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1
Lee, Minhwan. "Nano scale electrochemistry : application to solid electrolytes /." May be available electronically:, 2008. http://proquest.umi.com/login?COPT=REJTPTU1MTUmSU5UPTAmVkVSPTI=&clientId=12498.
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Elahi, A. "Plasma electrochemistry : electron transfer at the solid/gas interface." Thesis, University College London (University of London), 2014. http://discovery.ucl.ac.uk/1427871/.
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The ability to control redox reactions at the solid/gas interface is demonstrated for the first time, by considering gaseous flame plasma as an electrolyte. An innovative method to perform potentio-dynamic experiments in a liquid-free electrochemical system using flame plasma is described. This novel approach can help apply the well-established foundations of electrochemistry developed almost exclusively in liquids, to the new context of gas plasma. There are limited examples using plasmas as media to study redox reactions but no examples of voltammetry in the gas phase at true solid/gas interfaces. Successful electrochemical measurements are illustrated by doping the flame plasma with both inorganic and organic species, and recording distinct faradaic peaks at defined potentials in cyclic voltammograms. The sensitivity of the system is highlighted by the ability to distinguish between several amino acids, pinpointing specific functional groups. The most significant innovation responsible for these measurements is the development of a reference electrode able to function at temperatures over 1300 K. Extensive assessment of several materials has enabled the development and optimisation of a reference electrode, allowing an extension of the potential window to 10 V; an unprecedented value in electrochemistry. After careful experimentation and appropriate control experiments, the features observed are confirmed as specific reduction processes at the solid/gas interface. Undoubtedly, and perhaps expectedly, there are significant departures from the analogous process in condensed phases. The physical origin of these electrochemical signals is discussed and a framework of interpretation upon which a full mechanistic understanding can be based is provided. The scope of commercial and academic impact is extensive. Liquid-free electrochemistry presents access to a plethora of redox reactions, which lie outside potential limits defined by liquids. The prospect of new redox chemistries will enable new technological applications such as electrodeposition and electroanalysis, which have significant economic and environmental benefits.
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Roy, Stephen Campbell. "Alkali metal beams from solid state electrochemical sources." Thesis, University of St Andrews, 1995. http://hdl.handle.net/10023/15526.
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All solid state electrochemical cells capable of producing beams of lithium, sodium and potassium in ultrahigh vacuum have been developed and investigated. The evolution of alkali metal vapour has been demonstrated by deposition of the metal on a substrate during polarisation of the cell followed by ex-situ analysis of the metal using laser ionisation mass analysis (LIMA). The electrochemistry of alkali metal evolution from these unusual solid state cells has been investigated using cyclic voltammetry, chronoamperometry and AC impedance measurements at pressures of 10−3 mbar and 10−8 mbar (UHV). It has been found for all three sources that the mechanism at relatively high pressure involves the nucleation and growth of liquid alkali metals or compounds containing alkali metals on the working electrode prior to their evaporation. In UHV the mechanism for potassium and sodium emission appears to involve the transfer of atoms directly into the gas phase whereas lithium exhibits nucleation and growth. In order to obtain a more complete characterization of the electrochemical mechanisms a spectro-electrochemical technique involving the simultaneous mass spectrometric analysis of the evolved vapour under UHV conditions along with cyclic voltammetry was developed. The formation of p-type ZnSe is essential to the fabrication of blue light emitting diodes and semiconductor lasers but has long represented a major problem in optoelectronics. This work shows that the potassium source can be used to p-dope ZnSe during growth of the material by molecular beam epitaxy (MBE). Efforts directed to the preparation of n-type diamond using a lithium source in microwave enhanced chemical vapour deposition (MWECVD) apparatus have demonstrated that the source can introduce lithium to diamond, although full semiconductor characterization of this material has yet to be made.
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Nakagawa, Yasue. "Protein electrochemistry : applications of sonovoltammetry, microelectrode voltammetry and solid-state voltammetry." Thesis, University of Oxford, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.325772.
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Kirk, Thomas Jackson. "A solid oxide fuel cell using hydrogen sulfide with ceria-based electrolytes." Thesis, Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/11270.
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Jorgensen, Mette Juhl. "Lanthanum manganate based cathodes for solid oxide fuel cells." Thesis, Keele University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.343243.
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Simmonds, Michael C. "Synthesis of platinum and platinum alloy thin films and a study of their electrochemistry." Thesis, University of Salford, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.308459.
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Ca, Diep Vu. "NANOSTRUCTURED ASSEMBLIES FOR SOLID PHASE EXTRACTION OF METAL IONS." Miami University / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=miami1107552000.
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Janardhanan, Vinod. "A detailed approach to model transport, heterogeneous chemistry, and electrochemistry in solid-oxide fuel cells." Karlsruhe : Univ.-Verl. Karlsruhe, 2007. http://d-nb.info/986289124/34.
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Hernández, Malo Rafael. "Solid contact potentiometric sensors based on carbon nanomaterials." Doctoral thesis, Universitat Rovira i Virgili, 2014. http://hdl.handle.net/10803/401334.
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Aquesta tesi aporta un avanç en la construcció d'elèctrodes de contacte sòlid (SCE) basats en materials nanoestructurats de carboni. Es verifica per una banda, la possibilitat d'utilització dels nanotubs de carboni de capa Simple (SWCNTs) per a la determinació d'ions en mostres reals complexes com és la saba vegetal. Addicionalment, es porta a terme la utilització del grafè modificat químicament com a element transductor en els elèctrodes d'estat sòlid determinant el seu mecanisme de transducció i com a prova del seu funcionament es duen a terme dos elèctrodes, per una banda un elèctrode selectiu d'ions (ISE) per a la determinació de calci, i per una altra part un aptasensor per a la determinació selectiva de Staphylococcus aureus.Esta tesis aporta un avance en la construcción de electrodos de contacto sólido (SCE) basados en materiales nanoestructurados de carbono. Se verifica por una parte, la posibilidad de utilización de los nanotubos de carbono de capa simple (SWCNTs) para la determinación de iones en muestras reales complejas como es la savia vegetal. Adicionalmente, se lleva a cabo la utilización del grafeno modificado químicamente como elemento transductor en los electrodos de estado sólido determinando su mecanismo de transducción y como prueba de su funcionamiento se llevan a cabo dos electrodos, por una parte un electrodo selectivo de iones (ISE) para la determinación de calcio, y por otra parte, un aptasensor para la determinación selectiva de Staphylococcus aureus.
This thesis provides a breakthrough in the construction of solid contact electrode (SCE) based on nanostructured carbon materials. It is checked the possibility of using single walled carbon nanotubes (SWCNTs) for the determination of ions in real complex samples such as plant sap. Additionally, the use of chemically modified graphene is performed as a transducer in solid state electrodes to determine the transduction mechanism. As a proof of concept two electrodes have been developed, in one hand, an ion-selective electrode (ISE) for the determination of calcium, and on the other one, an aptasensor for the selective detection of Staphylococcus aureus.
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Bennett, Raffeal A. "Characterization of the Solid-Electrolyte Interface on Sn Film Electrodes by Electrochemical Quartz Crystal Microbalance." The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1399048324.
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Ni, Chengsheng. "Optimisation and testing of large ceramic-impregnated solid oxide fuel cells (SOFCs)." Thesis, University of St Andrews, 2014. http://hdl.handle.net/10023/6387.
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Solid oxide fuel cells (SOFCs) are the most efficient electrochemical devices to directly convert stored chemical energy to usable electrical energy. The infiltration of ceramic conductors and catalytic metals (e.g. Ni, Pt and Pd) into porous scaffolds that had been pre-sintered onto the electrolyte is regarded as an effective way of promoting the electrode performance via producing nano-scale particles by in-situ sintering at relatively low temperatures. Large-scale fuel cells (5 cm x 5 cm) are prepared with this method and tested to demonstrate its scalability so as to achieve industrial applications. Four configurations are examined in respect of variation in the thickness of cathode, anode and electrolyte to investigate their effect on the infiltration process and electrochemical losses. To further improve infiltration as a method of fabricating high-performance electrodes, much effort is also devoted to optimising and understanding the microstructure of pre-sintered scaffold and its effect on infiltration using image analysis and electrochemical impedance. First, we have prepared the nano-structured electrodes on the 200-μm thick electrolyte-supported planar fuel cell with a 5 x 5 cm dimension. The 8YSZ scaffold is impregnated with La₀.₈Sr₀.₂Cr₀.₅Mn₀.₅O₃ (LSCM) for the anode and La₀.₈Sr₀.₂FeO₃ (LSF) for the cathode. The large planar cell achieved a maximum power density of 116 mWcm⁻² at 700°C and 223 mWcm⁻² at 800°C in humidified hydrogen. Moreover, with the addition of catalyst of 10 wt.% CeO₂ and 1 wt.% Pd, the cell performance reached 209 mWcm⁻² at 700°C and 406 mWcm⁻² at 800°C. Compared to the cell without catalysts, ceria and Pd are efficient in decreasing the electrochemical reaction resistance but making the diffusion resistance more obvious. Second, supported thin electrolytes are prepared by scalable tape casting to reduce the ohmic losses as that in electrolyte-supported cell. The cell with thick LSF-infiltrated support is very efficient in decreasing the ohmic loss thanks to the high solubility of its nitrate precursors in water and fairly high electric conductivity, but the thick cathode causes higher diffusional losses, especially at 800°C. Even though with thinner electrolyte, the ohmic loss from the cell with thick infiltrated anode is comparable to that of 200-μm electrolyte supported cell. The extra ohmic loss can be attributed to the compositional segregation of La₀.₇Sr₀.₃VO₃ (LSV) in the infiltration process in the anode, and lower loading, ca. 25 wt %. A trade-off between the diffusional loss from the cathode and the extra ohmic loss from the thick anode can be achieved by sandwiching the electrolyte between electrodes with identical thickness. A flat large area cell prepared with this method can achieve a high performance of 300 mW cm⁻² and 489 mW cm⁻² at 700°C and 800°C, respectively, if Pd-ceria is added to the anode LSV as catalyst. Third, image analyses and modelling are performed on the constrained sintering of porous thin film on a rigid substrate to study the evolution of pores at different stages. Result shows that both the anisotropy of the pore former/pores in the green body and transport of materials during the sintering process have effect on the orientation of the final microstructure. Specifically, the in-plane orientation of large-scale pores will be intensified during the constrained sintering process, while those small pores whose shape are subjected to materials transport during sintering tend to erect during the constrained sintering process at 1300°C. Fourth, image analyses and semi-quantification are used to predict the correlation between the microstructure and performance of the LSF-infiltrated electrode. Two types of YSZ powders, Unitec 1-μm powder with a broad particle-size distribution having two maxima at ~ 0.1 μm and 0.8 μm, and Unitec 2-μm powder with only one at ~1 μm are selected to fabricate the porous scaffold for infiltration. The porous structure using Unitec 2-μm powder shows finer YSZ grains and a higher boundary length than the 2-μm powder. Ac impedance on symmetrical cells was used to evaluate the performance of the electrode impregnated with 35-wt.% La₀.₈Sr₀.₂FeO₃. At 700°C, the electrode from Unitec 2-μm powder shows a polarization resistance (Rp) of 0.21 Ω cm², and series resistance (Rs) of 8.5 Ω cm², lower than the electrode from Unitec 1-μm powder does. The quantitative study on image indicates that Unitec 2-μm powder is better in producing architecture of high porosity or long triple phase boundary (TPB), which is attributed as the reason for the higher performance of the LSF-impregnated electrode. Finally, oxides of transition metals are doped into the YSZ-infiltrated LSF electrode and the impedances of symmetrical cells are tested to evaluate their effect on the ohmic and polarization resistance. Cobalt oxides are able to reduce the ohmic resistance and polarization resistance only when it is calcined at 700°C, but nickel oxide can reduce both the ohmic and polarization resistance if it is well-mixed and fully reacted with the previously infiltrated LSF. Doping of manganese oxide into LSF-YSZ electrode slightly changes the ohmic resistance but significantly increases the polarization resistance. Detailed analyses of the impact of infiltration process on the impedance data and oxygen reduction process are also presented.
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Yin, Yijing. "An Experimental Study on PEO Polymer Electrolyte Based All-Solid-State Supercapacitor." Scholarly Repository, 2010. http://scholarlyrepository.miami.edu/oa_dissertations/440.
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Supercapacitors are one of the most important electrochemical energy storage and conversion devices, however low ionic conductivity of solid state polymer electrolytes and the poor accessibility of the ions to the active sites in the porous electrode will cause low performance for all-solid-state supercapacitors and will limit their application. The objective of the dissertation is to improve the performance of all-solid-state supercapactor by improving electrolyte conductivity and solving accessibility problem of the ions to the active sites. The low ionic conductivity (10-8 S/cm) of poly(ethylene oxide) (PEO) limits its application as an electrolyte. Since PEO is a semicrystal polymer and the ion conduction take place mainly in the amorphous regions of the PEO/Lithium salt complex, improvements in the percentage of amorphous phase in PEO or increasing the charge carrier concentration and mobility could increase the ionic conductivity of PEO electrolyte. Hot pressing along with the additions of different lithium salts, inorganic fillers and plasticizers were applied to improve the ionic conductivity of PEO polymer electrolytes. Four electrode methods were used to evaluate the conductivity of PEO based polymer electrolytes. Results show that adding certain lithium salts, inorganic fillers, and plasticizers could improve the ionic conductivity of PEO electrolytes up 10-4 S/cm. Further hot pressing treatment could improve the ionic conductivity of PEO electrolytes up to 10-3 S/cm. The conductivity improvement after hot pressing treatment is elucidated as that the spherulite crystal phase is convert into the fringed micelle crystal phase or the amorphous phase of PEO electrolytes. PEO electrolytes were added into active carbon as a binder and an ion conductor, so as to provide electrodes with not only ion conduction, but also the accessibility of ion to the active sites of electrodes. The NaI/I2 mediator was added to improve the conductivity of PEO electrolyte and provide pseudocapacitance for all-solid-state supercapacitors. Impedance, cyclic voltammetry, and gavalnostatic charge/discharge measurements were conducted to evaluate the electrochemical performance of PEO polymer electrolytes based all-solid-state supercapacitors. Results demonstrate that the conductivity of PEO electrolyte could be improved to 0.1 S/cm with a mediator concentration of 50wt%. A high conductivity in the PEO electrolyte with mediator is an indication of a high electron exchange rate between the mediator and mediator. The high electron exchange rates at mediator carbon interface and between mediator and mediator are essential in order to obtain a high response rate and high power. This automatically solves the accessibility problem. With the addition of NaI/I2 mediator, the specific capacitance increased more than 30 folds, specific power increased almost 20 folds, and specific energy increased around 10 folds. Further addition of filler to the electrodes along with the mediator could double the specific capacitor and specific power of the all-solid-state supercapacitor. The stability of the corresponded supercapacitor is good within 2000 cycles.
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Sauer, David Edward. "Investigation of the solid-liquid interface of systems with fuel cell and semiconductor applications /." Thesis, Connect to this title online; UW restricted, 1994. http://hdl.handle.net/1773/9913.
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Rue, Amy. "Development of Nano-scale Featured Materials for Electrode Modification and Solid Supports." VCU Scholars Compass, 2012. http://scholarscompass.vcu.edu/etd/421.
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This work utilized the sol-gel process in two ways. First, macroporous silica thin films were developed using a combination of casting techniques and templating. Macroporsity was introduced to the silica thin films by either doping the silica sol before casting or by ordering the template on a substrate and then casting a sol over it. These techniques were first used to create silica thin films with long microchannel pores (200 nm x 60 µm) from a doped sol with the bacteria, B. Megaterium, as the template for nanomaterial formation. To enable the formation long microchannels, the flexible bacteria chains were aligned by using light scratches on the substrate surface as anchors for the bacteria’s adhesive cell capsule. Polystyrene (PS) sphere templates were then used in several studies to obtain silica thin films with well-ordered “nanowells,” single-layer hemispherical pores that allowed direct access to the substrate beneath the film. Copper and gold nanoparticles were integrated into moderately packed films by electrodepostion and monolayer self-assembly, respectfully. The size of the nanoparticles was controlled by the time of the electrodeposition or the time of exposure to an electroless growth solution. The final study with polystyrene latex sphere templates produced high quality, well-packed films containing well-defined nanowells over almost the entire conductive substrate. This was accomplished by separating the ordering of the templates on the substrate from film formation. Electroless growth was used to control the size and shape of the gold nanoparticles and the electrochemical properties of the resultant films were studied, showing an enhanced response to negatively charged redox probes. Sol-gel techniques were then used to create high aspect ratio silica nanotubes and pillars. The electroassisted deposition of silica was carried out in the pores of track-etched membranes, allowing supported nanotubes with dimensions of 100 – 400 nm x 10 µm to be obtained. The mechanism of silica formation in the tubular template was studied and it was found that growth occurred first by nanotube formation, followed by further growth through tube from the electrode to the other side of the pore. This allowed for partially filled tubes and solid pillars to be obtained. The method was found to be flexible and characteristics such as tube length, chemical functionality and porosity to be controlled.
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Janardhanan, Vinod [Verfasser]. "A detailed approach to model transport, heterogeneous chemistry, and electrochemistry in solid-oxide fuel cells / von Vinod Janardhanan." Karlsruhe : Univ.-Verl. Karlsruhe, 2007. http://d-nb.info/986289124/34.
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Wu, Jing. "Conductance Switching of Carbon Based Molecular Heterojunctions." The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1227844170.
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Henke, Moritz [Verfasser], and Andreas [Akademischer Betreuer] Friedrich. "Pressurised solid oxide fuel cells : from electrode electrochemistry to hybrid power plant system integration / Moritz Henke. Betreuer: Andreas Friedrich." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2016. http://d-nb.info/1082538108/34.
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Grenier, Antonin. "Development of solid-state Fluoride-ion Batteries : cell design, electrolyte characterization and electrochemical mechanisms." Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066128/document.
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Les batteries tout-solides à ions fluorures reposent sur l'échange réversible d'ions F- entre un métal et un fluorure métallique au travers d'un électrolyte solide. Ces dispositifs électrochimiques peuvent théoriquement permettre l'obtention de fortes densités énergétiques, bien supérieures à celles des batteries conventionnelles Li-ion commerciales. En conséquence, les batteries à ions F- suscitent un fort engouement. Dans ce contexte, une partie de nos travaux ont portés sur le développement d'une cellule permettant d'évaluer leurs performances. De plus, les propriétés électrochimiques de l'électrolyte solide LaF3 dopé BaF2, La1-xBaxF3-x, ont fait l'objet d'une attention particulière. Finalement, les changements structuraux s'effectuant au sein des électrodes lors des cycles de charge/décharge ont été étudiés afin de mieux comprendre les mécanismes électrochimiques mis en jeuSolid-state fluoride-ion batteries rely on the reversible exchange of the F- ion between a metal and a metal fluoride through a solid electrolyte. These electrochemical devices can theoretically reach energy densities superior to conventional Li-ion commercial batteries. Consequently, fluoride-ion batteries can be seen as a new promising chemistry generating a growing interest. In this context, a part of our work has been dedicated to the development of a cell allowing the evaluation of their electrochemical performance. Moreover, particular attention was given to the electrochemical properties of the solid electrolyte, BaF2-doped LaF3, La1-xBaxF3-x. Finally, the structural changes taking place at the electrodes upon charge/discharge were studied in order to gain insight into the electrochemical mechanisms involved in these devices
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CEYLAN, OZCAN. "ELECTROCHEMICALLY-AIDED CONTROL OF SOLID PHASE MICRO-EXTRACTION (EASPME) USING CONDUCTING POLYMER COATED FIBER." University of Cincinnati / OhioLINK, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1069853643.
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Torres-Caceres, Jonathan. "Manufacturing of Single Solid Oxide Fuel Cells." Master's thesis, University of Central Florida, 2013. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5875.
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Solid oxide fuel cells (SOFCs) are devices that convert chemical energy into electrical energy and have the potential to become a reliable renewable energy source that can be used on a large scale. SOFCs have 3 main components; the electrolyte, the anode, and the cathode. Typically, SOFCs work by reducing oxygen at the cathode into O2- ions which are then transported via the electrolyte to the anode to combine with a fuel such as hydrogen to produce electricity. Research into better materials and manufacturing methods is necessary to reduce costs and improve efficiency to make the technology commercially viable. The goal of the research is to optimize and simplify the production of single SOFCs using high performance ceramics. This includes the use of 8mol% Y2O3-ZrO2 (YSZ) and 10mol% Sc2O3-1mol%CeO2-ZrO2 (SCSZ) layered electrolytes which purport higher conductivity than traditional pure YSZ electrolytes. Prior to printing the electrodes onto the electrolyte, the cathode side of the electrolyte was coated with 20mol% Gd2O3-CeO2 (GDC). The GDC coating prevents the formation of a nonconductive La2Zr2O7 pyrochlore layer, which forms due to the interdiffusion of the YSZ electrolyte ceramic and the (La0.6Sr0.4)0.995Fe0.8Co0.2O3 (LSCF) cathode ceramic during sintering. The GDC layer was deposited by spin coating a suspension of 10wt% GDC in ethanol onto the electrolyte. Variation of parameters such as time, speed, and ramp rate were tested. Deposition of the electrodes onto the electrolyte surface was done by screen printing. Ink was produced using a three roll mill from a mixture of ceramic electrode powder, terpineol, and a pore former. The pore former was selected based on its ability to form a uniform well-connected pore matrix within the anode samples that were pressed and sintered. Ink development involved the production of different ratios of powder-to-terpineol inks to vary the viscosity. The different inks were used to print electrodes onto the electrolytes to gauge print quality and consistency. Cells were produced with varying numbers of layers of prints to achieve a desirable thickness. Finally, the densification behaviors of the major materials used to produce the single cells were studied to determine the temperatures at which each component needs to be sintered to achieve the desired density and to determine the order of electrode application, so as to avoid over-densification of the electrodes. Complete cells were tested at the National Energy Technology Laboratory in Morgantown, WV. Cells were tested in a custom-built test stand under constant voltage at 800°C with 3% humidified hydrogen as the fuel. Both voltage-current response and impedance spectroscopy tests were conducted after initial startup and after 20 hours of operation. Impedance tests were performed at open circuit voltage and under varying loads in order to analyze the sources of resistance within the cell. A general increase in impedance was found after the 20h operation. Scanning electron micrographs of the cell microstructures found delamination and other defects which reduce performance. Suggestions for eradicating these issues and improving performance have been made.M.S.M.E.
Masters
Mechanical and Aerospace Engineering
Engineering and Computer Science
Mechanical Engineering; Mechanical Systems
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MAGAR, YOGESH NARESH. "CONVECTIVE COOLING AND THERMAL MANAGEMENT OPTIMIZATION OF PLANAR ANODE-SUPPORTED SOLID OXIDE FUEL CELLS." University of Cincinnati / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1155839005.
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Sheehan, Stafford Wheeler. "Atomic Layer Deposition Synthesis and Photoelectrochemical Charge Behavior in Tungsten, Iron, and Titanium Oxide Heterostructures." Thesis, Boston College, 2011. http://hdl.handle.net/2345/2203.
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Thesis advisor: Dunwei WangThis thesis explores new approaches to synthesizing and understanding photoanodes for water splitting. By tuning materials' mophology on the nanoscale, their ability to absorb light energy and efficiently convert it in to chemical energy is improved. This is evident by an increase in photocatalytic efficiency and can be demonstrated with visible light sensitive catalysts. Production of these materials involved the development of alternative synthesis routes for traditional water splitting catalysts. Our hypothesis is further supported by probing charge dynamics using microwave reflectivity measurements, which show that the lifetime of charges in these new nanostructures is optimized
Thesis (BS) — Boston College, 2011
Submitted to: Boston College. College of Arts and Sciences
Discipline: Chemistry Honors Program
Discipline: Chemistry
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Zhou, Junfeng. "Scanning electrochemical microscope (SECM) study of charge transfer through solid/liquid interfaces, liquid/liquid interfaces, and bilayer lipid membranes /." Digital version accessible at:, 2000. http://wwwlib.umi.com/cr/utexas/main.
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Neidhardt, Jonathan Philipp [Verfasser], and Wolfgang G. [Akademischer Betreuer] Bessler. "Nickel oxidation in solid oxide cells : modeling and simulation of multi-phase electrochemistry and multi-scale transport / Jonathan Philipp Neidhardt. Betreuer: Wolfgang G. Bessler." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2014. http://d-nb.info/1046833669/34.
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Sano, Mitsuru, and Takao Inoue. "An Investigation of Capacity Fading of Manganese Spinels Stored at Elevated Temperature." The Electrochemical Society, 1998. http://hdl.handle.net/2237/18422.
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Chiabrera, Francesco Maria. "Interface Engineering in Mixed Ionic Electronic Conductor Thin Films for Solid State Devices." Doctoral thesis, Universitat de Barcelona, 2019. http://hdl.handle.net/10803/667601.
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Interface-dominated materials such as nanocrystalline thin films have emerged as an enthralling class of materials able to engineer functional properties of transition metal oxides widely used in energy and information technologies. In this direction, it has been recently proved that grain boundaries (GBs) in the perovskite La1-xSrxMnO3±δ (manganite) deeply impact its functional properties, boosting the oxygen mass transport while abating the electronic and magnetic order. The impact of grain boundary in nanocrystalline thin films is so relevant to radically change the behaviour of the material, transforming an electronic conductor into a mixed ionic-electronic conductor functional for redox-based solid state devices. Based on these preliminary studies, it became crucial to understand the origin of this enhancement, in order to gain engineering capabilities and potentially extend it to other functional perovskite materials.
Following this approach, this thesis focuses in analysing the remarkable properties of GBs in manganites and, ultimately, investigating the possibility of engineering these interfaces. First, the structural and chemical characterization of the LSM thin films deposited by pulsed laser deposition (PLD) is presented. The compositional analysis of the layers revealed a severe Mn deficiency, ascribed to the plasma-background interactions during the deposition. The analysis of the GBs of these Mn-deficient thin films revealed a remarkable local modification of ionic composition, consisting in a Mn and O depletion along with a La and Sr enrichment (viz. GBdef). Then, through a PLD combinatorial approach, Mn was progressively inserted in the perovskite structure, altering the overall cationic ratio of the thin films (Mn/(La+Sr)). The variation of cationic chemical potential of the thin films was observed to significantly affect the GB composition, which passed from Mn depletion (La-enrichment) to Mn enrichment (La-depletion), while maintaining an O deficiency character (viz. GBrich). This behaviour suggests that through the tuning of the overall cationic concentration in the thin films the GB composition can be altered, offering an innovative way for engineering chemical defects in strained interfaces.
The effect of these different GBs on the electrical conductivity and the oxygen mass transport properties of LSM thin films with different Mn content was then measured. It was found that in the layers characterized by GBdef, the lack of Mn hinders the low temperature metal insulator transition and, in its place, a variable range hopping mechanism occurs, where electrons tunnels across the GBs for reaching distant Mn atoms. Moreover, a simultaneous decrease of activation energies of both GB oxygen diffusivity and GB oxygen surface exchange coefficient was observed further decreasing the Mn concentration in these thin films, indicating a strong interdependence between the two phenomena. The results suggest that the GB accumulation of oxygen vacancies is at the origin of the large improvement of both oxygen mass transport parameters observed in LSM polycrystalline thin films.
In LSM thin films characterized by GBrich, the low temperature metallic behaviour is progressively restored and an increase of electronic conductivity is observed in the entire temperature range. Additionally, in these layers relative changes of Mn do not give rise to a variation of the oxygen diffusivity, meaning that the GBs oxygen vacancy concentration is not altered anymore. Overall, the results demonstrate the possibility of engineering the functional properties of LSM polycrystalline thin films by modifying the GB cationic composition.
In the third part of the thesis, the effect of Co substitution on LSMC functional properties was investigated. The LSMC thin films were produced by combinatorial PLD, which allow a direct measure of real-continuous spread LSMC system. The oxygen mass transport properties of bulk and GB were evaluated by finite element model fitting of 18O exchange profiles. The results revealed that GBs enhance the transport properties of the whole material in the range of composition under study, although for high Co concentration the GB effect is concealed by the high bulk diffusion.
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Lilley, Scott J. "Enhancing the conductivity of crystalline polymer electrolytes." Thesis, St Andrews, 2007. http://hdl.handle.net/10023/481.
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Lynch, Matthew Earl. "Modeling, simulation, and rational design of porous solid oxide fuel cell cathodes." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/45852.
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This thesis details research performed in modeling, simulation, and rational design of porous SOFC cathodes via development, extension, and use of the key tools to aid in the fundamental understanding and engineering design of cathode materials. Phenomenological modeling of triple phase boundary (TPB) reactions and surface transport on La₁₋ₓSrₓMnO₃ (LSM) was conducted, providing insight into the role of the bulk versus surface oxygen reduction pathway and the role of sheet resistance in thin-film patterned electrode measurements. In response to observation of sheet resistance deactivation, a modeling study was conducted to design thin-film patterned electrodes with respect to sheet resistance. Additionally, this thesis outlines the application of phenomenological chemical kinetics to describe and explain the performance and stability enhancements resulting from surface modification of La₁₋ₓSrₓCo₁₋yFeyO₃₋delta (LSCF) with a conformal LSM coating. The analysis was performed in close coordination with electrochemical experiments and transmission electron microscopy. Finally, the thesis describes conformal modeling of porous cathode microstructures using chemical kinetics and transport models. A novel application of conservative point defect ensembles was developed to allow simulations with complicated chemical surface kinetics to be efficiently coupled with bulk transport within the porous structure. The finite element method was employed to simulate electrochemical response conformal to sintered porous ceramic structures using actual 3D microstructural reconstructions obtained using x-ray microtomography. Mesh refinement, linear, and nonlinear reaction rate kinetics were employed to study the bulk versus surface oxygen reduction pathways and the effect of near-TPB nanostructure.
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Norman, Sofia. "Extraction of Heavy Metals from Fly Ash using Electrochemical Methods." Thesis, Linköpings universitet, Institutionen för fysik, kemi och biologi, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-64361.
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In today’s society large quantities of waste is produced. In Sweden this is reused as fuel for incineration processes where electricity and district heating are generated. However, during this process two hazardous by-products are formed, namely slag and fly ash. These contain relatively high concentrations of heavy metals, which make them harmful to the environment if not taken care of, but also make them valuable resources if the metals could be extracted and reutilized. One possible way to extract metals from the waste products is to use electrochemical methods. In order to implement these techniques on an industrial scale, there are several parameters that have to be considered. One important parameter is the choice of material of the electrode, which needs to have a large surface area, a high chemical inertness and electrical conductivity, and preferably also a reasonable price. A material that fulfills these qualifications is reticulated vitreous carbon (RVC), and therefore the extraction efficiency of this porous material has been evaluated in this thesis. Studies were also performed to evaluate how several other parameters affected the extraction efficiency, since this does not rely on the choice of electrode material alone. The results showed that RVC is suitable as electrode material for efficient metal extraction from fly ash. The most efficient electrode combination was RVC with a pore size of 10 pores per linear inch as working electrode, stainless steel as counter electrode, and Ag/AgCl as reference electrode. Both the amperometric and galvanostatic experiments extracted equal amounts of copper within the same time interval, which means that the choice of using either controlled potential or controlled current for an efficient extraction of copper was not of significant importance. The mass transfer rate for copper was 0.12 mg·h-1·cm-2 in both methods, where an electrolyte of 200 ml was used with an initial copper concentration of 50 mg/l. Regarding stirring of the electrolyte, circulation in the solution is an advantage, but not critical for an efficient reduction. The extraction efficiency for one particular metal did not seem to be affected by the presence of other metals in the electrolyte. It was also shown that a selective extraction of metals was possible by applying different potentials. Lastly, an experiment with fly ash was performed, with the optimal conditions and electrode combination based on the previous experiments. This yielded a mass transfer rate of 0.59 mg·h-1·cm-2 for zinc using an electrolyte of 200 ml, which initially contained 595 mg/l of zinc.
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Fee, Michele. "Electrochemical Investigation of Thin Nickel, Copper and Silver Films Interfaced with Yttria-Stabilized Zirconia." Thèse, Université d'Ottawa / University of Ottawa, 2013. http://hdl.handle.net/10393/24360.
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The electrochemical investigation of nickel, copper and silver thin films interfaced with yttria stabilized zirconia (YSZ) solid electrolyte was accomplished to determine their response to polarization in dilute oxygen environments at 350 °C and assess their viability for electrochemical promotion of catalysis (EPOC). Polycrystalline YSZ (8 mol % Y2O3-ZrO2) pellets were synthesized in the lab and films deposited onto them using evaporative physical vapor deposition (PVD). The critical thickness of copper, silver and nickel thin films were foundusing in-situ resistance measurements. Following this, 50 and 100 nm copper and nickel films were studied using solid electrolyte cyclic voltammetry (SECV) to determine their response to polarization. Given that silver thin films at such thicknesses are thermally unstable, a film of 800 nm was used in this study. The materials were found to respond to polarization in different ways, forming oxides according to Wagner and Mott-Cabrera oxidation models.
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Salles, Corinne. "Performance et vieillissement de membranes céramiques à transport d'oxygène." Thesis, Montpellier, Ecole nationale supérieure de chimie, 2018. http://www.theses.fr/2018ENCM0001/document.
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Les membranes à transport d’oxygène (OTM) sont des membranes céramiques denses qui sont capables de transporter l’oxygène de manière totalement sélective à travers un gradient de pression partielle d’oxygène. Elles peuvent être utilisées pour diminuer les émissions de gaz à effet de serre dans le cadre de la capture et du stockage du CO2 ou pour augmenter l’efficacité de l’oxydation partielle du méthane. La semi-perméabilité de l’oxygène est proportionnelle à la conductivité ambipolaire du matériau. Cependant, les OTM avec des conductivités ambipolaires élevées sont plus susceptibles de se dégrader rapidement dans les conditions d’utilisation. Pour être compétitives, les OTMs doivent donc remplir plusieurs critères, notamment avoir un flux élevé mais être aussi stables chimiquement, thermiquement, mécaniquement et être peu chères. CaTi0.9Fe0.1O3−δ (CTF) a été récemment présenté comme étant un matériau prometteur pouvant remplir ces critères et mérite d’être étudié plus en détail.Cette thèse se focalise sur les performances (mesurées par le flux d’oxygène) et la stabilité chimique et thermique du CTF. Pour améliorer les performances d’une membrane, il est nécessaire de savoir si la semi-perméation est limitée par les réactions en surface ou par la diffusion en volume. Les premiers résultats de ces travaux détaillent les étapes limitantes du transport de l’oxygène dans le CTF. En particulier, grâce à un montage expérimental spécifique et des expériences complémentaires, il a été montré que le CTF est limité à la fois par la diffusion en volume et les réactions de surfaces pour T < 750°C mais est majoritairement limité par la diffusion en volume à plus haute température. Les chapitres suivant détaillent la diffusion dans le volume et la conductivité électrique en fonction de la pression partielle d’oxygène et de la température, au vu de la chimie des défauts du CTF. Dans les conditions de fonctionnement, le CTF doit être considéré comme étant un conducteur mixte, avec une conductivité ionique qui devient prédominante pour des températures supérieures à 800°C.La seconde partie est consacrée à l’étude de la stabilité du CTF sous des atmosphères réactives, spécifiques aux OTM, qui sont connues comme provoquant des dégradations pour certains matériaux. Des tests de vieillissement sous atmosphères de CO2, CO, H2 n’ont montré aucune dégradation du flux de semi-perméation sur plusieurs centaines d’heures. Seulement une légère diminution du flux (- 25%) a été observée en présence de CO2 et de vapeur d’eau mais après cent heures sous hélium, le flux initial a été retrouvé. Des analyses DRX, MEB et Raman post-mortem n’ont révélé aucun signe notable de dégradation en surface et dans le volume. Un test sous CH4 a également été effectué, et la formation de CO, CO2, H2 et H2O a été suivie pendant des centaines d’heures. Malgré la présence de ces gaz réactifs, la même valeur du flux de semi-perméation a été retrouvée après 1000 heures de test sous méthane, témoignant d’une très bonne stabilité du CTF dans ces conditions réductrices. En conséquence, malgré des valeurs de flux relativement faibles (5×10-3 mL.min-1.cm-1 à 900°C), ce matériau est plein de promesse et son excellente stabilité sous méthane notamment peut être très intéressante pour certaines applicationsOxygen transport membranes (OTM) are dense ceramic membranes that allow oxygen diffusion along a chemical potential gradient. OTMs can increase the efficiency of oxycombustion processes or partial oxidation of methane, resulting in lower CO2 emissions overall. The oxygen transport is proportional to the ambipolar conductivity of the OTM material. However, OTM materials with the highest ambipolar conductivity are more prone to fast degradation under operation conditions. To be competitive, OTMs must associate high oxygen transport properties but also must be chemically, thermally, and mechanically stable, and preferably not expensive. CaTi0.9Fe0.1O3−δ (CTF) has recently been shown to match these demands, appearing as a promising OTM material that is worth studying in further detail.This PhD is therefore dedicated to study the performance and stability of CTF in typical operation conditions of an OTM. To improve the performance of a membrane, it is necessary to determine if the semi-permeation is limited by surface exchange reactions or by bulk diffusion. The first results of this work will detail the nature of the limiting reaction step for oxygen transport in CTF. Specifically, CTF is co-limited by bulk diffusion and surface exchange reactions at T < 750 °C, but is mainly limited by bulk diffusion at higher temperatures. The following chapter details the bulk diffusion process and electrical conductivity in light of the defect chemistry of CTF, as a function of oxygen partial pressure and temperature. Under typical operation conditions, CTF must be regarded as a mixed ionic and electronic conductor, with increasing predominance of ionic conductivity at T > 800°C. The second part is dedicated to the stability of the CTF under atmospheric compositions typically found in standard operating conditions, known to degrade the performance of usual membrane materials. The oxygen transport of CTF is shown to remain extremely stable under CO2, CO, and H2 atmospheres over several hundred hours. Some degradation (- 25% of oxygen semi permeation flux) was observed when exposed to humidified CO2, but returning to initial values when exposed to dry helium for a hundred hour. Post-mortem XRD, SEM and Raman analyses did not show any obvious signs of surface or bulk degradation. CTF was tested for CH4 oxidation for a thousand hours and the formation of CO, CO2 and H2O was followed. Despite this reactive environment, the oxygen transport CTF membrane fully regenerates upon returning to helium atmosphere. Therefore, despite relatively low performance (5×10-3 mL.min-1.cm-1 at 900°C), this material is full of promises and especially its outstanding stability under methane can be very interesting for some applications
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VENKATA, PADMA PRIYA. "Computational Modeling of Heat and Mass Transfer in Planar SOFC: Effects of Volatile Species/Oxidant Mass Flow Rate and Electrochemical Reaction Rate." University of Cincinnati / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1205169104.
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CHIBA, RUBENS. "Sintese, processamento e caracterizacao das meia-celulas de oxido solido catodo/eletrolito de manganito de lantanio dopado com estroncio/zirconia estabilizada com itria." reponame:Repositório Institucional do IPEN, 2010. http://repositorio.ipen.br:8080/xmlui/handle/123456789/9503.
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Made available in DSpace on 2014-10-09T12:27:23Z (GMT). No. of bitstreams: 0Made available in DSpace on 2014-10-09T14:06:51Z (GMT). No. of bitstreams: 0
Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
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Junior, Roberto Janny Teixeira. "On governing equations and closure relations for the multiscale modeling of concentration polarization in solid-oxide fuel cells: mass transfer and concentration-induced voltage losses." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/3/3137/tde-07112017-075939/.
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The aim of this dissertation is to appraise and critically reflect on the physical pertinence of governing equations and closure relations often used for the modeling of gas-phase transport phenomena in high-temperature solid-oxide fuel cells (SOFCs). More precisely, this work conducts a critical literature review on the concentration-induced voltage losses (i.e., concentration polarization) resulting from mass transfer limitations. Thus, the overall object of this work was to stress awareness of the limits of mathematical models studied and developed in the SOFC literature to date, and which are specifically related to concentration polarization processes. To a great extent, the design of SOFC porous layers is likened to that of optimizing the transport of multicomponent gas mixtures in structured porous catalysts, for which diffusional and flow limitations are of cardinal importance. In both cases, severe inconsistencies in mass transport models cannot be simply ignored and the main uncertainties in utilizing such models should be clarified. It is hoped that the information herein will serve usefully to support future developments of more consistent theoretical frameworks, thereby improving the confidence on the results of numerical simulations. The critical literature review has been carried out so to identify a number of physical inconsistences, ill-defined approximations, and misleading mathematical derivations. Along the review, it is argued that the choice (or, more properly, the lack of conceptual refinement) of a particular mathematical model can significantly impair the \"prediction\" of transport processes relevant to concentration-induced power losses in SOFCs. One of the keystones of this work was therefore to re-interpret and thus to reassess the frequently contradictory literature related to certain classes of gas-phase transport models pertinent to the evaluation of concentration polarization. With this revisionary approach, it is expected that one could reduce confusion, clear up apparent contradictions, and improve the possibility of gaining new insights.Esta dissertação tem o objetivo de avaliar e refletir criticamente sobre a pertinência física de equações de conservação e de relações de fechamento, frequentemente utilizadas na modelagem multiescala de fenômenos de transporte em células a combustível de óxido-sólido (SOFC). Dêu-se atenção especial ao escoamento em \"microescala\" de misturas gasosas multicomponentes, dentro de meios porosos quimicamente reativos. Em outras palavras, esta monografia busca ressaltar quais os limites para aplicação de certas classes de modelos matemáticos, os quais têm sido desenvolvidos e utilizados na literatura de SOFCs até o presente momento. O projeto de camadas porosas de SOFCs assemelha-se à tarefa de otimizar processos de transporte em catalisadores estruturados, para os quais a existência de limitações de transporte por difusão e por escoamento tem importância primordial. Por esta razão, inconsistências originadas em modelos de fenômenos de transporte não podem ser, simplesmente, negligenciadas e, portanto, as principais incertezas ao se utilizar tais modelos devem ser devidamente esclarecidas. Espera-se, com efeito, que as informações contidas neste trabalho sejam úteis para futuros desenvolvimentos teóricos mais consistentes, de forma a aumentar a confiabilidade no uso de resultados obtidos por simulações numéricas.
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Pfaff, Ulrike, Grzegorz Filipczyk, Alexander Hildebrandt, Marcus Korb, and Heinrich Lang. "1,3,5-Triferrocenyl-2,4,6-tris(ethynylferrocenyl)-benzene – a new member of the family of multiferrocenyl-functionalized cyclic systems." Universitätsbibliothek Chemnitz, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-152459.
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The consecutive synthesis of 1,3,5-triferrocenyl-2,4,6-tris(ethynylferrocenyl)benzene (6c) is described using 1,3,5-Cl3-2,4,6-I3-C6 (2) as starting compound. Subsequent Sonogashira C,C cross-coupling of 2 with FcC[triple bond, length as m-dash]CH (3) in the molar ratio of 1 : 4 afforded solely 1,3,5-Cl3-2,4,6-(FcC[triple bond, length as m-dash]C)3-C6 (4c) (Fc = Fe(η5-C5H4)(η5-C5H5)). However, when 2 is reacted with 3 in a 1 : 3 ratio a mixture of 1,3,5-Cl3-2-(FcC[triple bond, length as m-dash]C)-4,6-I2-C6 (4a) and 1,3,5-Cl3-2,4-(FcC[triple bond, length as m-dash]C)2-6-I-C6 (4b) is obtained. Negishi C,C cross-coupling of 4c with FcZnCl (5) in the presence of catalytic amounts of [Pd(CH2C(CH3)2P(tC4H9)2)(μ-Cl)]2 gave 1,3-Cl2-5-Fc-2,4,6-(FcC[triple bond, length as m-dash]C)3-C6 (6a), 1-Cl-3,5-Fc2-2,4,6-(FcC[triple bond, length as m-dash]C)3-C6 (6b) and 1,3,5-Fc3-2,4,6-(FcC[triple bond, length as m-dash]C)3-C6 (6c) of which 6b is the main product. Column chromatography allowed the separation of these organometallic species. The structures of 4a,b and 6a in the solid state were determined by single crystal X-ray diffractometry showing a π–π interacting dimer (4b) and a complex π–π pattern for 6a. The electrochemical properties of 4a–c and 6a–c were studied by cyclic voltammetry (=CV) and square wave voltammetry (=SWV). It was found that the FcC[triple bond, length as m-dash]C-substituted benzenes 4a–c show only one reversible redox event, indicating a simultaneous oxidation of all ferrocenyl units, whereby 4c is most difficult to oxidise (4a, E°′1 = 190, ΔEp = 71; 4b, E°′1 = 195, ΔEp = 59; 4c, E°′1 = 390, ΔEp = 59 mV). In case of 4c, the oxidation states 4cn+ (n = 2, 3) are destabilised by the partial negative charge of the electronegative chlorine atoms, which compensates the repulsive electrostatic Fc+–Fc+ interactions with attractive electrostatic Fc+–Clδ− interactions. When ferrocenyl units are directly attached to the benzene C6 core, organometallic 6a shows three, 6b five and 6c six separated reversible waves highlighting that the Fc units can separately be oxidised. UV-Vis/NIR spectroscopy allowed to determine IVCT absorptions (=Inter Valence Charge Transfer) for 6cn+ (n = 1, 2) (n = 1: νmax = 7860 cm−1, εmax = 405 L mol−1 cm−1, Δν1/2 = 7070 cm−1; n = 2: νmax = 9070 cm−1, εmax = 620 L mol−1 cm−1, Δν1/2 = 8010 cm−1) classifying these mixed-valent species as weakly coupled class II systems according to Robin and Day, while for 6a,b only LMCT transitions (=ligand to metal charge transfer) could be detectedDieser Beitrag ist aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich
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Huynh, Le Thanh Nguyen. "Les accumulateurs au sodium et sodium-ion, une nouvelle génération d’accumulateurs électrochimiques : synthèse et électrochimie de nouveaux matériaux d’électrodes performants." Thesis, Paris Est, 2016. http://www.theses.fr/2016PESC1123/document.
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Les accumulateurs au lithium jouent un rôle important comme source d'alimentation pour les appareils électroniques portables en raison de leur forte capacité gravimétrique et volumétrique et leur haute tension. En outre, la technologie lithium-ion est la mieux placée pour une application à grande échelle, telle que le véhicule électrique, ce qui pose un problème de ressource et à terme, de coût. Une des réponses envisagées sur le plan économique et environnemental est le développement d’accumulateurs sodium-ion. Dans tous les cas, le problème scientifique consiste à proposer des matériaux d’insertion des ions sodium avec un caractère réversible de la réaction électrochimique, et une durée de vie compétitive par rapport aux systèmes au lithium. Le travail présenté se situe dans cet effort de recherche. Les potentialités de matériaux dérivés du pentoxyde de vanadium, de structure 2D, sont étudiées comme composés d’intercalation du sodium: le composé de référence V2O5, le bronze performant dérivé de V2O5 de formule K0,5V2O5, ε’-V2O5, ainsi que le composé au manganèse de type lamellaire : la birnessite sol-gel et sa forme dopée au cobalt. Les relations structure-électrochimie sont élucidées à travers une étude combinant propriétés électrochimiques, diffraction des Rayons X et spectroscopie Raman des matériaux à différents taux d’insertion, en fin de réaction et après cyclages galvanostatiques. De nouvelles phases sont obtenues et des capacités spécifiques comprises entre 100 et 160 mAh/g dans le domaine de potentiel 4V-1V peuvent être obtenues avec parfois une stabilité remarquable comme dans le cas de NaV2O5 et ε’-V2O5Since commercialization, Li-ion batteries have been playing an important role as power source for portable electronic devices because of high gravimetric, volumetric capacity and high voltage. Furthermore, the lithium-ion technology is best suited for large-scale application, such as electric vehicles, which poses a resource problem and ultimately cost. On the contrary, sodium is a most abundant element, inexpensive and similarly properties as lithium. In order to solve the problem of lithium raw resource, sodium is proposed as a solution for next generation power source storage. This work investigates the potential derivative vanadium pentoxide materials as sodium intercalation compounds: the V2O5 reference compound, the promizing potassium bronze K0,5V2O5, ε'-V2O5, as well as a lamellar manganese oxide: the sol-gel birnessite and its doped cobalt form. The structure-electrochemistry relationships are clarified through a study combining electrochemical properties, X-ray diffraction and Raman spectroscopy of materials at different insertion rate, end of the reaction and after galvanostatic cycling. New phases are highlighted and specific capacities between 100 and 160 mAh / g in the field of 4V-1V potential can be obtained with sometimes remarkably stable as in the case of NaV2O5 and ε'-V2O5
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Feng, Shi. "Elucidation of hydrogen oxidation kinetics on metal/proton conductor interface." Thesis, Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/48941.
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High temperature proton conducting perovskite oxides are very attractive materials for applications in electrochemical devices, such as solid oxide fuel cells (SOFCs) and hydrogen permeation membranes. A better understanding of the hydrogen oxidation mechanism over the metal/proton conductor interface, is critical for rational design to further enhance the performances of the applications. However, kinetic studies focused on the metal/proton system are limited, compared with the intensively studied metal/oxygen ion conductor system, e.g., Ni/YSZ (yttrium stabilized zirconia, Zr₁-ₓYₓO₂-δ). This work presents an elementary kinetic model developed to assess reaction pathway of hydrogen oxidation/reduction on metal/proton conductor interface. Individual rate expressions and overall hydrogen partial pressure dependencies of current density and polarization resistance were derived in different rate limiting cases. The model is testified by tailored experiments on Pt/BaZr₀.₁Ce₀.₇Y₀.₁Yb₀.₁O₃-δ (BZCYYb) interface using pattern electrodes. Comparison of electrochemical testing and the theoretical predictions indicates the dissociation of hydrogen is the rate-limiting step (RLS), instead of charge transfer, displaying behavior different from metal/oxygen ion conductor interfaces. The kinetic model presented in this thesis is validated by high quantitative agreement with experiments under various conditions. The discovery not only contributes to the fundamental understanding of the hydrogen oxidation kinetics over metal/proton conductors, but provides insights for rational design of hydrogen oxidation catalysts in a variety of electrochemical systems.
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Gohmann, Andrew Kaden. "Calcium phosphate nucleation induced by electrochemical methods." Miami University / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=miami1627572348324976.
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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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Usseglio-Viretta, François. "Optimisation des performances et de la robustesse d’un électrolyseur à hautes températures." Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GREAI036/document.
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La réponse thermique, électrochimique et mécanique d'un électrolyseur de la vapeur d'eau à haute température (EVHT) a été analysée dans ce travail. Pour ce faire, une approche de modélisation multi-physique et multi-échelle a été employée : • Un modèle local, à l'échelle de la microstructure des électrodes, a été utilisé pour analyser le comportement électrochimique apparent des électrodes de la cellule d'électrolyse étudiée. Le fonctionnement du système au sein d'un empilement de plusieurs cellules a ensuite été analysé grâce à un modèle thermoélectrochimique à l'échelle macroscopique de l'EVHT. Un élément de validation expérimentale du modèle accompagne les résultats. • Un modèle thermomécanique pour le calcul de l'état de contrainte de l'EVHT a été développé. Celui-ci tient compte des phénomènes physiques intrinsèques à la cellule et à son fonctionnement sous courant à hautes températures et à ceux imputables aux interactions mécaniques entre la cellule et son environnement. Les données manquantes nécessaires à l'exécution des modèles ont été obtenues par la caractérisation et par des calculs d'homogénéisation de la microstructure tridimensionnelle des électrodes. Par ailleurs le comportement viscoplastique du matériau de la cathode a été mis évidence par des essais de fluage en flexion quatre points. L'étude a permis de définir un domaine de fonctionnement optimal garantissant des performances électrochimiques élevées avec des niveaux de température acceptables. Des propositions visant à réduire l'endommagement mécanique du système ont également été produitesThe thermal, electrochemical and mechanical response of a high temperature steam electrolyzer (HTSE) has been analyzed in this work. To this end, a multi-physics and multi-scale modelling approach has been employed: • A local model, at the microstructure scale of the electrodes, has been used to analyze the apparent electrochemical behavior of the electrodes related to the studied electrolysis cell. System operation, in a stack of several cells, has been then analyzed using a thermoelectrochemical model at the macroscopic scale of the HTSE. An element of experimental validation of the model comes with the results. • A thermomechanical model for the calculation of the stress state of the HTSE has been developed. In this model, the intrinsic physical phenomena of the cell, of its operation under current at high temperatures and those ascribable to the mechanical interactions between the cell and its environment have been considered. The unknown data required for the models have been obtained by the characterization and homogenization calculations of the three-dimensional microstructure of the electrodes. Besides, the viscoplastic behavior of the cathode material has been determined by a four-point bending creep test. The study made it possible to define an optimal operating zone, ensuring both high electrochemical performances and acceptable temperature levels. Proposals aiming to reduce the mechanical damage of the system have been also produced
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Assis, Lucas Marinho Nobrega de. "Dispositivos eletrocrômicos com azul da Prússia e eletrólitos sólidos poliméricos." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/75/75134/tde-09082016-143409/.
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Este trabalho apresenta os resultados do preparo e caracterização de dispositivos eletrocrômicos (ECD - electrochromic devices) contendo filmes finos de azul da Prússia (PB) como camada eletrocrômica, CeO2-TiO2 como contra-eletrodo e eletrólitos à base de polímeros contendo glicerol, formaldeído e γ-butirolactona. Os filmes finos de azul da Prússia foram preparados pelo método de eletrodeposição galvanostática e usados para montagem de dispositivos eletrocrômicos com eletrólitos de composição polimérica variada. Os filmes finos foram caracterizados através de medidas de densidade de carga, voltametria cíclica e transmitância no UV-Vis, além de análises morfológicas por microscopia de força atômica (AFM) e microscopia de varredura eletrônica (MEV), elipsometria, medidas de espessura, ângulo de contato e eficiência de coloração. O filme eletrodepositado por 300 s apresentou densidade de carga de 1,62 mC.cm-2 e 0,98 de reversibilidade com rugosidade de 17,7 nm, espessura de 315 nm via elipsometria e 216 nm via perfilometria. A eficiência de coloração calculada foi de 131,4 cm2.C-1 e os valores de ângulo de contato e energia livre de superfície também foram calculadas. As análises voltamétricas dos filmes finos revelaram picos característicos dos processos de oxidação e redução e as análises espectroscópicas apresentaram variação de transmitância de 71,6 % em 686 nm em solução eletrolítica de KCL 1 mol.L-1. Foram preparados e caracterizados dispositivos com eletrólitos a base de gelatina comercial com sal LiClO4; poli(vinil butirato) (PVB) com par iônico LiI/I2; PVB com LiClO4; PVB com par iônico LiI/I2+disperse red; ágar com LiClO4; ágar com sal Eu(CF3SO3)3; DNA com LiClO4; DNA com sal Er(CF3SO3)3; pectina com LiClO4; HPC com ácido acético; HPC com LiClO4 e PVDF com LiClO4. Dentre os resultados obtidos, os melhores resultados de densidade de carga de 10,1 e 8,5 mC.cm-2 foram obtidos para os dispositivos com eletrólitos de HPC e pectina, ambas com sal LiClO4. Voltamogramas cíclicos das amostras estudadas revelaram picos anódicos e catódicos referentes à extração e inserção de íons de lítio e/ou prótons, e elétrons no filme de PB. As análises de transmitância em 686 nm entre o estado colorido e descolorido dos dispositivos mostraram os valores de 40,2% para a janela contendo eletrólito à base de gelatina com LiClO4 e 35,2 % para a janela com ágar e sal Eu(CF3SO3). Além disso, também foi verificada a estabilidade dos dispositivos revelando a duração entre 400 a 2200 ciclos cronoamperométricos, dependendo do eletrólito usado. Os resultados obtidos mostram que os dispositivos estudados neste trabalho são potenciais candidatos para aplicações práticas em dispositivos eletrocrômicos.This work presents the results of the preparation and characterization of electrochromic devices (ECDs) containing a thin film of Prussian blue (PB) as electrochromic layer, CeO2-TiO2 as a counter electrode and electrolytes based on polymers containing glycerol, formaldehyde, and γ-butyrolactone. Thin films of Prussian blue were prepared by galvanostatic electrodeposition method and used for the assembly of electrochromic devices with varying polymer composition of electrolytes. The thin films were characterized by charge density measurements, cyclic voltammetry, transmittance in the UV-Vis, and morphological analyzes such as atomic force microscopy (AFM) and scanning electron microscopy (SEM). Moreover, there were subjected to ellipsometry, thickness, contact angle, and coloring efficiency measurements. The electrodeposited film of 300 s had charge density of 1.62 mC.cm-2 and 0.98 of reversibility with roughness of 17.7 nm and thickness of 315 nm via ellipsometry and 216 nm via profilometry. The calculated color efficiency was 131.4 cm2.C-1 and the contact angle values and surface free energy were calculated. The voltammetric analyzes of thin films showed characteristic peaks of oxidation and reduction processes and spectroscopic analysis showed 71.6% transmittance variation at 686 nm in 1 mol.L-1 KCL electrolyte solution. ECD were prepared and characterized, using electrolytes such as commercial gelatin with LiClO4 salt; poly (vinyl butyrate) (PVB) with ion pair LiI/I2; PVB with LiClO4; PVB with ion pair LiI/I2 + disperse red; agar with LiClO4; agar with Eu(CF3SO3)3 salt; DNA with LiClO4; DNA with Er(CF3SO3)3 salt; pectin with LiClO4; HPC with acetic acid; HPC with LiClO4 and PVDF LiClO4. The best results of charge density of 8.5 and 10.1 mC.cm-2 were obtained for devices with HPC electrolytes and pectin, both with LiClO4 salt. Cyclic voltammetry of the studied samples revealed anodic and cathodic peaks relating to the extraction and insertion of lithium ions and/or protons and electrons in the PB film. The transmittance at 686 nm analysis between the colored state and discolored windows showed values of 40.2% for the window containing electrolyte of gelatin with LiClO4 and 35.2% for the window with agar and Eu(CF3SO3) salt. Furthermore, the stability of the devices was also recorded revealing the duration between 400-2200 chronoamperometric cycles, depending on the used electrolyte. The results show that the windows studied in this work are potential candidates for electrochromic devices applications.
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Pilli, Aparna. "Atomic Layer Deposition of Boron Oxide and Boron Nitride for Ultrashallow Doping and Capping Applications." Thesis, University of North Texas, 2020. https://digital.library.unt.edu/ark:/67531/metadc1752373/.
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The deposition of boron oxide (B₂O₃) films on silicon substrates is of significant interest in microelectronics for ultrashallow doping applications. However, thickness control and conformality of such films has been an issue in high aspect ratio 3D structures which have long replaced traditional planar transistor architectures. B₂O₃ films are also unstable in atmosphere, requiring a suitable capping barrier for passivation. The growth of continuous, stoichiometric B₂O₃ and boron nitride (BN) films has been demonstrated in this dissertation using Atomic Layer Deposition (ALD) and enhanced ALD methods for doping and capping applications.
Low temperature ALD of B₂O₃ was achieved using BCl₃/H₂O precursors at 300 K. In situ x-ray photoelectron spectroscopy (XPS) was used to assess the purity and stoichiometry of deposited films with a high reported growth rate of ~2.5 Å/cycle. Free-radical assisted ALD of B₂O₃ was also demonstrated using non-corrosive trimethyl borate (TMB) precursor, in conjunction with mixed O₂/O-radical effluent, at 300 K. The influence of O₂/O flux on TMB-saturated Si surface was investigated using in situ XPS, residual gas analysis mass spectrometer (RGA-MS) and ab initio molecular dynamics simulations (AIMD). Both low and high flux regimes were studied in order to understand the trade-off between ligand removal and B₂O₃ growth rate. Optimization of precursor flux was discovered to be imperative in plasma and radical-assisted ALD processes.
BN was investigated as a novel capping barrier for B₂O₃ and B-Si-oxide films. A BN capping layer, deposited using BCl₃/NH₃ ALD at 600 K, demonstrated excellent stoichiometry and consistent growth rate (1.4 Å/cycle) on both films. Approximately 13 Å of BN was sufficient to protect ~13 Å of B₂O₃ and ~5 Å of B-Si-oxide from atmospheric moisture and prevent volatile boric acid formation. BN/B₂O₃/Si heterostructures are also stable at high temperatures (>1000 K) commonly used for dopant drive-in and activation. BN shows great promise in preventing upward boron diffusion which causes a loss in the dopant dose concentration in Si.
The capping effects of BN were extended to electrochemical battery applications. ALD of BN was achieved on solid Li-garnet electrolytes using halide-free tris(dimethylamino)borane precursor, in conjunction with NH₃ at 723 K. Approximately 3 nm of BN cap successfully inhibited Li₂CO₃ formation, which is detrimental to Li-based electrolytes. BN capped Li-garnets demonstrated ambient stability for at least 2 months of storage in air as determined by XPS. BN also played a crucial role in stabilizing Li anode/electrolyte interface, which drastically reduced interfacial resistance to 18 Ω.cm², improved critical current density and demonstrated excellent capacitance retention of 98% over 100 cycles. This work established that ALD is key to achieving conformal growth of BN as a requirement for Li dendrite suppression, which in turn influences battery life and performance.
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Assat, Gaurav. "Anionic redox for high-energy batteries. Fundamental understanding, practical challenges, and future outlook." Electronic Thesis or Diss., Sorbonne université, 2018. http://www.theses.fr/2018SORUS396.
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Notre dépendance croissante vis-à-vis des batteries lithium-ion pour le stockage d’énergie exige une amélioration de leurs électrodes positives, qui fonctionnent encore grâce au redox cationique des métaux de transition. L’émergence du redox anionique – une approche transformationnelle qui double la capacité des électrodes positives « Li-riches » – a récemment suscité de grands espoirs mondialement. Toutefois, des questions subsistent sur les origines fondamentales du redox anionique et sur son potentiel dans les applications pratiques. Cette thèse vise à répondre précisément à ces questions, en utilisant les connaissances de la chimie des solides, de l’électrochimie, de la spectroscopie des rayons X, et de la thermochimie. Pour ce faire, nous fournissons d’abord un compte rendu historique, un cadre théorique, les règles de conception de nouveaux matériaux, ainsi qu’un résumé des techniques de caractérisation propres au redox anionique. Ensuite, à travers des études expérimentales menées à la fois sur un matériau « modèle » (à base de métal 4d) et sur un matériau « pratique » (à base de métal 3d), nous montrons comment l’interaction fondamentale entre les processus de redox cationique et anionique régit les propriétés pratiques de ces matériaux (c’est-à-dire hystérésis de tension, performance de vitesse, chute de tension, et production de chaleur). Enfin, en utilisant ces résultats, nous décrivons les approches possibles pour améliorer ces matériaux et en concevoir de nouveaux. Nous résumons également leurs chances d’implantation sur le marché face aux cathodes lamellaires à base de nickel qui prévalent aujourd’huiOur increasing dependence on lithium-ion batteries for energy storage applications calls for continual performance improvements of their positive electrodes, which have so far relied solely on cationic redox of transition-metal ions for driving the electrochemical reactions. Great hope has recently been placed on the emergence of anionic redox – a transformational approach for designing Li-rich positive electrodes as it leads to a near-doubling of capacity – hence generating worldwide research interest. However, questions have been raised on the fundamental origins of anionic redox and whether its full potential can be realised in applications. This is exactly what this thesis aims to answer by using the knowledge from the fields of solid-state chemistry, electrochemistry, X-ray spectroscopy, and thermochemistry. We first provide a comprehensive historical account, a theoretical framework, some materials’ design rules, and a survey of characterization techniques specific to anionic redox. Then, through comprehensive experimental studies that were performed in parallel on one ‘model’ (4d metal based) and one ‘practical’ (3d metal based) material, we highlight how the fundamental interplay between cationic and anionic redox processes governs the application-wise important properties of these promising battery materials (i.e. voltage hysteresis, rate performance, voltage decay, and heat generation,). Finally, using these results, we outline possible approaches for improving such materials and for designing novel ones. We also summarize their chances for market implementation in face of the competing nickel-based layered cathodes that are prevalent today
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Bellini, Elizabete Maria. "Proposta de uma sequência didática para o ensino de eletroquímica e a sensibilização ambiental quanto aos impactos do descarte de pilhas e baterias." Universidade Tecnológica Federal do Paraná, 2018. http://repositorio.utfpr.edu.br/jspui/handle/1/3205.
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Contém produto: Produto Educacional 1: manual do professor. Produto Educacional 2: manual do aluno.O crescente avanço científico, tecnológico e a ampla acessibilidade à informação atribuem à escola a função de tornar conhecimentos sobre Tecnologia de Informação (TI) significativos a indivíduos inseridos em uma sociedade em constante transformação. Para tanto, a escola precisa de metodologias educacionais que propiciem aos jovens uma maior autonomia para que sejam qualificados a participar de forma ativa na comunidade, promovendo mudanças que produzam progressos para o desenvolvimento da cidadania. Um dos pilares desta construção é o Ensino de Ciências, onde se destacam os saberes referentes à disciplina de Química que são importantes para o desenvolvimento econômico, social e tecnológico da população. Entretanto, o Ensino de Química no espaço escolar está distante da vida prática do adolescente e da sociedade, restringindo-se à memorização de fórmulas, nomenclaturas e teorias. Para esta investigação científica, estabeleceu-se como objetivo analisar se os conhecimentos sobre gerenciamento de resíduos e logística reversa articulados à conteúdos de Eletroquímica, no Ensino de Química, podem sensibilizar alunos do 2º ano do Ensino Médio quanto aos impactos ambientais causados por descarte inadequado de pilhas e baterias, por meio de uma proposta de desenvolvimento e aplicação de uma Sequência Didática (SD). O delineamento metodológico para este estudo envolveu a pesquisa participativa e uma abordagem quanti-qualitativa. A pesquisa foi aplicada no Colégio Estadual Zumbi dos Palmares no município de Colombo, Região Metropolitana de Curitiba, e destinada a quatro turmas de 2º ano do Ensino Médio, totalizando 96 discentes. Os resultados foram obtidos utilizando como instrumento de coleta de dados questionários anterior e posterior à aplicação da Sequência Didática (SD), com perguntas abertas e de múltipla escolha. Foi possível ponderar que os estudantes já tinham um certo conhecimento sobre os impactos ambientais decorrentes do descarte inadequado de pilhas e baterias, sabiam sobre postos de coleta, conseguiram avaliar e declarar que tipo de pilha utilizam em seu cotidiano. Após a aplicação da SD, foi possível evidenciar que houve compreensão quanto ao conteúdo de Eletroquímica, além da sensibilização ambiental dos participantes. Disponibilizou-se o produto educacional com versões para professor e educandos a fim de tornar mais hábil o processo de ensino dos educandos, pretendendo, desta maneira, contribuir com a reflexão e o trabalho dos docentes e discentes no Ensino de Química.
The scientific and technological progress, as well as the wide accessibility to information, all assign to school the function of making knowledge about Information Technology (IT) meaningful to individuals who are inserted in a society which one is in constant transformation. Therefore, the school needs educational methodologies to provide Youth a great autonomy, in order to help them to be better qualified and participate in an actively way in their community promoting importante changes towards progress and development of citizenship. One of the main pillars of this construction is the elementary and middle school Science Education which emphasizes the knowledge related to the discipline of Chemistry so important for the economic, social and technological development of the population. However, the Chemistry for teaching in school environment is far from the real life of the adolescents and society. It remains limited to the memorization skills of formulas, nomenclatures and theories. Thus, the objective of this scientific investigation was to analyze if knowledge about waste management and reverse logistics, articulated to the contents of Eletrochemistry in the Teaching of Chemistry, can sensitize second year-students of High School about the environmental impacts caused by inappropriated disposal of used batteries. In this regard, it was created, developed, and applicated a Didactic Sequence (DS) as a tool to raise students awareness about those environmental impacts. The methodological development for this study was to envolve a participatory research and a quantitative-qualitative approach. The research was applied at the Zumbi dos Palmares State College in the city of Colombo, Metropolitan Region of Curitiba, and was destined to four high school classes, totaling 96 students. The results were obtained by using data collection instrument - the questionnaires – they were used before and after the application of the Didactic Sequence (DS), with open and multiple choice questions. It was possible to consider that the students already had a certain knowledge about the environmental impacts, resulting from the inadequate disposal of batteries. They knew about collection points, they were able to evaluate and declare what type of battery they use in their daily lives. After the application of DS, it was possible to show that there was understanding of the content of Electrochemistry. In addition, there was the environmental sensitization of the participants at the end of this research. The educational product was to provide with teachers and students versions in order to make the teaching and learning process more proficient so that it contributes to the reflection and works for teachers and students in the Teaching of Chemistry.
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Marty, Aurélie. "Etude des interactions matériaux et des mécanismes électrochimiques aux interfaces des électrodes d’un empilement mémoire à base d’oxydes métalliques." Thesis, Université Grenoble Alpes (ComUE), 2018. http://www.theses.fr/2018GREAT038/document.
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Cette thèse porte sur la compréhension des mécanismes de forming dans les mémoires à pont conducteur (CBRAM) à base d’oxydes métalliques. Pour cela nous avons admis que l’empilement mémoire est une cellule électrochimique à l’échelle du nanomètre et considéré que les principaux mécanismes de forming sont basés sur des effets électrochimiques. Nous avons débuté nos études à partir d’un couple de référence CuxTey/Oxyde, analysé par HAXPES et ToF-SIMS avant et après l’electro-forming, dans le but d’observer les diffusions et les modifications de l’environnement chimique durant le forming. Ensuite, la couche fournissant les ions, basée sur un alliage CuxTey, ainsi que le diélectrique (Ta2O5, GdOx, or Al2O3) ont été modifiés étape par étape. Les résultats de leurs analyses ont été comparés avec ceux de l’empilement de référence dans le but de comprendre le rôle de chaque couche et des éléments présents dans l’empilement.Nous avons vu que les propriétés du diélectrique, telles que la force des liaisons métal-oxygène, l’hygroscopicité, ou l’éventuelle présence de défauts comme les lacunes d’oxygène, peuvent favoriser un comportement mémoire plutôt OXRAM, CBRAM ou hybride OXRAM/CBRAM. De plus, quand le cuivre diffuse durant le forming, une contre diffusion d’oxygène apparaît également dans le diélectrique. Ensuite, la présence de tellure dans la couche fournissant les ions est nécessaire pour permettre l’effacement de la mémoire, car il permet la re-dissolution du filament de cuivre dans la couche fournissant les ions. Nous avons également vu que le germanium amorphise l’alliage de CuxTeyGez et donc permet son intégration tout en le protégeant de l’oxydation. De plus, il est possible de remplacer le germanium par du zirconium, réduisant ainsi le diélectrique, ce qui facilite le formingThis thesis focuses on the understanding of forming mechanisms in oxide-based conductive bridge memories (CBRAM), based on metallic oxides. For this purpose, we compared the memory stack to an electrochemical cell at nanometer scale and consider that the main mechanisms occurring in the memory rely on electrochemical effects. We started our studies from a reference couple CuxTey/Oxide, analyzed by HAXPES and ToF-SIMS before and after electro-forming, in order to observe the diffusions and the modifications of the chemical environment occurring during forming. Then, the ion source layer based on CuxTey alloy and the dielectric (Ta2O5, GdOx or Al2O3) were sequentially modified and results of their analyses were compared to the reference stack, in order to understand the role of each layer and chemical elements present in the memory stack.We evidenced that the properties of the dielectric, such as the strength of its oxygen-metal bonds, its hygroscopicity or the eventual presence of defects such as oxygen vacancies, can promote a given memory behavior from OXRAM to CBRAM or hybrid OXRAM/CBRAM behavior. Moreover, when copper diffuses during the forming, an oxygen counter diffusion also takes place in the dielectric. Also, the presence of tellurium in the ion source layer is required to reset the memory as it enables the dissolution of the copper filament in the ion source layer. We also show that germanium amorphizes the CuxTeyGez alloy, thus enables its integration, and protects it from oxidation. Moreover, it is possible to substitute germanium by zirconium resulting in the dielectric reduction, which eases the forming
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Griffith, Kent Joseph. "Atomic and electronic structure of complex metal oxides during electrochemical reaction with lithium." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/271191.
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Lithium-ion batteries have transformed energy storage and technological applications. They stand poised to convert transportation from combustion to electric engines. The discharge/charge rate is a key parameter that determines battery power output and recharge time; typically, operation is on the timescale of hours but reducing this would improve existing applications and open up new possibilities. Conventionally, the rate at which a battery can operate has been improved by synthetic strategies to decrease the solid-state diffusion length of lithium ions by decreasing particle sizes down to the nanoscale. In this work, a different approach is taken toward next-generation high-power and fast charging lithium-ion battery electrode materials. The phenomenon of high-rate charge storage without nanostructuring is discovered in niobium oxide and the mechanism is explained in the context of the structure–property relationships of Nb2O5. Three polymorphs, T-Nb2O5, B-Nb2O5, and H-Nb2O5, take bronze-like, rutile-like, and crystallographic shear structures, respectively. The bronze and crystallographic shear compounds, with unique electrochemical properties, can be described as ordered, anion-deficient nonstoichiometric defect structures derived from ReO3. The lessons learned in niobia serve as a platform to identify other compounds with related structural motifs that apparently facilitate high-rate lithium insertion and extraction. This leads to the synthesis, characterisation, and electrochemical evaluation of the even more complicated composition–structure–property relationships in ternary TiO2–Nb2O5 and Nb2O5–WO3 phases. Advanced structural characterisation including multinuclear solid-state nuclear magnetic resonance spectroscopy, density functional theory, X-ray absorption spectroscopy, operando high-rate X-ray diffraction, and neutron diffraction is conducted throughout to understand the evolution of local and long-range atomic structure and changes in electronic states.
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Ellis, Brian. "Synthesis, Electrochemistry and Solid-Solution Behaviour of Energy Storage Materials Based on Natural Minerals." Thesis, 2013. http://hdl.handle.net/10012/7398.
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Polyanionic compounds have been heavily investigated as possible electrode materials in lithium- and sodium-ion batteries. Chief among these is lithium iron phosphate (LiFePO4) which adopts the olivine structure and has a potential of 3.5 V vs. Li/Li+. Many aspects of ion transport, solid-solution behaviour and their relation to particle size in olivine systems are not entirely understood. Morphology, unit cell parameters, purity and electrochemical performance of prepared LiFePO4 powders were greatly affected by the synthetic conditions. Partially delithiated olivines were heated and studied by Mössbauer spectroscopy and solid-solution behaviour by electron delocalization was observed. The onset of this phenomenon was around 470-500 K in bulk material but in nanocrystalline powders, the onset of a solid solution was observed around 420 K. The isostructural manganese member of this family (LiMnPO4) was also prepared hydrothermally. Owing to the thermal instability of MnPO4, partially delithiated LiMnPO4 did not display any solid-solution behaviour.
Phosphates based on the tavorite (LiFePO4OH) structure include LiVPO4F and LiFePO4(OH)1-xFx which may be prepared hydrothermally or by solid state routes. LiVPO4F is a high capacity (2 electrons/transition metal) electrode material and the structures of the fully reduced Li2VPO4F and fully oxidized VPO4F were ascertained. Owing to structural nuances, the potential of the iron tavorites are much lower than that of the olivines. The structure of Li2FePO4F was determined by a combined X-ray and neutron diffraction analysis.
The electrochemical properties of very few phosphates based on sodium are known. A novel fluorophosphate, Na2FePO4F, was prepared by both solid state and hydrothermal methods. This material exhibited two two-phase plateau regions on cycling in a half cell versus sodium but displayed solid-solution behaviour when cycled versus lithium, where the average potential was 3.3 V. On successive cycling versus Li a decrease in the sodium content of the active material was observed, which implied an ion-exchange reaction occurred between the material and the lithium electrolyte.
Studies of polyanionic materials as positive electrode materials in alkali metal-ion batteries show that some of these materials, namely those which contain iron, hold the most promise in replacing battery technologies currently available.
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Jiang, Yi. "Solid electrolytes and their applications in heterogeneous catalysis." Thesis, 1994. http://nemertes.lis.upatras.gr/jspui/handle/10889/2132.
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Moorhead-Rosenberg, Zachary. "Magnetic, electronic, and electrochemical properties of high-voltage spinel cathodes for lithium-ion batteries." Thesis, 2015. http://hdl.handle.net/2152/31329.
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Lithium-ion technology has revolutionized the electronics and electric vehicle industry in the past two decades. First commercialized by Sony in 1991, the lithium-ion battery is composed of three main components: (i) the cathode, (ii) the anode, and (iii) the electrolyte. Graphitic carbon remains the most widely used anode material due to its low voltage vs. the Li/Li+ redox couple and high specific capacity. However, there are several popular cathode materials, including layered oxides, spinel oxides, and polyanion materials.
In an effort to increase the energy density of lithium-ion batteries, much focus is given to improving the gravimetric charge capacity and the overall cell voltage. The latter must be accomplished by employing high-voltage cathodes, the most promising of which is the lithium manganese nickel oxide spinel with a specific capacity of 146 mAh/g and a redox voltage of 4.7 V vs. Li/Li+. However, there are still several problems with this material that must be understood and overcome in order to develop high-voltage spinel as a viable commercial cathode.
Physical property measurements can reveal the underlying electronic and atomic interactions in the solid in order to better understand high-voltage spinel and its odd behavior. Novel magnetic techniques have been developed, which reliably indicate the degree of Mn-Ni ordering and quantitative determination of the concentration of the Mn3+ ion. Measurements of several physical properties as a function of lithium content were also undertaken to determine the effects of Mn-Ni ordering on the electronic conductivity and the importance of electron-ion interactions.
In addition to understanding the physical properties of high voltage spinel, the understanding of the solid state chemistry and unique structure was utilized to realize a new full cell construction technique. The spinel structure offers a unique way to deal with first cycle irreversible capacity loss in full cells stemming from solid-electrolyte interphase (SEI) layer growth on the anode surface. To that end, a novel microwave-assisted chemical lithiation process was developed using non-toxic and air-stable chemicals. New composite anode chemistry was combined with a pre-lithiated spinel cathode to demonstrate the feasibility of this approach to realizing practical next-generation Li-ion cells.text