO3 and BaThO3 suggest strong proton trapping effects. Finally, a study of multiferroic BiFeO3 is presented, in which the defect, dopant and migration properties of this highly topical phase are investigated. The reduction process involving the formation of oxygen vacancies and Fe2+ is the most favourable redox process. In addition, the results suggest that oxide-ion migration is anisotropic within this system.

"Lithium ion batteries have dominated the portable electronics market and have the potential to dominate large-scale battery applications including hybrid and electric vehicles, as well as grid storage, because of their high energy and power densities1,2. It is well known that conventional electrolytes show poor anodic stabilities above 4.5 V versus Li/Li+.3 As a result, high voltage electrolytes are essential for the development of next generation high energy lithium ion batteries. Both fluorinated electrolytes and additives can be introduced into the electrolyte system.4 In this work, fluorinated electrolytes were used in both graphite-LiNi0.5Co0.2Mn0.3O2 (NCM523) (operated between 3.0 - 4.6 V) and graphite- LiNi0.5Mn1.5O4 (LNMO) (operated between 3.5 - 4.9 V) full cell systems. The baseline electrolyte for all cells (referred to as Gen2) was composed of 1.2M LiPF6 dissolved in a mixture of EC and EMC (3:7 in weight ratio). After a series of electrochemical tests, compared to the baseline electrolyte, the fluorinated electrolytes displayed significantly enhanced performance under both high cut off voltage and high temperature (55 oC). The post test analysis results showed that the cycled electrode can not only reach a much more stable interface but also overcome the crystal structure change after long term cycling when the fluorinated electrolyte system was used. In addition to changing the solvent, a series of additives were designed, synthesized and evaluated for high-voltage Li-ion battery cells using a Ni-rich layered cathode materials LiNi0.5Co0.2Mn0.3O2 (NCM523). The repeated charge/discharge cycling for NCM523/graphite full cells using Gen2 with 1 wt % of these additives as electrolytes was performed. Electrochemical performance testing and post analysis result demonstrated that our as selected or designed cathode additives could passivate the cathode and prevent the cathode from side reactions. The developed methodology could provide fundamental direction in the design and investigation of better electrolytes for the next generation lithium ion batteries."

While there is a substantial amount of information regarding the electrochemical behavior of fuel cells and there components little to no information is available regarding the mechanical properties of fuel cell materials in stack setups. This set of experiments was set up to test mechanical properties of gas diffusion layer and bipolar plate materials in a one cell setup. Samples were clamped to specified pressures and deformation properties were observed and measured. Measurements were taken of impingements of the gas diffusion layers into the gas flow channels. A limit for compression of cell configurations was found to be approximately 300psi. Upon reaching the compression limit bipolar plates collapse and materials between plates show signs of breakage. Under compression diffusion media showed impingement into the gas flow channels as well as substantial compression of the three layer stack.