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The electrification of transportation is gradually becoming more prominent as it is more efficient and sustainable than conventional transportation alternatives found today. At the centre of this growth is battery testing and research, as they are the primary energy storage devices used to power electric vehicles. With the growing complexity of battery systems, testing and monitoring their performance relies on highly specialized and precise equipment. Furthermore, the use of battery models helps researchers improve their research while reducing the time and costs involved in testing. As such, accurate battery modelling is a critical component in predicting how a battery will behave in specific applications and under various conditions. In this research, a lithium-ion cell is tested extensively, and its performance is characterized across a wide range of operating conditions including temperature, current rates and state of charge (SOC) values. An equivalent circuit model for impedance modelling is proposed, which utilizes constant phase elements represented in the time domain to improve fitting accuracy. This is done concurrently with the development of a state of the art, fully automated battery test system which is showcased throughout the course of the research. In addition to this, an analysis is conducted on the low frequency impedance data used during research, as well as its effect on model accuracy. To provide significance behind the results and relevance to real-world applications, all of the impedance modelling is experimentally validated using temporal drive cycle data. This research was able to demonstrate that the use of a ZARC element can improve the mid-frequency fitting of impedance data relative to a conventionally used modelling approach. It also showcases how the use of low frequency electrochemical impedance spectroscopy (EIS) data can negatively impact the accuracy of impedance modelling. / Thesis / Master of Applied Science (MASc)

This dissertation describes the impact of defects on monolayer properties for self-assembled monolayers (SAMs) created by interfacial patterning methods. When forming a two-dimensional interfacial pattern with n-alkanethiols on gold, the desired electrochemical properties are those of a homogeneous, solution adsorbed monolayer. However, even well-ordered SAMs contain a small degree of defects, especially at domain boundaries where two nucleating domains converge. Patterning a surface creates user-defined domain boundaries within the monolayer, potentially having a significant impact on the properties of the interface. This dissertation investigates the effect that user-created domain boundaries have on the properties of a monolayer, as studied by electrochemical impedance spectroscopy. Two patterning methods are investigated for creating user-defined domain boundaries: the soft lithography method of contact printing and site-selective reductive desorption. The electrochemical properties of homogeneous contact printed monolayers are measured and compared to those of monolayers prepared by solution adsorption. The contact printed monolayers are found to have dramatically different impedance behavior from the solution prepared monolayers, consistent with the contact printed monolayers having greater defect density. In addition, these studies show that the overall defect density depends on the concentration of the solutions used for contact printing. In this work, simple patterns are created by contact printing a pattern onto the substrate and then backfilling the remaining gold substrate by solution adsorption. Backfilling with the same alkanethiol used to create the pattern generates a homogeneous monolayer; however, it is found that the contact printed/backfilled monolayer has an impedance intermediate between the homogeneous contact printed and the homogeneous solution adsorbed monolayer. This result suggests that the backfilling process also saturates the pinhole defects associated with the contact printed areas. In addition to exploring defects that arise from contact printing, simple patterns with user-defined defects, created by site-selective reductive desorption (SSRD), were also investigated. Following the backfill step, the impedance behavior of the SSRD produced patterns was similar to that of the impedance of the initial pattern before backfilling. This important result implies that the domain boundaries play the most important role in defining the overall impedance of the patterned interface. / Ph. D.

Philosophiae Doctor - PhD / Electroanalytical and optical properties of nanoscale materials are very important for biosensing applications as well as for understanding the unique one-dimensional carrier transport mechanism. One-dimensional semiconductor nanomaterials such as semiconductor quantum dots are extremely attractive for designing high-density protein arrays. Because of their high surfaceto-volume ratio, electro-catalytic activity as well as good biocompatibility and novel electron transport properties make them highly attractive materials for ultra-sensitive detection of biological macromolecules via bio-electronic or bio-optic devices. A genosensor or gene based biosensor is an analytical device that employs immobilized deoxyribonucleic acid (DNA) probes as the recognition element and measures specific binding processes such as the formation of deoxyribonucleic acid-deoxyribonucleic acid (DNA-DNA), deoxyribonucleic acid- ribonucleic acid (DNA-RNA) hybrids, or the interactions between proteins or ligand molecules with DNA at the sensor surface.In this thesis, I present four binary and two ternary-electrochemically and optically modulated selenide and telluride quantum dots, all synthesised at room temperature in aqueous media. Cationic gallium (Ga3+) synthesized in form of hydrated gallium perchlorate salt[Ga(ClO4)3.6H2O] from the reaction of hot perchloric acid and gallium metal was used to tailor the optical and electrochemical properties of the selenide and telluride quantum dots. The synthesized cationic gallium also allowed successful synthesis of novel water soluble and biocompatible capped gallium selenide nanocrystals and gallium telluride quantum dots. Cyclic voltammetric studies inferred that presence of gallium in a ZnSe-3MPA quantum dot lattice improved its conductivity and significantly increased the electron transfer rate in ZnTe-3MPA.Utraviolet-visible (UV-vis) studies showed that incorporation of gallium into a ZnSe-3MPA lattice resulted in a blue shift in the absorption edge of ZnSe-3MPA from 350 nm to 325 nm accompanied by decrease in particle size. An amphiphilic bifunctional molecule, 3-Mercaptopropionic acid (3-MPA) was used as a capping agent for all quantum dots. It was found that 3-MPA fully solubilised the quantum dots, made them stable, biocompatible, non agglomerated and improved their electron transfer kinetics when immobilized on gold electrodes.Retention of the capping agent on the quantum dot surface was confirmed by Fourier transform infrared spectroscopy (FTIR) which gave scissor type bending vibrations of C-H groups in the region 1365 cm-1 to 1475 cm-1, stretching vibrations of C=O at 1640 cm-1, symmetric and asymmetric vibrations of the C-H in the region 2850 cm-1 to 3000 cm-1 as well as stretching vibrations of –O-H group at 3435 cm-1. The particle size and level of non-agglomeration of the quantum dots was studied by high resolution transmission electron microscopy (HRTEM). The optical properties of the quantum dots were studied using UV-vis and fluorescence spectroscopic techniques.Quantum dot/nanocrystal modified gold electrodes were prepared by immersing thoroughly cleaned electrodes in the quantum dot/nanocrystal solution, in dark conditions for specific periods of time. The electrochemical properties of the modified electrodes were characterized by cyclic voltammetry (CV), square wave voltammetry (SWV), electrochemical impedance and spectroscopy (EIS). Six sensing platforms were then prepared using quantum dot/nanocrystal, one of which was used for detection of dopamine while the rest were used for detection of a DNA sequence related to 5-enolpyruvylshikimate-3-phosphate synthase, a common vector gene in glyphosate resistant transgenic plants.The first sensing platform, consisting of ZnSe-3MPA modified gold electrode (Au|ZnSe-3MPA) gave rise to a novel method of detecting dopamine in presence of excess uric acid and ascorbic acid. Using a potential window of 0 to 400 mV, the ZnSe-3MPA masked the potential for oxidation of uric and ascorbic acids, allowing detection of dopamine with a detection limit of 2.43 x 10-10 M (for SWV) and 5.65 x 10-10 M (for steady state amperometry), all in presence of excess uric acid (>6500 higher) and ascorbic acid (>16,000 times higher). The detection limit obtained in this sensor was much lower than the concentration of dopamine in human blood(1.31 x 10-9 M), a property that makes this sensor a potential device for detection of levels of dopamine in human blood.The other sensing platforms were prepared by bioconjugation of amine-terminated 20 base oligonucleotide probe DNA (NH2-5′-CCC ACC GGT CCT TCA TGT TC-3′) onto quantum dot modified electrodes with the aid of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS). The prepared DNA electrodes were electrostatically hybridized with different sequences which included 5′-GAA CAT GAA GGA CCG GTG GG-3′ (complementary target), 5′-CATAGTTGCAGCTGCCACTG-3′ (non complementary target) and 5′-GATCATGAAGCACCGGAGGG-3′ (3-base mismatched target).The hybridization events were monitored using differential pulse voltammetry (DPV) and SWV by monitoring the guanine oxidation signal or using EIS by monitoring changes in the charge transfer resistance. The quantum dot genosensors were characterized by low detection limits (in the nanomolar range), long linear range (40 - 150 nM) and were able to discriminate among complementary, non-complementary and 3-base mismatched target sequences.

In response to the present and projected growth of the EV industry, the development of a large-scale, reliable and efficient lithium-ion battery recycling sector is vital to ensure circularity of the embedded valuable metals and ensure overall sustainability of the technology. One of the main recycling procedures under development is based on hydrometallurgy. As a pretreatment step before lithium-ion batteries can undergo this process, they have to be deactivated to prevent uncontrolled release of the contained electrical energy. This deactivation step is often performed by deep discharging batteries to 0.0 V, instead of the usual lower cut-off around 3.0 V. Usually, deep discharging is performed by connection to resistors or through submersion in a salt solution. However, due to the discharge current derating proportionally to the terminal voltage, this procedure can be quite slow, especially if considerable rebound voltages are to be prevented. This work explores the feasibility of a faster discharge procedure in terms of discharge speed, effectiveness, and safety. The proposed procedure entails deep discharging at constant current using a controllable load, followed by applying an external short-circuit immediately. The C-rate during constant current discharging is varied to study its effects. The short-circuit is applied at a terminal voltage of 0.0 V or 1.0 V. The safety of both process steps is assessed experimentally. The main safety risks that are reviewed are the temperature rise and subsequent risk of thermal runaway, as well as the risk of electrolyte leakage due to pressure increase and swelling. In the experimental work, two types of large format prismatic NMC811 cells are deep discharged starting from an SoC of 0%. The experiments are limited to single cells. It is found that an additional 4% of additional capacity is available in the deep discharging region for a stationary cell at 0% SoC. The risk of thermal runaway is assessed as low based on the temperature measurements and a literature review. To investigate the rise in pressure, the thickness of all cells are measured, and the in situ pressure is measured for three samples. The risk for electrolyte leakage is assessed as low. The rebound voltage and cell thickness are followed up to one week after the discharge procedure. After a short-circuit of 30 minutes, the rebound voltage of all cells is near 2.0 V, but a slightly longer short circuit duration would be necessary to reliably achieve this threshold. The total procedure time is much shorter than those of alternative discharge procedures, while still remaining safe. / Som svar på den nuvarande och förväntade tillväxten inom elbilsindustrin är utvecklingen av en storskalig, tillförlitlig och effektiv återvinningssektor för litiumjonbatterier avgörande för att säkerställa cirkularitet för de inbäddade värdefulla metallerna och säkerställa teknikens övergripande hållbarhet. En av de viktigaste återvinningsmetoderna som är under utveckling baseras på hydrometallurgi. Som ett förbehandlingssteg innan litiumjonbatterier kan genomgå denna process måste de avaktiveras för att förhindra okontrollerad frisättning av den elektriska energi som de innehåller. Detta deaktiveringssteg utförs ofta genom djupurladdning av batterierna till 0.0 V, istället för den vanliga lägre gränsen runt 3.0 V. Vanligtvis utförs djupurladdning genom anslutning till resistorer eller genom nedsänkning i en saltlösning. Eftersom urladdningsströmmen avtar proportionellt mot terminalspänningen kan denna procedur dock vara ganska långsam, särskilt om man vill förhindra stora återkopplingsspänningar. I detta arbete undersöks genomförbarheten av en snabbare urladdningsprocedur när det gäller urladdningshastighet, effektivitet och säkerhet. Det föreslagna förfarandet innebär djupurladdning vid konstant ström med en kontrollerbar belastning, följt av omedelbar applicering av en extern kortslutning. C-hastigheten under urladdning med konstant ström varieras för att studera dess effekter. Kortslutningen appliceras vid en terminalspänning på 0.0 V eller 1.0 V. Säkerheten för båda processtegen bedöms experimentellt. De huvudsakliga säkerhetsriskerna som granskas är temperaturökningen och den efterföljande risken för termisk rusning, samt risken för elektrolytläckage på grund av tryckökning och svullnad. I det experimentella arbetet djupurladdas två typer av prismatiska NMC811-celler i storformat från en SoC på 0%. Experimenten är begränsade till enstaka celler. Det visade sig att ytterligare 4% kapacitet finns tillgänglig i djupurladdningsområdet för en stationär cell vid 0% SoC. Risken för termisk urladdning bedöms som låg baserat på temperaturmätningarna och en litteraturgenomgång. För att undersöka tryckökningen mäts tjockleken på alla celler och in situ-trycket mäts för tre prover. Risken för elektrolytläckage bedöms som låg. Återkopplingsspänningen och cellernas tjocklek följs upp upp till en vecka efter urladdningsproceduren. Efter en kortslutning på 30 minuter är returspänningen för alla celler nära 2.0 V, men en något längre kortslutningstid skulle vara nödvändig för att tillförlitligt uppnå detta tröskelvärde. Den totala tiden för proceduren är mycket kortare än för alternativa urladdningsprocedurer, samtidigt som den fortfarande är säker.

This thesis is concerned with the study of morphology and properties of sub-micron thin Nafion® films. The motivation of the work arises from the need to characterize the 4 -10 nm thin ionomer films in the catalyst layer of polymer electrolyte fuel cell (PEFC). A protocol for the fabrication of self-assembled ultra-thin Nafion® films on planar substrates was successfully developed. Films of thickness ranging 4 nm-300 nm, determined by three different techniques - variable angle spectroscopy ellipsometry (VASE), atomic force microscope (AFM) and x-ray photo-electron spectroscopy (XPS), could be reproducibly generated on SiO2/Si wafer. The 4 nm thin film is one of the thinnest, continuous film of Nafion® ever reported. This is the first time that the structure/properties of such thin Nafion® film have been investigated. An interesting finding is the thickness-dependent structure and property of these films. Films with thickness <55 nm exhibited hydrophilic-free surface but thicker films (>55 nm) had hydrophobic surface. Similarly, sub-55 nm films had a lower and thickness-independent protonic conductivity compared to thicker films that exhibited thickness-dependent conductivity. Anomalously high water uptake (by quartz crystal microbalance) and swelling (by ellipsometry) of sub-55nm films indicate that low conductivity is not due to low water content However, differences in surface morphology were observed by the AFM phase contrast analysis. The lack of ionic domain was also observed in the thinner films (4-30 nm) from the grazing incidence small x-ray scattering (GISAXS) experiments. Thermal annealing over a range of temperature (110-160 oC) revealed a dramatic switching of the film surface from hydrophilic to hydrophobic was observed for sub-55 nm films with lower thickness film requiring higher annealing temperature. Bulk proton conductivity was significantly reduced after annealing for all films. An interesting finding was the regeneration of conductivity after to prolonged liquid water exposure and a corresponding switching back of the surface to hydrophilic. The thickness-dependent structure/property of ultra-thin Nafion® films is attributed to substrate induced confinement effect. Self-assembly of Nafion® on various substrates (SiO2, carbon, Pt and Au) was studied. The ionomer/substrate interaction and resulting film morphology followed a trend with respect to substrate surface energies and Nafion® dispersion compositions. / Thesis (Ph.D, Chemical Engineering) -- Queen's University, 2013-09-29 12:36:19.05

Um dos principais problemas no emprego do biodiesel como combustível de automóveis é a corrosão que ele pode provocar nos motores, devido à facilidade com que pode degradar. A natureza corrosiva do biodiesel é relacionada com a presença de água, ácidos graxos livres, ions metálicos, impurezas, a incidência da luz, a temperatura e a presença de insaturações na cadeia de alquil ésteres. Na atualidade existem poucos trabalhos na literatura sobre a corrosão dos metais em contato com biodiesel e a maioria deles têm um enfoque mais qualitativo que quantitativo. O maior desafio para avaliar a corrosividade do biodiesel mediante técnicas eletroquímicas é sua baixa condutividade. A espectroscopia de impedância eletroquímica (EIE) é uma técnica sensível que tem sido empregada para estudar meios resistivos como o etanol, por muitos anos. No entanto, os experimentos são difíceis assim como a análise dos resultados, principalmente pelo desenvolvimento da queda ôhmica no meio, devido à alta resistividade do meio ao fluxo da corrente elétrica. Os microeletrodos têm sido empregados em várias pesquisas em eletroquímica e têm apresentado algumas vantagens com respeito aos eletrodos de tamanhos convencionais. O principal benefício é a redução da queda ôhmica em meios resistivos, devido às baixas correntes registradas. No presente trabalho foi avaliada a corrosão do cobre e do aço inoxidável, os quais se encontram presentes no circuito de combustível dos motores, quando entram em contato com o biodiesel obtido a partir do óleo de soja (B100) e etanol. A avaliação foi feita mediante técnicas eletroquímicas com auxilio dos microeletrodos clássicos e na forma de arranjos (de 25 m de diâmetro), sem adição de eletrólito suporte. Adicionalmente, os resultados foram correlacionados com as mudanças nas propriedades fisicoquímicas do biodiesel (viscosidade, teor de água, teor de acidez e estabilidade oxidativa) e com ensaios gravimétricos segundo a norma ASTM G31. Os ensaios de impedância eletroquímica com os microeletrodos clássicos e os arranjos de microeletrodos mostraram duas constantes de tempo e foi possível demostrar que a constante em altas frequências está relacionada com a qualidade do biodiesel, enquanto que a constante nas baixas frequências é uma resposta da interface metal-biodiesel. A viscosidade e o teor de umidade aumentaram com a degradação do biodiesel e a estabilidade oxidativa diminuiu na mesma proporção independentemente do metal que estava em contato com o biocombustível. A presença de defeitos nos arranjos de microeletrodos obtidos por fotolitografia é um problema importante e é preciso estar sempre atento para evitar resultados equivocados. A voltametria cíclica se mostrou como técnica quantitativa para caracterizar e controlar a área exposta dos microeletrodos simples e em arranjos. Finalmente se corroborou com os ensaios eletroquímicos, a maior velocidade de corrosão para o cobre obtida nos ensaios gravimétricos, comparada à do aço inoxidável. / One of the most relevant aspects related with the use of biodiesel in automobile motors is its corrosivity, due to its susceptibility to oxidation reactions. The corrosive nature of biodiesel is related with the presence of water, free fatty acids, metallic ions, impurities, incidence of light, temperature, as well as the insaturation degree of the main chain of the alkyl esters. Currently there are few works in literature about corrosion of metals in contact with biodiesel, and most of them have more a qualitative than a quantitative focus. The main issue for electrochemical studies in biodiesel is its low conductivity. Electrochemistry impedance spectroscopy (EIS) is a sensitive technique that has been used for studying resistive media like ethanol for many years. However the experiments are difficult and the results are complex to understand, mainly because of the ohmic drop developed in this media due to the inherent solution resistance to the flow of electrical current. Microelectrodes have been used in many researches in electrochemistry showing some advantages with respect to conventional electrodes. The principal benefit is the reduction of the ohmic drop in resistive media, due to its negligible value when small currents are registered. In this work corrosiveness of copper and stainless steel which are present in fuel circuit of an automobile motor was evaluated when they come in contact with biodiesel, obtained from soybean oil and ethanol (B100). The evaluation was made using classic microelectrodes and arrays of microelectrodes (25m diameter) without addition of supporting electrolyte. Aditionally the results were correlated with the changes in biodiesel physicochemical properties (viscosity, water content, acid number and oxidation stability) and weight loss tests according to ASTM G31. The electrochemical results with classic microeletrodes and arrays of microelectrodes showed two time constants and it was demonstrated that the time constant at high frequencies is related with biodiesel quality, while the time constant at low frequencies is due to the response of metal-biodiesel interface. The viscosity and water content increased with biodiesel degradation and oxidation stability decrease in the same proportion independently of the metal in contact with biofuel. The presence of defects in the microelectrodes arrays obtained by photolitography is an important issue and the researcher must be atempt to them to avoid equivocated results. Cyclic voltammetry has shown to be a useful technique to characterize and control the exposed are in microlectrodes and their arrays. Finally, the electrochemical measurements corroborate the higher corrosion rate for copper obtained from weight loss tests compaired to corrosion rate for stainless steel.

A corrosão provocada pelo biodiesel é um problema relevante associado à incompatibilidade do biodiesel com diversos materiais metálicos e poliméricos, sendo de suma importância quanto à durabilidade dos motores automotivos. O objetivo deste trabalho foi avaliar a corrosividade do biodiesel sobre os metais presentes no circuito de combustível dos motores que trabalham segundo o ciclo diesel aplicando técnicas gravimétricas e eletroquímicas. Todos os ensaios foram realizados em biodiesel puro obtido pela reação de transesterificação do óleo de soja refinado com etanol na presença de um catalisador alcalino. Foi avaliada a influência de dois métodos de purificação na corrosividade do biodiesel. A corrosividade do biodiesel e a degradação após contato com os íons metálicos foram avaliadas bem como em função da incidência de luz natural, temperatura e disponibilidade de oxigênio. Os resultados foram comparados com um biodiesel comercial fornecido pela Petrobrás. Ensaios de perda de massa segundo as normas ASTM G1 e ASTM G31 foram realizados para determinar a taxa de corrosão para cada metal nas diferentes condições de incidência de luz e temperatura. Na caracterização eletroquímica foi empregada a técnica de espectroscopia de impedância eletroquímica para avaliar o comportamento de corrosão dos metais em contato com o biodiesel puro, sem adição de eletrólito suporte. A qualidade do biodiesel e a degradação após contato com metais foram avaliadas pelas medidas do teor de água, teor de ácidos livres, viscosidade e estabilidade à oxidação a 110 °C. Além disso, foram empregadas na caracterização química do biodiesel a cromatografia gasosa associada à espectrometria de massas, a espectroscopia vibracional Raman e a fluorescência de Raios-X. Alguns produtos de corrosão foram caracterizados por difração de Raios-X. Os resultados dos testes de imersão segundo ASTM G1 mostraram que a perda de espessura é levemente maior quando há incidência de luz e estes valores diminuem significativamente quando o biodiesel é exposto à alta temperatura em atmosfera natural de oxigênio. A inibição da corrosão provocada em temperatura mais elevada quando o biodiesel é exposto em atmosfera natural de oxigênio deve-se à redução da solubilidade de oxigênio no biodiesel provocada pela temperatura mais elevada. Os resultados dos testes segundo a ASTM G31 indicaram que o borbulhamento de ar que favorece a reposição constante de oxigênio no meio, favorece o aumento da velocidade de corrosão, afetando principalmente os metais parcial ou totalmente imersos em biodiesel. Os testes de imersão realizados nas diferentes condições de luz, temperatura e oxigênio permitiram concluir que a corrosividade do biodiesel e a resistência à corrosão apresentada pelos metais dependem de um conjunto de variáveis os quais incluem a composição do biodiesel (matéria prima empregada na sua obtenção), grau de purificação do biodiesel somado ao efeito provocado pelo conjunto de fatores externos, tais como, incidência da luz, calor, presença de íons metálicos e oxigênio. Os ensaios eletroquímicos por espectroscopia de impedância eletroquímica permitiram usar uma célula de condutividade com eletrodos de platina como sensor da qualidade do biodiesel, mas os resultados com dois eletrodos iguais e com grande área não permitiram quantificar a corrosividade do biodiesel, apenas a qualidade do biodiesel. Os poucos resultados com microeletrodo de platina indicaram a possibilidade de uso dessa técnica para avaliar os fenômenos na interface metal/biodiesel. / Corrosion caused by biodiesel is a relevant issue regarding the problem of biodiesel compatibility with various metallic and polymeric materials, which is extremely important to assure durability of engines. The objective of this study was to evaluate the corrosiveness of the biodiesel on the metals commonly encountered in the automotive fuel system in diesel engine by gravimetric and electrochemical techniques. The influence of two purification methods was investigated. The biodiesel corrosiveness and degradations after the contact with metallic ions were also evaluated in relation to the influence of natural light incidence, temperature and oxygen availability. The results were compared with a commercial biodiesel supplied by Petrobras. Immersion tests according to ASTM G1 and ASTM G31 standards were performed to determine the corrosion rate for each metal at different conditions. The electrochemical characterization was performed by electrochemical impedance spectroscopy (EIS) to evaluate the metals corrosion behavior in contact with pure biodiesel, without addition of supporting electrolyte. The biodiesel quality and degradation after contact with metals were evaluated by assessing water content, viscosity and oxidation stability at 110 °C. In addition, the vibrational Raman spectroscopy and X-ray fluorescence were also performed. Some of the corrosion products were characterized by X-ray diffraction. The results of ASTM G1 tests showed that the thickness loss for metals determined at room temperature is slightly higher when there is light incidence and these values significantly decrease for the highest temperature at low availability of oxygen. The main conclusion is that the significant reduction in corrosion rate when the biodiesel is exposed to high temperature (heat) in a natural atmosphere of oxygen (ASTM G1) should be assigned to the impressive decrease of oxygen solubility caused by high temperature. The results of ASTM G31 tests indicated that air bubbling along with higher temperature affects mostly partial or totally immersed samples. The increase of corrosion rate evidenced by the weight loss measurements according to ASTM G31 for different metals is attributed to the effect of high concentration of dissolved oxygen. The immersion tests showed that biodiesel corrosiviness as well as corrosion resistance presented by metals depends on a set of variables including composition (dependent on feedstock), biodiesel purity summed to external factors like incidence of light, heat, oxygen and presence of metallic ions. The degradation of biodiesel is strongly affected by heat, light and presence of metallic ions as evidenced by the increase in water content and viscosity as reduction in induction period and Raman peaks intensity decrease for assigned double bonds. The electrochemical characterization by EIS allowed finding that a classical conductivity cell can be used as an interesting quality of sensor for biodiesel quality, but the results with two similar electrodes and big exposed area could not evaluate the biodiesel corrosiveness. The potenciostatic tests performed for copper and carbon steel indicated that it is possible to evaluate both metals corrosion behavior in biodiesel and this is promising technique for this purpose and needs deeper investigation. The few results with a platinum microelectrode have indicated the possibility of using the technique to assess the metal/biodiesel interface phenomena.

Electrochemical techniques have potential for use in conservation, both to evaluate the protectiveness of existing coatings on metal artefacts and to evaluate potential new conservation coatings. Three electrochemical methods have been examined in this study for their applicability to conservation problems. Corrosion Potential Measurement is simple but provides only minimal information on the corrosion processes occurring in an electrochemical system. Electrochemical Impedance Spectroscopy provides both mechanistic and predictive information on coating performance, but the data are complex to interpret and measurements require equipment that is at present too bulky for effective on-site use and beyond the budget of most conservation laboratories. Electrochemical Noise Measurement can be performed using cheap, portable instrumentation and theoretically requires relatively simple statistical processing and interpretation, making it attractive for conservation applications. This project looks at the development of a simple, low cost electrochemical noise measurement system for conservation needs, and uses it to compare Electrochemical Noise Measurement with the other two techniques.

This thesis is concerned with kinetic characterisation of theinsertion compound LiMn2O4, which is used as positive electrodematerial in rechargeable lithium batteries. Three different typesof electrode configurations have been investigated, namely singleparticles, thin films and composite electrodes. Differentelectrochemical techniques, i.e. linear sweep voltammetry (LSV),electrochemical impedance spectroscopy (EIS), potential step, andgalvanostatic experiments were applied under various experimentalconditions. The majority of the experimental data were analysedby relevant mathematical models used for describing the reactionsteps of insertion compounds. It was concluded that a model based on interfacialcharge-transfer, solid-phase diffusion and an external iR-dropcould be fairly well fitted to LSV data measured on a singleelectrode system over a narrow range of sweep rates. However, itwas also found that the fitted parameter values vary greatly withthe characteristic length and the sweep rate. This indicates thatthe physical description used is too simple for explaining theelectrochemical responses measured over a large range of chargeand discharge rates. EIS was found to be a well-suited technique for separatingtime constants for different physical processes in the insertionand extraction reaction. It was demonstrated that the impedanceresponse is strongly dependent on the current collector used.According to the literature, reasonable values of theexchange-current density and solid-phase diffusion coefficientwere determined for various states-of-discharge, temperatures andelectrolyte compositions. Experiments were carried out in bothliquid and gel electrolytes. A method which improves thedistinction between the time constants related to thematerial’s intrinsic properties and possible porous effectsis presented. The method was applied to composite electrodes.This method utilises, in addition to the impedance responsemeasured in front of the electrode, also the impedance measuredat the backside of the electrode. Finally, the kinetics of a composite electrode was alsoinvestigated by in situ X-ray diffraction (in situ XRD) incombination with galvanostatic and potentiostatic experiments. Noevidence of lithium concentration gradients could be observedfrom XRD data, even at the highest rate applied (i.e. ~6C), thusexcluding solid-phase diffusion and also phase-boundary movement,as described by Fick’s law, as the ratelimiting step. <b>Key words:</b>linear sweep voltammetry, electrochemicalimpedance spectroscopy, potential step, in situ X-raydiffraction, microelectrodes, electrode kinetics, LiMn2O4cathode, rechargeable lithium batteries