Dissertations / Theses on the topic 'Material Electrochemistry'
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Bolger, Paul Thomas. "The electrochemistry of silver co-ordination complexes." Thesis, Queen's University Belfast, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.287292.
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Siritanaratkul, Bhavin. "Enzyme-material composites for solar-driven reactions." Thesis, University of Oxford, 2017. https://ora.ox.ac.uk/objects/uuid:55df8993-254b-4960-8ef4-fd9624206f3b.
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Using sunlight to drive chemical reactions has long been one of the goals in developing sustainable processes. Previous research has focused on solar fuel production in the form of H2, but this thesis demonstrates that solar-to-chemicals processes can be constructed to produce more complex compounds, using hybrid systems composed of enzymes and inorganic materials. Tetrachloroethene reductive dehalogenase (PceA), an enzyme that catalyzes the conversion of tetrachloroethene (PCE) to trichloroethene (TCE) and subsequently to cis-dichloroethene (cDCE), was shown to accept electrons from both graphite and TiO2 electrodes. Irradiation by UV light onto PceA-adsorbed TiO2 particles led to the selective production of TCE and cDCE, which was not possible without PceA as a catalyst. Ferredoxin-NADP+ reductase (FNR) is a key enzyme in photosynthesis, as it receives energetic electrons from Photosystem I and produces NADPH as an energy carrier for downstream 'Dark' reactions involving CO2 assimilation. This thesis presents the discovery of FNR activity on indium tin oxide (ITO) electrodes which led to direct electrochemical investigation of the properties of FNR, both in the absence and presence of its substrate, NADP+. The FNR-adsorbed electrode, termed 'the electrochemical leaf', rapidly interconverts NADP+/NADPH, and this was coupled to a downstream NADPH-dependent enzyme, thus demonstrating a new approach to cofactor regeneration for enzyme-catalyzed organic synthesis. The NADP+ reduction by FNR was also driven by light using a photoanode made of visible-light responsive semiconductors.
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Braham, Victoria Jane. "Corrosion of aluminium in contact with cutting fluids : electrochemistry of corrosion." Thesis, University of Newcastle Upon Tyne, 1997. http://hdl.handle.net/10443/797.
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The work in this thesis concerns the behaviour of cutting fluids used for drilling aluminium. A cutting fluid which is useful must neither corrode nor stain aluminum unduly. The compositional factors which lead to a successful cutting fluid have been investigated using electrochenucal techniques. Linear sweep and impedance measurements were used to assess the corrosion of pure alummium and aluminium alloys in contact with aqueous solutions in the pH range 8-11 , in the presence and absence of oxygen. It was found that a low corrosion rate required that the solution pH was kept lower than 9.5. Clear and stable cutting fluids were formulated with and without the use of amines and the corrosion of aluminium in contact with these cutting fluid emulsions was studied. The corrosion rate of aluminium was found to be a factor of ten times lower when in contact with a typical emulsion compared to contact with an aqueous borax solution of the same pH. The most important factor in respect of corrosion control was the pH. The presence/absence of amines did not significantly affect the corrosion rates. In order to simulate the drilling process,a glass cell was designed with a glass frit situated at the base onto which an aluminium rotating disc electrode was lowered, and electrochemical measurements were made, in situ in this way. Abrasion of the electrode caused the anodic process on the metal to be affected to a greater extent than the cathodic process. The electrochemical techniques used in this work have readily allowed us to assess the suitability of different cutting fluid formulations.
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Jia, Jingshu. "Fabrication of high quality one material anode and cathode for water electrolysis in alkaline solution /." View abstract or full-text, 2008. http://library.ust.hk/cgi/db/thesis.pl?EVNG%202008%20JIA.
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Libot, Cecile. "The influence of cathode material on the reduction of aryl carbonyl compounds : formation of radicals." Thesis, University of Southampton, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.313211.
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Grosu, Cristina. "Correlation between structure and electrochemistry of LiMO2 cathode materials (M = Ni, Co)." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2017. http://amslaurea.unibo.it/13355/.
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Technical diversity and various knowledge is required for the understanding of undoubtedly complex system such as a Lithium-ion battery. The peculiarity is to combine different techniques that allow a complete investigation while the battery is working. Nowadays, research on Li-ion batteries (LIBs) is experiencing an exponential growth in the development of new cathode materials. Accordingly, Li-rich and Ni-rich NMCs, which have similar layered structure of LiMO2 oxides, have been recently proposed. Despite the promising performance on them, still a lot of issues have to be resolved and the materials need a more in depth characterisation for further commercial applications. In this study LiMO2 material, in particular M = Co and Ni, will be presented. We have focused on the synthesis of pure LiCoO2 and LiNiO2 at first, followed by the mixed LiNi0.5Co0.5O2. Different ways of synthesis were investigated for LCO but the sol-gel-water method showed the best performances. An accurate and systematic structural characterization followed by the appropriate electrochemical tests were done. Moreover, the in situ techniques (in-situ XRD and in situ OEMS) allowed a deep investigation in the structural change and gas evolution upon the electrochemically driven processes.
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Ranganathan, Srikanth. "Preparation, modification and characterization of a novel carbon electrode material for applications in electrochemistry and molecular electronics /." The Ohio State University, 2001. http://rave.ohiolink.edu/etdc/view?acc_num=osu1486398528558482.
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Tan, Chuting Tan. "Radiation-Induced Material and Performance Degradation of Electrochemical Systems." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu151448116966595.
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Beaussant, Törne Karin. "Investigation of corrosion properties of metals for degradable implant applications." Doctoral thesis, KTH, Materialfysik, MF, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-215970.
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Nedbrytbara metaller utgör en ny klass av biomaterial med potential attersätta permanenta material i tillfälliga applikationer. Detta för att minskarisken för långvariga biverkningar. I den pågående forskningen för att utvecklanya nedbrytbara metaller är screening av nya material genom in vitro testmetoderett attraktivt alternativ för att undvika onödiga, tidskrävande ochdyrbara djurstudier.Denna avhandling fokuserar på in vitro-testning av zink- och magnesiumbaserademetaller. Inverkan av faktorer såsom sammansättningen av testlösningen,buffersystemet, belastning samt mikrostruktur hos legeringar undersöktes.Genom att använda elektrokemiska in situ tekniker såsom impedansspektroskopi(EIS) är det möjligt att studera gränssnittet mellan metall ochlösning och karakterisera egenskaperna hos den korroderande ytan. Ex situytkaraktäriseringstekniker som svepelektronmikroskopi och infraröd spektroskopianvändes sedan för att komplettera resultaten av de elektrokemiskamätningarna.Korrosionen av zink i Ringer’s lösning fanns vara närmare in vivo korrosionän korrosionen i fosfatbuffrad saltlösning (PBS). Ringers lösning är därför denföredragna testmiljön för långsiktig utvärdering av zinkbaserade metallerDet biologiska buffersystemet (CO2/H2CO3) bör företrädesvis användasför att stabilisera pH-värdet på testlösningen vid magnesiumnedbrytning. NärHEPES användes för att stabilisera pH ökade korrosionshastigheten på grundav bildning av mindre skyddande skikt av korrosionsproduktMöjligheten att använda helblod och plasma som mer kliniskt relevantatestmiljöer utvärderades och befanns producera reproducerbara resultat.Bildning av ett korrosionsskikt bestående av både organiskt och oorganisktmaterial detekterades på zink i både plasma och helblod.När zink prover i helbod utsattes för belastning förhindrade korrosionsskiktetbildningen av mikrosprickor och förtidigt brott av provet. Det varvidare möjligt att detektera tidig sprickbildning på grund av belastning avMagnesium AZ61-legering med EIS.Adsorption av organiska species på zinkytan under anodisk polariseringökar yttäckningen av Zn-joner i helblod. Den ökade yttäckningen leder sedantill utfällningen av ett skyddande skikt av zinkfosfater och en minskadkorrosionshastighet vid högre potentialer.Korrosion av Zn-Mg och Zn-Ag legeringar i Ringers lösning befanns skevia selektiv upplösning. Lokal utfällning av korrosionsprodukter och bildningav ett poröst, mindre skyddande skikt av korrosionsprodukter hittades påZn-Mg legeringar. Den selektiva upplösningen av Zn-Ag legering orsakade enanrikning av AgZn3 vilket kan påverka biokompatibiliteten av ett implantatmed tiden.Degradable metallic implants are a new class of biomaterials with potentialto replace permanent materials in temporary applications to reduce therisk of long term adverse effects.This thesis focuses on in vitro testing of zinc and magnesium based metals.As new degradable metals are developed screening of new materials within vitro test methods is an attractive option to avoid unnecessary, time consumingand expensive animal studies. The influence of factors such as ioniccomposition of the test solution, buffer system, strain and alloy compositionwas investigated. By employing electrochemical in situ techniques such asimpedance spectroscopy it is possible to study the metal-solution interfaceand determine the properties of the corroding surface. Ex situ surface characterizationtechniques such as scanning electron microscopy and infraredspectroscopy were then used to complement the results of the electrochemicalmeasurements.The importance of appropriate selection of the test solution is highlightedin this work. Zinc was found to corrode in Ringer’s solution by a mechanismcloser to in vivo corrosion than in a phosphate buffered saline solution(PBS).Ringer’s solution is therefore the more appropriate test environment for longterm evaluation of zinc based metals.When evaluating the corrosion of Zn-Mg and Zn-Ag alloys in Ringer’ssolution selective dissolution was found to occur for both types of alloys. Localprecipitation and formation of a porous, less protective, layer of corrosionproducts was found for Zn-Mg alloys. The selective dissolution of Zn-Agalloy caused an enrichment of AgZn3 on the surface which may affect thebiocompatibility of the alloy.The use of HEPES to maintain the pH of the test solution increasedthe corrosion rate of magnesium due to formation of a less protective layerof corrosion products. Magnesium corrosion should therefore preferably bestudied in solutions where the pH is maintained by the biological buffer systemCO2/H2CO3.In addition to saline solutions human whole blood and plasma were evaluatedas more clinically relevant in vitro environments. They were found toproduce reproducible results and to be suitable for short term experiments.Formation of a corrosion product layer comprised of both organic and inorganicmaterial was detected on zinc in both plasma and whole blood.During anodic polarization the adsorption of organic species on the zincsurface was found to increase the surface coverage of Zn ions in whole blood.The increased surface coverage then allowed for precipitation of a protectivelayer of Zn5(PO4)3 and a subsequent decrease in corrosion rate at higherpotentials.When subjecting zinc samples to strain the organic/inorganic corrosionproduct formed in whole blood was observed by impedance spectroscopy toprevent micro cracking and premature failure.The cracking of magnesium alloy samples under applied strain was alsocharacterized by impedance. Changes in surface properties due to crack initiation
QC 20171019
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Sobkowiak, Adam. "LiFeSO4F as a Cathode Material for Lithium-Ion Batteries : Synthesis, Structure, and Function." Doctoral thesis, Uppsala universitet, Institutionen för kemi - Ångström, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-262715.
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In this thesis, two recently discovered polymorphs of LiFeSO4F, adopting a tavorite- and triplite-type structure, were investigated as potential candidates for use as cathode materials in Li-ion batteries. The studies aimed at enriching the fundamental understanding of the synthetic preparations, structural properties, and electrochemical functionality of these materials. By in situ synchrotron X-ray diffraction (XRD), the formation mechanism of the tavorite-type LiFeSO4F was followed starting from two different sets of precursors, FeSO4∙H2O + LiF, and Li2SO4 + FeF2. The results indicated that the formation of LiFeSO4F is possible only through the structurally related FeSO4∙H2O, in line with the generally recognized topotactic reaction mechanism. Moreover, an in-house solvothermal preparation of this polymorph was optimized with the combined use of XRD and Mössbauer spectroscopy (MS) to render phase pure and well-ordered samples. Additionally, the triplite-type LiFeSO4F was prepared using a facile high-energy ball milling procedure. The electrochemical performance of as-prepared tavorite LiFeSO4F was found to be severely restricted due to residual traces of the reaction medium (tetraethylene glycol (TEG)) on the surface of the synthesized particles. A significantly enhanced performance could be achieved by removing the TEG residues by thorough washing, and a subsequent application of an electronically conducting surface coating of p-doped PEDOT. The conducting polymer layer assisted the formation of a percolating network for efficient electron transport throughout the electrode, resulting in optimal redox behavior with low polarization and high capacity. In the preparation of cast electrodes suitable for use in commercial cells, reducing the electrode porosity was found to be a key parameter to obtain high-quality electrochemical performance. The triplite-type LiFeSO4F showed similar improvements upon PEDOT coating as the tavorite-type polymorph, but with lower capacity and less stable long-term cycling due to intrinsically sluggish kinetics and unfavorable particle morphology. Finally, the Li+-insertion/extraction process in tavorite LiFeSO4F was investigated. By thorough ex situ characterization of chemically and electrochemically prepared LixFeSO4F compositions (0≤x≤1), the formation of an intermediate phase, Li1/2FeSO4F, was identified for the first time. These findings helped redefine the (de)lithiation mechanism which occurs through two subsequent biphasic reactions, in contrast to a previously established single biphasic process.
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Lewis, Courtney-Elyce. "Carbon-integrated vanadium oxide hydrate as a high-performance cathode material for zinc-ion batteries." Thesis, Queensland University of Technology, 2022. https://eprints.qut.edu.au/230254/1/Courtney-Elyce_Lewis_Thesis.pdf.
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This thesis investigates the viability of a new vanadium oxide cathode material to improve the performance of zinc ion battery technologies. Such systems promote the development of eco-friendly, renewable energy storage, and green portable devices. The focus material was thoroughly tested and characterised to gain a deeper understanding of the internal reaction and mechanisms of the battery cells, providing valuable insights relevant to the wider energy storage research community.
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Khatib, Maher Al. "EPR Spectroscopy for the investigation of materials of technological and industrial interest." Doctoral thesis, Università di Siena, 2019. http://hdl.handle.net/11365/1070360.
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The research presented in this Doctoral Thesis discusses mainly the use of Electron Paramagnetic Spectroscopy for the characterization of materials of technological interest. The longitudinal relaxation properties of a vanadyl porphyrin complex have been investigated using pulse EPR experiments at Q (34 GHz) and J-band (263 GHz) frequencies, and the molecule proposed as suitable candidate for quantum processors engineering. The experimental knowledge developed through these relaxation studies, have been transferred to the field of melanins biopigments characterization. The interest for this class of biopigments was derived from the vast amount of applications melanin can cover in the electrochemical and optoelectronic field (e.g. low immunoresponse coating for medical electroanalytical devices, or UV-Vis radiation absorber for solar energy harvesting devices). A novel bacterial melanin from Streptomyces cyaneofuscatus bacteria, and melanin pigments of enzymatic origin, were first studied through S (4 GHz), X (9 GHz) and Q-band (34 GHz) multifrequency EPR. The composition of the bacterial and enzymatic pigments was described, with the support of computer simulation and existing literature in the field. The relaxation properties of these melanin pigments were investigated by means of X and Q-band continuous wave EPR, as well as with Q-band pulse EPR experiments. Differences in terms of longitudinal relaxation times were observed for the melanin pigments of different origin, so that pulse EPR could be proposed either as a tool to distinguish among different melanin species, as well as probe to investigate the structure and dynamics of the radical species present in these natural pigments. A last chapter on the use of computer simulations for the modeling of the electrochemical devices that could be designed to host melanin coated electrodes is presented. In that context, a general model for the evaluation of electrodic currents generated under different geometrical and physical parameters of the systems has been proposed. The physical description was carried out using a dimensionless form of the governing equations, so that the findings of that research can be adapted to particular cases of study. The diverse content of the thesis is thought to reflect the multidisciplinary nature of materials research.
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Plattard, Tiphaine. "Modélisation du vieillissement d'une batterie Lithium-ion : couplage d'un modèle de fatigue avec un modèle comportemental." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLS323.
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Le développement rapide des batteries lithium-ion nécessite des études de vieillissement précises. L'objectif de la thèse est de préciser sur une nouvelle chimie de cellule (NMC) l'impact des paramètres sur le vieillissement, à savoir la température, l'intensité du courant et l'état de charge, et de le mettre en œuvre dans un modèle prédictif et reparamétrable.Une campagne de tests permet de quantifier l'impact unitaire des paramètres de vieillissement sur la perte de capacité de chaque batterie. Nous intégrons les résultats dans un modèle de fatigue. Celui-ci module l'impact d'un ampère-heure échangé par les conditions d’échange de cet ampère-heure au moyen de fonctions de pondération. Ce modèle est ensuite implémenté dans un logiciel, muni de son interface homme machine. Il permet à l'utilisateur de se familiariser avec le vieillissement et de faire des calculs de prédiction de perte de capacité de la batterie.Cependant, ce modèle peut dériver avec le temps en raison de sollicitations répétées. Par conséquent, ses paramètres doivent être mis à jour au moyen de mesures sur le terrain, afin de rester précis. Ces mesures sur le terrain sont soumises à la méthode dite d'analyse incrémentielle des capacités (ICA), consistant à analyser la quantité dQ/dV en fonction de V. Nous avons montré que l’évolution des pics observables sur l’ICA peut être corrélée à la cinétique du premier modèle de fatigue, ce qui permet de se servir de cette mesure pour le recalibrer. Cette mesure permet de réaliser le couplage avec le modèle de fatigue. Enfin, des tests applicatifs permettent de valider la méthode développéeReliable development of LIBs requires accurate aging studies. The objective of the thesis is to clarify on a new cell chemistry (NMC) the impact of the parameters on aging, namely the temperature, the rated current intensity and the state of charge, and to implement it in a predictive and updatable model.A test campaign makes it possible to quantify the unit impact of the aging parameters on the loss of capacity of each battery cell. We integrate the results into a fatigue model. The latter modulates the impact of an exchanged ampere-hour by the exchange conditions of this ampere-hour by means of weighting functions. This model is then implemented in a software, equipped with its man/machine interface. It allows the user to become familiar with aging and to make prediction calculations of loss of battery capacity.This model can drift with time due to repeated solicitation, so its parameters need to be updated by on-field measurements, to remain accurate. These on-field measurements are submitted to the so-called Incremental Capacity Analysis method (ICA), consisting in the analysis of dQ/dV as a function of V. We have shown that the evolution of the peaks observable on the ICA can be correlated with the kinetics of the first fatigue model. This measurement makes it possible to couple with the fatigue model. Finally, application tests validate the method developed
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Hussain, Noor Feuza. "Electrochemical Remedy and Analysis for the Environment Based on the New Polymer-DNA Composite Material." Digital Commons @ East Tennessee State University, 2005. https://dc.etsu.edu/etd/1047.
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In this work a new material, the conducting polymer-DNA composite, has been reported for the first time due to its promise in micro extraction, transfer, and release of cations under controlled potential conditions by using electrochemically assisted solid phase micro extraction (SPME). The Polypyrrole/DNA composite can be formed easily by oxidation of pyrrole monomers in the presence of chromosomal DNA by electropolymerization. Environmental significant pollutants such as Cd, Pb, Hg, Co, Zn, Cu, and Bi metal ions can be extracted from the aqueous solution and are able to be transferred to another medium defined as the release solution where the metals were detected by anodic stripping voltammetry. Using Cd2+ as a model, this method has been examined to optimize its operational condition. Extraction efficiency and potential interference for this method were studied.
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Yuan, Qifan. "Physical, electrical and electrochemical characterizations of transition metal compounds for electrochemical energy storage." Diss., Virginia Tech, 2015. http://hdl.handle.net/10919/71869.
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Electrochemical energy storage has been widely used in various areas, including new energy sources, auto industry, and information technology. However, the performance of current electrochemical energy storage devices does not meet the requirements of these areas that include both high energy and power density, fast recharge time, and long lifetime. One solution to meet consumer demands is to discover new materials that can substantially enhance the performance of electrochemical energy storage devices. In this dissertation we report four transition metal materials systems with potential applications in electrochemical energy storage.
Nanoscale and nanostructured materials are expected to play important roles in energy storage devices because of their enhanced and sometimes unique physical and chemical properties. Studied here is the comparative electrochemical cation insertion into a nanostructured vanadium oxide, a promising electrode material candidate, for the alkali metal ions Li+, Na+ and K+ and the organic ammonium ion, in aqueous electrolyte solutions. Observed are the distinctive insertion processes of the different ions, which yield a correlation between physical degradation of the material and a reduction of the calculated specific charge. The results reveal the potential of this nanostructured vanadium oxide material for energy storage. Vanadium based electrochemical systems are of general interest, and as models for vanadium based solid-state electrochemical processes, the solution state and the solid-state electrochemical properties of two cryolite-type compounds, (NH4)3VxGa1-xF6, and Na3VF6, are studied. The electrochemical behavior of (NH4)3VxGa1-xF6 explored the possibility of using this material as an electrolyte for solid state energy storage systems.
Zeolite-like materials have large surface to volume ratios, with ions and neutral species located in the nanometer sized pores of the 3-dimensional framework, potentially yielding high energy density storage capabilities. Yet the insulating nature of known zeolite-like materials has limited their use for electrical energy storage. Studied here are two vanadium based zeolite-like structures, the oxo-vanadium arsenate [(As6V15O51)-9]∞, and the oxo-vanadium phosphate [(P6V15O51)-9]∞, where the former shows electronic conduction in the 3-dimensional framework. Mixed electronic and ionic conductivity, from the framework and from the cations located within the framework, respectively, is measured in the oxo-vanadium arsenate, and allows the use of this material in electrochemical double-layer capacitor configuration for energy storage. By contrast, the oxo-vanadium phosphate shows ionic conduction only. Lastly, a new strontium manganese vanadate with a layered structure exhibiting mixed protonic and electronic conductivity is studied. The various transition metal compounds and materials systems experimentally studied in this thesis showcase the importance of novel materials in future energy storage schemes.Ph. D.
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Cabelguen, Pierre-Etienne. "Analyse de la microstructure des matériaux actifs d'électrode positive de batteries Lithium-ion." Thesis, Université Grenoble Alpes (ComUE), 2016. http://www.theses.fr/2016GREAI069/document.
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Ce travail de thèse se base sur quatre matériaux modèles, de composition LiNi1/3Mn1/3Co1/3O2, qui différent de par leur microstructure. Le lien entre leur morphologie et les performances électrochimiques est étudié par la combinaison de la caractérisation exhaustive de leur microstructure, l’étude de leur comportement en batterie et la modélisation de leur réponse électrochimique. L’étape limitant le processus électrochimique est identifiée par voltampérométrie cyclique et nous montrons que la transition attendue d’une limitation par le transfert de charge à une limitation par la diffusion en phase solide a lieu à différents régimes selon la microstructure. Ce comportement est expliqué par l’utilisation d’outils de simulations numériques. Selon leur forme et leur agglomération, les cristallites agissent collectivement ou indépendamment les unes des autres. Ces résultats rationalisent les performances en puissance obtenues sur nos matériaux. Les résultats de simulation montrent également qu’une faible fraction de la surface développée est électroactive, ce qui remet en question la large utilisation de la surface BET dans la littérature. Nous montrons également que, si les matériaux poreux sont les plus performants en puissance gravimétrique, la tendance est inversée pour la puissance volumique. Les stratégies de nanostructuration largement employées, qui se basent sur la capacité spécifique pour caractériser les matériaux, ne doivent pas oublier faire oublier le compromis nécessaire entre surface développée et volumeFour NMC materials are synthesized by co-precipitation. They exhibit a hierarchical architecture made of reasonably spherical agglomerates. One is constituted of flake-shaped, spatially oriented, crystallites that leave large apparent void spaces in the agglomerate, while the other results from the tight agglomeration of micron-sized cuboids. Porous material exhibits the best power performances. It is impossible to identify a geometrical parameter that predict performances, even after achieving the full characterization of the microstructures. Cyclic voltammetry reveals two behaviours depending on the shape of crystallites: processes limited by solid-state diffusion (cuboids) and the ones limited by charge transfer even at high rates (flake-shaped). This observation challenges active materials design strategies that assume diffusion as the limiting process of lithium intercalation. Focusing on enhancing kinetics could be the way to increase performances. Charge-transfer is first investigated by measuring electronic conductivities over a wide range of frequencies, allowing to discriminate relaxations arising at various length scales. We show that flake-shaped crystallites facilitate the motion of electrons at all scale levels compared to cuboids. Charge-transfer limitations originate from the electrolyte/material interface in materials exhibiting high surface areas. Numerical simulations reveal that BET measurements largely overestimate the actual electroactive surface, which is understood by HRTEM images of flake-shaped crystallites. Only a small percentage, limited to the edge plane is truly electroactive
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Dabo, Ismaila. "Towards first-principles electrochemistry." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/44320.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2008.Includes bibliographical references (p. 143-151).
This doctoral dissertation presents a comprehensive computational approach to describe quantum mechanical systems embedded in complex ionic media, primarily focusing on the first-principles representation of catalytic electrodes under electrochemical conditions. The accurate electrostatic description of electrified metal-solution interfaces represents a persistent challenge for ab-initio simulations and an essential requisite for predicting the electrical response of electrochemical convertors-i.e., the correspondence between the macroscopic voltage and the microscopic interfacial charge distribution. The approach consists of controlling the electrode voltage via its conjugate extensive variable, namely, the charge of the system. As a preliminary to the study of electrified interfaces in ionic media, we analyze charged slabs in vacuum subject to periodic boundary conditions. We show that the corrective potential (defined as the difference between the exact open-boundary potential and the periodic potential obtained from a Fourier transform) varies smoothly over space, allowing for its determination on a coarse mesh using optimized electrostatic solvers. Because this scheme takes into account exact open boundary conditions, its performance is considerably superior to that of conventional corrective methods. Extending this computational scheme, we present an efficient approach to model electrochemical systems under realistic conditions, based on a first-principles description of the interface region and on a continuum representation of the ionic solvent.
(cont.) We demonstrate that the ionicsolution contribution to the electrostatic potential-the ionic solvent reaction field--can be computed independently at low cost simultaneously using fast Fourier transforms and multigrid techniques, and highlight the importance of adopting adequate electrochemical boundary conditions to correctly predict the electrical response of electrode-electrolyte interfaces. In order to probe and validate the electrochemical model, we study the vibrational Stark effect-i.e., the influence of the applied voltage on the vibrational properties-for carbon monoxide adsorbed on transition metal surfaces, a phenomenon whose description requires an accurate representation of the interfacial electric field. We start out the analysis by examining the vibrational properties of CO adsorbed on clean and ruthenium-covered platinum substrates. The calculated C-O stretching frequencies are found to be in excellent agreement with experimental measurements despite the frequent qualitative failures of local and semilocal exchange-correlation functionals in predicting adsorption energies for CO on transition metals. We then introduce an orbital-resolved force analysis to clarify the electronic origins of the C-O red shifts, and present a sensitivity analysis to assess the influence the HOMO and LUMO hybridizations on the calculated frequencies, thereby establishing the remarkable accuracy of conventional density-functional theory methods in determining the vibrational properties of adsorbed CO. Based on these results, we apply the electrochemical model to provide the first comprehensive ab-initio description of the vibrational Stark effect for CO on transition metal surfaces, finding excellent agreement with spectroscopic measurements.
(cont.) As related projects, we have implemented a molecular-dynamics algorithm for metallic systems and developed a self-interaction correction method to rectify the tendency of density-functional theory calculations to overestimate binding energies. The present computational electrochemistry toolkit open promising perspectives for the application of first-principles methods to assist the microstructural engineering of electrochemical convertors.
Ismaila Dabo.
Ph.D.
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Xiao, Shaorong. "The electrochemistry of phenothiazine derivatives." Thesis, University of Central Lancashire, 2000. http://clok.uclan.ac.uk/20876/.
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Methylene blue derivatives (MBDs) such as methylene blue (MB -), 1-methyl methylene blue (1MMB) and 1,9-dimethyl-methylene blue (DMMB) have potential use as drugs within photodynamic therapy (PDT). Knowing the redox properties of MBDs will help in understanding the way in which MBDs interact with a range of biological systems. In this work, the electrochemical behaviour of MBDs at various solution pHs have been studied for the first time on gold microdisc electrodes using steady state and non-steady state cyclic voltammetric methods. Steady-state studies The reduction of MBDs is an ECE(CC) process where the C steps are protonation reactions. The number (m) of W participating in the overall electrode process increases from 1 to 2 or 3 with decreasing pH although the profile is different among MBDs. The half-wave potential (E 112) of each methylene blue derivative (MBD) shifts to more negative potential with increasing pH values. The E 112 of MBD at the same pH shifts to more cathodic potentials with an increasing number of -CH 3 substituent, indicating that the thermodynamic facility of MB, lMMB and DMMB reduction decreases with increasing the number of -CH3 substituents. The reduction products of MBDs depend strongly on pH, sweep rate, and sweep potential limit, as well as number of -CH 3 substituents. Non-steady state studies The redox behaviour of MBDs under non-steady-state conditions is complicated. Their common characteristics are that (i) the initial reduction of MBD is a diffusion controlled process; (ii) the onset potentials for MBD reduction shift to more negative potentials with increasing pH and number of CH 3 substituents; (iii) the facility of observation of the charge transfer complex increases with increasing pH; (vi) the charge transfer complex can be further reduced at more cathodic potentials; and (v) the amounts of charge transfer complex and leuco form depend on sweep rate and sweep potential window. They also have some differences among the electrochemical behaviour of the three drugs, such as, some anodic and cathodic processes may occur in one of MBDs, and some may not. Possible mechanisms for the electroreduction of MBDs are suggested and discussed in the light of the effect of pH and potential sweep rate on the reaction products.
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Boni, Alessandro <1987>. "Electrochemistry of Nanocomposite Materials for Energy Conversion." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2016. http://amsdottorato.unibo.it/7510/1/boni_alessandro_tesi.pdf.
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Energy is the most relevant technological issue that the world experiences today, and the development of efficient technologies able to store and convert energy in different forms is urgently needed. The storage of electrical energy is of major importance and electrochemical processes are particularly suited for the demanding task of an efficient inter-conversion.
A potential strategy is to store electricity into the chemical bonds of electrogenerated fuels, like hydrogen and/or energy-dense hydrocarbons. This conversion can be accomplished by water splitting and CO2 electrolysis. In this context, are herein presented three different electrochemical approaches towards water and CO2 reduction.
In Chapter 1 is reported a novel class of nanostructured electrocatalysts, MWCNTs@Pd/TiO2, able to efficiently reduce water at neutral pH. Multi-walled carbon nanotubes, Pd nanoparticles and titanium dioxide are mutually integrated within the nanocomposites, whose electrocatalytic properties are thoroughly investigated and optimized. By electrochemical methods it is rationalized the effect of each building block on the overall activity, which originate from the synergic cooperation of the three units.
In Chapter 2 is presented an electrochemical study of MWCNTs@CeO2, a noble-metal free electrocatalyst with a similar architecture to MWCNTs@Pd/TiO2. The electroreduction of CO2 has often the drawbacks of a poor selectivity and high energy losses for the high overpotential required to drive the reaction. However, detailed studies of MWCNTs@CeO2 highlights the possibility to convert CO2 to formic acid at very low overpotential and with a high selectivity. A reaction mechanism that involves the participation of surface hydride species and the CeO2 shell is proposed.
Finally, in Chapter 3 is presented a photo-electrochemical approach to hydrogen production. Solar energy is converted to hydrogen via water reduction on the surface of a catalyst-free, oxide-protected solar cell. The large solar-to-hydrogen activity of the photocathode assembly has been explained by a combination of experimental and theoretical studies.
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Kloppers, Marius Jacques 1962. "Electrochemistry of iron-chromium alloys." Thesis, Massachusetts Institute of Technology, 1991. http://hdl.handle.net/1721.1/106706.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1991.Vita.
Includes bibliographical references (leaves 307-314).
by Marius Jacques Kloppers.
Ph.D.
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Ziebro, Thomas R. "In vivo PPy(DBS) sensors to quantify excitability of cells via sodium fluctuations in extracellular solution." The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1492031927557033.
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Loget, Gabriel. "Electric field-generated asymmetric reactivity : from materials science to dynamic systems." Thesis, Bordeaux 1, 2012. http://www.theses.fr/2012BOR14572/document.
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L’électrochimie bipolaire est un phénomène générant une réactivité asymétrique à la surface d’objets conducteurs, sans contact électrique direct. Ce concept est basé sur le fait que lorsqu’un objet conducteur est localisé dans un champ électrique, il se polarise. Par conséquent, une différence de potentiel est générée entre ses deux extrémités, et peut être utilisée pour induire des réactions redox localisées. Dans cette thèse, l’utilisation de l’électrochimie bipolaire pour la science des matériaux et pour la locomotion d’objets est présentée.Jusqu’à présent, la plupart des méthodes ou procédés utilisés pour générer des objets asymétriques,appelés aussi objets « Janus », nécessitent l’introduction d’une interface pour briser la symétrie. Nous avons développé une nouvelle approche basée sur l’électrodéposition bipolaire pour générerce type d’objet en grande quantité. Grâce à cette technologie différents matériaux tels que des métaux, des polymères et des semi‐conducteurs ont pu être déposés sur diverses particulesconductrices. Il a été aussi démontré que l’électrochimie bipolaire pouvait être utilisée pour lamicrostructuration de substrats conducteurs.Nous avons induit des mouvements à des objets conducteurs en exploitant le phénomèned’électrochimie bipolaire. Certains objets Janus synthétisés par l’approche précédente ont pu être utilisés comme micronageurs. La brisure de symétrie qui est générée par l’électrochimie bipolaire peut être aussi utilisée directement pour générer un mouvement de particules isotropes. En employant ce concept, nous avons pu provoquer des mouvements de translation, rotation et lévitation pour des particules de carbones ou métalliquesThe phenomenon of bipolar electrochemistry generates an asymmetric reactivity on the surface ofconductive objects in a wireless manner. This concept is based on the fact that when a conducingobject is placed in an electric field, it gets polarized. Consequently, a potential difference appearsbetween its two extremities, that can be used to drive localized redox reactions. In the presentthesis, bipolar electrochemistry was used for material science and the locomotion of objects.So far, the majority of methods and processes used for the generation of asymmetric objects, alsocalled “Janus” objects, is based on using interfaces to break the symmetry. We developed a newapproach based on bipolar electrodeposition for generating this type of objects in the bulk. Using thistechnology, various materials like metals, polymers and semiconductors could be deposited ondifferent types of conducting particles. We also showed that bipolar electrochemistry can be used forthe microstructuration of conducting substrates.Motion generation by bipolar electrochemistry has also been demonstrated. Some of the Janusobjects synthesized by the previous approach can be used as microswimmers. The asymmetricreactivity that is induced by bipolar electrochemistry can also be used directly to generate motion ofnon‐hybrid objects. With this concept we induced translations, rotations and levitations of carbonand metal particles
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au, minakshi@murdoch edu, and Manickam Minakshi Sundaram. "Electrochemistry of Cathode Materials in Aqueous Lithium Hydroxide Electrolyte." Murdoch University, 2006. http://wwwlib.murdoch.edu.au/adt/browse/view/adt-MU20061210.143803.
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Electrochemical behavior of electrolytic manganese dioxide (EMD), chemically prepared battery grade manganese dioxide (BGM), titanium dioxide (TiO2), lithium iron phosphate (LiFePO4) and lithium manganese phosphate (LiMnPO4) in aqueous lithium hydroxide electrolyte has been investigated. These materials are commonly used as cathodes in non-aqueous electrolyte lithium batteries. The main aim of the work was to determine how the electroreduction/oxidation behavior of these materials in aqueous LiOH compares with that reported in the literature in non-aqueous electrolytes in connection with lithium batteries. An objective was to establish whether these materials could also be used to develop other battery systems using aqueous LiOH as electrolyte.
The electrochemical characteristics of the above materials were investigated by subjecting them to slow scan cyclic voltammetry and determining the charge/discharge characteristics of Zn/cathode material-aqueous LiOH batteries. The products of electroreduction/oxidation were characterized by physical techniques using X-ray diffraction (XRD), scanning electron micrography (SEM), X-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS), Thermogravimetric analysis (TG) and infra-red spectrometry (IR).
The reduction of ã-MnO2 (EMD) in aqueous lithium hydroxide electrolyte is found to result in intercalation of Li+ into the host structure of ã-MnO2. The process was found to be reversible for many cycles. This is similar to what is known to occur for ã-MnO2 in non-aqueous electrolytes. The mechanism, however, differs from that for reduction/oxidation of ã-MnO2 in aqueous potassium hydroxide electrolyte. KOH electrolyte is used in the state-of-art aqueous alkaline Zn/MnO2 batteries. Alkaline batteries based on aqueous KOH as the electrolyte rely upon a mechanism other than K+ intercalation into MnO2. This mechanism is not reversible. This is explained in terms of the relative ionic sizes of Li+ and K+. The lithium-intercalated MnO2 lattice is stable because Li+ and Mn4+ are of approximately the same size and hence Li+ is accommodated nicely into the host lattice of MnO2. The K+ ion which has almost double the size of Li+ cannot be appropriately accommodated into the host structure and hence the K+ -intercalated MnO2 phase is not stable.
Chemically prepared battery grade MnO2 (BGM) is found to undergo electroreduction/oxidation in aqueous LiOH via the same Li+ intercalation mechanism as for the EMD. While the Zn/BGM- aqueous LiOH cell discharges at a voltage higher than that for the Zn/EMD- aqueous LiOH cell under similar conditions, the rechargeability and the material utilization of the BGM cell is poorer.
The cathodic behavior of TiO2 (anatase phase) in the presence of aqueous LiOH is not reversible. In addition to LiTiO2, Ti2O3 is also formed. The discharge voltage of the Zn/TiO2- aqueous LiOH cell and material utilization of the TiO2 as cathode are very low. Hence TiO2 is not suitable for use in any aqueous LiOH electrolyte battery.
LiFePO4 (olivine-type structure) as a cathode undergoes electrooxidation in aqueous LiOH forming FePO4. However the subsequent reduction forms not only the original LiFePO4 but also Fe3O4. Thus the process is not completely reversible and hence LiFePO4 is not a suitable material for use as a cathode in aqueous battery systems.
LiMnPO4 (olivine-type structure) undergoes reversible electrooxidation in aqueous LiOH forming MnPO4. The charge/discharge voltage profile of the Zn/MnPO4-aqueous LiOH cell, its coulombic efficiency and rechargeability are comparable to that of the cell using ã-MnO2. EMD and LiMnPO4 both have the potential for use in rechargeable batteries using aqueous LiOH as the electrolyte. Recommendations for further developmental work for such batteries are made.
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Manickam, Minakshi. "Electrochemistry of cathode materials in aqueous lithium hydroxide electrolyte /." Access via Murdoch University Digital Theses Project, 2006. http://wwwlib.murdoch.edu.au/adt/browse/view/adt-MU20061210.143803.
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Gillard, Stephen Paul. "Environmental electrochemistry : reactor design, electrode materials and process monitoring." Thesis, University of Portsmouth, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.407225.
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Minakshi, Sundaram Manickam. "Electrochemistry of cathode materials in aqueous lithium hydroxide electrolyte." Thesis, Minakshi Sundaram, Manickam ORCID: 0000-0001-6558-8317 (2006) Electrochemistry of cathode materials in aqueous lithium hydroxide electrolyte. PhD thesis, Murdoch University, 2006. https://researchrepository.murdoch.edu.au/id/eprint/450/.
Full textAbstract:
Electrochemical behavior of electrolytic manganese dioxide (EMD), chemically prepared battery grade manganese dioxide (BGM), titanium dioxide (TiO2), lithium iron phosphate (LiFePO4) and lithium manganese phosphate (LiMnPO4) in aqueous lithium hydroxide electrolyte has been investigated. These materials are commonly used as cathodes in non-aqueous electrolyte lithium batteries. The main aim of the work was to determine how the electroreduction/oxidation behavior of these materials in aqueous LiOH compares with that reported in the literature in non-aqueous electrolytes in connection with lithium batteries. An objective was to establish whether these materials could also be used to develop other battery systems using aqueous LiOH as electrolyte.
The electrochemical characteristics of the above materials were investigated by subjecting them to slow scan cyclic voltammetry and determining the charge/discharge characteristics of Zn/cathode material-aqueous LiOH batteries. The products of electroreduction/oxidation were characterized by physical techniques using X-ray diffraction (XRD), scanning electron micrography (SEM), X-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS), Thermogravimetric analysis (TG) and infra-red spectrometry (IR).
The reduction of gamma-MnO2 (EMD) in aqueous lithium hydroxide electrolyte is found to result in intercalation of Li+ into the host structure of gamma-MnO2. The process was found to be reversible for many cycles. This is similar to what is known to occur for gamma-MnO2 in non-aqueous electrolytes. The mechanism, however, differs from that for reduction/oxidation of gamma-MnO2 in aqueous potassium hydroxide electrolyte. KOH electrolyte is used in the state-of-art aqueous alkaline Zn/MnO2 batteries. Alkaline batteries based on aqueous KOH as the electrolyte rely upon a mechanism other than K+ intercalation into MnO2. This mechanism is not reversible. This is explained in terms of the relative ionic sizes of Li+ and K+. The lithium-intercalated MnO2 lattice is stable because Li+ and Mn4+ are of approximately the same size and hence Li+ is accommodated nicely into the host lattice of MnO2. The K+ ion which has almost double the size of Li+ cannot be appropriately accommodated into the host structure and hence the K+ -intercalated MnO2 phase is not stable.
Chemically prepared battery grade MnO2 (BGM) is found to undergo electroreduction/oxidation in aqueous LiOH via the same Li+ intercalation mechanism as for the EMD. While the Zn/BGM- aqueous LiOH cell discharges at a voltage higher than that for the Zn/EMD- aqueous LiOH cell under similar conditions, the rechargeability and the material utilization of the BGM cell is poorer.
The cathodic behavior of TiO2 (anatase phase) in the presence of aqueous LiOH is not reversible. In addition to LiTiO2, Ti2O3 is also formed. The discharge voltage of the Zn/TiO2- aqueous LiOH cell and material utilization of the TiO2 as cathode are very low. Hence TiO2 is not suitable for use in any aqueous LiOH electrolyte battery.
LiFePO4 (olivine-type structure) as a cathode undergoes electrooxidation in aqueous LiOH forming FePO4. However the subsequent reduction forms not only the original LiFePO4 but also Fe3O4. Thus the process is not completely reversible and hence LiFePO4 is not a suitable material for use as a cathode in aqueous battery systems.
LiMnPO4 (olivine-type structure) undergoes reversible electrooxidation in aqueous LiOH forming MnPO4. The charge/discharge voltage profile of the Zn/MnPO4-aqueous LiOH cell, its coulombic efficiency and rechargeability are comparable to that of the cell using gamma-MnO2. EMD and LiMnPO4 both have the potential for use in rechargeable batteries using aqueous LiOH as the electrolyte. Recommendations for further developmental work for such batteries are made.
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Minakshi, Sundaram Manickam. "Electrochemistry of cathode materials in aqueous lithium hydroxide electrolyte." Minakshi Sundaram, Manickam (2006) Electrochemistry of cathode materials in aqueous lithium hydroxide electrolyte. PhD thesis, Murdoch University, 2006. http://researchrepository.murdoch.edu.au/450/.
Full textAbstract:
Electrochemical behavior of electrolytic manganese dioxide (EMD), chemically prepared battery grade manganese dioxide (BGM), titanium dioxide (TiO2), lithium iron phosphate (LiFePO4) and lithium manganese phosphate (LiMnPO4) in aqueous lithium hydroxide electrolyte has been investigated. These materials are commonly used as cathodes in non-aqueous electrolyte lithium batteries. The main aim of the work was to determine how the electroreduction/oxidation behavior of these materials in aqueous LiOH compares with that reported in the literature in non-aqueous electrolytes in connection with lithium batteries. An objective was to establish whether these materials could also be used to develop other battery systems using aqueous LiOH as electrolyte.
The electrochemical characteristics of the above materials were investigated by subjecting them to slow scan cyclic voltammetry and determining the charge/discharge characteristics of Zn/cathode material-aqueous LiOH batteries. The products of electroreduction/oxidation were characterized by physical techniques using X-ray diffraction (XRD), scanning electron micrography (SEM), X-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS), Thermogravimetric analysis (TG) and infra-red spectrometry (IR).
The reduction of gamma-MnO2 (EMD) in aqueous lithium hydroxide electrolyte is found to result in intercalation of Li+ into the host structure of gamma-MnO2. The process was found to be reversible for many cycles. This is similar to what is known to occur for gamma-MnO2 in non-aqueous electrolytes. The mechanism, however, differs from that for reduction/oxidation of gamma-MnO2 in aqueous potassium hydroxide electrolyte. KOH electrolyte is used in the state-of-art aqueous alkaline Zn/MnO2 batteries. Alkaline batteries based on aqueous KOH as the electrolyte rely upon a mechanism other than K+ intercalation into MnO2. This mechanism is not reversible. This is explained in terms of the relative ionic sizes of Li+ and K+. The lithium-intercalated MnO2 lattice is stable because Li+ and Mn4+ are of approximately the same size and hence Li+ is accommodated nicely into the host lattice of MnO2. The K+ ion which has almost double the size of Li+ cannot be appropriately accommodated into the host structure and hence the K+ -intercalated MnO2 phase is not stable.
Chemically prepared battery grade MnO2 (BGM) is found to undergo electroreduction/oxidation in aqueous LiOH via the same Li+ intercalation mechanism as for the EMD. While the Zn/BGM- aqueous LiOH cell discharges at a voltage higher than that for the Zn/EMD- aqueous LiOH cell under similar conditions, the rechargeability and the material utilization of the BGM cell is poorer.
The cathodic behavior of TiO2 (anatase phase) in the presence of aqueous LiOH is not reversible. In addition to LiTiO2, Ti2O3 is also formed. The discharge voltage of the Zn/TiO2- aqueous LiOH cell and material utilization of the TiO2 as cathode are very low. Hence TiO2 is not suitable for use in any aqueous LiOH electrolyte battery.
LiFePO4 (olivine-type structure) as a cathode undergoes electrooxidation in aqueous LiOH forming FePO4. However the subsequent reduction forms not only the original LiFePO4 but also Fe3O4. Thus the process is not completely reversible and hence LiFePO4 is not a suitable material for use as a cathode in aqueous battery systems.
LiMnPO4 (olivine-type structure) undergoes reversible electrooxidation in aqueous LiOH forming MnPO4. The charge/discharge voltage profile of the Zn/MnPO4-aqueous LiOH cell, its coulombic efficiency and rechargeability are comparable to that of the cell using gamma-MnO2. EMD and LiMnPO4 both have the potential for use in rechargeable batteries using aqueous LiOH as the electrolyte. Recommendations for further developmental work for such batteries are made.
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Belding, Stephen Richard. "Computational electrochemistry." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:e997642f-fbaa-469c-98a3-f359b0996f03.
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Electrochemistry is the science of electron transfer. The subject is of great importance and appeal because detailed information can be obtained using relatively simple experimental techniques. In general, the raw data is sufficiently complicated to preclude direct interpretation, yet is readily rationalised using numerical procedures. Computational analysis is therefore central to electrochemistry and is the main topic of this thesis. Chapters 1 and 2 provide an introductory account to electrochemistry and numerical analysis respectively. Chapter 1 explains the origin of the potential difference and describes its relevance to the thermodynamic and kinetic properties of a redox process. Voltammetry is introduced as an experimental means of studying electrode dynamics. Chapter 2 explains the numerical methods used in later chapters. Chapter 3 presents a review of the use of nanoparticles in electrochemistry. Chapter 4 presents the simulation of a random array of spherical nanoparticles. Conclusions obtained theoretically are experimentally confirmed using the Cr3+/Cr2+ redox couple on a random array of silver nanoparticles. Chapter 5 presents an investigation into the concentration of supporting electrolyte required to make a voltammetric experiment quantitatively diffusional. This study looks at a wide range of experimental conditions. Chapter 6 presents an investigation into the deliberate addition of insufficient supporting electrolyte to an electrochemical experiment. It is shown that this technique can be used to fully study a stepwise two electron transfer. Conclusions obtained theoretically are experimentally confirmed using the reduction of anthracene in acetonitrile. Chapter 7 presents a new method for simulating voltammetry at disc shaped electrodes in the presence of insufficient supporting electrolyte. It is shown that, under certain conditions, the results obtained from this complicated simulation can be quantitatively obtained by means of a much simpler ‘hemispherical approximation’. Conclusions obtained theoretically are experimentally confirmed using the hexammineruthenium ([Ru(NH3)6]3+/[Ru(NH3)6]2+) and hexachloroiridate ([IrCl6]2−/[IrCl6]3−) redox couples. Chapter 8 presents an investigation into the voltammetry of stepwise two electron processes using ionic liquids as solvents. It is shown that these solvents can be used to fully study a stepwise two electron transfer. Conclusions obtained theoretically are experimentally confirmed using the oxidation of N,N-dimethyl-p-phenylenediamine in the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate ([C4 mim][BF4]). The work presented in this thesis has been published as 7 scientific papers.
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Sallis, Shawn. "Understanding the Intrinsic Electrochemistry of Ni-Rich Layered Cathodes." Thesis, State University of New York at Binghamton, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10689173.
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The demand for energy is continually increasing overtime and the key to meeting future demand in a sustainable way is with energy storage. Li-ion batteries employing layered transition metal oxide cathodes are one of the most technologically important energy storage technologies. However, current Li-ion batteries are unable to access their full theoretical capacity and suffer from performance limiting degradation over time partially originating from the cathode and partially from the interface with the electrolyte. Understanding the fundamental limitations of layered transition metal oxide cathodes requires a complete understanding of the surface and bulk of the materials in their most delithiated state.
In this thesis, we employ LiNi0.8Co0.15Al 0.05O2 (NCA) as a model system for Ni-rich layered oxide cathodes. Unlike its parent compound, LiCoO2, NCA is capable of high states of delithiation with minimal structural transitions. Furthermore, commercially available NCA has little to no transition metals in the Li layer. X-ray spectroscopies are an ideal tool for studying cathodes at high states of delithiation due their elemental selectivity, range of probing depths, and sensitivity to both chemical and electronic state information. The oxidation state of the transition metals at the surface can be probed via X-ray photoelectron spectroscopy (XPS) while both bulk and surface oxidation states as well as changes in metal oxygen bonding can be probed using X-ray absorption spectroscopy (XAS).
Using X-ray spectroscopy in tandem with electrochemical, transport and microscopy measurements of the same materials, the impedance growth with increasing delithiation was correlated with the formation of a disordered NiO phase on the surface of NCA which was precipitated by the release of oxygen. Furthermore, the surface degradation was strongly impacted by the type of Li salt used in the electrolyte, with the standard commercial salt LiPF6 suffering from exothermic decomposition at high voltages and temperatures. Substituting LiPF6with LiBF4 suppressed NCA surface degradation and the dissolution of the transition metals into the electrolyte which is responsible for the impedance growth. Even in the most extreme conditions (4.75V vs Li +/Li0 at 60 °C for > 100 hrs) the degradation (i.e. metal reduction) was restricted to the first 10-30 nm and no evidence of oxygen loss was observed in the bulk.
However, the transition metal ions were found to cease oxidizing above 4.25 V vs Li+/Li0 despite it being possible to extract 20% more lithium. Using a newly developed high efficiency resonant inelastic x-ray scattering (RIXS) spectrometer to probe the O K-edge of NCA electrodes at various conditions, it was concluded that oxygen participates in the charge compensation at the highest states of delithiation instead of the transition metals. These results are intrinsic to the physical and electronic structure of NCA and appear general to the other layered transition metal oxides currently under consideration for use as cathodes in Li-ion batteries.
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Fattah, Zahra Ali. "Applications of bipolar electrochemistry : from materials science to biological systems." Phd thesis, Université Sciences et Technologies - Bordeaux I, 2013. http://tel.archives-ouvertes.fr/tel-00917770.
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Bipolar electrochemistry deals with the exposure of an isolated conducting substrate that has no direct connection with a power supply except via an electric field. Therefore it can be considered as a "wireless technique". The polarization of the substrate with respect to the surrounding medium generates a potential difference between its opposite ends which can support localized electrochemical oxidation reduction reactions and break the surface symmetry of the substrate. The method was applied in the present thesis to materials science and biological systems. In the frame of designing asymmetric particles, also called "Janus" particles, bipolar electrochemistry was adapted for the bulk preparation of these objects. Conductive substrates with different nature, sizes and shapes have been modified with various materials such as metals, ionic and inorganic compounds using this approach. Moreover, a control over the deposit topology could be achieved for substrates at different length scales. Bipolar electrodeposition is also a good tool for investigating the generation of different metal morphologies. Further developments in the bipolar setup allowed us to use the technology for microstructuration of conductive objects. Furthermore the concept has shown to be very useful in the field of the induced motion of particles. The asymmetric objects that have been prepared by bipolar electrodeposition were employed as microswimmers which could show both translational and rotational motion. The application of electric fields in the bipolar setup can be used for the direct generation of motion of isotropic objects through bubble generation. A levitation motion of objects combined with light emission was possible using this concept. Finally, bipolar electrochemistry was also used for studying the intrinsic conductivity of biological molecules (DNA), which is of great importance in the nanotechnology.
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SÌŒljukicÌ, Biljana. "Novel carbon materials and their application in electrochemistry and electroanalysis." Thesis, University of Oxford, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.442654.
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Bikkarolla, Santosh Kumar. "Oxygen electrochemistry on inorganic/graphene hybrid materials for energy applications." Thesis, Ulster University, 2015. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.673823.
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Developing low cost oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalysts that perform with high efficiency is desirable for the commercial success of energy conversion devices, such as fuel cells and metal-air batteries. In this thesis, electrochemically reduced graphene oxide (ErGO) and Mn304 nanoflakes anchored on nitrogen doped reduced graphene oxide (NrGO) sheets synthesised by electrodeposition method were developed as ORR catalysts. CUC0204 nanoparticles were integrated with NrGO sheets through solvothermal method as a potential OER catalyst. A partially reduced graphene oxide electrocatalyst synthesised by electrochemical reduction of graphene oxide exhibited significantly enhanced catalytic activity towards the ORR in alkaline solutions compared to the starting GO. The resultant ErGO electrode also showed an enhanced capacitance and an ORR onset potential similar to that of NrGO electrode, produced by a solvothermal process. However, the ErGO exhibited considerably lower electron transfer numbers, indicating that although both catalysts operate under combined 4e- and 2e- ORR processes, ErGO followed a more predominant 2e- pathway. The ORR process in ErGO has been linked to the presence of quinone functional groups, which in turn favoured the 2e- ORR pathway. Also in this work, a three dimensional Mn304 hierarchical network was grown on NrGO by a facile and controllable electrodeposition process, and its electrocatalytic performance for ORR was assessed. The directly electrodeposited MnO. on the glassy carbon electrode (GCE) exhibited little electrocatalytic activity, whereas the integrated Mn304/NrGO catalyst was more ORR active than the NrGO. The resulting electrode architecture exhibited an "apparent" 4e-oxygen reduction pathway involving a dual site reduction mechanism due to a synergetic effect between Mn304 and NrGO. In addition, the 3D Mn304/NrGO hierarchical al'chitectur~ exhibited improved durability and methanol tolerance, far exceeding that of commercial ptlC. A composite material consisting of CUC020 4 nanoparticles anchored on NrGO sheets (CuCo204/NrGO) was prepared by a solvothermal method as a highly efficient OER electrocatalyst in both alkaline and neutral solutions. The CuCo204/NrGO exhibited high OER performance when compared to the other control materials, as well as good stability under strong alkaline condition. The enhanced OER performance of CuCo204/NrGO can be related to: (i) a reduction in the size of the CUC0204 nanoparticles as measured by the TEM, (ii) an enhancement of electrochemically active surface area (ECSA), (iii) a replacement of the least OER active C02+ ions with Cu2+ ions as confirmed by XPS and (iv) a synergetic effect between CuCo204 nanoparticles and NrGO sheets.
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Keeley, Deborah Michelle. "Electrochemical studies of biologically important materials." Thesis, University of Oxford, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.325879.
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Zhang, Guohui. "Electrochemistry and applications of sp2 carbon materials : from graphite to graphene." Thesis, University of Warwick, 2016. http://wrap.warwick.ac.uk/89303/.
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This thesis can be divided into three themes: (i) the electrochemistry of sp2 carbon materials, with a focus on graphite and graphene, where electron transfer (ET) kinetics and surface functionalisation were considered; (ii) methodology development for graphene transfer, to facilitate the fabrication of versatile tools for microscopy research and allow the properties of supported and suspended graphene to be readily assessed and compared; (iii) the electrowetting of graphite, providing a new mechanism for droplet actuation on a conducting surface with an applied electric field. There is a large body of literature that the basal plane of highly oriented pyrolytic graphite (HOPG) is inert or has little electroactivity for outer-sphere redox couples and adsorbed species. Here, the model is revisited with the macroscopic ET kinetics studies of three classical (outer-sphere) redox couples on different grades of HOPG using a droplet-cell setup. It is shown that the ET kinetics for all of the redox species studied is fast on all grades of HOPG (comparable to metal electrodes), despite the low density of electronic states (DOS) on graphite. This is in line with the results where the ‘special’ redox couple, Fe3+/2+, associated with a slow kinetics, is tested. Moreover, localised surface mapping measurements of HOPG using scanning electrochemical cell microscopy (SECCM), reveal a relatively uniform activity on basal plane and step edges of HOPG towards Fe3+/2+, highlighting that the basal plane is electroactive and the major site for the ET kinetics of Fe3+/2+. The next goal is to elucidate whether adsorbed electroactive anthraquinone-2,6-disulfonate (AQDS) can be used as a marker of step edges, previously regarded as the main electroactive sites of graphite. Step edges are shown to have little effect on the extent of adsorbed electroactive AQDS in macroscopic studies. The amount of adsorbed electroactive AQDS and the ET kinetics are independent of the step edge coverage, as determined by fast scan cyclic voltammetry-SECCM. Further, SECCM reactive patterning shows essentially uniform and high activity across the basal surface of HOPG, indicative of the dominance of basal plane in HOPG electroactivity. Regarding the close relation between graphene and graphite, effort is put to introduce a polymer-free method for transferring chemical vapour deposition (CVD)-grown graphene, to arbitrary substrates, using an organic/aqueous biphasic configuration. Avoiding any polymeric contamination, graphene is coated on arbitrary substrates, such as atomic force microscopy (AFM) tips and transmission electron microscopy (TEM) grids, generating tools for conductive AFM and high resolution TEM imaging. Furthermore, electrochemical and wetting measurements at either a freestanding graphene film or a copper-supported graphene area, are readily made and compared. As an example of the myriad potential applications of graphite, electrowetting is demonstrated at HOPG, using cyclic voltammetry, with significant changes in contact angle and relative contact diameter seen. These are comparable to the widely studied electrowetting-on-dielectric (EWOD) system, but over a much lower voltage range. Electrowetting is found to be due to the intercalation/de-intercalation of anions between the graphene layers of graphite, driven by the applied potential, providing a new mechanism for electrowetting and diversifying the means by which electrowetting can be controlled and applied.
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Ussano, Eleonora <1982>. "Electrochemistry of Molecular Systems for New Nanostructured Materials and Bioelectronic Devices." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2016. http://amsdottorato.unibo.it/7641/1/Ussano_Eleonora_tesi.pdf.
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Nanomaterials have a tremendously increasing importance in our daily lives but their world is extremely wide. The main aim of this work is to implement the knowledge about these materials, focusing in particular on some of the nano allotropic forms of Carbon. This precise choice is consequence of their extreme versatility and promising properties for electronic, energetic and biological applications, which can be further improved with doping or functionalization.
In the first part of my work I introduced nanotechnology and nanomaterials, highlighting their importance, recent developments and applications, trying to focus on the importance of electrochemistry in the study of such a field. Electrochemistry, in fact, through the investigation of fundamental electronic processes can exploit electrical and catalytic processes of nanomaterials and become an interface between nano and macroscopic world.
The second chapter of this thesis is dedicated to the investigation of a new synthetic pathway for bottom up nano-Graphene production, using polyaromatic hydrocarbons precursors. The chemical and morphological analysis of the obtained deposits gives encouraging results about the proficient production of Carbon-base nano-assemblies.
The third chapter is dedicated to the study and application of nanocarbons for energy production with particular attention to the incoming environmental problem. The objects of my study were Nitrogen-doped Graphene, as an alternative to metal catalysts for Oxygen reduction reaction (ORR), and a Bodipy chromophore coupled with a Fullerene, as an efficient system for photoelectrochemical conversion.
The results obtained until now in the study of Carbon-based nanomaterials represent a good reason to further investigate their behaviour, properties and possible applications and I hope this thesis is a contribution to such a complex topic.
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Ussano, Eleonora <1982>. "Electrochemistry of Molecular Systems for New Nanostructured Materials and Bioelectronic Devices." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2016. http://amsdottorato.unibo.it/7641/.
Full textAbstract:
Nanomaterials have a tremendously increasing importance in our daily lives but their world is extremely wide. The main aim of this work is to implement the knowledge about these materials, focusing in particular on some of the nano allotropic forms of Carbon. This precise choice is consequence of their extreme versatility and promising properties for electronic, energetic and biological applications, which can be further improved with doping or functionalization.
In the first part of my work I introduced nanotechnology and nanomaterials, highlighting their importance, recent developments and applications, trying to focus on the importance of electrochemistry in the study of such a field. Electrochemistry, in fact, through the investigation of fundamental electronic processes can exploit electrical and catalytic processes of nanomaterials and become an interface between nano and macroscopic world.
The second chapter of this thesis is dedicated to the investigation of a new synthetic pathway for bottom up nano-Graphene production, using polyaromatic hydrocarbons precursors. The chemical and morphological analysis of the obtained deposits gives encouraging results about the proficient production of Carbon-base nano-assemblies.
The third chapter is dedicated to the study and application of nanocarbons for energy production with particular attention to the incoming environmental problem. The objects of my study were Nitrogen-doped Graphene, as an alternative to metal catalysts for Oxygen reduction reaction (ORR), and a Bodipy chromophore coupled with a Fullerene, as an efficient system for photoelectrochemical conversion.
The results obtained until now in the study of Carbon-based nanomaterials represent a good reason to further investigate their behaviour, properties and possible applications and I hope this thesis is a contribution to such a complex topic.
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Giddens, Richard M. "Synthesis and electrochemistry of photoantimicrobial agents based on the azine chromophore." Thesis, University of Central Lancashire, 2007. http://clok.uclan.ac.uk/20791/.
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Photodynamic Therapy (PDT) is a ôancer treatment involving selective retention of a photoactive drug in tumour cells and tissue. Subsequent illumination with light of the correct wavelength can result in tumour destruction, generally assumed to be mediated by singlet oxygen ( 102) generated by the light-excited drug. Among such compounds, the biological stains methylene blue and toluidine blue 0, both phenothiazinium derivatives, have been widely studied with respect to their use in PDT and potential antimicrobial applications. However, studies of novel methylene blue derivatives (MBD) for PDT are scarce in the literature. We have synthesised a range of novel phenothiazinium derivatives, in particular 3,7-disubstituted analogues and explored the use of electrochemical methods in assessing their potential efficacy in PDT. A range of phenothiaziniums were synthesised by oxidation of the appropriate precursor phenothiazines by iodine and were characterised for synthetic purposes by infrared spectroscopy, nuclear magnetic resonance, ultravioletvisible spectroscopy, mass spectrometry and thin layer chromatographic techniques. The ability of the photosensitiser to resist reduction to the colourless Leuco form by tumour cells means that the efficiency of photosensitisation is maximised. The thermodynamic and kinetic susceptibilities of the synthesised phenothiaziniums to reductive bleaching was assessed using cyclic voltammetric and electrogravimetric methods.
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Tan, Yu-May. "Mesoporous materials." Thesis, University of Southampton, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.370067.
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Bjelkevig, Cameron. "Surface Chemical Deposition of Advanced Electronic Materials." Thesis, University of North Texas, 2010. https://digital.library.unt.edu/ark:/67531/metadc67938/.
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The focus of this work was to examine the direct plating of Cu on Ru diffusion barriers for use in interconnect technology and the substrate mediated growth of graphene on boron nitride for use in advanced electronic applications. The electrodeposition of Cu on Ru(0001) and polycrystalline substrates (with and without pretreatment in an iodine containing solution) has been studied by cyclic voltammetry (CV), current-time transient measurements (CTT), in situ electrochemical atomic force microscopy (EC-AFM), and X-ray photoelectron spectroscopy (XPS). The EC-AFM data show that at potentials near the OPD/UPD threshold, Cu crystallites exhibit pronounced growth anisotropy, with lateral dimensions greatly exceeding vertical dimensions. XPS measurements confirmed the presence and stability of adsorbed I on the Ru surface following pre-treatment in a KI/H2SO4 solution and following polarization to at least −200 mV vs. Ag/AgCl. CV data of samples pre-reduced in I-containing electrolyte exhibited a narrow Cu deposition peak in the overpotential region and a UPD peak. The kinetics of the electrodeposited Cu films was investigated by CTT measurements and applied to theoretical models of nucleation. The data indicated that a protective I adlayer may be deposited on an air-exposed Ru electrode as the oxide surface is electrochemically reduced, and that this layer will inhibit reformation of an oxide during the Cu electroplating process. A novel method for epitaxial graphene growth directly on a dielectric substrate of systematically variable thickness was studied. Mono/multilayers of BN(111) were grown on Ru(0001) by atomic layer deposition (ALD), exhibiting a flat (non-nanomesh) R30(3x3) structure. BN(111) was used as a template for growth of graphene by chemical vapor deposition (CVD) of C2H4 at 1000 K. Characterization by LEED, Auger, STM/STS and Raman indicate the graphene is in registry with the BN substrate, and exhibits a HOPG-like 0 eV bandgap density-of-states (DOS).
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Raekelboom, Emmanuelle Angeline. "Synthesis, structure and electrochemistry of positive insertion materials for rechargeable lithium batteries." Thesis, University of Southampton, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.393971.
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Wells, Andrea Dawn. "Deposition, surface chemistry, and electrochemistry of YBa₂Cu₃O₇₋(subscript delta) materials." Access restricted to users with UT Austin EID, 2001. http://wwwlib.umi.com/cr/utexas/fullcit?p3036611.
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Henrotte, Olivier. "Méthode pour l’analyse de l’activité de la réduction de l’oxygène de catalyseurs sans métaux nobles par microscopie électrochimique." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLS473.
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La synthèse de catalyseurs sans métaux nobles est une voie prometteuse pour rendre accessible à l’échelle mondiale les piles à combustible. L’analyse électrochimique de ces matériaux n’est pas aisée que ce soit pour comparer les propriétés électro catalytiques ou pour comprendre le fonctionnement de ces catalyseurs. Ceci provient du fait que la communauté scientifique évalue les performances catalytiques à l’échelle du matériau, donc sur un très grand nombre d’objets dont la réponse est moyennée. Les travaux présentés dans ce mémoire ont mis en place une méthode d’analyse de l’activité électrocatalytique de matériaux sans métaux nobles pour la réduction de l’oxygène en milieu acide par microscopie électrochimique à balayage. Cette approche permet d’étudier aussi bien macroscopiquement que microscopiquement les catalyseurs et d’étudier simultanément plusieurs catalyseurs, ce qui rend plus fiable la comparaison des résultats. Le dispositif présenté dans ce travail a permis de comparer différents catalyseurs avec des compositions proches ainsi que d’étudier l’influence de différentes paramètres sur un catalyseur : le chargement, la surface, la masse déposée et la quantité de Nafion ajoutée. Il a aussi été montré qu’il était possible d’étudier la stabilité des catalyseurs via ce dispositif. Ces différents résultats suggèrent que la méthode mise en place est polyvalente et permettra de nombreuses autres étudesThe decrease of fuel cells cost is necessary to provide a worldwide access to the technology. Synthesis of noble metal-free catalysts is a promising way to achieve this goal. The electrochemical analysis of these materials is however not easy either to compare the electrocatalytic properties or to understand the performances of these catalysts. The scientific community generally studies catalysts at a macroscale, where the recorded response is averaged on a very large number of catalytic objects. The works presented here shows the setup of a method to analyze the electrocatalytic activity of noble metal-free catalyst for the oxygen reduction reaction in acidic media by scanning electrochemical microscopy. This method brings several advantages such as the possibility to study and compare multiple catalysts on the same sample at a macro- or a microscale. The comparison of several catalysts with this setup is then. A catalyst has been studied under various conditions of: loading, surface area, weight of catalyst and quantity of additives such as Nafion. The investigation of the material stability is also illustrated. These results suggest large range of application of the technique and many possibilities in the future are now open to investigated noble metal-free electrocatalytic materials
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Ndungu, Patrick Gathura Bradley Jean-Claude. "The use of bipolar electrochemistry in nanoscience : contact free methods for the site selective modification of nanostructured carbon materials /." Philadelphia, Pa. : Drexel University, 2004. http://dspace.library.drexel.edu/handle/1860/275.
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Hedman, Jonas. "Characterization of reaction products in sodium-oxygen batteries : An electrolyte concentration study." Thesis, Uppsala universitet, Strukturkemi, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-317969.
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In this thesis, the discharge products formed at the cathode and the performance and cell chemistry of sodium-oxygen batteries have been studied. This was carried out using different NaOTf salt concentrations. The influence of different salt concentrations on sodium-oxygen batteries was investigated since it has been shown that increasing the salt concentration beyond conventional concentrations could result in advantages such as increased stability of the electrolytes towards decomposition, higher thermal stability and lower volatility. An increase in salt concentration has also been shown to influence the electrochemical potential window. The solubility of NaOTf was investigated in two different solvents, DME and diglyme. NaOTf was found to be more soluble in DME compared to diglyme but due to the volatile nature of DME, three different concentrations of NaOTf were prepared with diglyme as solvent. Experimentation involved discharging the batteries to either maximum or limited capacity. The discharge products were examined and characterized using XRD and SEM. The main discharge product was identified as sodium superoxide although sodium peroxide dihydrate was also identified in one battery. A trend of higher capacity and voltage plateaus with higher salt concentration was also found. The influence of trace amounts of water was suggested as one explanation as it works as a catalyst, promoting sodium superoxide cube growth due to improved transportation of superoxide. Another or contributing explanation could be a possible change in donor number with increased salt concentration, resulting in higher solubility and longer lifetime of superoxide, promoting the growth of sodium superoxide cubes.
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LONGONI, GIANLUCA. "Investigation of Sodium-ion Battery Materials." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2017. http://hdl.handle.net/10281/153278.
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La tecnologia delle batterie Sodio-ione ha negli ultimi tempi suscitato una crescente attenzione da parte della comunità scientifica mondiale grazie al fatto di poter rappresentare una valida alternativa alla tecnologia Litio-ione, più sostenibile dal punto di vista ambientale ed economico. Il lavoro di Dottorato è stato principalmente dedicato alla ricerca di materiali attivi per batterie Sodio ione.
I materiali presi in considerazione, sia catodici che anodici, sono stati indagati ponendo particolare attenzione ai limiti e difficolta pratiche che gli stessi possono manifestare nei confronti dell'intercalazione di sodio. Tra questi sono stati considerati: i) la valutazione della diffusione di Na+ in una struttura host intercalante, ii) e prodotti, gli intermedi e la reversibilità di reazione di conversione di ossidi dei metalli di transizione, iii) gli effetti delle proprietà cristalline dei materiali sulle performance elettrochimiche e iv) le caratteristiche chimico-fisiche caratterizzanti la generale stabilità di un materiale funzionale per batterie. Durante il lavoro di tesi è stato perpetrato un continuo parallelismo tra le caratteristiche morfologiche e strutturali e le performance elettrochimiche, ottenendo infine una dettagliata visione di molteplici classi di materiali attivi per sodio-ione. Ciò ha reso necessario un approccio inter-disciplinare in cui ad avanzate tecniche analitiche di tipo elettrochimico, è stato affiancato un approccio più specificatamente ingegneristico dei materiali stessi, al fine di evidenziare le correlazione proprietà-struttura. Tra le classi di materiali attivi investigate un ruolo di primaria importanza è stato riservato a materiali ad intercalazione catodici e materiali a conversione basati su ossidi di metalli di transizione. I primi, tipicamente materiali con struttura cristallina lamellare di natura ossidica, o a base di fosfati e pirofosfati, promuovono l’intercalazione di sodio con cinetiche veloci e con molteplici geometrie e pattern assunti dai cationi intercalati. I materiali a conversione invece permettono di ottenere lo stoccaggio energetico tramite reazione chimiche spontanee che avvengono tra materiale attivo e lo ione sodio. Paragonati a materiali ad intercalazione, i materiali a conversione presentano molteplici problematiche, tra cui: i) la variazione di volume considerevole che accompagna la reazione di conversione che introduce stress meccanici considerevoli e porta alle tipiche frammentazioni d’elettrodo e ii) processi irreversibili che solitamente corredano la reazione di conversione. Un aspetto che rende tali materiali meritevoli di essere studiati è la loro capacità di stoccare elevate quantità di sodio rendendoli capaci di capacità specifiche teoriche straordinarie (> 800 mAh/g). Tutti questi aspetti sono stati affrontati e tenuti in profonda considerazione al fine di mettere a punto un materiali a conversione anodica nano-strutturato a base di Co3O4 che rappresentasse una valida soluzione al problema di perfezionamento delle batterie sodio-ione.
Assieme a materiali anodici, è stato altresì condotto lo studio di materiali catodici caratterizzati da elevate performance ma bassi costi di sintesi. Lo studio preliminare del composito ad intercalazione Na2FeP2O7/MWCNT a condotto ad interessanti risultati legati ad estremamente veloci cinetiche di diffusione di sodio all’interno del network di canali del materiale e ad una generale stabilità durante la ciclazione. All’anatasio (TiO2) nano-crystallino sintetizzato ad-hoc è stata dedicata l’ultima parte del lavoro di ricerca. Tale lavoro ha permesso di confermare importanti correlazioni tra le caratteristiche cristalline superficiali dei nano-cristalli e i meccanismi di interazione con sodio attraverso meccanismi pseudocapacitivi; e significativi avanzamenti sono stati ottenuti nella definizione di tale meccanismo e nella messa a punto di un efficiente materiale anodico a basso costo.Na-ion battery technology has recently aroused great interest among all the scientific community, as a valid and more environmentally friendly alternative to Li-ion batteries. The PhD research activity has been mostly devoted to the investigation of reliable active materials for sodium ion battery technology. All the investigated materials, either anode or cathode, have been investigated trying to highlight the major limits and difficulties connected to sodium intercalation and conversion reactions. Among these, some are: i)assessment of Na diffusion in an intercalating host structure, ii)products and reversibility of transition metal oxides conversion reactions, iii) effects of materials crystalline properties on electrochemical performances and iv) features influencing the overall stability of a functional material. In order to keep the most broad-based overview of the problem, it has been chosen to systematically start, for each species electrochemically investigated, from its synthesis and thorough chemical-physical characterization. Rather than a pure electrochemical analysis, a continuous parallelism between morphological features, structural characteristics and performances was encouraged, eventually obtaining a detailed overlook of different classes of active materials for sodium batteries. What has been screened all along the three year-long research period has been a comprehensive investigation of new generation electrochemically active materials for energy storage applications. This implied an inter-disciplinary work in which advanced electro-analytical techniques have been widely used to characterize inorganic compounds or ad-hoc synthesized composites keeping in mind precise structure-performance correlations. Among the investigated classes, a role of relevance has been reserved to intercalating cathode species and conversion anode materials. The former, typically layered transition metal oxides, phosphates and pyrophosphates, are capable of sodium cations insertion, with fast kinetics, between layers or inside channels generated from peculiar atoms arrangement. Conversion anode materials on the other hand, carries out the sodium storage via spontaneous chemical reactions with oxide-based material, such as Co3O4 or Fe2O3, a chalcogenide or a halide. Compared to intercalation materials, conversion ones are more challenging to deal with, due to the following difficulties: i)their not negligible volume change during conversion reaction and the correlated induced mechanical stresses leading to electrode fracturing and pulverization, ii)occurrence of irreversible and parasitic reactions and iii)material operating potentials is often too high (around 1.0 V vs. Na/Na+) and thus not suitable for being used as anode materials inside a sodium cell. A positive feature that makes these material worthy to be studied is the high sodium uptake they are able to bare, bestowing them high theoretical specific capacities (>800 mAh∙g-1). All these aspects have been tackled in designing a conversion anode that might constitute a valid solution toward a sodium secondary battery whole-cell assembly. Together with anode materials also a high-performing and low-cost cathode material has been investigated. The exploratory study of pyrophosphate-MWCNT composite intercalation material led to interesting results referred to fast kinetics and material reliability throughout the cycles. To TiO2 nanocrystals synthesis and crystalline appearance-electrochemical properties correlation has beeb dedicated an exhaustive analysis which allowed to achieve significative advancements in defining the sodium uptake mechanism for pseudo-capacitive oxide-based anode material for sodium-ion batteries.
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Vutetakis, David George. "Electrochemical oxidation of carbonaceous materials dispersed in molten carbonate /." The Ohio State University, 1985. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487264603217609.
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Arnaboldi, S. "CHIRAL ELECTROCHEMISTRY IN IONIC LIQUIDS." Doctoral thesis, Università degli Studi di Milano, 2014. http://hdl.handle.net/2434/244316.
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This thesis has been initially conceived as a study of molecular electrochemistry and electrocatalysis in ionic liquids, emerging media for safe and environmentally friendly chemical and electrochemical processes, particularly focusing on the combined effects of the ionic liquid molecular structure and the nature of the electrode surface, and considering two model processes:
• the electroreductive cleavage of the carbon-halogen bond in organic halides, of high interest in the synthetic, analytical and environmental fields;
• the electrooxidative coupling of thiophene-based monomers, resulting in electrodeposition of conducting films for applications in photovoltaic, optoelectronic and sensor devices.
Both processes are thus of great applicative interest and, at the same time, two convenient model cases for electron transfer studies in ionic liquids, one reductive (via radical anion) and one oxidative (via radical cation), on which the cation and the anion of the ionic liquid should be more determining, respectively.
However, the 3-year research results actually went well beyond these initial targets, with the discovery of the outstanding properties of inherently chiral electroactive thiophene-based oligomers, on which we then concentrated most of our efforts.
In particular:
• electrooligomerization in ionic liquids of "inherently chiral" thiophene-based monomers developed by Professor Sannicolò's partner group afforded the preparation of enantiopure chiral electrodes of new concept and unprecedented enantiodiscrimination ability, resulting for the first time in a neat separation of voltammetry peaks for the enantiomers of a series of different chiral probes, also of pharmaceutical interest, in different media and operating conditions;
• such inherently chiral electroactive oligomers turned out to be mostly cyclic, idealizing chiral conducting polymers without ends, and displaying a pool of extraordinary properties, both as racemates (promising performance in organic solar cells, photoactivity, electrochromism, possibility to complex other semiconductors, outstanding oligomerization ability...) and as enantiopure antipodes (chirality tunable with electric potential, unprecedented enantiodiscrimination ability as electrodes, circularly polarized luminescence, possibility of preparation as self-supported membranes...). Such properties prompted a patent application for the new molecule class.
Furthermore, having verified the general validity and effectiveness of the inherent chirality concept, and considering our concern for ionic liquid media, we have started, again in cooperation with Professor Sannicolò's group, a further research line, aimed to the implementation of inherent chirality in new-concept ionic liquids, with the target of obtaining new, attractive media for chemical and electrochemical processes, possibly of cheap and simple synthesis, affording safe, mild and environmentally friendly operating conditions, intrinsic to the ionic liquid class, combined with powerful chirality manifestations. Three approaches, all based on the implementation of inherent chirality in the ionic liquid cation, are being developed and compared. As a valuable ancillary research product, a very simple "Egg of Columbus" protocol has been developed, providing an effective solution to the important issue of halide impurity removal from ionic liquid media.
Most of the present research has been supported by Fondazione Cariplo (Grants No. 2011-0417 and No. 2011-1851)
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Rong, Yuanyang. "Intrinsically microporous polymer materials for electrodes and membranes." Thesis, University of Bath, 2017. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.720657.
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Microporous materials have received much attention and offer new opportunities in electrochemistry because of their interesting properties. Compared with the corresponding nonporous materials, the highly porous structure may facilitate internal mass transport process, provide accessibility to binding sites and provide size selectivity. A new class of microporous materials, polymers of intrinsic microporosity (PIMs) emerged about ten years ago. They combine the microporosity generated from the rigid and contorted backbones and the processibility of linear molecular polymers, which make them particularly attractive for the applications in gas storage, membrane separations and also in electrochemistry. PIM-EA-TB containing ethanoanthracene (EA) and Tröger’s base (TB) is one of the most interesting PIMs and has a high BET surface area around 1000 m2 g-1. Most of the work in this thesis are based on PIM-EA-TB. Results chapters focus on catalysis in PIM films, ion flux in free-standing PIM membranes and carbonization of PIM-EA-TB. Electrochemical oxidation of glucose is important due to the practical applications in glucose sensing and in biological fuel cells. However, the practical application of many catalysts is limited by the poisoning by interferences such as proteins and chloride. Here, PIM-EA-TB was spin-coated onto the surface of supported gold nanoparticles to protect the catalysts from poisoning. It was demonstrated that the PIM-EA-TB film would not negatively affect the catalytic performance of gold nanoparticles for glucose oxidation. Also, it provided effective protection against protein poisoning because of its rigid backbone and rigid molecular structure preventing protein access. Chloride poisoning was reduced but not surpressed. In addition to nanoparticle catalysts, water-insoluble molecular catalysts were investigated. PIM-EA-TB was used as a rigid host for model catalyst, tetraphenylporphyrin (FeTPP). FeTPP was immobilised in the PIM-EA-TB film and then deposited on the electrode to create a high density heterogenised catalysts. Different compositions of PIM and FeTPP and different scanrates were investigated to reveal the catalytic mechanism. The PIM hosted FeTPP catalysts showed facile electron transfer and effective electrocatalytic reduction of oxygen and peroxide. The 4-(3-phenyl-propyl)-pyridine was applied to the PIM-FeTPP film to give an organogel in 12 order to investigate the liquid-liquid interface. The PIM immobilisation method could offer a new opportunity to the immobilisation of a wide range of the molecular catalysts. The understanding of transport processes in PIM-EA-TB membranes is important for the development of further applications in the electrochemistry. Different types of anions were investigated to see the anion uptake and charge transport in PIM-EA-TB films. Three cases were investigated, including the oxidation of ferrocene, the reduction of protons and the transport of anions and protons in the PIM-EA-TB thick films. In all three cases, the diameter and hydrophobicity of anions are important in the competing effects. The pKa of PIM-EA-TB was determined and novel ionic diode effects were observed. Nanofluidic devices are used to regulate the flow of ions to one preferential direction and they have great importance because of the similarity to biological ion channels and the application in biochemical fields. PIMs were explored to the possibility to establish an artificial ion channel with the gate function. A thin film preparative method was introduced to produce thin free-standing polymer films. The 300 nm PIM-EA-TB films supported on a poly-ethylene-terephthalate (PET) film with a 20 m diameter microhole exhibited ionic diode behaviour. Only when the cation and anion had different mobility, the current rectification effects were observed. Different pH values of the electrolyte were also investigated and resulted in a gradual change in rectification effects. Porous carbon materials have wide applications in different fields such as gas separation, water purification, catalyst supports, and fuel cells. One of the common methods to produce the porous carbon is the carbonization of polymers. However, the challenge is that it is difficult to control the pore size and pore distribution. PIM-EA-TB was carbonized at 500 °C in vacuum to produce a novel type of microporous carbon. The microporosity and morphology of the PIM precursor remained after carbonization. The new material exhibited relatively low electrical conductivity and low activity in the electrochemical oxygen reduction. The capacitance of the new carbon material was investigated and found to vary with pH depending on the protonation status of micropores. 13 Finally, the carbonized PIM films were used to control the formation of platinum nanoparticles. Platinum nanoparticles are important catalysts in many areas but may suffer from high costs and lack of reproducibility. Therefore, it is important to reduce the amount of platinum, increase the utilization of platinum as well as control the particle size. The carbonized PIM films still have the microporosity and offer an ideal substrate for platinum nanoparticles. The platinum nanoparticles were formed at the same time with the carbonization of PIM, which helped to control the size of platinum nanoparticles. Compared with bare platinum, the platinum nanoparticles produced by PIM-EA-TB showed a high electrochemically active surface area and good catalytic performances for oxygen reduction, methanol oxidation and glucose oxidation. Much less platinum (1μg per cm2) was needed to achieve the same catalytic performance compared to the bulk platinum.
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Singh, Kulveer. "Structure-function studies of the oxidoreductase bilirubin oxidase from Myrothecium verrucaria using an electrochemical quartz crystal microbalance with dissipation." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:0376cc7e-f572-4e0c-96f0-43b0b4b91d99.
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This thesis presents the development and redesign of a commercial electrochemical quartz crystal microbalance with dissipation (E–QCM–D). This was used to study factors affecting the efficiency of the four electron reduction catalysed by the fuel cell enzyme bilirubin oxidase from Myrothecium verrucaria immobilised on thiol modified gold surfaces. Within this thesis, the E–QCM–D was used to show that application of a constant potential to bilirubin oxidase adsorbed to thiol-modified gold surfaces causes activity loss that can be attributed to a change in structural arrangement. Varying the load by potential cycling distorts the enzyme by inducing rapid mass loss and denaturation. Attaching the enzyme covalently reduces the mass loss caused by potential cycling but does not mitigate activity loss. Covalent attachment also changes the orientation of the surface bound enzyme as verified by the position of the catalytic wave (related to the overpotential for catalysis) and reactive labelling followed by mass spectrometry analysis. The E–QCM–D was used to show how electrostatic interactions affect enzyme conformation where high pH causes a reduction in both mass loading at the electrode and a reduction in activity. At pH lower than the enzyme isoelectric point, there is a build up of multilayers in a clustered adsorption. When enzyme adsorbs to hydrophobic surfaces there is a rapid denaturation which completely inactivates the enzyme. Changing the surface chemistry from carboxyl groups to hydroxyl and acetamido groups shows that catalysis is shifted to more negative potentials as a result of an enzyme misorientation. Further to this, increasing the chain length of the thiol modifier indicates that an increased distance between surface and enzyme reduces activity, enzyme loading and results in a conformational rearrangement that permits electron transfer over longer distances.
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Vieira, Jocicler Claudio. "Estudo de interfases eletroquímicas envolvendo materiais metálicos de uso odontológico." Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/46/46132/tde-02022007-134525/.
Full textAbstract:
Interfases \"metal - solução eletrolítica de interesse odontológico\" foram estudadas a 36,5 graus Celsius por técnicas eletroquímicas estacionárias. Duas ligas, Au-Pt-Pd e Ni-Cr-Mo-Ti, foram comparadas e, neste caso, empregadas a impedância eletroquímica, a microscopia eletrônica de varredura e a espectroscopia de dispersão de energia. Os estudos também incluíram o Ti-cp e a amálgama Ag-Cu-Sn-Zn. Verificou-se o efeito da adição de NaF, de ácido cítrico (H3Cit) e de albumina de soro bovino (BSA) ao meio de NaCl. A liga Ni-Cr-Mo-Ti, desenvolvida para substituir a liga Au-Pt-Pd, apresenta comportamento bem diverso da segunda, caracterizado por uma superfície irreprodutível, potencial de corrosão 200 mV a 500 mV mais negativo, dependendo do meio, e faixa passiva inexistente ou de pequena amplitude de potencial. O Ti-cp está passivado em todo o intervalo de potencial estudado (2 V/ECS) em meios de NaCl e NaCl+H3Cit; em NaCl+NaF, a faixa passiva é bem mais restrita, e a BSA a eleva de 100 mV. O H3Cit destrói o filme passivo sobre as ligas Ni-Cr-Mo-Ti e amálgama. A BSA exerce efeitos distintos dependendo da natureza do material metálico e do meio, sugerindo ora adsorção física, ora ação complexante. São discutidos diferentes tipos de embutimento para as amostras metálicas, como teflon, resinas epóxi e epóxi-vinil-éster (EVER). O embutimento com EVER é o mais recomendável para materiais de uso odontológico.Different metal electrolytic interphases with relevance for dental prosthesis and implants were studied at 36,5 degrees Celsius by stationary electrochemical techniques. Two alloys, Au-Pt-Pd and Ni-Cr-Mo-Ti, were compared and in this case, EIS, SEM and EDS were also employed as techniques. The studies also included Ti-cp and Ag-Cu-Sn-Zn amalgam. It was studied the effect of adding NaF, citric acid (H3Cit) and bovine serum albumin (BSA) to NaCl medium. Ni-Cr-Mo-Ti alloy, developed to substitute Au-Pt-Pd alloy, presents a distinct behaviour from the last mentioned alloy, characterized by an irreproducible surface, corrosion potential situated at 200 mV to 500 mV more negative value, depending of the medium, and narrow or absence of passive range. Ti-cp is passive in all the potential range studied (2 V/SCE) in NaCl and NaCl+H3Cit media; in NaCl+NaF the passive range is narrower and it increases 100 mV in the presence of BSA. H3Cit breaks down the passive film deposited on the Ni-Cr-Mo-Ti and amalgam alloy surfaces. BSA exhibits distinct effects depending upon both the nature of the alloy and the media suggesting either physical adsorption either complex formation. Different kinds of polymers for fitting the metallic samples are discussed, such as teflon, epoxy resin and epoxy vinyl ester resin (EVER). The results suggest that the EVER polymer is the most recommendable for fitting dental materials.