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1
Nwosu, Nkem O. E. "Optimisation of electroless co-deposited solid oxide fuel cell electrodes". Thesis, Edinburgh Napier University, 2013. http://researchrepository.napier.ac.uk/Output/6448.
Testo completoAbstract (sommario):
Research already carried out on the use of the recently patented electroless nickel ceramic codeposition technique as a method of manufacturing solid oxide fuel cell (SOFC) electrodes has thus far indicated that, while functional electrodes can be manufactured by the technique, for optimum performance of the cell, amplification of the ceramic content of the coatings is still required. By mainly employing external agents such as surface active agents (surfactants) and magnetic fields (in a bid to aid ceramic particle stability), this research focused on the prospect of increasing the ceramic content of cermets co-deposited for use as SOFC electrodes. A total of 137 co-deposited samples were produced from different bath compositions. As a prelude to the study, the interactions between the ceramic powders used (yttria stabilised zirconia (YSZ) / lanthanum strontium manganate (LSM)) and the medium for the deposition process – the electroless nickel solution, were investigated by zeta potentiometry and ultraviolet-visible spectroscopy techniques. The results obtained from the studies led to a variation of a series of fundamental plating factors such as the ceramic bath loading and particle size of the powders. While the former was found to yield the highest ceramic content in the coating at a bath loading of 50 g/l, variation of latter notably produced mixed results. With the introduction of surfactants, it was noted that above the surfactant's (sodium dodecyl sulphate) critical micelle concentration, the incorporation of ceramic particles (YSZ) into the nickel matrix steadily increased to as much as 60 volume %. An inverse relationship was though found to exist between the coating thickness and the surfactant's bath concentration. Uniform coatings were found to be associated with low magnetic field strengths while although increased magnetic field strengths positively resulted in the amplification of particle incorporation into the coating, a lack of cohesion between the coating and the substrate – as indicated by coating flake-off, was observed at such strengths. It is suggested that because the magnetic flux was more dominant than the normally ionic plating mechanism, the particles co-deposited under the influence of a high magnetic field were relatively unstable after the coating process. Since LSM is alkaline in nature this work confirms that future research on the application of electroless nickel ceramic co-deposition as a method of manufacturing SOFC cathodes, be focused on the use of alkaline electroless nickel baths rather than the acidic solutions, which better suite YSZ particles.
2
Astuti, Yeni. "Bio-functionalised nanostructured metal oxide electrodes". Thesis, Imperial College London, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.429459.
Testo completo
3
Makgae, Mosidi Elizabeth. "Environmental electrochemistry of organic compounds at metal oxide electrodes". Thesis, Stellenbosch : Stellenbosch University, 2004. http://hdl.handle.net/10019.1/49947.
Testo completoAbstract (sommario):
Dissertation (PhD)--Stellenbosch University, 2004.ENGLISH ABSTRACT: This study investigates the electrochemical oxidation of phenol. Phenol is a major toxin and water pollutant. In addition, during water treatment it reacts with chlorine to produce carcinogenic chlorophenols. lts treatment down to trace levels is therefore of increasing concern. For this purpose, dynamically stable anodes for the breakdown of phenols to carbon dioxide or other less harmful substances were developed and characterized. The anodes were prepared from mixed oxides of tin (Sn) and the precious metals ruthenium (Ru), tantalum (Ta) and iridium (Ir), which in tum were prepared using sol-gel techniques. This involved dip-coating the aqueous salts of the respective metals onto titanium substrates and heating to temperatures of several hundreds of degree Celsius. The properties of these mixed oxide thin films were investigated and characterized using thermal gravimetric analysis (TGA), scanning electron microscopy (SEM), atomic force microscopy (AFM), elemental dispersive energy X-ray analysis (EDX), X-ray diffraction (XRD), Rutherford backscattering spectrometry (RBS), particle induced X-ray emission (PIXE) and electrochemical measurements. A variety of different electrode materials including Til Sn02-Ru02-Ir02, Ti/Ta20s-Ir02 and Ti/RhOx-Ir02 were developed and tested for their potential as oxidation catalysts for organic pollutants in wastewaters. Depending on the anode type, phenol was found to be electrochemically degraded, to different extents, on these surfaces during electrolysis. It was however found that the oxidation rate not only depended on the chemical composition but also on the oxide morphology revealed, resulting from the preparation procedure. The Ti/SnOz-Ru02-Ir02 film was found to be the most efficient surface for the electrolytic breakdown of phenol. This film oxidized phenol at a potential of 200 mV vs Ag/AgC!. The activity of the catalytic systems was evaluated both on the basis of phenol removal efficiency as well as the kinetics of these reactions. Phenol removal efficiency was more than 90% for all the film surfaces prepared and the rate of the reaction followed first order kinetics. A pathway for the electrochemical degradation of phenol was derived using techniques such as HPLC to identify the breakdown products. These pathway products included the formation of benzoquinone and the further oxidation of benzoquinone to the carboxylic acids malic, malonic and oxalic.
AFRIKAANSE OPSOMMING: Die onderwerp van hierdie studie is die elektrochemiese oksidasie van fenol deur nuwe gemengde-oksied elektrodes. Fenol is 'n belangrike gifstof en besoedelingsmiddel in water. Daarbenewens kan fenolook met chloor reageer tydens waterbehandeling om sodoende karsinogeniese chlorofenole te vorm. Dit is dus belangrik dat metodes ondersoek word wat die konsentrasie van fenol in water verminder. Hierdie studie behels die bereiding en karakterisering van nuwe dinamiese stabiele anodes (DSA) vir die afbreek van fenol tot koolstofdioksied en ander minder gevaarlike verbindings. Hierdie nuwe anodes is berei vanaf die gemengde-okside van die edelmetale tin (Sn), ruthenium (Ru), tantalum (Ta) en iridium (Ir), met behulp van sol-gel tegnieke. Die finale stap in die bereiding behels kalsinering van die oksides by temperature van "n paar honderd grade Celsius. Hierdie nuwe elektrodes is later gebruik om die oksidasie van fenol te evalueer. Die gemengde-oksied dunlae/anodes IS d.m.v. die volgende analitiesetegnieke gekarakteriseer: termiese-gravimetriese analise (TGA), skandeerelektronmikroskopie (SEM), atoomkragmikroskopie (AFM), elementverstrooiingsenergie- X-straalanalise (EDX), X-straaldiffraksie (XRD), Rutherford terug-verstrooiingspektroskopie (RBS), partikel-geinduseerde X-straal emissie (PIXE), en elektrochemiese metings. 'n Verskeidenheid elektrodes van verskillende materiale is berei en hul potensiaal as oksidasie-kataliste vir organiese besoedelingsmiddels in afloopwater bepaal. Hierdie elektrodes het die volgende ingesluit: Ti/Sn02-Ru02-Ir02, Ti/Ta20s-Ir02 en Ti/RhOx-Ir02. Gedurende elektrolise is fenol elektrochemies afgebreek tot verskillende vlakke, afhangende van die tipe elektrode. Die oksidasietempo het egter nie alleen van die chemiese samestelling van die elektrode afgehang nie, maar ook van die morfologie van die okside, wat op hulle beurt van die voorbereidingsprosedure afgehang het. Daar is bevind dat die Ti/Sn02-Ru02-Ir02 elektrode die mees effektiewe oppervlakke vir die afbreek van fenol is. Hier het die oksidasie van fenol by 'n potensiaal van 200 mV plaasgevind. Die aktiwiteite van die katalitiese sisteme IS bepaal op grond van hulle fenolverwyderingsdoeltreffendheid. Die kinetika van die reaksies is ook bepaal. Al die elektrodes het >90% fenolverwyderingsdoeltreffendheid getoon en die reaksietempos was van die eerste-orde. Deur van analitiese tegnieke soos hoëdrukvloeistofchromatografie (HPLC) gebruik te maak is die afbreekprodukte van fenol geïdentifiseer en 'n skema vir die elektrochemiese afbreek van fenol uitgewerk. Daar is bevind dat bensokinoon gevorm het, wat later oksidasie ondergaan het om karboksielsure te vorm.
4
Hernández, Rodríguez Elba María. "Solid Oxide Electrolysis Cells electrodes based on mesoporous materials". Doctoral thesis, Universitat de Barcelona, 2018. http://hdl.handle.net/10803/665269.
Testo completoAbstract (sommario):
The need of substituting the current energetic model by a system based on clean Renewable Energy Sources (RES) have gained more importance in the last decades due to the environmental issues related to the use of fossil fuels. These energy sources are site-specific and intermittent, what makes essential the development of Energy Storage Systems (ESS) that allows the storage of the electricity generated by renewable energies.
Among the technologies under development for the storage of electrical energy, Solid Oxide Electrolysis Cells (SOECs) have been proposed in the last decades as a promising technology. Achieving efficiencies higher than 85%, SOEC technology is able to convert electrical energy into chemical energy through the reduction of H2O, CO2 or the combination of both; generating H2, CO or syngas (H2 +CO). The implementation of this technology based on renewable electrical energy, combined with fuel cells would allow closing the carbon cycle.
The work presented in this thesis has been devoted to enhance the performance of SOEC. The approach that is presented for that propose is based on the implementation of high surface area and thermally stable mesoporous metal oxide materials on the fabrication of SOEC electrodes. High performance and stability of the electrodes was expected during its characterization. Structural and electrochemical characterization techniques have been applied during the development of this thesis for this purpose.
The thesis is organized in eight chapters briefly described in the following:
Chapter 1 briefly analyses the current energy scenario presenting electrolysers as a promising technology for the storage of electrical energy. Besides, basic principles of SOECs operation and the state-of-the-art materials of SOECs are reviewed.
Chapter 2 describes all the experimental methods and techniques employed in this thesis for the synthesis and characterization of synthesised materials and fabricated cells.
Chapter 3 presents the results obtained from the structural characterization of the mesoporous materials and fabricated electrodes, revealing the successful implantation of the hard-template method for obtaining Sm0.2Ce0.8O1.9 (SDC), Ce0.8Gd0.2O1.9 (CGO) and NiO mesoporous powders, and the fabrication of SDC-SSC (Sm0.5Sr0.5CoO3-δ), CGO- LSCF (La0.6Sr0.4Co0.2Fe0.8O3) and NiO-SDC electrodes based on mesoporous materials. The attachment of the mesoporous scaffold for the fabrication of oxygen electrodes has been optimized at 900 °C.
Chapter 4 compares electrolyte- and fuel electrode-supported cell configurations based on the same oxygen electrode. The electrochemical performance and the microstructural characterization of these cells are considered for that purpose. Showing a maximum current density of -0.83 and -0.81 A/cm2 on electrolysis and co- electrolysis modes respectively, fuel electrode-supported cells are considered more suitable for SOEC fabrication.
Chapter 5 presents a study focused on analysing the influence of the oxygen electrode interface on the SOEC performance. The electrochemical and microstructural characterization of barrier layers and oxygen electrodes fabricated applying different methods are discussed in this chapter. The combination of a barrier layer fabricated by Pulsed Laser Deposition (PLD) with an oxygen electrode based on mesoporous materials resulted on the injection of up to -1 A/cm2, what allows concluding that this
interface microstructure is directed related with the best performing SOECs in this thesis.
Chapter 6 shows the performance of SOEC cells on co-electrolysis mode containing the optimized oxygen electrode, fabricated by infiltration of mesoporous scaffolds. The long-term stability of infiltrated mesoporous composites have been demonstrated during 1400 h, registering degradation rates of 2%/kh and <1%/kh when current densities of -0.5 A/cm2 and -0.75 A/cm2 are injected, respectively.
Chapter 7 shows results of the scale-up of the mesoporous-based electrodes for the fabrication of large area cells. Their electrochemical performance shows high fuel flexibility, injecting -0.82 A/cm2 on co-electrolysis mode; and long-term stability injecting -0.5 A/cm2 for 600 h.
The conclusions of this thesis are presented in Chapter 8.Una de las principales desventajas de las fuentes de energías renovables es que producen energía eléctrica de forma discontinua. Los electrolizadores de alta temperatura basados en óxidos sólidos (SOEC) se presentan como una tecnología prometedora para el almacenamiento de energía eléctrica. Alcanzando eficiencias mayores de un 85%, los electrolizadores SOEC permite convertir energía eléctrica en energía química mediante la reducción de las moléculas de agua (H2O), dióxido de carbono (CO2), o la combinación de ambas; generándose hidrógeno (H2), monóxido de carbono (CO) o gas de síntesis (H2 +CO) como producto. El trabajo que se presenta en esta tesis tiene como objetico mejorar el rendimiento de los electrolizadores SOEC mediante la utilización de óxidos metálicos mesoporosos, caracterizados por poseer alta área superficial y ser estables a altas temperaturas. Esta tesis está organizada en ocho capítulos. Los capítulos 3, 4, 5, 6 y 7 presentan los resultados alcanzados: El capítulo 3 presenta la caracterización estructural de los materiales mesoporosos y de los electrodos fabricados. Además, la temperatura de adhesión del material mesoporoso ha sido optimizada y se ha fijado a 900 °C. El capítulo 4 compara electrolizadores fabricados soportados por el electrodo de combustible y por el electrolito. Los resultados muestran que las densidades de corriente más altas fueron inyectadas en los electrolizadores soportados por el electrodo de combustible, considerándose esta configuración la más apropiada. El capítulo 5 presenta la influencia de la microstructura de la intercara del electrodo de oxígeno en el rendimiento de los electrolizadores SOEC. La caracterización electroquímica, apoyada por la caracterización microestructural, ha demostrado que la máxima densidad de corriente ha sido inyectada por el electrolizador cuya barrera de difusión ha sido depositado por láser pulsado (PLD) y la capa funcional del electrodo de oxígeno mediante infiltración de materiales mesoporosos. El capítulo 6 estudia el electrodo de oxígeno optimizado. Durante 1400 h de operación continua y caracterización microstructural, se ha demostrado la estabilidad de este electrodo. Por último, el capítulo 7 muestra los resultados obtenidos del escalado de los electrodos mesoporosos en celdas de mayor área (25 cm2). La caracterización electroquímica muestra alta flexibilidad ante las composiciones de gases utilizadas, y estabilidad de los electrodos mesoporosos propuestos.
5
Koep, Erik Kenneth. "A Quantitative Determination of Electrode Kinetics using Micropatterned Electrodes". Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/10524.
Testo completoAbstract (sommario):
Interfacial polarization resistances limit the performance of many thin film solid-state devices, especially at low temperatures. To improve performance, a fundamental understanding of the electrode kinetics that govern interfacial reaction rates must be developed. The goal of this work is to determine site-specific reaction mechanisms and the relative significance of various reactions in order to quantify optimum structural parameters within the cathode microstructure. Key parameters include the length of triple phase boundary (TPB), the quantity of exposed electrolyte/electrode surface, and the ratio of electrolyte to electrode material. These parameters, when studied in a specific system, can be incorporated into broader models, which will encompass the specific conductivity of each component to develop an optimized three-dimensional network.
The emphasis of this work is the systematic control and manipulation of potential cathodic reaction sites in order to develop an understanding of the relative importance of specific reaction sites. Since the physical dimensions of reaction sites are relatively small, an approach has been developed that utilizes micro-fabrication (similar to that used in integrated-circuit fabrication) to produce small and highly controlled microstructures.
Investigations were made into the nature and reactivity of Triple Phase Boundaries (hereafter TPB) through the use of patterned platinum electrodes since only the TPBs are active in these electrodes. After the processing details of micro-fabrication were established for the platinum electrodes, patterned Mixed-Ionic/Electronic Conducting (MIEC) electrodes were fabricated and studied using impedance spectroscopy to determine the contributions from the MIEC surface versus the TPB. Systematically changing the geometry of the MIEC electrodes (thickness and line width) allowed for the determination of the effect of ambipolar transport within the MIEC on the activity of MIEC surfaces versus the TPB. This information is critical to rational design of functionally graded electrodes (with optimal particle size, shape, porosity and conductivity). In addition to experimental studies, representative patterned electrode samples were made available for collaborative studies with surface scientists at other institutions to provide additional techniques (such as Raman Spectroscopy) on the carefully designed and controlled cathode surfaces.
6
Baez, Baez Victor Antonio. "Metal oxide coated electrodes for oxygen reduction". Thesis, University of Southampton, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.241271.
Testo completo
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Graves, John Edward. "The electrochemistry of titanium oxide ceramic electrodes". Thesis, University of Southampton, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.305486.
Testo completo
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MacDonald, Gordon Alex. "Nanoscale Characterization of the Electrical Properties of Oxide Electrodes at the Organic Semiconductor-Oxide Electrode Interface in Organic Solar Cells". Diss., The University of Arizona, 2015. http://hdl.handle.net/10150/347338.
Testo completoAbstract (sommario):
This dissertation focuses on characterizing the nanoscale and surface averaged electrical properties of transparent conducting oxide (TCO) electrodes such as indium tin oxide (ITO) and transparent metal-oxide (MO) electron selective interlayers (ESLs), such as zinc oxide (ZnO), the ability of these materials to rapidly extract photogenerated charges from organic semiconductors (OSCs) used in organic photovoltaic (OPV) cells, and evaluating their impact on the power conversion efficiency (PCE) of OPV devices. In Chapter 1, we will introduce the fundamental principles regarding the need for low cost power generation, the benefits of OPV technologies, as well as the key principles that govern the operation of OPV devices and the key innovations that have advanced this technology. In Chapter 2 of this dissertation, we demonstrate an innovative application of conductive probe atomic force microscopy (CAFM) to map the nanoscale electrical heterogeneity at the interface between an electrode, such as ITO, and an OSC such as the p-type OSC copper phthalocyanine (CuPc).(MacDonald et al. (2012) ACS Nano, 6, p. 9623) In this work we collected arrays of J-V curves, using a CAFM probe as the top contact of CuPc/ITO systems, to map the local J-V responses. By comparing J-V responses to known models for charge transport, we were able to determine if the local rate-limiting step for charge transport is through the OSC (ohmic) or the CuPc/ITO interface (nonohmic). These results strongly correlate with device PCE, as demonstrated through the controlled addition of insulating alkylphosphonic acid self-assembled monolayers (SAMs) at the ITO/CuPc interface. Subsequent chapters focus on the electrical property characterization of RF-magnetron sputtered ZnO (sp-ZnO) ESL films on ITO substrates. We have shown that the energetic alignment of ESLs and the organic semiconducting (OSC) active materials plays a critical role in determining the PCE of OPV devices and the appearance of, or lack thereof, UV light soaking sensitivity. For ZnO and fullerene interfaces, we have shown that either minimizing the oxygen partial pressure during ZnO deposition or exposure of ZnO to UV light minimizes the energetic offset at this interface and maximizes device PCE. We have used a combination of device testing, device modeling, and impedance spectroscopy to fully characterize the effects that energetic alignment has on the charge carrier transport and charge carrier distribution within the OPV device. This work can be found in Chapter 3 of this dissertation and is in preparation for publication. We have also shown that the local properties of sp-ZnO films varies as a function of the underlying ITO crystal face. We show that the local ITO crystal face determines the local nucleation and growth of the sp-ZnO films. We demonstrate that this effects the morphology, the chemical resistance to etching as well as the surface electrical properties of the sp-ZnO films. This is likely due to differences in the surface mobility of sputtered Zn and O atoms on these crystal faces during film nucleation. This affects the nanoscale distribution of electrical and chemical properties. As a result we demonstrate that the PCE, and UV sensitivity of the J-V response of OPVs using sp-ZnO ESLs are strongly impacted by the distribution of ITO crystal faces at the surface of the substrate. This work can be found in Chapter 4 of this dissertation and is in preparation for publication. These studies have contributed to a detailed understanding of the role that electrical heterogeneity, insulating barriers and energetic alignment at the MO/OSC interface play in OPV PCE.
9
Liu, Yujing. "Nanostructured transparent conducting oxide electrodes through nanoparticle assembly". Diss., lmu, 2012. http://nbn-resolving.de/urn:nbn:de:bvb:19-149076.
Testo completo
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Baker, Priscilla G. L. "Sol-gel preparation, characterisation and electrochemistry of mixed metal tin oxide electrodes". Thesis, Stellenbosch : Stellenbosch University, 2004. http://hdl.handle.net/10019.1/50096.
Testo completo
11
Gavanier, Beatrice. "Stability of thin film insertion electrodes". Thesis, University of Southampton, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.324003.
Testo completo
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Olson, Carol Louise. "Charge accumulation and recombination in nanocrystalline metal oxide electrodes". Thesis, Imperial College London, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.405970.
Testo completo
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Jiang, San-Ping. "A study of teflon-bonded cobalt oxide/graphite electrodes". Thesis, City University London, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.306058.
Testo completo
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Qian, Weizhong, e 钱伟忠. "Microbial electrodes and Cu2O-based photoelectrodes for innovative electricity generation and pollutant degradation". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2011. http://hub.hku.hk/bib/B47170281.
Testo completoAbstract (sommario):
Photoelectrochemical cells (PEC) and microbial fuel cells (MFC) are two promising environmental technologies with the purposes of energy production and pollutant degradation. In this study, p-type Cu2O thin film electrodes were synthesized by electrodeposition on the ITO glass. The influences of various electrodeposition conditions, including the deposition potential, temperature, electrolyte pH, substrates and deposition duration on the morphology and the photoelectrochemical properties of the Cu2O films were investigated. The so-called p-type micro-crystal Cu2O thin film photocathodes were synthesized at -0.4 V, 70 °C and pH 10. An innovative composite Cu2O/TiO2 photoelectrode was developed by dip-coating TiO2 on the surface of the Cu2O film. The outer TiO2 layer would help reduce the electron-hole recombination and hence improve the catalyst stability. The photocatalyst was shown to be capable of photocatalytic degradation of model pollutants. Under simulated solar irradiation, methylene blue, acridine orange, and bromocresso brilliant blue G were effectively degraded in the Cu2O-based PEC. The composite Cu2O/TiO2 photoelectrode could further enhance the photodegradation of the dyes.
For the study on MFC with the saline wastewater-inoculated MFCs, an electricity output of 581 mW/m2 could be achieved at a NaCl concentration of 200 mM. Based on the characterization of the bioande using the electrochemical impedance spectroscopy (EIS) technique, the R(QR)(QR) model, instead of the conventional R(QR) model, was found to fit well with the EIS data of the carbon cloth bioanode. The results support the two-interface-based physical model for the description of the bioanode, including an interface on the flat electrode and the other for the porous biofilm matrix. The new model was employed to monitor the biofilm formation and development on the carbon clothe anode during the MFC start-up. In addition, photocatalytic MFC was developed by using the Cu2O film as the photocathode for the MFC. With the simulated solar light illumination, the PMFC open circuit voltage could be increased by 200 mV comparing to the MFC test. Moreover, the cathode material (Cu2O) is much less expensive than Pt used by common MFCs.published_or_final_version
Civil Engineering
Master
Master of Philosophy
15
Chari, Tarun. "Reduced graphene oxide based transparent electrodes for organic electronic devices". Thesis, McGill University, 2011. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=104534.
Testo completoAbstract (sommario):
This thesis explores the utility of reduced graphene oxide and hybrid reduced graphene oxide/single walled carbon nanotubes as a transparent electrode. Graphene oxide was fabricated using the modified Hummers method, transferred to arbitrary substrates by a vacuum filtration method, and reduced chemically and thermally thus creating thin, large area reduced graphene oxide films. Films were characterized electrically, optically, spectroscopically, and topographically. Raman and X-ray photoelectron spectroscopy techniques were utilized to ensure successful fabrication of reduced graphene oxide. The reduced graphene oxide electrodes exhibit sheet resistances on the order of 10 – 100 kΩ/sq with transparencies between 60 – 90 %. To ameliorate these electronic properties, single walled nanotubes were introduced during the filtration process to separate the graphene oxide nanoplatelets and prevent structural deformation during reduction. This nanotube doping yielded a two-fold decrease in sheet resistance for low nanotube to graphene oxide ratios, but increased sheet resistance for higher nanotube to graphene oxide ratios. Reduced graphene oxide electrodes and nanotube/reduced graphene oxide hybrid electrodes were used in organic light emitting diode and organic solar cell applications. Organic light emitting diodes exhibited current efficiencies of about 1 cd/A and organic solar cells exhibited power conversion efficiencies less than 1 % for both reduced graphene oxide and hybrid electrodes.Cette thèse examine l'utilité de l'oxyde de graphène réduit et de l'hybride oxyde de graphène réduit et nanotubes carbone en fonction d'une utilisation comme électrode transparente. L'oxyde de graphène a été fabriqué par la méthode de Hummers modifié puis a été transféré sur un substrat arbitraire par la méthode de filtration avec suction à vide, et a été réduit chimiquement et thermiquement pour créer des feuilles d'oxyde de graphène réduit qui sont minces et qui couvrent une grande surface. Les feuilles ont été caractérisées par des mesures électriques, optiques, spectroscopiques, et topographiques. Les spectroscopies Raman et par photoélectron induits par rayons-X ont été utilisées pour s'assurer que la fabrication de l'oxyde de graphène reduit a été obtenue. Les électrodes d'oxyde de graphène reduit montrent des résistances de feuille de 10– 100 kΩ/sq avec des transparences entre 60 – 90 %. Pour améliorer ces propriétés, des nanotube de carbone monoparois ont été introduits pendant le processus de filtration pour séparer les nanoplatelets d'oxyde de graphène et pour éviter la déformation structurelle pendant la processus de réduction. Ce dopage de nanotubes a diminué la résistance de feuille par un facteur deux pour des proportion faibles de nanotubes avec l'oxyde de graphène, mais a augmenté la resistance pour les hautes proportions. Les électrodes d'oxyde de graphène reduit et les électrodes hybrides nanotubes/oxyde de graphène reduit ont été utilisées dans des dispositifs optoélectroniques organiques; spécialement des diodes électroluminescentes et des cellules solaires. Les diodes électroluminescentes organiques ont des rendements de courant inferieurs à 1 cd/A et les cellules solaire ont des rendements de puissance inferieurs à 1 % pour les deux types d'életrodes: oxyde de graphène réduit et hybrides.
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Cooper, Samuel J. "Quantifying the transport properties of solid oxide fuel cell electrodes". Thesis, Imperial College London, 2015. http://hdl.handle.net/10044/1/31600.
Testo completoAbstract (sommario):
The performance of Solid Oxide Fuel Cell (SOFC) electrodes is determined both by their porous microstructure and the intrinsic properties of their component materials. This thesis details the development of two characterisation tools for analysis of mass and charge transport processes in SOFC electrode materials. Firstly, a new approach to isotopic exchange is described, which allows the oxygen self-diffusion (D*) and effective surface exchange (k*) to be measured in ambient atmospheres. This is significant as many similar studies in the literature are limited to investigations in pure, dry oxygen, or other proxy environments, which are not representative of realistic SOFC operating conditions. A finite difference simulation was created to generate profiles that were used to extract material parameters from this 'back-exchange' data. The technique was then validated by comparison of the results from two experiments in pure, dry oxygen (both single step and back-exchange), which demonstrated good agreement with values of D* and k* in the literature, for the common SOFC cathode material La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ (LSCF6428). A third experiment found the surface exchange coefficient to increase by a factor of 5 when exchanged under ambient conditions compared with pure, dry oxygen. Secondly, following an introduction to the tortuosity factor, X-ray tomography was used to 3D image micro-tubular (MT) samples ( c. 1 mm diameter) at three key length-scales. A zirconia based MT-Solid Oxide Electrolyser Cell (SOEC) was imaged at the whole cell level, both before and after 300 hours operation at 750°C . Current collector contact was found to be poor even before operation, but afterwards the paste was seen to agglomerate into metallic silver and no longer span the gap to the current collector wire, which further degraded contact. A ceria based MT-SOFC with a hierarchical microstructure was then imaged at both the micro- and nanoscale. The geometry data was used to determine that the tortuosity factor of this radial system was significantly higher when measured at either length-scale in isolation, than when considered together in a multi length-scale model.
17
Golden, Stephen John. "Behaviour of thin film oxide based electrodes in electrochromic applications". Thesis, Imperial College London, 1988. http://hdl.handle.net/10044/1/47080.
Testo completo
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Chen, Youjiang. "Fundamental Aspects of Electrocatalysis at Metal and Metal Oxide Electrodes". Case Western Reserve University School of Graduate Studies / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=case1284390270.
Testo completo
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Chang, Ci'En Sharon. "Graphene modified indium tin oxide electrodes for organic solar cells". Thesis, Imperial College London, 2014. http://hdl.handle.net/10044/1/27645.
Testo completoAbstract (sommario):
In this thesis, we explore the use of graphene incorporated onto indium tin oxide (G/ITO) as a structural template to modify the orientation of copper phthalocyanine (CuPc) molecules for organic photovoltaic (OPV) device applications. We also investigate the effectiveness of 2,3,5,65 tetrafluoro57,7,8,85tetracyanoquinodimethane (F45TCNQ) as a work function modifier for G/ITO without compromising the templating properties of graphene. Photoemission spectroscopy (PES) is employed to assess the electronic properties at the anode5CuPc interface, while X5ray diffraction (XRD) and near5edge X5ray absorption fine structure (NEXAFS) are used to determine the molecular orientation of CuPc. OPV devices are fabricated to attempt to correlate the observations at the microscopic level with the macroscopic device performance. First, we investigate the electronic properties of CuPc deposited on G/ITO and ITO using PES. While the interaction between CuPc molecules and ITO and G/ITO is similar, the hole injection barrier (HIB) is ~0.9 eV for CuPc/G/ITO as compared to 0.5 eV for CuPc/ITO. Therefore, further modification of G/ITO to reduce the HIB is required. The XRD spectrum of CuPc molecules deposited onto graphene grown on copper foil (G/Cu) verifies that graphene is an effective structural template, causing CuPc molecules to 'lie' on the substrate. NEXAFS data shows that the orientation of CuPc molecules changes from 'standing' on ITO to 'tilted' on G/ITO. Next, the effectiveness of F45TCNQ deposited on ITO and G/ITO as a work function modifier is assessed. A thin layer of F45TCNQ is able to increase the substrate work function to ~5 eV, which is close to the ionization potential of CuPc molecules. This suggests that barrierless extraction of holes from CuPc into F45TCNQ modified ITO or G/ITO may be possible. F45TCNQ molecules are found to be predominantly tilted on G/ITO, suggesting that the templating property of graphene may be propagated through F45TCNQ molecules. CuPc molecules deposited onto F45 TCNQ/G/ITO attain a 'lying' configuration, confirming that the templating property of graphene is preserved despite the inclusion of a layer of F45TCNQ. The HIB is dramatically reduced to ~0.2 eV for CuPc/F45TCNQ/G/ITO, and ~0.1 eV for CuPc/F45TCNQ/ITO. Optical absorption of templated CuPc molecules over the visible range is enhanced by over 40% as compared to the non5templated molecules. Therefore, the structure of F45TCNQ/G/ITO appears to be a potential anode design to improve OPV device performance. Our test cells however do not show an improvement in OPV parameters due to the poor quality of transferred graphene, and the high series resistance in our unoptimized OPV device. Finally, the diffusion of F45TCNQ through a CuPc film is studied using time5of5flight secondary ion mass spectrometry (TOF5SIMS). The F5 depth profiles establish that a higher quantity of F45 TCNQ molecules diffuse into CuPc on the G/ITO sample. This is attributed to the weaker interfacial adhesion between F45TCNQ and graphene, and the crystallinity of the templated CuPc film. The quantity of diffused F45TCNQ in the G/ITO sample is only about 0.2 mol%. At this dopant concentration, the conductivity of the film should increase; thus doping of the whole organic film may be favourable for OPV devices.
20
Stefan, Elena. "Development of spinel-based electrode supports for solid oxide fuel cells". Thesis, University of St Andrews, 2013. http://hdl.handle.net/10023/3605.
Testo completoAbstract (sommario):
The high temperature oxidation of ferritic stainless steel interconnects results in chromium poisoning of the solid oxide fuel cell (SOFC) electrodes, which is a limiting factor for their utilisation as SOFC interconnects. Chromium-rich spinel materials were studied as electrode supports that would be situated at the interface between interconnect and electrode, in order to reduce the effect of chromium poisoning of the electrodes. The main goal of this thesis was to find chromium-rich spinel materials with good electrical conductivity (σ ≥ 0.1 S∙cm⁻¹) in air and reducing atmosphere, chemically and mechanically stable in SOFC testing conditions. The structure and properties of newly formulated chromium-rich spinels, such as Mn₁₊ₓCr₂₋ₓO₄ (x = 0, 0.5), MnFeₓCr₂₋ₓO₄ (x = 0.1, 1), MgMnCrO₄, MnLiₓCr₂₋ₓO₄ (x = 0.1) and MgMₓCr₂₋ₓO₄, (M = Li, Mg, Ti, Fe, Cu, Ga) were studied aiming at their application as electrode support material for solid oxide fuel cells. Cation distributions were determined by Rietveld refinement from X-ray diffraction (XRD), within the limits of XRD precision and correlated with electrical properties determined experimentally. The chemical stability in reducing conditions was studied and the reduction effects upon materials were evaluated by XRD phase analysis and microstructure analysis. It was found that MnMₓCr₂₋ₓO₄ materials have a limited stability to reduction, only MnCr₂O₄ proved to have good stability when reduced, with negative influence for its p-type semiconductor conductivity. Even though MnFeCrO₄ had limited stability to reduction, in reducing conditions the conductivity changed from p-type to n-type semiconductor. A similar behaviour to reduction was observed for MgFeCrO₄. Also the mechanical and chemical compatibility of some spinels with YSZ was studied in terms of thermal expansion coefficient (TEC/K⁻¹), sintering step and possible chemical reactions. Lithium titanate spinels, starting with LiCrTiO₄, were investigated in terms of structure, properties and spinel - ramsdellite phase transition temperature also with the purpose of new material development. For these materials positive results were obtained in conductivity and chemical stability in reducing conditions. The performance of MnFeCrO₄ and MgFeCrO₄ as electrode support materials was investigated when used alone or impregnated with (La₀.₇₅Sr₀.₂₅)₀.₉₇Cr₀.₅Mn₀.₅O₃, La₀.₈Sr₀.₂FeO₃, Ce₀.₉Gd₀.₁O₂, CeO₂ or Pd. Composite anodes for SOFC were prepared by aqueous infiltration of nitrate salts into porous MnFeCrO₄ and MgFeCrO₄ scaffolds and studied by electrochemical impedance spectroscopy (EIS) in symmetrical cell configuration. The performance of the composite anodes was evaluated in humidified 5%H₂/Ar in order to understand their stability and performance at 850 °C or lower temperature with respect to the porous substrates. It was found that all the impregnated phases adhere very well to the spinel and considerably enhance performance and stability to a level required for SOFC applications. An interesting next step in this work would be to apply such spinel materials on steel interconnects, integrate them into testing SOFC devices and evaluate their effect upon chromium poisoning of the electrodes.
21
Fehse, Marcus. "Nanostructured titanium oxide as active insertion material for negative electrodes in Li-ion batteries". Phd thesis, Université Montpellier II - Sciences et Techniques du Languedoc, 2013. http://tel.archives-ouvertes.fr/tel-01018975.
Testo completoAbstract (sommario):
Titania based electrode materials are promising candidates to replace widely used graphite as negative electrode material in lithium ion batteries (LIB), due to their increased safety, volumetric capacity, and high rate performance.In this thesis different low-cost synthesis approaches are evaluated to prepare nanostructured TiO2 with various phase composition and morphology. The influence of these parameters on its ability to reversibly insert lithium are studied in electrochemical measurements. In this regard we also investigated the effect of aliovalent doping and porous structures on the insertion properties of two main polymorphs of TiO2, Anatase and TiO2(b), revealing encouraging results in overcoming the low charge transfer, which is the main drawback of titanium oxide based materials.In order to understand the mechanism of lithium storage process of the two synthesized TiO2 phases, diffraction and spectroscopic characterization methods were carried out under operando conditions. We show that, regardless of their chemical similarity, both phases reveal very different lithium insertion processes, leading to distinct electrochemical cycling properties.Another field of interest is the adaptation of electrode components to the nanostructured TiO2 active insertion material. The choice of binder, carbon additive, and electrolyte components can have significant impacts on the performance. Especially the origin and prevention of parasitic side reactions were in the focus of our work, as these pose an under estimated hindrance in the application of titania based electrode materials in LIB.
22
Wang, Yunhai. "Electrochemical generation of ozone on antimony and nickel doped tin oxide". Click to view the E-thesis via HKUTO, 2006. http://sunzi.lib.hku.hk/hkuto/record/B37749882.
Testo completo
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Wang, Yunhai, e 王云海. "Electrochemical generation of ozone on antimony and nickel doped tin oxide". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2006. http://hub.hku.hk/bib/B37749882.
Testo completo
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Elhag, Sami. "Chemically Modified Metal Oxide Nanostructures Electrodes for Sensing and Energy Conversion". Doctoral thesis, Linköpings universitet, Institutionen för teknik och naturvetenskap, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-134275.
Testo completoAbstract (sommario):
The goal of this thesis is the development of scalable, low cost synthesis of metal oxide nanostructures based electrodes and to correlate the chemical modifications with their energy conversion performance. Methods in energy conversion in this thesis have focused on two aspects; a potentiometric chemical sensor was used to determine the analytical concentration of some components of the analyte solution such as dopamine, glucose and glutamate molecules. The second aspect is to fabricate a photo-electrochemical (PEC) cell. The biocompatibility, excellent electro-catalytic activities and fast electron transfer kinetics accompanied with a high surface area to volume ratio; are properties of some metal oxide nanostructures that of a potential for their use in energy conversion. Furthermore, metal oxide nanostructures based electrode can effectively be improved by the physical or a chemical modification of electrode surface. Among these metal oxide nanostructures are cobalt oxide (Co3O4), zinc oxide (ZnO), and bismuth-zincvanadate (BiZn2VO6) have all been studied in this thesis. Metal oxide nanostructures based electrodes are fabricated on gold-coated glass substrate by low temperature (< 100 0C) wet chemicalapproach. X-ray diffraction, x-ray photoelectron spectroscopy and scanning electron microscopy were used to characterize the electrodes while ultraviolet-visible absorption and photoluminescence were used to investigate the optical properties of the nanostructures. The resultant modified electrodes were tested for their performance as chemical sensors and for their efficiency in PEC activities. Efficient chemically modified electrodes were demonstrated through doping with organic additives like anionic, nonionic or cationic surfactants. The organic additives are showing a crucial role in the growth process of metal oxide nanocrystals and hence can beused to control the morphology. These organic additives act also as impurities that would significantly change the conductivity of the electrodes. However, no organic compounds dependence was observed to modify the crystallographic structure. The findings in this thesis indicate the importance of the use of controlled nanostructures morphology for developing efficient functional materials.
25
Ho, Mui Yen. "Transition metal oxide and phosphate-based/carbon composites as supercapacitor electrodes". Thesis, University of Nottingham, 2017. http://eprints.nottingham.ac.uk/40274/.
Testo completoAbstract (sommario):
Electrochemical capacitors, also known as supercapacitors, have attracted considerable attention over the past decades owing to their higher power density, long cycle life and moderate energy density compared. A high-performance supercapacitor integrates innovative electrode materials with desirable properties coupled with low cost and sustainability. In this thesis, a series of low cost transition metal oxide-activated carbon composite materials, lithium iron phosphate-activated carbon composite materials as well as metal oxide-graphene composite materials were prepared, characterized and evaluated as supercapacitor electrodes. Iron oxide (Fe3O4) – activated carbon (AC), zinc oxide (ZnO) – AC and titanium oxide (TiO2) – AC nanocomposites were prepared by using simple mechanical mixing method. The charge storage capabilities of these metal oxide-based composites with different loading ratios were evaluated in both mild aqueous 1 M Na2SO3 and 1 M Na2SO4 electrolytes. The incorporation of small amount of metal oxides onto AC could effectively enhance the capacitive performance of pure AC electrodes. It is believed that the presence of metal oxide nanoparticles can provide favourable surface adsorption sites for sulphite anions (SO32-). Nevertheless, bulk increasing of the metal oxide content is found to distort the capacitive performance and deteriorate the specific surface area of the electrode, mainly due to the aggregation of the metal oxide particles within the composite. On the other hand, composite materials consisting of lithium iron phosphate (LiFePO4) and AC exhibit high specific capacitance of 112.41 F/g in 1 M Na2SO3 with the incorporation of 40 wt % of LiFePO4. The synergistic effect between the faradaic battery type materials and the EDLC-based materials is greatly demonstrated. The intercalation and extraction of Li+ ions in LiFePO4 lattices are responsible for the reversible Faradaic reaction on top of the adsorption and de-adsorption of SO32- anions from Na2SO3 electrolyte. In the preparation of SnO2-graphene and MoO3-graphene nanocomposites, low-temperature solvothermal method using mild reducing agents was adopted. The preparation steps do not require high pressure or extreme synthetic condition and do not involve the usage of hazardous reactants. The electrochemical results of SnO2-graphene composite electrodes demonstrate that the composite electrodes possess a high specific energy (14 Wh/kg) with 93 % capacitive retention after 1500 cycles while MoO3-graphene composite electrodes yield an enhanced specific energy (16.3 Wh/kg) which is 28 % higher than that of pure MoO3 (11.8 Wh/kg). A maximum specific capacitance of 99 F/g was obtained from the optimized SnO2-graphene composite electrodes while a high average specific capacitance of 148 F/g was achieved for MoO3-graphene composites at a scan rate of 5mV/s in neural 1 M Na2SO3 electrolyte. The incorporation of graphene onto both SnO2 and MoO3 respectively, can promote the electrochemical utilization of metal oxides as well as the electrical conductivity of the electrodes. The graphene sheet serves as a good support in promoting effective charge transfer for redox reactions of MoO3. Additionally, deposition of metal oxides on graphene sheets prevents the graphene sheets from agglomeration, resulting in facile ion transportation pathway for electrolyte to access the surface of active material.
26
Hunter, Katherine. "Fundamental studies of electrochemical oxide formation on platinum single crystal electrodes". Thesis, Cardiff University, 2016. http://orca.cf.ac.uk/100871/.
Testo completoAbstract (sommario):
Platinum single crystal electrodes were used to investigate electrochemical oxides and related surface species and their impact upon important catalytic reactions such as the oxygen reduction reaction (ORR). Notions of perchlorate anions being “non-specifically adsorbed” were re-evaluated and challenged. For example, the voltammetry of Pt single crystal electrodes as a function of perchloric acid concentration (0.05–2.00 M) was studied in order to test the assertion by Watanabe et al. that perchlorate anions specifically adsorb on polycrystalline platinum. Specific adsorption of perchlorate anions was found in varying degrees for Pt(hkl) surfaces. By flame-annealing and cooling a series of Pt n(110)x(111) and Pt n(110)x(100) single crystal electrodes in a CO ambient, new insights into the nature of the electrosorption processes associated with Pt{110} voltammetry in aqueous acidic media were elucidated. For Pt n(110)x(111) electrodes, a systematic change in the intensities of voltammetric peaks indicated a lack of surface reconstruction (in contrast to hydrogen cooled analogues). Pt n(110)x(100) stepped electrodes displayed a marked tendency towards surface reconstruction irrespective of cooling environment. Pt(110) terrace sites were found to afford a specific affinity for sulphonate groups contained within a Nafion adlayer. Pt n(100)x(110) surfaces showed rapid quenching of the Nafion ‘spike’ as a function of increasing step density. Reactivity measurements involving oxygen reduction and hydrogen peroxide oxidation/reduction largely revealed the importance of adsorbed oxide/OH in regulating activity. Kinetic studies suggested that for Pt(100) terraces, oxide formation was also accompanied by rapid surface reconstruction. Fast potential cycling of all electrode surfaces confirmed the likelihood of structural changes occurring in real fuel cells. It is deduced that roughened catalyst particles should actually exhibit an enhanced ORR activity, even in the presence of Nafion.
27
Wang, Bin, e 王滨. "Properties of nickel and antimony doped tin oxide electrode material in relation to electrochemical generation of ozone". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2013. http://hub.hku.hk/bib/B50434305.
Testo completoAbstract (sommario):
In this study, the properties of nickel and antimony doped tin oxide (NATO) electrode materials were investigated in relation to the electrochemical generation of ozone. The performance of NATO materials was correlated to ·OH radical generation and oxygen adsorption properties.
Long-time ozone generation results suggested that surface property changes, including surface morphology, chemical composition and electro-catalyst thickness, could lead to ozone production rate decreased from 137 to 0 mg·h-1 and the current efficiency declined from 18% to 0. The loss of Ni in the electrode was suggested for the decrease in ozone generation. Moreover, material characterization results indicated the presence of NiOOH and multiple oxidation states of Sb (+3 and +5), which were proposed as the critical sites for the electrochemical generation of ozone.
In addition, NATO nanocrystals of 3.5 ~ 7.5 nm in size prepared by the hydrothermal method were used as an alternative route to fabricate electrodes. The highest current efficiency of 41% was achieved on NATO material of 6% Sb in the precursor, which led to the lowest resistivity of 2.38 ± 0.03 Ω·cm in the product NATO material. This further demonstrated the applicability of NATO materials used as electro-catalysts for the electrochemical generation of ozone.
Hydroxyl free radicals (·OH) can be regarded as one of the most important intermediates for ozone generation. The presence of ·OH radicals was quantified by fluorescence spectroscopy with terephthalic acid as probes. Quantitative analysis results showed that Ni dopant could significantly enhance ·OH generation, while over-doping of Sb and Ni can decrease the generation of ·OH radicals.
An oxygen chemisorption study on NATO materials showed that more active sites available for oxygen chemisorption lead to higher catalytic activity for ozone generation. The highest oxygen chemisorption capacity of 49.76 μmol·g-1 was achieved on NATO-5 (Sn:Sb:Ni=1000:16:2), which showed the highest current efficiency of 43%. In addition, temperature programmed oxygen adsorption and desorption showed different patterns on different NATO materials. This suggested that oxygen adsorption on NATO materials has a correlation to the electrochemical generation of ozone.
In addition, oxygen adsorption was further investigated with near ambient oxygen adsorption. Oxygen adsorption isotherm results indicated that both physisorption and chemisorption can occur on the surface of SnO2 based material (NATO-5) with or without hydrogen pretreatment. When NATO-5 was treated with hydrogen, adsorption was mainly in the form of chemisorption. However, it was mainly in the form of physisorption without hydrogen pretreatment. By comparing NATO-6 (Sn:Sb:Ni=1000:16:0) with NATO-7 (Sn:Sb:Ni=1000:0:2), it was found that Sb was more important in the oxygen adsorption ability of NATO materials compared to Ni doping. Based on the findings in this study, two active sites (Sb and Ni sites) were proposed for ·OH generation and oxygen adsorption in order to explain the mechanism of ozone generation on NATO materials. Also, electrochemical generation of ozone was correlated with oxygen adsorption and ·OH generation.published_or_final_version
Chemistry
Doctoral
Doctor of Philosophy
28
Zhang, Shenjia. "Quantitative characterization and modeling of the microstructure of solid oxide fuel cell composite electrodes". Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/37174.
Testo completoAbstract (sommario):
Three-phase porous composites containing electrolyte (ionic conductor), electronic conductor, and porosity phases are frequently used for solid oxide fuel cell (SOFC) electrodes. Performance of such electrodes is microstructure sensitive. Topological connectivity of the microstructural phases and total length of triple phase boundaries are the key microstructural parameters that affect the electrode performance. These microstructural attributes in turn depend on numerous process parameters including relative proportion, mean sizes, size distributions, and morphologies of the electrolyte and electronic conductor particles in the powder mix used for fabrication of the composites. Therefore, improvement of the performance of SOFC composite electrodes via microstructural engineering is a complex multivariate problem that requires considerable input from microstructure modeling and simulations. This dissertation presents a new approach for geometric modeling and simulation of three-dimensional (3D) microstructure of three-phase porous composites for SOFC electrodes and provides electrode performance optimization guidelines based on the parametric studies on the effects of processing parameters on the total length and topological connectivity of the triple phase boundaries. The model yields an equation for total triple phase boundary length per unit volume (LTPB) that explicitly captures the dependence of LTPB on relative proportion of electrolyte and electronic conductor phases; volume fraction of porosity; and mean size, coefficient of variation, and skewness of electrolyte and electronic conductor particle populations in the initial powder mix. The equation is applicable to electrolyte and electronic conductor particles of any convex shapes and size distributions. The model is validated using experimental measurements performed in this research as well as the measurements performed by other researchers. Computer simulations of 3D composite electrode microstructures have been performed to further validate the microstructure model and to study topological connectivity of the triple phase boundaries in 3D microstructural space. A detailed parametric analysis reveals that (1) non-equiaxed plate-like, flake-like, and needle-like electrolyte and electronic conductor particle shapes can yield substantially higher LTPB; (2) mono-sized electrolyte and electronic conductor powders lead to higher LTPB as compared to the powders having size distributions with large coefficients of variation; (3) LTPB is inversely proportional to the mean sizes of electrolyte and electronic conductor particles; (4) a high value of LTPB is obtained at the lowest porosity volume fraction that permits sufficient connectivity of the pores for gas permeability; and (5) LTPB is not sensitive to the relative proportion of electrolyte and electronic conductor phases in the composition regime of interest in composite electrode applications.
29
Marikkar, Fathima Saneeha. "Molecular Design of Electrode Surfaces and Interfaces: For Optimized Charge Transfer at Transparent Conducting Oxide Electrodes and Spectroelectrochemical Sensing". Diss., The University of Arizona, 2006. http://hdl.handle.net/10150/193952.
Testo completoAbstract (sommario):
This dissertation has focused on i) optimizing charge transfer rates at indium-tinoxide (ITO) electrodes, and ii) characterization of the supramolecular structure and properties of ultra thin surface modifier films on modified electrodes for various device applications. Commercial ITO surfaces were modified using conducting polymer thin film architectures with and without various chemical activation procedures. Ferrocene derivatives were used as redox probes, which showed dramatic changes in electron transfer rate as the SA-PANI/PAA layers were added to the ITO surface. Highest rates of electron transfer were observed for DMFc, whose oxidation potential coincides with the potential region where these SA-PANI/PAA films reach their optimal electroactivity. Apparent heterogeneous electron transfer rate constants, kS, measured voltammetrically, were ca.10 x higher for SA-PANI/PAA films on ITO, versus clean ITO substrates. These films also showed linear potentiometric responses with retention of the ITO transparency with the capability to create smoothest films using an aqueous deposition protocol, which proved important in other applications. ITO electrodes were also modified via chemisorption of carboxy functionalized EDOTCA and electropolymerization of PEDOTCA/PEDOT copolymers, when properly optimized for thickness and structure, enhance voltammetrically determined electron transfer rates (kS) to solution probe molecules, such as dimethylferrocene (DMFc). Values of kS ≥ 0.4 cm•sec⁻¹, were determined, approaching rates seen on clean gold surfaces. ITO activation combined with formation of these co-polymer films has the effect of enhancing the electroactive fraction of electrode surface, versus a non-activated, unmodified ITO electrode, which acts as a “blocked” electrode. The electroactivity and spectroelectrochemistry of these films helped to resolve the electron transfer rate mechanism and enabled the construction of models in combination with AFM, XPS, UPS and RAIRS studies. The surface topography, structure, composition, work function and contact angle, also revealed other desirable properties for molecular electronic devices. The carboxylic functionality of the EDOTCA molecule adds more desirable properties compared to normal PEDOT films, such as favoring the deposition of smooth films, increasing the optical contrast, participating in hydrogen-bonding, chemisorption to oxide surface, self-doping and providing a linker for incorporation of different functional groups, new molecules, or nanoparticles. Periodic sub-micron electrode arrays can be created using micro-contact printing and electropolymerization. The sinusoidal modulation of the refractive index of such confined conducting polymer nanostructures or nanoparticle stripes allows efficient visible light diffraction. The modulation of the diffraction efficiency at PANI and PEDOT gratings in the presence of an analytical stimulus such as pH or potential demonstrate the sensing capability at these surfaces. The template stripped gold surfaces that are being developed in our lab demonstrate several advantages over commercially available evaporated gold films especially for nanoscale surface modification.
30
Kim, Yong Hyun. "Alternative Electrodes for Organic Optoelectronic Devices". Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-113279.
Testo completoAbstract (sommario):
This work demonstrates an approach to develop low-cost, semi-transparent, long-term stable, and efficient organic photovoltaic (OPV) cells and organic light-emitting diodes (OLEDs) using various alternative electrodes such as conductive polymers, doped ZnO, and carbon nanotubes. Such electrodes are regarded as good candidates to replace the conventional indium tin oxide (ITO) electrode, which is expensive, brittle, and limiting the manufacturing of low-cost, flexible organic devices. First, we report long-term stable, efficient ITO-free OPV cells and transparent OLEDs based on poly(3,4-ethylene-dioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) electrodes by using a solvent post-treatment or a structure optimization. In addition, a high performance internal light out-coupling system for white OLEDs based on PEDOT:PSS-coated metal oxide nanostructures is developed. Next, we demonstrate highly efficient ITO-free OPV cells and OLEDs with optimized ZnO electrodes doped with alternative non-metallic elements. The organic devices based on the optimized ZnO electrodes show significantly improved efficiencies compared to devices with standard ITO. Finally, we report semi-transparent OPV cells with free-standing carbon nanotube sheets as transparent top electrodes. The resulting OPV cells exhibit very low leakage currents with good long-term stability. In addition, the combination of various kinds of bottom and top electrodes for semi-transparent and ITO-free OPV cells is investigated. These results demonstrate that alternative electrodes-based OPV cells and OLEDs have a promising future for practical applications in efficient, low-cost, flexible and semi-transparent device manufacturingDie vorliegende Arbeit demonstriert einen Ansatz zur Verwirklichung von kostengünstigen, semi-transparenten, langzeitstabilen und effizienten Organischen Photovoltaik Zellen (OPV) und Organischen Leuchtdioden (OLEDs) durch die Nutzung innovativer Elektrodensysteme. Dazu werden leitfähige Polymere, dotiertes ZnO und Kohlenstoff-Nanoröhrchen eingesetzt. Diese alternativen Elektrodensysteme sind vielversprechende Kandidaten, um das konventionell genutzte Indium-Zinn-Oxid (ITO), welches aufgrund seines hohen Preises und spröden Materialverhaltens einen stark begrenz Faktor bei der Herstellung von kostengünstigen, flexiblen, organischen Bauelementen darstellt, zu ersetzten. Zunächst werden langzeitstabile, effiziente, ITO-freie Solarzellen und transparente OLEDs auf der Basis von Poly(3,4-ethylene-dioxythiophene):Poly(styrenesulfonate) (PEDOT:PSS) Elektroden beschrieben, welche mit Hilfe einer Lösungsmittel-Nachprozessierung und einer Optimierung der Bauelementstruktur hergestellt wurden. Zusätzlich wurde ein leistungsfähiges, internes Lichtauskopplungs-System für weiße OLEDs, basierend auf PEDOT:PSS-beschichteten Metalloxid-Nanostrukturen, entwickelt. Weiterhin werden hoch effiziente, ITO-freie OPV Zellen und OLEDs vorgestellt, bei denen mit verschiedenen nicht-metallischen Elementen dotierte ZnO Elektroden zur Anwendung kamen. Die optimierten ZnO Elektroden bieten im Vergleich zu unserem Laborstandard ITO eine signifikant verbesserte Effizienz. Abschließend werden semi-transparente OPV Zellen mit freistehenden Kohlenstoff-Nanoröhrchen als transparente Top-Elektrode vorgestellt. Die daraus resultierenden Zellen zeigen sehr niedrige Leckströme und eine zufriedenstellende Stabilität. In diesem Zusammenhang wurde auch verschiedene Kombinationen von Elektrodenmaterialen als Top- und Bottom-Elektrode für semi-transparente, ITO-freie OPV Zellen untersucht. Zusammengefasst bestätigen die Resultate, dass OPV und OLEDs basierend auf alternativen Elektroden vielversprechende Eigenschaften für die praktische Anwendung in der Herstellung von effizienten, kostengünstigen, flexiblen und semi-transparenten Bauelement besitzen
31
Morselli, Serena. "Thermally reduced Graphene Oxide: a well promising way to transparent flexible electrodes". Master's thesis, Alma Mater Studiorum - Università di Bologna, 2015. http://amslaurea.unibo.it/9324/.
Testo completoAbstract (sommario):
L'elaborato tratta dell'ottimizzazione del processo di riduzione termica dell'ossido di grafene in termini di conduttività e trasmittanza ottica. Definiti gli standard di deposizione tramite spin-coating e riduzione termica, i film prodotti vengono caratterizzati tramite XPS, AFM, UPS, TGA, ne vengono testate la conducibilità, con e senza effetto di gate, e la trasmittanza ottica, ne si misura l'elasticità tramite spettroscopia di forza, tutto al fine di comprendere l'evoluzione del processo termico di riduzione e di individuare i parametri migliori al fine di progredire verso la produzione di elettrodi flessibili e trasparenti a base di grafen ossido ridotto.
32
Vandana, Singh. "Development of High Performance Electrodes for High Temperature Solid Oxide Electrolysis Cells". 京都大学 (Kyoto University), 2016. http://hdl.handle.net/2433/215556.
Testo completo
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Müller, Vesna. "Mesoporous transparent conducting films of antimony doped tin oxide as nanostructured electrodes". Diss., Ludwig-Maximilians-Universität München, 2013. http://nbn-resolving.de/urn:nbn:de:bvb:19-158995.
Testo completo
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Wang, L. "Electrochemical and spectroscopic studies of copper oxide modified electrodes for CO2 reduction". Thesis, University College London (University of London), 2016. http://discovery.ucl.ac.uk/1532101/.
Testo completoAbstract (sommario):
The global carbon balance has changed substantially with major increases in atmospheric CO2 levels by anthropogenic emission, causing growing concerns about global warming and extreme climate issues. This is one of the crucial global challenges in the 21st century. Electrochemical reduction of CO2 is a promising technology to convert CO2 to chemicals and fuels. There are various candidate materials for CO2 reduction, but only copper and copper oxide catalysts are effective for the reduction of CO2 to hydrocarbons and organic substances. This research aims to explore CuO nanoparticle materials for CO2 reduction by electrochemical and spectroscopic studies. Different techniques are used in this research. The electrochemical behaviour of CuO was monitored by cyclic voltammetry. The oxidation states and proportion of different components of copper were investigated by ex situ XPS and Raman spectroscopy. A novel in situ spectroelectrochemical experiment was designed using electrocatalysis and FTIR technique to study adsorption of solution species onto the CuO surface. Two types of buffer solutions with five pH values, from pH 4 to pH 11, were introduced to investigate the appropriate pH conditions for the CO2 reduction processes. Based on the present experimental data and further analysis, it reveals the electrochemical behaviour of CuO catalyst, including the reduction reaction equations, proportion of different oxidation states and adsorption species at different applied potentials. The pH 4 solutions shows the most suppression of current magnitude in cyclic voltammograms in CO2 saturated conditions. CuO was reduced to Cu2O and Cu at cathodic potential, then oxidised to CuO in pH 4 and 7 solutions, while oxidised to Cu(OH)2 in higher pH solutions after application of one cyclic potential. The lower pH conditions show better stability of CuO catalyst after multi-cyclic sweeps. Therefore, the pH 7, 8 and 9 solutions are shown to be suitable pH conditions for CO2 reduction on CuO catalyst. The major liquid phase product of CO2 electrochemical reduction obtained in our study was formic acid. Combining our research results, a reaction pathway is proposed. Adsorbed CO2- is the first reduction step and carboxyl is an important intermediate to form formic acid. Finally, several future areas of research are proposed to improve the understanding of the CO2 reduction processes on CuO catalyst. Copper oxide materials of different oxidation states and mixed phases can be used to clarify the active sites. Gas phase products and quantitative liquid phase products can be measured to study the reduction rate and efficiency.
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Rossouw, Margaretha Hendrina. "Synthesis and characterization of lithium-manganese-oxide electrodes for lithium battery applications". Master's thesis, University of Cape Town, 1994. http://hdl.handle.net/11427/18339.
Testo completoAbstract (sommario):
As the electronics industry moves more towards portable equipment the demand for batteries, especially rechargeable batteries, is increasing. Lithium batteries have several advantages over other competitive systems. Coupled with the inexpensive and environmentally friendly manganese dioxide, Li/MnO₂ batteries are being used extensively for powering a range of devices, but particular electronic systems.
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Lomberg, Ma'ayan Marina. "Novel fabrication routes to nickel-based cermet electrodes for solid oxide cells". Thesis, Imperial College London, 2014. http://hdl.handle.net/10044/1/24866.
Testo completoAbstract (sommario):
Solid oxide cells (SOCs) are promising energy conversion devices in which the chemical energy of fuels is converted into electrical energy in an efficient manner. It is generally accepted that electrode microstructure plays an important role in determining the performance and durability of SOCs. The electrode is required to contain large amount of active reaction sites, termed triple phase boundaries (TPBs), to promote the electrochemical reaction. At the same time, effective transport pathways need to be established to and from each TPB. Therefore, the microstructure-performance relationships need to be understood in order to develop highly efficient electrodes. In this study a novel electrode, prepared by infiltration of nickel nano-particles into Gadolinium doped Ceria porous scaffold, is proposed. The research aims to understand the fundamental phenomena underpinning SOC operation for steam electrolysis/H2 oxidation in these electrodes and to establish the relationship between the microstructure of the infiltrated electrode and electrode performance. The electronic conductivity of infiltrated electrodes was tested by the van der Pauw method over the temperature range 20-700 °C. Electrochemical behaviour was assessed for fuel cell and electrolysis modes using three electrode AC and DC measurements. The microstructure was studied by SEM and FIB techniques, including 3-D imaging and quantification. Ultimately, this is to allow electrodes to be designed with desired characteristics. In addition, a novel approach for electrode preparation by Selective Laser Sintering (SLS) was evaluated by conducting a proof of concept study. This fabrication technique enables the porosity and pattern of the electrode to be controlled by regulating the parameters of the laser (laser power and laser speed). The feasibility of using this novel technique for solid oxide cells was demonstrated. A method for the fabrication of high performance 'electrodes by design' through the combination of the two techniques in which the scaffold preparation by SLS is followed by infiltration is in prospect.
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Liu, Ying. "Fabrication of Nanostructured Electrodes and Interfaces Using Combustion CVD". Diss., Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/7937.
Testo completoAbstract (sommario):
Reducing fabrication and operation costs while maintaining high performance is a major consideration for the design of a new generation of solid-state ionic devices such as fuel cells, batteries, and sensors. The objective of this research is to fabricate nanostructured materials for energy storage and conversion, particularly porous electrodes with nanostructured features for solid oxide fuel cells (SOFCs) and high surface area films for gas sensing using a combustion CVD process.
This research started with the evaluation of the most important deposition parameters: deposition temperature, deposition time, precursor concentration, and substrate. With the optimum deposition parameters, highly porous and nanostructured electrodes for low-temperature SOFCs have been then fabricated. Further, nanostructured and functionally graded La0.8Sr0.2MnO2-La0.8SrCoO3-Gd0.1Ce0.9O2 composite cathodes were fabricated on YSZ electrolyte supports. Extremely low interfacial polarization resistances (i.e. 0.43 Wcm2 at 700¡ãC) and high power densities (i.e. 481 mW/cm2 at 800¡ãC) were generated at operating temperature range of 600¡ãC-850¡ãC.
The original combustion CVD process is modified to directly employ solid ceramic powder instead of clear solution for fabrication of porous electrodes for solid oxide fuel cells. Solid particles of SOFC electrode materials suspended in an organic solvent were burned in a combustion flame, depositing a porous cathode on an anode supported electrolyte.
Combustion CVD was also employed to fabricate highly porous and nanostructured SnO2 thin film gas sensors with Pt interdigitated electrodes. The as-prepared SnO2 gas sensors were tested for ethanol vapor sensing behavior in the temperature range of 200-500¡ãC and showed excellent sensitivity, selectivity, and speed of response.
Moreover, several novel nanostructures were synthesized using a combustion CVD process, including SnO2 nanotubes with square-shaped or rectangular cross sections, well-aligned ZnO nanorods, and two-dimensional ZnO flakes. Solid-state gas sensors based on single piece of these nanostructures demonstrated superior gas sensing performances. These size-tunable nanostructures could be the building blocks of or a template for fabrication of functional devices.
In summary, this research has developed new ways for fabrication of high-performance solid-state ionic devices and has helped generating fundamental understanding of the correlation between processing conditions, microstructure, and properties of the synthesized structures.
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Richard, Flesner Reuben. "Modeling of Solid Oxide Fuel Cell functionally graded electrodes and a feasibility study of fabrication techniques for functionally graded electrodes". [Ames, Iowa : Iowa State University], 2009. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:1473204.
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Chen, Liang. "Electrochemical studies and modifications of CVD diamond electrodes". Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:637568ae-5d1a-4a6e-b6c4-764bf461cd80.
Testo completoAbstract (sommario):
CVD diamond possesses certain attractive electrochemical properties inter alia low background current, broad potential window, chemical inertness and resistance to electrocorrosion and fouling. As a consequence its use in various areas of electrochemistry, such as electrochemical sensing, wastewater treatment and electrocatalysis is being explored. Unfortunately, alongside these attractive features, bare CVD diamond electrodes, in common with all other electrode materials, cannot be effectively applied in all electrochemical systems of interest, since for example it may not display useful electrochemical activity for the redox process of interest. In these circumstances it may be possible to modify the electrode by addition of other chemical species to the surface, to introduce the relevant activity. One of the main aims of this thesis was therefore to investigate the properties of certain chemical modifications to the diamond electrode surface. A second aim was also to explore for the first time the use of a practically useful form of single crystal diamond, so-called heteroepitaxial diamond, in electrochemistry. The diamond electrodes used were boron-doped material grown by chemical vapour deposition. A range of electrochemical methods, including especially cyclic voltammetry, square-wave voltammetry, impedance spectroscopy and scanning electrochemical microscopy, were used to characterise electrode properties. Other physical methods employed included scanning electron and atomic force microscopy, X-ray photoelectron spectroscopy and dynamic light scattering techniques. The electrochemical properties of heteroepitaxial single crystal diamond were explored and compared to polycrystalline counterparts. The single crystal diamond electrode was found to show superior properties in terms of wide potential window, low background current and homogeneous activity across the electrode surface, coupled with resistance to fouling. Heterogenous electron transfer rate constants were found to be lower than normally found on polycrystalline diamond; this was attributed to reduced density of states and absence of functional groups. An electrochemical route to the preparation of diamond electrodes, modified by PrOx@Pt core-shell particles was demonstrated. It was observed that these electrode modifiers were far less susceptible to poisoning than bare Pt nanoparticles when used in the electrochemical oxidation of methanol. It was also shown that diamond electrodes with these core-shell particles deposited on them, displayed useful activity for the electrochemical oxidation of nitric oxide. The presence of the PrOx layer was shown to impart useful selectivity against the oxidation of interfering compounds such as nitrite and ascorbic acid, without the loss of sensitivity which normally occurs if nafion coatings are used instead. Basic electrochemical characterisation of the PrOx coating showed that the layer was chemically active and did not serve as a simple blocking layer when deposited on the electrode. The activity of Pt modified diamond electrodes for the oxidation of nitrite species was also studied. It was also shown that the addition of carbon black to a diamond electrode resulted in much enhanced electrochemical properties in the detection of riboflavin.
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Mebane, David Spencer. "Discrete Numerical Simulations of Solid Oxide Fuel Cell Electrodes: Developing New Tools for Fundamental Investigation". Diss., Atlanta, Ga. : Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/19864.
Testo completoAbstract (sommario):
Thesis (Ph.D)--Materials Science and Engineering, Georgia Institute of Technology, 2008.Committee Chair: Meilin Liu; Committee Co-Chair: Yingjie Liu; Committee Member: David McDowell; Committee Member: Ian Ferguson; Committee Member: Tom Fuller.
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Boukhalfa, Sofiane. "Studies of ion electroadsorption in supercapacitor electrodes". Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/52976.
Testo completoAbstract (sommario):
Electrochemical capacitors, now often termed supercapacitors, are high power electrochemical energy storage devices that complement or replace high power batteries in applications ranging from wind turbines to hybrid engines to uninterruptable power supplies to electronic devices. My dissertation explores the applications of relatively uncommon techniques for both supercapacitor material syntheses and gaining better mechanistic understanding of factors impacting electrochemical performance of supercapacitors. From fundamental ion electroadsorption studies made possible by using small angle neutron scattering (SANS), to the systematic investigations of coating thickness and microstructure in metal oxide / carbon nanocomposite electrodes realized through the novel use of the atomic layer deposition (ALD) technique, new avenues of material characterization and fabrication have been studied.
In this dissertation I first present the motivation to expand the knowledge of supercapacitor science and technology, and follow with an in-depth literature review of the state of the art. The literature review covers different types of supercapacitors, the materials used in the construction of commercial and exploratory devices, an exploration of the numerous factors which affect supercapacitor performance, and an overview of relevant materials synthesis and characterization techniques The technical objectives for the work performed in this dissertation are then presented, followed by the contributions that I made in this field in my two primary research thrusts: advances to the understanding of ion electroadsorption theory in both aqueous and organic electrolytes through the development of a SANS-based methodology, and advances to metal-oxide carbon nanocomposites as electrodes through the use of ALD.
The understanding of ion electro-adsorption on the surface of microporous (pores < 2 nm) solids is largely hindered by the lack of experimental techniques capable of identifying the sites of ion adsorption and the concentration of ions at the nanoscale. In the first research thrust of my dissertation, I harness the high penetrating power and sensitivity of neutron scattering to isotope substitution to directly observe changes in the ion concentration as a function of the applied potential and the pore size. I have conducted initial studies in selected aqueous and organic electrolytes and outlined the guidelines for conducting such experiments for the broad range of electrode-ions-solvent combinations. I unambiguously demonstrate that depending on the solvent properties and the solvent-pore wall interactions, either enhanced or reduced ion electro-adsorption may take place in sub-nanometer pores. More importantly, for the first time I demonstrate the route to identify the critical pore size below which either enhanced or reduced electrosorption of ions takes place. My studies experimentally demonstrate that poor electrolyte wetting in the smallest pores may indeed limit device performance. The proposed methodology opens new avenues for systematic in-situ studies of complex structure-property relationships governing adsorption of ions under applied potential, critical for rational optimization of device performance.
In addition to enhancing our understanding of ion sorption, there is a critical need to develop novel supercapacitor electrode materials with improved high-energy and high-power characteristics. The formation of carbon-transition metal oxide nanocomposites may offer unique benefits for such applications. Broadly available transition metal oxides, such as vanadium oxide, offer high ion storage capabilities due to the broad range of their oxidation states, but suffer from high resistivities. Carbon nanomaterials, such as carbon nanotubes (CNT), in contrast are not capable to store high ion content, but offer high and readily accessible surface area and high electrical conductivity. In the second research thrust of my thesis, by exploiting the ability of atomic layer deposition (ALD) to produce uniform coatings of metal oxides on CNT electrodes, I demonstrated an effective way to produce high power supercapacitor electrodes with ultra-high energy capability. The electrodes I developed showed stable performance with excellent capacitance retention at high current densities and sweep rates. Electrochemical performance of the oxide layers were found to strongly depend on the coating thickness. Decreasing the vanadium oxide coating thickness to ~10 nm resulted in some of the highest values of capacitance reported to date (~1550 F·g⁻¹VOx at 1 A·g⁻¹ current density). Similar methodology was utilized for the deposition of thin vanadium oxide coatings on other substrates, such as aluminum (Al) nanowires. In this case the VOₓ coated Al nanowire electrodes with 30-50% of the pore volume available for electrolyte access show volumetric capacitance of 1390-1950 F cc⁻¹, which exceeds the volumetric capacitance of porous carbons and many carbon-metal oxide composites by more than an order of magnitude. These results indicated the importance of electrode uniformity and precise control over conformity and thickness for the optimization of supercapacitor electrodes.
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Williams, Robert Earl Jr. "Simulation and Characterization of Cathode Reactions in Solid Oxide Fuel Cells". Diss., Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/16309.
Testo completoAbstract (sommario):
In this study, we have developed a dense La0.85Sr0.15MnO3-δ (LSM) Ce0.9Gd0.1O1.95 (GDC) composite electrode system for studying the surface modification of cathodes. The LSM and GDC grains in the composite were well defined and distinguished using energy dispersive x-ray (EDX) analysis. The specific three-phase boundary (TPB) length per unit electrode surface area was systematically controlled by adjusting the LSM to GDC volume ratio of the composite from 40% up to 70%. The TPB length for each tested sample was determined through stereological techniques and used to correlate the cell performance and degradation with the specific TPB length per unit surface area.
An overlapping spheres percolation model was developed to estimate the activity of the TPB lines on the surface of the dense composite electrodes developed. The model suggested that the majority of the TPB lines would be active and the length of those lines maximized if the volume percent of the electrolyte material was kept in the range of 47 57%. Additionally, other insights into the processing conditions to maximize the amount of active TPB length were garnered from both the stereology calculations and the percolation simulations.
Steady-state current voltage measurements as well as electrochemical impedance measurements on numerous samples under various environmental conditions were completed. The apparent activation energy for the reduction reaction was found to lie somewhere between 31 kJ/mol and 41 kJ/mol depending upon the experimental conditions. The exchange current density was found to vary with the partial pressure of oxygen differently over two separate regions. At relatively low partial pressures, i0 had an approximately dependence and at relatively high partial pressures, i0 had an approximately dependence. This led to the conclusion that a change in the rate limiting step occurs over this range.
A method for deriving the electrochemical properties from proposed reaction mechanisms was also presented. State-space modeling was used as it is a robust approach to addressing these particular types of problems due to its relative ease of implementation and ability to efficiently handle large systems of differential algebraic equations. This method combined theoretical development with experimental results obtained previously to predict the electrochemical performance data. The simulations agreed well the experimental data and allowed for testing of operating conditions not easily reproducible in the lab (e.g. precise control and differentiation of low oxygen partial pressures).
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Li, Wei. "Composite polymer/graphite/oxide electrode systems for supercapacitors". University of Cincinnati / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1439309266.
Testo completo
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Qwesha, Sibusiso. "Electrodeposition of multi-valent metal oxides at 1-methyl-3-octylimidazolium bis(trifluoromethylsulfonyl) imide ionic liquid - carbon paste electrode". University of the Western Cape, 2012. http://hdl.handle.net/11394/4618.
Testo completoAbstract (sommario):
>Magister Scientiae - MScA study on carbon paste electrode (CPE) materials containing 1-methyl-3-octylimidazolium bis (trifluoromethylsulfonyl) imide [MOIM[Tƒ2N] – a hydrophobic room temperature ionic liquid (IL) - is reported. CPEs with (a) the IL as the only binder (ILCPE) and (b) 1:1 (v/v) IL: paraffin mixture as the binder (ILPCPE) were prepared, characterized, and applied to the electrodeposition of films of multivalent transition metal oxides (MV-TMO) from five precursor ions (Fe2+, Mn2+, Cu2+, Co2+, Ce4+) in aq. KCl. Cyclic voltammetry (CV) showed a potential window of +1.5 V to -1.8 V regardless of the electrode type, including the traditional paraffin CP electrode (PCPE). However, the IL increased the background current by 100-folds relative to paraffin. The electrochemical impedance spectroscopy (EIS) of ILPCPE in aq. KCl (0.1M) revealed two phase angle maxima in contrast with the single maxima for PCPE and ILCP. The study also included the CV and EIS investigation of the electrode kinetics of the Fe(CN)6 3-/4 redox system at these electrodes. The electrodeposition of Fe2+, Co2+, and Mn2+ possibly in the form of the MV-TMOs FexOy, CoxOy, and MnxOy, respectively, onto the electrodes was confirmed by the observation of new and stable cathodic and anodic peaks in a fresh precursor ion –free medium. CVs of H2O2 as a redox probe supported the same conclusions. Both ATR-FTIR spectra and SEM image of surface samples confirmed the formation of electrodeposited films. This study demonstrated that the use of this hydrophobic IL alone or in combination with paraffin as a binder gives viable alternative CPE materials with better performance for the electrodeposition of MV-TMOs films than the paraffin CPE. Thus, in combination with the easy preparation methods and physical “morpheability” in to any shape, these CPEs are potentially more useful in electrochemical technologies based on high surface-area MV-TMO films in general, and MnxOy films in particular.
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Zaczek, Christoph. "Electrolysis of Palladium in Heavy Water". PDXScholar, 1995. https://pdxscholar.library.pdx.edu/open_access_etds/5051.
Testo completoAbstract (sommario):
Following several reports in the past few years about compositional changes on palladium used as a cathode in heavy water electrolysis, the purpose of this research project was to reproduce this results. Two experiments were performed using two cells connected in series, an experimental cell and a control cell. Both experiments used platinum anodes, the experimental cell had a palladium cathode and the control cell had a platinum cathode. The electrolyte was D20 with H2S04. Radiation was monitored during both experiments. Also temperature and voltage were recorded for both experiments, to allow statements about excess heat of the experimental cell in comparison to the control cell. Both experiments had problems with unequal electrolyte loss, so that no statements about excess heat could be made. No significant radiation was detected in either experiment. Also no compositional changes on the palladium cathodes after electrolysis in both experiments could be detected. Impurities in grain-shaped defects on the palladium cathode before the experiment were found in either experiment. These impurities were Si, Ca, 0, and sometimes also Mg, Na and Fe. Localized findings of Au and Pt, in a distance of 1-2μm to each other, were made on the palladium cathode from the second experiment before electrolysis. Spot, grain-shaped and longitudinal defects were found on the original palladium foil used for the cathodes in either experiment No evidence for fusion, or any other nuclear reaction in the crystal lattice of palladium, used as cathode in heavy water electrolysis, was observed.
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Tiyash, Bose. "Ruthenium Oxide Based Combined Electrodes as Nitric Oxide (NO) Sensors: Towards Measuring NO in Cystic Fibrosis Cell Line Models". Cleveland State University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=csu1557496991784383.
Testo completo
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Stinson, Jelynn A. "The Electroanalytical Performance of Sonogel Carbon Titanium (IV) Oxide Electrodes versus Conducting Polymer Electrodes in the Electrochemical Detection of Biological Molecules". Wright State University / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=wright1181068417.
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Kang, Laeugu. "Study of HFO₂ as a future gate dielectric and implementation of polysilicon electrodes for HFO₂ films /". Full text (PDF) from UMI/Dissertation Abstracts International, 2000. http://wwwlib.umi.com/cr/utexas/fullcit?p3004301.
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Henriques, Alexandra J. "Nano-Confined Metal Oxide in Carbon Nanotube Composite Electrodes for Lithium Ion Batteries". FIU Digital Commons, 2017. http://digitalcommons.fiu.edu/etd/3169.
Testo completoAbstract (sommario):
Lithium ion batteries (LIB) are one of the most commercially significant secondary batteries, but in order to continue improving the devices that rely on this form of energy storage, it is necessary to optimize their components. One common problem with anode materials that hinders their performance is volumetric expansion during cycling. One of the methods studied to resolve this issue is the confinement of metal oxides with the interest of improving the longevity of their performance with cycling. Confinement of metal oxide nanoparticles within carbon nanotubes has shown to improve the performance of these anode materials versus unconfined metal oxides. Here, electrostatic spray deposition (ESD) is used to create thin films of nano-confined tin oxide/CNT composite as the active anode material for subsequent property testing of assembled LIBs. This thesis gives the details of the techniques used to produce the desired anode materials and their electrochemical characterization as LIB anodes.
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Krishnan, Vivek Fergus Jeffrey Wayne. "Development of CaZrO3-based hydrogen sensors with oxide reference electrodes for molten aluminum". Auburn, Ala., 2006. http://repo.lib.auburn.edu/2006%20Fall/Dissertations/KRISHNAN_VIVEK_58.pdf.
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