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Bardini, Luca <1985>. "Oxygen: problems and solutions in electrochemistry." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2013. http://amsdottorato.unibo.it/5618/1/tesiDoc.pdf.
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Different aspects of the electrochemistry of oxygen are examined through four experimental examples: corrosion,
passivation via organic thin films, oxygen reduction and
water oxidation catalysis are outlined in order to outline the very different ways and circumstances in which oxygen plays a major role in electrochemistry.
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Bardini, Luca <1985>. "Oxygen: problems and solutions in electrochemistry." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2013. http://amsdottorato.unibo.it/5618/.
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Different aspects of the electrochemistry of oxygen are examined through four experimental examples: corrosion,
passivation via organic thin films, oxygen reduction and
water oxidation catalysis are outlined in order to outline the very different ways and circumstances in which oxygen plays a major role in electrochemistry.
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Sönmez, Turgut. "Studies of oxygen electrochemistry on spinel oxides." Thesis, University of Southampton, 2017. https://eprints.soton.ac.uk/415516/.
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Electrochemical studies of the spinels, Co3O4 and NiCo2O4, in alkaline media were conducted and show that the products and the oxygen reduction mechanisms vary. The 4e- reduction strongly predominates at NiCo2O4, a substantial amount of the 2e- reduction product (H2O2), 43%, is formed at the cobalt spinel. NiCo2O4 is a significantly better catalyst than Co3O4 in terms of both the overpotential for reduction and its limiting current density. The differences come from the enhanced rate of O – O bond cleavage early in the reduction sequence at the mixed spinel. Based on the full physical, spectroscopic and electrochemical studies of a wide range of Mn content (MnxCo3-xO4, 0.0 ≤ x ≤ 2.0) in spinel cobalt oxide, the phase transition (from cubic to tetragonal), particle size, surface area, crystallinity and electrochemical activities towards the ORR can be tuned with Mn content in spinel cobalt oxide. The Mn ions are in oxidation state +3 and they have tendency to occupy tetrahedral sites rather than octahedral sites in the spinels. In terms of the highest limiting current and lowest onset potential for oxygen reduction, cubic phase MnCo2O4 (x = 1.0) possesses the highest catalytic activity amongst Mn doped spinels and follows the 4e- reduction mechanism with early cleavage of the O – O bond. Three different synthesis methods for MnCo2O4 (co-precipitation, thermal decomposition and hydrothermal method) and the influence of conditions within hydrothermal method were investigated. The preparation conditions and methods were found to affect the morphology, phase, crystallinity, and ORR activity of the catalyst. Co-precipitation produced the catalyst with the highest surface area, smallest particle size, highest crystallinity and the highest ORR activity.
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Bikkarolla, Santosh Kumar. "Oxygen electrochemistry on inorganic/graphene hybrid materials for energy applications." Thesis, Ulster University, 2015. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.673823.
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Developing low cost oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalysts that perform with high efficiency is desirable for the commercial success of energy conversion devices, such as fuel cells and metal-air batteries. In this thesis, electrochemically reduced graphene oxide (ErGO) and Mn304 nanoflakes anchored on nitrogen doped reduced graphene oxide (NrGO) sheets synthesised by electrodeposition method were developed as ORR catalysts. CUC0204 nanoparticles were integrated with NrGO sheets through solvothermal method as a potential OER catalyst. A partially reduced graphene oxide electrocatalyst synthesised by electrochemical reduction of graphene oxide exhibited significantly enhanced catalytic activity towards the ORR in alkaline solutions compared to the starting GO. The resultant ErGO electrode also showed an enhanced capacitance and an ORR onset potential similar to that of NrGO electrode, produced by a solvothermal process. However, the ErGO exhibited considerably lower electron transfer numbers, indicating that although both catalysts operate under combined 4e- and 2e- ORR processes, ErGO followed a more predominant 2e- pathway. The ORR process in ErGO has been linked to the presence of quinone functional groups, which in turn favoured the 2e- ORR pathway. Also in this work, a three dimensional Mn304 hierarchical network was grown on NrGO by a facile and controllable electrodeposition process, and its electrocatalytic performance for ORR was assessed. The directly electrodeposited MnO. on the glassy carbon electrode (GCE) exhibited little electrocatalytic activity, whereas the integrated Mn304/NrGO catalyst was more ORR active than the NrGO. The resulting electrode architecture exhibited an "apparent" 4e-oxygen reduction pathway involving a dual site reduction mechanism due to a synergetic effect between Mn304 and NrGO. In addition, the 3D Mn304/NrGO hierarchical al'chitectur~ exhibited improved durability and methanol tolerance, far exceeding that of commercial ptlC. A composite material consisting of CUC020 4 nanoparticles anchored on NrGO sheets (CuCo204/NrGO) was prepared by a solvothermal method as a highly efficient OER electrocatalyst in both alkaline and neutral solutions. The CuCo204/NrGO exhibited high OER performance when compared to the other control materials, as well as good stability under strong alkaline condition. The enhanced OER performance of CuCo204/NrGO can be related to: (i) a reduction in the size of the CUC0204 nanoparticles as measured by the TEM, (ii) an enhancement of electrochemically active surface area (ECSA), (iii) a replacement of the least OER active C02+ ions with Cu2+ ions as confirmed by XPS and (iv) a synergetic effect between CuCo204 nanoparticles and NrGO sheets.
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Knoche, Krysti Lynn. "Density gradient films, lanthanide electrochemistry, and magnetic field effects on hydrogen evolution, oxygen reduction, and lanthanide electrochemistry." Diss., University of Iowa, 2015. https://ir.uiowa.edu/etd/3124.
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Electroanalytical techniques are used to investigate mass transport through density gradient films; lanthanide triflate reduction and oxidation in a Nafion/acetonitrile matrix; and magnetic field effects on hydrogen evolution reaction (HER), oxygen reduction reaction (ORR), and lanthanide electrochemistry.
Graded density films are more dense at the electrode surface and become less dense out into solution due to a brush polymer structure. Fick's second law expands to account for a diffusion coefficient that varies with distance x normal to the electrode surface. Confocal microscopy, cyclic voltammetry, and computer simulations are used to investigate density graded Ficoll® films. Mass transport approaches steady state (scan rate independence) at slow scan rates where the diffusion length samples the entire film. The use of Ficoll to template an ion exchange polymer is explored by casting Nafion® Ficoll composites.
Lanthanide electrochemistry is enabled in acetonitrile at a Nafion modified platinum electrode in the presence of triflate ligands. Formal potentials are shifted into the voltage window of acetonitrile accessible due to triflate complexation. The Nafion further solubilizes the compounds. The mechanism (ECEC) is studied with cyclic voltammetry and x-ray photoelectron spectroscopy.
Magnetic field effects on electrochemical systems have been of interest to researchers for the past 65 years. Mass transport effects, such as magnetohydrodynamics and magnetic field gradient effects have been reported, but the Leddy group focuses on electron transfer effects. Electrode surfaces are modified with composite films of magnetic microparticles suspended in ion exchange polymer Nafion. Effects are verified to be electron transfer related and due to the magnetization of chemically inert microparticles. The magnets catalyze the rates of important electron transfer reactions such as hydrogen evolution and oxygen reduction.
Magnetic field effects on HER at various noncatalytic metal electrodes are explored with linear scan voltammetry. There is a correlation between the magnetic susceptibility of the electrode metals and the HER exchange currents (reaction rates). Exchange currents are 103× larger for a paramagnetic metal electrode than a diamagnetic one with the same work function. The overpotential at diamagnetic electrodes is decreased by modification with a Nafion + magnetic microparticle composite film. A decrease in overpotential of ∼70 % for all electrodes except platinum is observed. The overpotential decrease correlates with the magnetic susceptibility of the particles.
Magnets can enhance differences between lanthanide cyclic voltammograms by shifting current densities at a given potential and enhancing current based on the number of 4f electrons and magnetic moment of each lanthanide ion.
Magnetic field effects on ORR in acetonitrile are investigated with cyclic voltammetry. In aprotic solvents, ORR proceeds by a one electron transfer reaction to paramagnetic O2.–. Enhanced reversibility and electron transfer kinetics are observed as well as a decrease in overpotential of ∼100 mV. Magnetic field effects on ORR in a lanthanide triflate solution are also examined. Electron transfer kinetics and reversibility are further enhanced in the presence of lanthanide triflate.
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Turner, Steven Christopher. "Electrochemical release of oxygen from metal complexes." Thesis, Heriot-Watt University, 1991. http://hdl.handle.net/10399/867.
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Siriwatcharapiboon, Wilai. "The electrochemistry of metal nanoparticles for oxygen reduction and nitrate/nitrite reduction." Thesis, University of Birmingham, 2013. http://etheses.bham.ac.uk//id/eprint/4475/.
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This research has scientific aims focused on two important electrochemical reactions: oxygen reduction and nitrate/nitrite reduction. A series of rhodium (Rh) deposited on gold nanorods (Au NRs) and gold nanoparticles (Au NPs) were synthesised by wet chemical reduction. The scanning transmission electron microscopy (STEM) showed that Rh has a preferential deposition and epitaxial growth at the end of Au NRs. Cyclic voltammetry and rotating disc electrode (RDE) measurements were performed to study the oxygen reduction at these Au:Rh/C catalysts. Pyrolysed cobalt triethylenetetraamine on a carbon substrate (Co/TET A/C) was employed to produce H20 2 from the ORR. The results from the rotating ring disc electrode (RRDE) reveal that the heat treatment influences the H20 2 selectivity. The Co/TETA/C heated at 1000 oc yields the highest H20 2 selectivity while the Co/TETA/C heated at 700 oc yields the lowest H20 2 selectivity. Rh/C, Au:Rh/C nanoparticles and Sn modified Rh/C nanoparticles were employed for nitrate/nitrite reduction in acidic media. Results from on-line electrochemical mass spectrometry (OLEMS) reveal that the modified electrode generates N2 from further reduction of the nitrous oxide (N20) intermediate. Ion chromatography (IC) shows that ammonium is the main product at Rh/C. Hydroxylamine can also be detected after Sn modification on Rh/C.
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Yu, Kyle Kai-Hung. "Interfacial Electrochemistry of Copper and Spectro-Electrochemical Characterization of Oxygen Reduction Reaction." Thesis, University of North Texas, 2011. https://digital.library.unt.edu/ark:/67531/metadc103416/.
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The first part of this dissertation highlights the contents of the electrochemical characterization of Cu and its electroplating on Ru-based substrates. The growth of Ru native oxide does diminish the efficiency of Cu plating on Ru surface. However, the electrochemical formed irreversible Ru hydrate dioxide (RuOxHy) shows better coverage of Cu UPD. The conductive Ru oxides are directly plateable liner materials as potential diffusion barriers for the IC fabrication. The part II of this dissertation demonstrates the development of a new rapid corrosion screening methodology for effective characterization Cu bimetallic corrosion in CMP and post-CMP environments. The corrosion inhibitors and antioxidants were studied in this dissertation. In part III, a new SEC methodology was developed to study the ORR catalysts. This novel SEC cell can offer cheap, rapid optical screening results, which helps the efficient development of a better ORR catalyst. Also, the SEC method is capable for identifying the poisoning of electrocatalysts. Our data show that the RuOxHy processes several outstanding properties of ORR such as high tolerance of sulfation, high kinetic current limitation and low percentage of hydrogen peroxide.
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Su, Yuhlong Oliver. "Electrochemistry of metalloporphyrins and their catalytic reduction of oxygen at carbon electrodes /." The Ohio State University, 1985. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487260135354882.
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Jorgensen, Mette Juhl. "Lanthanum manganate based cathodes for solid oxide fuel cells." Thesis, Keele University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.343243.
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Xiao, Neng. "Investigating Growth Mechanism of Potassium Superoxide in K-O2 Batteries and Improvements of Performance and Anode Stability upon Cycling." The Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1462890425.
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Li, Qian. "Electrochemical reduction of oxygen." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:2f37a1ae-dab0-4581-a8fd-e01ce59246c4.
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The main aim of the work reported is the design of proof-of-concept of at point-of-use hydrogen peroxide electrogeneration from air. The experimental work discussed within this thesis explores five major areas: the kinetics of electrocatalysis, ion-pairing, change of solvent media, the electrode surface modication by a redox mediator, and the electrochemical reduction of oxygen within enhanced mass transport systems. The electrocatalytic rates and mass transport of two oxygen reduction redox meditors, viz. anthraquinone and methyl viologen, are studied in aqueous solutions. The investigation is facilitated through the use of a boron-doped diamond electrode, allowing the catalytic response to be clearly delineated from that of the direct oxygen reduction process. The use of simulation software is highlighted in combination with experimental voltammograms to extract kinetic data. Specifically, the voltammetric features, such as the `reverse' peak and the `split waves', are given particular attention. Consequently, it is possible to deconvolute the electrocatalytic reaction mechanisms. The reactivity of the viologen radical cation is comparable to the semiquinone radical anion in aqueous solution ((4.8~6)x10^9 M^-1 s^-1), but over a far wider pH range (pH 2.5 - pH 8.5). The change of local proton concentration, and sequential electron transfers play key roles here. Moreover, the reduced reactivity of semiquinone is observed upon formation of ion-pairs with tetrabutylammonium cations in alkaline solutions. The electro-reduction of oxygen and its mediated pathways are also investigated in non-aqueous media; in particular the thermodynamics, the kinetics, and mass transport involved in these processes. Through a variable temperature study in electrolytic acetonitrile solution, the oxygen dissolution is quantitatively shown to be an endothermic process. Moreover, the diffusion coeficients and concentration of oxygen upon change of acetonitrile mole fraction is also explored in water-acetonitrile mixtures. The rates of bimolecular reactions are extracted from simulation programs, involving semiquinone in anhydrous acetonitrile and viologen radical cation in ethanol, and show a 3 - 4 orders of magnitude reduction compared to that in aqueous solution. Although the solubility of oxygen is ca. 6 - 8 times larger in non-aqueous solvents, the much reduced homogeneous rates limit the electrogeneration of hydrogen peroxide in pure organic media. Novel surface modification methodologies for graphitic surfaces with covalently attached anthraquinonyl groups are studied and characterised. The anthraquinonyl-modified carbon surfaces show much reduced overpotentials required for oxygen reduction. In the final chapter, utilising the new surface modification methodology and novel designs, two gravity-feed flow cells for electrochemical reduction of oxygen in aqueous solutions are proposed and characterised, one based upon the tubular electrode geometry. The other exhibits much enhanced current conversion by using a porous reticulated vitreous carbon electrode. The latter may provide a prototype hydrodynamic system to produce dilute hydrogen peroxide solution at point-of-use.
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Trotochaud, Lena. "Structure-Composition-Activity Relationships in Transition-Metal Oxide and Oxyhydroxide Oxygen-Evolution Electrocatalysts." Thesis, University of Oregon, 2014. http://hdl.handle.net/1794/18312.
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Solar water-splitting is a potentially transformative renewable energy technology. Slow kinetics of the oxygen evolution reaction (OER) limit the efficiency of solar-water-splitting devices, thus constituting a hurdle to widespread implementation of this technology. Catalysts must be stable under highly oxidizing conditions in aqueous electrolyte and minimally absorb light. A grand goal of OER catalysis research is the design of new materials with higher efficiencies enabled by comprehensive understanding of the fundamental chemistry behind catalyst activity. However, little progress has been made towards this goal to date.
This dissertation details work addressing major challenges in the field of OER catalysis. Chapter I introduces the current state-of-the-art and challenges in the field. Chapter II highlights work using ultra-thin films as a platform for fundamental study and comparison of catalyst activity. Key results of this work are (1) the identification of a Ni0.9Fe0.1OOH catalyst displaying the highest OER activity in base to date and (2) that in base, many transition-metal oxides transform to layered oxyhydroxide materials which are the active catalysts. The latter result is critical in the context of understanding structure-activity relationships in OER catalysts. Chapter III explores the optical properties of these catalysts, using in situ spectroelectrochemistry to quantify their optical absorption. A new figure-of-merit for catalyst performance is developed which considers both optical and kinetic losses due to the catalyst and describes how these factors together affect the efficiency of composite semiconductor/catalyst photoanodes. In Chapter IV, the fundamental structure-composition-activity relationships in Ni1-xFexOOH catalysts are systematically investigated. This work shows that nearly all previous studies of Ni-based catalysts were likely affected by the presence of Fe impurities, a realization which holds significant weight for future study of Ni-based catalyst materials. Chapter V discusses the synthesis of tin-titanium oxide nanoparticles with tunable lattice constants. These materials could be used to make high-surface-area supports for thin layers of OER catalysts, which is important for maximizing catalyst surface area, minimizing the use of precious-metal catalysts, and optimizing 3D structure for enhanced mass/bubble transport. Finally, Chapter VI summarizes this work and outlines directions for future research.
This work contains previously published and unpublished co-authored material.2015-03-29
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Yin, Zhewen. "Non-precious Metal Catalysts for Oxygen Reduction Reaction in Alkaline Solutions." Scholar Commons, 2018. http://scholarcommons.usf.edu/etd/7250.
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Mesoporous WO3 powders were prepared via sol-gel processing synthesis using nonionic surfactant Pluronic (P-123) as the template. The influences of heating temperature on the pore structure and properties of WO3 powders were investigated. Three kinds of modifications were compared and evaluated after finding out the best heating condition. Different amount of lanthanum was doped into mesoporous WO3 to improve its Oxygen Reduction Reaction (ORR) activity. Several factors contributing to the increase of catalytic performance were discussed. Vulcan carbon powder was also used as a support to increase the catalysts’ electrical conductivity as well as dispersity. The component, microstructure and specific surface area of samples were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM) and N2 adsorption-desorption analysis. A three-electrode system with a rotating disk electrode (RDE) was used to detect samples’ electrochemical performance towards ORR in alkaline solutions. The as-prepared mesoporous La/WO3 powder with a ratio of La: W = 1: 10, calcined at 550℃ and supported by 25 wt% Vulcan carbon powder, exhibited highest ORR catalytic activity.
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Sayeed, Md Abu. "Electrochemical fabrication of nanostructured metal oxides for the oxygen evolution reaction." Thesis, Queensland University of Technology, 2018. https://eprints.qut.edu.au/116769/1/Md%20Abu_Sayeed_Thesis.pdf.
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This research developed a new approach to synthesise novel catalysts for electrochemical water splitting. Hydrogen and oxygen production from water mostly depends upon the performance of the water-splitting catalyst, in particular for the oxygen evolution reaction which is the focus of this thesis. The ability to efficiently produce oxygen and hydrogen from water will result in a chemical means to store intermittent renewable energy for later use. In this thesis, a room temperature electrochemical synthesis approach under ambient conditions is presented to produce highly active catalyst materials that is highly beneficial for the difficult oxygen evolution half reaction.
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St, John Samuel. "Hierarchical Electrocatalyst Structure Control to Study Cathodic and Anodic Overpotential in Proton Exchange Membrane Fuel Cells." University of Cincinnati / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1384334674.
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Stevens, Michaela. "Fundamentals and Industrial Applications: Understanding First Row Transition Metal (Oxy)Hydroxides as Oxygen Evolution Reaction Catalysts." Thesis, University of Oregon, 2017. http://hdl.handle.net/1794/22633.
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Intermittent renewable energy sources, such as solar and wind, will only be viable if the electrical energy can be stored efficiently. It is possible to store electrical energy cleanly by splitting the water into oxygen (a clean byproduct) and hydrogen (an energy dense fuel) via water electrolysis. The efficiency of hydrogen production is limited, in part, by the high kinetic overpotential of the oxygen evolution reaction (OER). OER catalysts have been extensively studied for the last several decades. However, no new highly active catalyst has been developed in decades. One reason that breakthroughs in this research are limited is because there have been many conflicting activity trends. Without a clear understanding of intrinsic catalyst activity it is difficult to identify what makes catalysts active and design accordingly. To find commercially viable catalysts it is imperative that electrochemical activity studies consider and define the catalyst’s morphology, loading, conductivity, composition, and structure.
The research goal of this dissertation is twofold and encompasses 1) fundamentally understanding how catalysis is occurring and 2) designing and developing a highly active, abundant, and stable OER catalyst to increase the efficiency of the OER. Specifically, this dissertation focuses on developing methods to compare catalyst materials (Chapter II), understanding the structure-compositional relationships that make Co-Fe (oxy)hydroxide materials active (Chapter III), re-defining activity trends of first row transition metal (oxy)hydroxide materials (Chapter IV), and studying the role of local geometric structure on active sites in Ni-Fe (oxy)hydroxides (Chapter V). As part of a collaboration with Proton OnSite, the catalysts studied are to be integrated into an anion exchange membrane water electrolyzer in the future.
This dissertation includes previously published and unpublished co-authored material.10000-01-01
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Singh, Deepika. "Non-Precious Metal Electrocatalysts for the Oxygen Reduction Reaction in Proton Exchange Membrane (PEM) Fuel Cells." The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1397727211.
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MOTOKI, YOSHIDA. "Synthesis of Ruthenium-based Water Oxidation Catalysts and Mechanistic Study." Thesis, KTH, Skolan för kemivetenskap (CHE), 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-173843.
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Two series of new mononuclear ruthenium complexes with hydrophobic or hydrophilic ligands [Ru(bda)L2] and [Ru(pdc)L3] (H2bda = 2,2'-bipyridine-6,6'-dicarboxylic acid; H2pdc = 2,6-pyridinedicarboxylic acid; L = pyridyl ligands) were synthesized and their electrochemical properties and catalytic activity toward water oxidation were examined. It was revealed that the hydrophobic ligands introduced to [Ru(bda)L2 ] improved the catalytic performance, ahnost twofold TON and TOF values were achieved compared to the [Ru(bda)] catalyst with hydrophilic ligands. The cyclic voltammogram of [Ru(bda)L2] exhibited marginal difference between the catalysts with hydrophobic ligands and hydrophilic ones, implying that the hydrophobic ligands promoted the catalytic activity by :lacilitating formation of a reaction intermediate dimer.
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Kashyap, V. "High-performance Pt-free oxygen reduction reaction electrocatalysts derived from carbon supported spinel cobalt ferrite and Co/Fe-nitrogen coordinated active centers for advanced energy applications." Thesis(Ph.D.), CSIR-National Chemical Laboratory, Pune, 2019. http://dspace.ncl.res.in:8080/xmlui/handle/20.500.12252/4595.
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Although the metal oxides are capable of displaying interesting catalytic activity characteristics, the intrinsic activities of these types of systems are found to be largely depending on other parameters such as particle size, morphology, and how well the catalyst particles are dispersed on a conducting substrate and additionally the surface intermediates involved in the process. Herein, we have explored the close relation of particle size, dispersion characteristics of the active particles on a conducting carbon, substitution effect of other metals and controlled interplay of the surface intermediates for the cobalt and iron metal atoms in facilitating the reactions like ORR and OER. Substituting some portion of Fe by Zn in the spinel lattice of cobalt ferrite nanocrystals can favorably influence the overpotential for ORR. However, the substitution of Zr in a cobalt ferrite matrix shows a significant level of improvement for the overpotentials of both ORR and OER, thereby positioning the composite as a potential bifunctional electrocatalyst. Basically, the electrochemical faradaic reactions are controlled by the transition states formed in between the reaction process and the adsorption energies of these states. In acidic and basic media, the stability of the transition states changes significantly with a direct impact on the ORR activity. To understand this and to gain insightful information on the mechanistic aspects, we have studied the variation in the ORR activity with the nature of the medium for cobalt and iron atom incorporated active centers. The functioning of the catalyst is demonstrated in the primary zinc-air battery in correlation of the transition states over the catalyst.V.K acknowledges University Grant Commission (UGC), New Delhi, India, for research fellowship and K.S acknowledges Council of Scientific and Industrial Research (CSIR), New Delhi, India, for research funding (TLP003526).
AcSIR
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Zhu, Huanfeng. "Experimental and Theoretical Aspects of Electrode Electrolyte Interfaces." Cleveland, Ohio : Case Western Reserve University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=case1259680393.
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Thesis(Ph.D.)--Case Western Reserve University, 2010Title from PDF (viewed on 2009-12-30) Department of Chemistry Includes abstract Includes bibliographical references and appendices Available online via the OhioLINK ETD Center
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Enman, Lisa. "Structure-Property Relationships in Mixed-Metal Oxides and (Oxy)Hydroxides for Energy Applications." Thesis, University of Oregon, 2019. http://hdl.handle.net/1794/24227.
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Metal oxides and (oxy)hydroxides, particularly those containing two or more metals have many uses as electronic materials and catalyst, especially in energy applications. In this dissertation, the structure-property relationships of these mixed-metal materials are explored in order to understand how these materials work and to guide design of materials with even higher efficiency for a given application. Chapter I introduces the materials and studies undertaken. Chapter II presents a fundamental analysis of the electronic and local atomic properties of mixed-transition-metal aluminum oxide thin films.
The final three chapters focus on water electrolysis for hydrogen production, which is limited in part by the slow kinetics of the oxygen evolution reaction (OER). Nickel-iron and cobalt-iron (oxy)hydroxides have been shown to be the most active in alkaline conditions. Although it is evident that Fe is essential for high activity, its role is still unclear. Chapter III investigates the role of Fe in NiOOH by comparing the effects of Ti, Mn, La, and Ce incorporation on the OER activity of NiOOH in base. Chapter IV evaluates the OER activity and Tafel behavior of Fe3+ impurities on different noble metal substrates. Chapter V describes the results of in situ and in operando X-ray spectroscopy experiments, which shows that the local structure around Fe atoms in Co(Fe)OOH changes during OER while that of Co stays the same. This work adds to the growing body of literature that suggests Fe is essential to the catalytic active site for the OER on transition-metal (oxy)hydroxides.
This dissertation contains previously published and un-published coauthored material.2020-01-11
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Devoille, Aline M. J. "New cofacial binuclear complexes for the oxygen reduction reaction and selective anion binding." Thesis, University of Edinburgh, 2011. http://hdl.handle.net/1842/9963.
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This thesis describes the design, synthesis and reactivity of bimetallic complexes of doubly-pillared Schiff-base calixpyrrole ligands. Chapter One introduces the oxygen reduction reaction in light of the global energy scenario at present and in the future. Compounds and materials known to catalyse this reaction are discussed, with particular focus on transition metal complexes of pyrrole-containing macrocycles and the ability of these compounds to act as catalysts in redox reactions. Chapter Two describes the design and synthesis of several of the macrocyclic ligands developed during this project. The wide range of metals and geometries supported by one of the ligands, H4L, are outlined and include complexes of alkali-metals (Li, K), a rare earth metal (Mg), transition metals (Pd, Fe) and an actinide (UO2 2+). Chapter Three presents the use of [Co2(L)] for the reduction of dioxygen to water. The redox behaviour of the complex and its ability to reversibly bind oxygen were evaluated. The catalytic activity of [Co2(L)] was investigated in solution by UV-Vis spectrophotometry and electrochemically by rotating ring-disk electrochemistry. In Chapter Four, the ability of [Zn2(L)] to bind anions is described. Isothermal microcalorimetry, NMR, UV-Visible spectrophotometry, and fluorophotometry were used to study the de-aggregation of the anion free complex and the subsequent anion binding event. The stability of the complexes was estimated by DFT calculations. Chapter Five outlines the synthesis of complexes of L for other transition metals relevant to small molecule activation. Chapter Six contains a conclusion and suggestions on further investigations to carry out. Chapter Seven presents the full experimental details and analytical data for this work.
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Hedman, Jonas. "Characterization of reaction products in sodium-oxygen batteries : An electrolyte concentration study." Thesis, Uppsala universitet, Strukturkemi, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-317969.
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In this thesis, the discharge products formed at the cathode and the performance and cell chemistry of sodium-oxygen batteries have been studied. This was carried out using different NaOTf salt concentrations. The influence of different salt concentrations on sodium-oxygen batteries was investigated since it has been shown that increasing the salt concentration beyond conventional concentrations could result in advantages such as increased stability of the electrolytes towards decomposition, higher thermal stability and lower volatility. An increase in salt concentration has also been shown to influence the electrochemical potential window. The solubility of NaOTf was investigated in two different solvents, DME and diglyme. NaOTf was found to be more soluble in DME compared to diglyme but due to the volatile nature of DME, three different concentrations of NaOTf were prepared with diglyme as solvent. Experimentation involved discharging the batteries to either maximum or limited capacity. The discharge products were examined and characterized using XRD and SEM. The main discharge product was identified as sodium superoxide although sodium peroxide dihydrate was also identified in one battery. A trend of higher capacity and voltage plateaus with higher salt concentration was also found. The influence of trace amounts of water was suggested as one explanation as it works as a catalyst, promoting sodium superoxide cube growth due to improved transportation of superoxide. Another or contributing explanation could be a possible change in donor number with increased salt concentration, resulting in higher solubility and longer lifetime of superoxide, promoting the growth of sodium superoxide cubes.
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Liu, Zheng. "Synthesis and battery application of nanomaterials and the mechanism of O2 reduction in aprotic Li-O2 batteries." Thesis, University of St Andrews, 2016. http://hdl.handle.net/10023/15694.
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Hunting for improved energy storage devices based on rechargeable Li-ion batteries and other advanced rechargeable batteries is one of the hottest topics in today's society. Both Li- ion batteries and Li-O2 batteries have been studied within the thesis. The research work of this thesis contains two different parts. Part 1. The controlled synthesis of the extreme small sized nanoparticles and their application for Li-ion batteries; Part 2. The study of the O2 reduction mechanism in Li-O2 batteries with aprotic electrolytes. In the first part, two different types of extremely small-sized TiO2 nanoparticles with at lease on dimension less than 3 nm was synthesised via solvothermal/hydrothermal reaction, i.e., anatase nanosheets and TiO2(B). These nanoparticles were obtained without any contamination of long chain organic surfactants. A series of systematic characterisation methods were employed to analyse the size, phase purity, and surface condition. These extremely small-sized nanoparticles exhibit improved capacity, rate performance as anode materials for Li-ion batteries. The shapes of load curves of charge and discharge are significantly modified due to the reduced size of TiO2 nanoparticles. In chapter 3, we will see the variation of the capacity and the load curve shape of the anatase nanosheets according to their thickness and surface conditions. The origin of the excessive capacity is analysed based on the electrochemical data. It has been identified that both pseudocapacitive (interfacial) Li+ storage and the excessive Li+ -storage from the bulk contribute to the increased capacity. In chapter 4, the shape and size of the sub-3 nm TiO2(B) nanoparticles are studied, a method based the PXRD data is established. These nanoparticles demonstrate a reversible capacity of 221 mAh/g at a rate of 600 mA/g and remain 135 mAh/g at 18000 mA/g without significant capacity fading during cycling. In the last part, a systematic study of O2 reduction mechanism for aprotic Li-O2 batteries based on the combination of a series of electrochemical and spectroscopic data is presented. The novel mechanism unifies two previous models for the growth of Li2O2 during discharge, i.e., Li2O2 particle formation in the solution phase and Li2O2 film formation on the electrode surface. The new mechanism provides fundamental conceptions for the improvement of Li2O2 batteries and shed light on the future research of Li2O2 batteries.
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Strobl, Jonathan R. "ELECTROCATALYTIC STUDIES OF SUPEROXIDE AS AN INTERMEDIATE FOR THE OXYGEN REDUCTION REACTION IN BASIC ELECTROLYTES & THE REDUCTION OF SELENATE ON UNDERPOTENTIAL DEPOSITED Cu ON Au." Case Western Reserve University School of Graduate Studies / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=case1595623881870564.
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Heidary, Nina [Verfasser], Anna [Akademischer Betreuer] Fischer, Anna [Gutachter] Fischer, Peter [Gutachter] Hildebrandt, and Ulla [Gutachter] Wollenberger. "IR spectro-electrochemistry of an adsorbed oxygen-tolerant [NiFe] hydrogenase on conductive surfaces / Nina Heidary ; Gutachter: Anna Fischer, Peter Hildebrandt, Ulla Wollenberger ; Betreuer: Anna Fischer." Berlin : Technische Universität Berlin, 2017. http://d-nb.info/1156013992/34.
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Crawford, Jessica F. "Using room-temperature liquid metals as a new reaction environment." Thesis, Queensland University of Technology, 2022. https://eprints.qut.edu.au/232783/1/Jessica_Crawford_Thesis.pdf.
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When conducting a chemistry experiment, reactions are often completed in a liquid solvent. This thesis investigates the outcome of using liquid metals as a new reaction environment. Galinstan is an alloy comprised of 68.5% gallium, 21.5% indium and 10% tin that can remain a liquid at room temperature and is extremely useful due to its flexibility and conductivity. This thesis shows that liquid metals can be used to synthesise new 2D materials that catalyse oxygen production during water splitting, form new materials that can catalyse ammonia production from abundant nitrate sources and facilitate the degradation of organic dye pollutants.
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Wulff, Philip. "Principles of hydrogen catalysis in the presence of oxygen by a [NiFe] hydrogenase from E. coli." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:9e434467-d50b-484a-a17e-ef3091636269.
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[NiFe] hydrogenases are metalloenzymes that act as highly efficient molecular electrocatalysts for the interconversion of protons and molecular hydrogen. Unlike any other known molecular electrocatalyst, the members of a subgroup of respiratory membrane-bound [NiFe] hydrogenases are able to maintain H2 catalysis in the sustained presence of O2. This O2-tolerance depends on the ability to respond to oxidative inactivation by O2 by exclusively forming rapidly reactivated active site states, thus implying a catalytic cycle in which O2 acts as a competing substrate to H2. Using isotope ratio mass spectrometry it is proven that the O2-tolerant Escherichia coli Hydrogenase 1 responds to O2 attack by acting as a four-electron oxidoreductase, catalysing the reaction 2 H2 + O2 → 2 H2O, equivalent to hydrogen combustion. Special features of the enzyme’s electron relay system enable delivery of the required electrons. A small fraction of the H2O produced arises from side reactions proceeding via reactive oxygen species, an unavoidable consequence of the presence of low-potential relay centres that release electrons from H2 oxidation. While the ability to fully reduce O2 to harmless H2O at the active site to generate the rapidly reactivated state Ni-B, determines if a hydrogenase is O2-tolerant, the ratio of oxidative inactivation to reductive reactivation rates determines how tolerant the enzyme is. It is shown by protein film electrochemistry that the (αβ)2 dimeric assembly of Hyd-1 plays an important role in O2-tolerance by aiding reactivation of one catalytic unit through electron transfer from the other. The teamwork between two redundant partners implicates a new role for dimerisation and represents a new example of cooperativity in biology. Finally, the non-natural amino acid p-azido-L-phenylalanine was synthesised and incorporated into Hyd-1, testing the possibility of introducing labels at specific sites.
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von, Deak Dieter G. "Heteroatom-containing Carbon Nanostructures as Oxygen Reduction Electrocatalysts for PEM and Direct Methanol Fuel Cells." The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1313085489.
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Heath, Rachel Sarah. "Studies of a 'blue' copper oxidase electrocatalyst." Thesis, University of Oxford, 2008. http://ora.ox.ac.uk/objects/uuid:e8359408-d3d4-4fe3-910a-cc69265a1546.
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This thesis concerns the electrochemical investigation of high-potential laccases. These multicopper oxidases are efficient electrocatalysts for the dioxygen reduction reaction. A method for stabilising laccase on a graphite electrode was established. The method involved modification of the graphite surface by diazonium coupling of a 2-anthracene molecule. A laccase ‘film’ adsorbed on this modified surface remained stable for over two months and, typically, the current density for dioxygen reduction was doubled compared to a laccase ‘film’ on an unmodified surface. Protein film voltammetry was used to investigate thermodynamic and kinetic aspects of the electrochemical behaviour of laccase. The effect of inhibitors on the magnitude of reduction current and the position of the wave (related to the overpotential for the reaction) was also studied. Fluoride, chloride and azide showed different modes of inhibition and inhibition constants ranged from micromolar for azide to millimolar for chloride. In cyclic voltammetry experiments it was only in the presence of high concentrations of the inhibitors fluoride, chloride and azide that a non-turnover signal, corresponding to a one electron transfer process, was revealed. The evidence suggested that the non-turnover signal arose from interfacial electron transfer between the electrode and the type 1 or ‘blue’ copper. Evaluation of the peak areas allowed determination of the catalytic rate constant, kcat, as 300 s–1, and the electroactive surface coverage as four pmol cm–2. The rate of interfacial electron transfer was rapid enough to not limit catalysis at high overpotentials. A spectroelectrochemical cell was designed to investigate the behaviour of the type 1 copper in the presence of inhibitors and at different pH values. The inhibitors fluoride, chloride and azide had little effect on the reduction potential of the type 1 copper, but at higher pH values the reduction potential of the type 1 copper was decreased.
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Shen, Xiaochen. "Exploiting Electrocatalyst for Energy Conversion: From Structure to Property." University of Akron / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=akron1564492661618332.
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Zhang, Yibin. "Study of Ruthenium and Ruthenium Oxide's Electrochemical Properties and Application as a Copper Diffusion Barrier." Thesis, University of North Texas, 2005. https://digital.library.unt.edu/ark:/67531/metadc4825/.
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As a very promising material of copper diffusion barrier for next generation microelectronics, Ru has already obtained a considerable attention recently. In this dissertation, we investigated ruthenium and ruthenium oxide electrochemical properties and the application as a copper diffusion barrier. Cu under potential deposition (UPD) on the RuOx formed electrochemically was first observed. Strong binding interaction, manifesting by the observed Cu UPD process, exists between Cu and Ru as well as its conductive ruthenium oxide. Since UPD can be conformally formed on the electrode surface, which enable Ru and RuOx has a potential application in the next generation anode. The [Cl-] and pH dependent experiment were conducted, both of them will affect UPD Cu on Ru oxide. We also found the Cu deposition is thermodynamically favored on RuOx formed electrochemically. We have studied the Ru thin film (5nm) as a copper diffusion barrier. It can successfully block Cu diffusion annealed at 300 oC for 10min under vacuum, and fail at 450 oC. We think the silicidation process at the interface between Ru and Si. PVD Cu/Ru/Si and ECP Cu/Ru/Si were compared each other during copper diffusion study. It was observed that ECP Cu is easy to diffuse through Ru barrier. The function of RuOx in diffusion study on Cu/Ru/Si stack was discussed. In pH 5 Cu2+ solution, Ru and Pt electrochemical behavior were investigated. A sharp difference was observed compared to low pH value. The mechanism in pH 5 Cu2+ solution was interpreted. An interesting compound (posnjakite) was obtained during the electrochemical process. An appropriate formation mechanism was proposed. Also Cu2O was formed in the process. We found oxygen reduction reaction is a key factor to cause this phenomenon.
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Sultana, Ummul Khair. "Electrochemical synthesis of water splitting nanomaterials." Thesis, Queensland University of Technology, 2019. https://eprints.qut.edu.au/126972/1/Ummul%20Khair_Sultana_Thesis.pdf.
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This project was a step forward in electrochemically synthesizing nanomaterials for the water splitting reaction which directly produces hydrogen and oxygen. The thesis investigated the performances of newly developed nanomaterials for the energetically demanding water splitting reaction. In order to understand the reaction mechanism, thorough materials characterization was carried out to identify structure-activity relationships. This study also answers some fundamental questions such as "bifunctionality" in the field of water electrolysis. It also presents the modification of a readily available and cheap material, stainless steel, into an efficient water splitting catalyst that operates under industrial conditions.
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Luo, Jin. "The Development and Biocompatibility of Low Temperature Co-Fired Ceramic (LTCC) for Microfluidic and Biosensor Applications." UKnowledge, 2014. http://uknowledge.uky.edu/cme_etds/30.
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Low temperature co-fired ceramic (LTCC) electronic packaging materials are applied for their electrical and mechanical properties, high reliability, chemical stability and ease of fabrication. Three dimensional features can also be prepared allowing integration of microfluidic channels and cavities inside LTCC modules. Mechanical, optical, electrical, microfluidic functions have been realized in single LTCC modules. For these reasons LTCC is attractive for biomedical microfluidics and Lab-on-a-Chip systems. However, commercial LTCC systems, optimized for microelectrics applications, have unknown cytocompatibility, and are not compatible with common surface functionalization chemistries.
The first goal of this work is to develop biocompatible LTCC materials for biomedical applications. In the current work, two different biocompatible LTCC substrate materials are conceived, formulated and evaluated. Both materials are based from well-known and widely utilized biocompatible materials. The biocompatibilities of the developed LTCC materials for in-vitro applications are studied by cytotoxicity assays, including culturing endothelial cells (EC) both in LTCC leachate and directly on the LTCC substrates. The results demonstrate the developed LTCC materials are biocompatible for in-vitro biological applications involving EC.
The second goal of this work is to develop functional capabilities in LTCC microfluidic systems suitable for in-vitro and biomedical applications. One proposed application is the evaluation of oxygen tension and oxidative stress in perfusion cell culture and bioreactors. A Clark-type oxygen sensor is successfully integrated with LTCC technique in this work. In the current work, a solid state proton conductive electrolyte is used to integrate an oxygen sensor into the LTCC. The measurement of oxygen concentration in Clark-type oxygen sensor is based on the electrochemical reaction between working electrode and counter electrode. Cyclic voltammetry and chronoamperometry are measured to determine the electrochemical properties of oxygen reduction in the LTCC based oxygen sensor. The reduction current showed a linear relationship with oxygen concentration. In addition, LTCC sensor exhibits rapid response and sensitivity in the physiological range 1─9 mg/L. The fabricated devices have the capabilities to regulate oxygen supply and determination of local dissolved oxygen concentration in the proposed applications including perfusion cell culture and biological assays.
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Hagelin, Alexander. "ZnO nanoparticles : synthesis of Ga-doped ZnO, oxygen gas sensing and quantum chemical investigation." Thesis, Linköpings universitet, Institutionen för fysik, kemi och biologi, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-64730.
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Doped ZnO nanoparticles were synthesized by three different methods – electrochemical deposition under oxidizing conditions (EDOC) , combustion method and wet chemical synthesis – for investigating the oxygen gas sensing response. Ga-doped ZnO was mostly synthesized but also In-doped ZnO was made. The samples were analyzed by XRD, SEM, EDX and TEM. Gas response curves are given alongside with Langmuir fitted curves and data for pure ZnO and Ga-doped ZnO. DFT quantum chemical investigation of cluster models ZnO nanoparticles were performed to evaluate defect effects and oxygen and nitrogen dioxide reactions with the ZnO surface. Defects were investigated by DOS and HOMO-LUMO plots , and are oxygen vacancy, zinc vacancy, zinc interstitial and gallium doping by replacing zinc with gallium. Oxygen and nitrogen dioxide reactions were investigated by computing Mulliken charges, bond lengths, DOS spectra and HOMO-LUMO plots.
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Xiong, Linhongjia. "Amperometric gas sensing." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:a8dcbf36-14b6-4627-b380-3b81e83d446c.
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Amperometric gas sensors are widely used for environmental and industrial monitoring. They are sensitive and cheap but suffer from some significant limitations. The aim of the work undertaken in this thesis is the development of ‘intelligent’ gas sensors to overcome some of these limitations. Overall the thesis shows the value of ionic liquids as potential solvents for gas sensors, overcoming issues of solvent volatility and providing a wide potential range for electrochemical measurements. Methods have been developed for sensitive amperometry, the tuning of potentials and especially proof-of-concept (patents Publication numbers: WO2013140140 A3 and WO2014020347 A1) in respect of the intelligent self-monitoring of temperature and humidity by RTIL based sensors. Designs for practical electrodes are also proposed. The specific content is as follows. Chapter 1 outlines the fundamental principles of electrochemistry which are of importance for the reading of this thesis. Chapter 2 reviews the history and modern amperometric gas sensors. Limitations of present electrochemical approaches are critically established. Micro-electrodes and Room Temperature Ionic Liquids (RTILs) are also introduced in this chapter. Chapter 4 is focused on the study of analysing chronoamperometry using the Shoup and Szabo equation to simultaneously determine the values of concentration and diffusion coefficient of dissolved analytes in both non-aqueous and RTIL media. A method to optimise the chronoamperometric conditions is demonstrated. This provides an essential experimental basis for IL based gas sensor. Chapter 5 demonstrates how the oxidation potential of ferrocene can be tuned by changing the anionic component of room temperature ionic liquids. This ability to tune redox potentials has genetic value in gas sensing. Chapters 6 and 7 describe two novel patented approaches to monitor the local environment for amperometric gas detection. In Chapter 6, an in-situ voltammetric ‘thermometer’ is incorporated into an amperometric oxygen sensing system. The local temperature is measured by the formal potential difference of two redox couples. A simultaneous temperature and humidity sensor is reported in Chapter 7. This sensor shows advantageous features where the temperature sensor is humidity independent and vice versa. The Shoup and Szabo analysis (Chapter 4) requires ‘simple’ electron transfer and as such the reduction of oxygen in wet RTILs can be complicated by dissolved water. Chapter 8 proposes a method to stop oxygen reduction at the one electron transfer stage under humid conditions by using phosphonium based RTILs to ‘trap’ the intermediate superoxide ions. Chapters 9 and 10 report the fabrication of low cost disposable electrodes of various geometries and of different materials. The suitability of these electrode for use as working electrodes for electrochemical experiments in aqueous, non-aqueous and RTIL media is demonstrated. Their capability to be used as working probes for amperometric gas sensing systems is discussed.
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Stelter, Michael. "Elektrokatalytische Sauerstoffreduktion an übergangsmetallporphyrinmodifizierten Graphitelektroden." Doctoral thesis, Universitätsbibliothek Chemnitz, 2001. http://nbn-resolving.de/urn:nbn:de:swb:ch1-200100652.
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Die Arbeit befaßt sich mit Modellsystemen zur elektrokatalytischen Reduktion von Sauerstoff in wäßriger saurer Elektrolytlösung. Ziel ist es, zum Verständnis des Reduktionsmechanismus an makrozyklischen Elektrokatalysatoren beizutragen, da diese Stoffklasse ein Potential zum Einsatz in PEM-Brennstoffzellen besitzt. Untersucht wurden meso-arylsubstituierte Fe-, Co- und Ni-Metalloporphyrine auf einem graphitischen Träger. Die Moleküle wurden in systematischer Weise modifiziert, um Struktur-Reaktivitäts-Beziehungen zu finden. Synthese, spektroskopische Charakterisierung (UV-vis, IR, Raman) und Applikation sind beschrieben. Die Reduktion wurde mit klassischer Elektroanalytik (CV, RDE, RRDE, Impedanzmessung) und in situ-Ramanspektroskopie untersucht. Die Aktivität der Modellkatalysatoren ist abhängig vom Zentralion und den Arylsubstituenten und läßt sich teilweise mit den Hammett-Konstanten von Substituenten korrelieren. Aussagen zum Mechanismus lassen sich aus klassischer Elektroanalytik ableiten, es wurde jedoch ausschließlich 2-Elektronen-Reduktion beobachtet. Mit der in situ-Ramanspektroskopie läßt sich unter Ausnutzung des Resonanzeffekts der elektronische Zustand der Komplexe unter elektrochemischen Bedingungen beobachten. Aussagen zum Elektronentransfer und zur Redoxkatalyse werden gewonnen. Weiterhin lassen sich sowohl die geometrische Orientierung und Koordination der Chelate an die Kohlenstoffunterlage als auch die Art der Koordination des Sauerstoffmoleküls an den Katalysator untersuchen. Die untersuchten Moleküle waren parallel zur Kohlenstoffoberfläche orientiert, mit sauerstoffhaltigen Oberflächengruppen als axialem Ligand am Zentralion. Für Fe-Porphyrine wurde eine gewinkelt lineare Koordination des Sauerstoffmoleküls an das Metallzentrum gefunden.
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Aceta, Yara. "Optimization of the interfacial electron transfer by nanostructuring and surface modification." Thesis, Rennes 1, 2018. http://www.theses.fr/2018REN1S113.
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C'est la surface, et non le matériau qui interagit avec l'environnement. Par conséquent, en modifiant la surface d'un matériau de manière contrôlée, nous pouvons moduler ces interactions avec son environnement. Les sels d'aryles diazonium semblent très adaptés pour modifier les propriétés de surface de matériaux de par leurs diversités structurelles et leur capacité à modifier des surfaces conductrices par électrochimie. Ce travail de thèse se concentre sur l'étude du transfert électronique au travers de couches organiques de différentes épaisseurs (monocouches, couches ultraminces et multicouches), générées par électro-réduction de sels d'aryles diazonium. La molécule électroactive étudiée peut être alors soit fixée à la surface du matériau ou en solution. Différentes méthodes électrochimiques ont été utilisées au cours de cette thèse : CV, EIS et SECM. Dans un premier temps, l'étude des propriétés électrochimiques de surfaces carbonées modifiées par des monocouches d'alkyle-ferrocène a été entreprise dans différents solvants ; ainsi que leur évaluation pour des applications en stockage d'énergie. La deuxième étude s'intéresse à l'utilisation d'une approche « bottom-up » pour la fabrication de surfaces organisées. Des substrats de carbone et d'or ont été modifiés par électro-réduction d'un sel d'aryle diazonium pré-organisé en forme de tétraèdre. Ceci aboutit à l'obtention d'un film organique ultra-mince possédant des propriétés de tamisage moléculaire et de rectification de courant électrochimique vis-à-vis de sondes redox en solution. La troisième étude s'est ensuite focalisée sur la réaction de réduction du dioxygène et de ses intermédiaires, qui présentent un intérêt général aussi bien dans des processus naturels qu'en industrie. La détection de ces intermédiaires a été entreprise par SECM, utilisant une stratégie « d'empreinte » utilisant différentes couches organiques sensibles. L'influence du potentiel appliqué et de l'électrolyte a été étudiée. Dans ce travail, nous avons démontré que les propriétés électrochimiques de sondes redox en solution ou greffées à la surface d'un matériau peuvent être modulées par l'utilisation de couches organiques. Ces recherches fondamentales présentent un intérêt dans des domaines tels que le stockage d'énergie et la catalyseIt is the surface, not the bulk material that interacts with the surrounding environment; hence by altering the surface in a controlled manner we can modulate the properties of the material towards its environment. Aryldiazonium salts are suitable to tailor the surface properties since their structural diversity and their electrochemically-assisted bonding ability to modified conducting surfaces. This thesis focuses on the study of the electron transfer through different aryl layers by aryldiazonium electro-reduction at three different thickness levels, monolayer, near-monolayer, and multilayer, when the electroactive molecule is attached to the surface or in solution. Three different electrochemical methods have been used throughout this thesis, CV, EIS and SECM. The first study of this thesis focused on the investigation of the electrochemical properties of alkyl-ferrocene on-carbon monolayers in different solvents and its evaluation for improving the global charge density of carbon materials for energy storage applications. The second study used a bottom-up approach for the fabrication of well-organized surfaces. Carbon and gold substrates were modified by electro-reduction of a tetrahedral-shape preorganized aryldiazonium salt resulting in an ultrathin organic film that showed molecular sieving and current rectification properties towards redox probes in solution. The third study then focused on the oxygen reduction reaction and its intermediates, which are of general importance in natural and industrial processes. Detection of intermediates was achieved by SECM in a foot-printing strategy based on the use of different sensitive aryl multilayers. The role of the applied potential and electrolytes was investigated. Here we have demonstrated that the electrochemical properties of redox probes attached to a surface or in solution can be modulated by introducing aryl layers allowing fundamental research investigations of interest in fields such as energy storage and catalysis
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Tang, Yongan. "SYNTHESIS AND ELECTROCATALYSIS OF METAL NANOMATERIALS." Miami University / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=miami1402313477.
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Nylén, Linda. "Influence of the electrolyte on the electrode reactions in the chlorate process." Doctoral thesis, KTH, Tillämpad elektrokemi, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4681.
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The chlorate process is very energy intensive and a major part of the production costs are for electrical energy. Since the electricity prices are constantly increasing and may also vary periodically, the chlorate plants may be forced to adjust their production rate to the price at each moment in order to minimise their costs. Variation of current load requires increased knowledge regarding the electrode behaviour in a wide current range. In this thesis, the aim was to study the impact of the electrolyte on the electrode reactions in order to reduce the energy consumption. The work has mainly been experimental and additionally mathematical modelling has been carried out. A wide current range has been investigated in order to increase the understanding of the phenomena and to obtain results useful for low-load operation during the periods of high electricity cost. To operate the anode as energy efficiently as possible, the anode potential should not exceed the critical potential (Ecr), where the slope of the anodic polarisation curve increases, most likely due to ruthenium(VIII)-formation, and where the side reaction of oxygen evolution increases. In this work, the influence of different electrolyte parameters on Ecr has been studied. It was shown that a higher chloride concentration and an increased temperature lowered Ecr, which was expected to increase the risk of exceeding Ecr. However, this was not observed due to a simultaneous favouring of the chloride oxidation. Hence it was concluded that the electrolyte parameters should be optimised so that the lowest possible anode potential is obtained, which would enable higher current densities without exceeding Ecr. A further conclusion is that the increased slope of the polarisation curve at Ecr was possibly related to the lower activity for chloride oxidation on ruthenium oxidised to ruthenium(VIII). At full-load operation, the cathode potential was shown to be rather independent of the electrolyte composition despite a large variation of electrolyte parameters. The cathode composition appears to be more critical than the electrolyte composition when aiming at reducing the energy consumption. A strategy to increase the cathode activity could be to in situ apply a catalytic film onto the electrode surface. Therefore, Y(III) was added to a chloride electrolyte in order to form a yttrium hydroxide film on the alkaline cathode surface during hydrogen evolution. The yttrium-hydroxide film activated reduction of water (hydrogen evolution) and hindered hypochlorite reduction, proton reduction and nitrate reduction. The inhibiting properties are important for the prevention of side reactions, which currently are avoided by reducing Cr(VI) of the electrolyte on the cathode, producing an inhibiting chromium-hydroxide film. The studies on Y(III) increase the expectations for finding alternatives to the toxic Cr(VI). The addition of chromate to the chlorate electrolyte gives a high cathodic current efficiency and chromate has buffering properties in the electrolyte. The role of the buffer has been investigated for the oxygen evolution from water (one possible anodic side reaction), as well as cathodic hydrogen evolution. Models have been developed for these systems to increase the understanding of the interaction between buffer, electrode reactions and mass transport; the results have been verified experimentally. The chromate buffer increased the limiting current significantly for the cathodic H+ reduction and the cathodic overpotential was reduced drastically at currents lower than the limited current. A too low overpotential could result in the cathodic protection being lost. The presence of chromate buffer increased the limiting current for the oxygen evolution from OH-. The modelling of these systems revealed that the homogeneous reactions connected to the electrode reactions were not in equilibrium at the electrode surface. Further, a good resolution of the interface at the electrode surface was crucial since the, for the electrode reactions, important buffering takes place in an nm-thick reaction layer.Framställning av klorat är mycket energiintensiv och kräver stora mängder elenergi. Stigande elpriser, som dessutom ofta varierar under dygnet eller säsongsvis, gör att man vill reducera onödiga förluster samt ibland försöka anpassa produktionen så att man när elpriset är högt minskar den, för att sedan öka produktionen igen då elpriset sjunker. Denna flexibla drift kräver ny kunskap om hur elektroderna beter sig i ett större strömintervall än vad som tidigare varit av intresse. Målet med detta arbete var att, med fokus på elektrolytens betydelse, identifiera möjliga förbättringar för kloratprocessen och därmed minska energiförbrukningen. Studierna har i huvudsak varit experimentella men även matematisk modellering har använts. Ett brett strömintervall har undersökts för att bättre förstå fenomenen och för att även kunna använda resultaten då höga elpriser gör att man vill köra processen vid lägre laster än normalt. För att driften av anoden ska vara så energieffektiv som möjligt bör anodpotentialen inte överskrida den kritiska potentialen (Ecr), där den anodiska polarisationskurvan får en högre lutning (troligtvis pga Ru(VIII)-bildning) och bireaktionen syrgasutveckling ökar. I detta arbete har påverkan av olika elektrolytparametrar på Ecr undersökts. Det visade sig att en ökad kloridkoncentration och ökad temperatur sänkte Ecr. Trots att detta borde göra att Ecr lättare överskrids, blev inte detta fallet eftersom kloridoxidationen samtidigt gynnades. Slutsatsen blir därför att elektrolytparametrarna bör optimeras så att lägsta möjliga anodpotential uppnås, vilket då även gör att strömtätheten kan ökas utan att Ecr överskrids. Slutsatsen är vidare att polarisationskurvans högre lutning vid Ecr kan ha att göra med att rutenium oxiderat till rutenium(VIII) har lägre aktivitet för kloridoxidation. Vid full last visade sig katodens potential vara relativt oberoende av elektrolytsammansättningen trots att denna varierades kraftigt. Katodens sammansättning verkar vara viktigare att ta hänsyn till än elektrolytens för kunna åstadkomma en större energibesparing. Ett alternativ till att öka katodens aktivitet skulle vara att in-situ belägga elektrodytan med en katalytisk film. Försök gjordes att sätta till Y(III) till kloridelektrolyt för att under vätgasutveckling fälla ut en yttriumhydroxidfilm på den alkaliska katodytan. Yttriumhydroxidfilmen aktiverade vattenreduktion (vätgasutveckling) och inhiberade hypokloritreduktion, protonreduktion och nitratreduktion. De inhiberande egenskaperna är viktiga för att förhindra bireaktioner, vilka idag hindras av att Cr(VI) i elektrolyten reduceras på katoden och bildar en hindrande kromhydroxidfilm. Försöken med Y(III) visar att det finns goda möjligheter att hitta alternativ till det miljöfarliga Cr(VI). Kromattillsatsen i kloratelektrolyt ger förutom ett högt katodiskt strömutbyte även en buffrande effekt till elektrolyten. Effekten av buffert har undersökts för en av de anodiska bireaktionerna, syrgasutveckling ur vatten, samt för vätgasutvecklingen på katoden. Dessa system har modellerats för att bättre förstå samspelet mellan buffert, elektrodreaktioner och materietransport och resultaten har verifierats experimentellt. Kromatbufferten ökade gränsströmmen för katodisk H+-reduktion betydligt och katodöverpotentialen sjönk kraftigt vid lägre strömmar än gränsströmmen. Detta kan vara ett problem om överpotentialen sjunker så lågt att elektroden inte är katodiskt skyddad. För syrgasutvecklingen ökade närvaron av kromatbuffert gränsströmmen för syrgasutveckling ur OH-. Modellering av dessa system visar att de homogena reaktioner som var kopplade till elektrodreaktionerna inte var i jämvikt vid elektrodytan. Vidare visade det sig vara mycket viktigt med en bra upplösning av gränsskiktet vid elektrodytan, då den buffring som är viktig för elektrodreaktionerna sker i ett mycket tunt reaktionsskikt (nanometertjockt).
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PEZZOLATO, LORENZO. "Fe-N-C non-noble catalysts for applications in Fuel Cells and Metal Air Batteries." Doctoral thesis, Politecnico di Torino, 2020. http://hdl.handle.net/11583/2809320.
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Ma, Xiaoli. "Syntheses, structures, electrochemical and oxygen atom transfer properties of molybdenum and tungsten complexes with sulfur and selenium containing ligands." Doctoral thesis, [S.l.] : [s.n.], 2007. http://webdoc.sub.gwdg.de/diss/2007/ma.
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Blanes, Guàrdia Mireia. "Contribució al desenvolupament, optimització i regeneració de sensors d’oxigen per al control d’humitat en entorns d’alta temperatura." Doctoral thesis, Universitat de Barcelona, 2021. http://hdl.handle.net/10803/673223.
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Els treballs realitzats en aquesta tesi doctoral s’han dirigit cap al desenvolupament, optimització i regeneració dels sensors d’oxigen per a la detecció d’humitat en entorns d’alta temperatura per acomplir amb un objectiu concret: implementar un sensor d’oxigen planar basat en YSZ a l’interior d’un forn industrial per a la quantificació de la humitat present a l’interior de la cambra.
L’assoliment d’aquest objectiu concret s’han aconseguit gràcies al desenvolupament dels diversos estudis que es presenten en aquesta tesi.
En una primera part del treball més descriptiva s’emmarca la necessitat del desenvolupament (centrada en la detecció de la humitat en condicions d’alta temperatura) i es presenta la descripció dels processos de la fabricació dels sensors i d’obtenció dels materials mitjançant la tecnologia ceràmica multicapa d’alta temperatura. La robustesa dels mètodes de fabricació aplicats, han permès acotar diferents paràmetres de disseny dels sensors per garantir que tots els sensors fabricats es troben dins els intervals definits.
Posteriorment la tesi es centra en la caracterització electroquímica dels sensors i dels seus processos de degradació i regeneració en les condicions de treball.
S’ha aprofundit en l’estudi i coneixement de les propietats difusores dels sensors i s’ha determinat una geometria de la zona difusora que garanteix una resposta adequada dels sensors en diferents condicions de mesura. Per acomplir amb aquest objectiu, s’ha estudiat la resposta obtinguda per a diferents porositats dels canals difusors i s’ha determinat la geometria de la zona difusora per tal que ofereixi una lectura del corrent límit adequada en les atmosferes amb continguts d’oxigen més elevats. S’ha determinat la temperatura mínima operacional de T=750ºC per a garantir un corren límit adequat en aire quan els sensors presenten un corrent màxim de 6mA. A partir de l’anàlisi dels resultats en atmosferes humides, s’ha determinat la tensió de polarització màxima aplicable a la cel·la, quantificada en 0.5V, i la màxima temperatura de treball, quantificada en T=950ºC.
Seguidament es presenta un estudi electroquímic dels sensors i dels seus efectes de degradació en entorns d’humitat. Aquest estudi es basa en la caracterització mitjançant espectroscòpia d’impedància (EIS) dels sensors complerts. S’han pogut diferenciar tres contribucions RC amb freqüències de transició clarament diferenciades. Les correlacions entre les respostes obtingudes, les condicions operacionals de temperatura i les atmosferes de mesura han permès assignar la transició observada a altes freqüències (ArcAF) amb els punts triples (TPB), la transició que apareix a freqüències intermitges (ArcFM) s’ha relacionat amb l’elèctrode exterior i la transició observada a baixes freqüències (ArcBF) s’ha associat amb l’elèctrode interior. Els estudis realitzats amb diferents configuracions dels sensors (cavitats difusores més grans o capes protectores més gruixudes) han permès avaluar el solapament de les diferents contribucions i justificar les diferents formes de les respostes obtingudes en les mesures realitzades a 2 elèctrodes (que poden presentar 2 o 3 transicions diferenciables). A partir d’aquests resultats, s’han pogut determinar els efectes de la degradació dels sensors, concentrats sobretot en la desactivació dels punt triples generada per l’adsorció de molècules d’H2O i a la formació d’òxids de platí.
Finalment, en l’estudi de regeneració presentat s’ha pogut determinar el grau de reversibilitat de la degradació dels sensors i definir un cicle regeneratiu que permeti augmentar la durabilitat dels sensors en les atmosferes de treball. S’ha demostrat que la regeneració mitjançant l’aplicació d’un potencial catòdic és molt més efectiva i té uns efectes més perllongats en el temps. S’ha provat que la funcionalitat del sensor pot
recuperar-se amb només una reactivació parcial dels punts triples.The work carried out in this doctoral thesis has been directed towards the development, optimization, and regeneration of oxygen sensors for the detection of humidity in high temperature environments to fulfill a specific goal: to implement a planar YSZ-based oxygen sensor inside an industrial furnace for quantifying the moisture present inside the chamber. A detailed study of the diffusive properties of the sensors has been undergone so that a geometry of the diffuser zone was determined to guarantee an adequate response of the sensors in the different measurement conditions. An electrochemical study of sensors in humid environments is presented. This study is based on the impedance spectroscopy (EIS) characterization of complete sensors. Three RC contributions have been characterized with clearly differentiated transition frequencies. The correlations between the obtained responses with different operating conditions of temperature and atmospheres, have allowed to assign the transition observed to high frequencies (ArcAF) with the triple phase boundaries (TPBs), the transition that appears to intermediate frequencies (ArcFM) has been related to the outer electrode and the observed transition to low frequencies (ArcBF) has been associated with the inner electrode. Studies carried out with different configurations of the sensors have allowed to evaluate the overlap of the different contributions and justify the different forms of the responses obtained in the measurements made at 2 electrodes. From these results, it has been possible to determine the effects of the degradation of the sensors, concentrated mainly on the deactivation of the TPBs generated by the adsorption of H2O molecules and the formation of platinum oxides. Finally, it has been possible to determine the degree of reversibility of the degradation of the sensors and to define a regenerative cycle. Regeneration by applying a cathodic potential has been shown to be much more effective and has longer-lasting effects.
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Sanches, Cassandra Degelo. "Desempenho eletrocatalítico de eletrodos recobertos com filmes de quitosana frente a reação de redução de oxigênio em meio alcalino." Universidade de São Paulo, 2009. http://www.teses.usp.br/teses/disponiveis/75/75131/tde-14012010-105132/.
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A reação de redução de oxigênio (RRO) foi estudada em eletrodos lisos de platina e prata recobertos com filmes de quitosana e em eletrodos porosos de Pt/C, Ag/C, MnyOx/C e TiO2/C na ausência e na presença de filmes à base de quitosana, em eletrólito alcalino. Nestes estudos foram empregadas curvas de polarização em estado estacionário, obtidas em eletrodos de disco rotatório (EDR) e em células a combustível alcalina (CCA) unitárias, através das quais foram construídos os correspondentes diagramas de curvas de Tafel e os gráficos de Levich. Os estudos realizados em EDRs permitiram estabelecer-se uma boa compreensão da atividade catalítica e dos mecanismos envolvidos na RRO. Foi observada uma diminuição da atividade eletrocatalítica dos eletrodos metálicos (Pt e Ag lisos e porosos) quando na presença dos filmes de quitosana, havendo também uma mudança no mecanismo da reação. Assim, nos experimentos de EDR verificou-se que em altas densidades de corrente a etapa determinante da velocidade é a adsorção do oxigênio, em contraste com os eletrodos sem o filme para os quais a etapa determinante é a difusão do oxigênio. Nestes casos não foi possível calcular o número de elétr. Já, nos casos dos eletrodos de MnyOx/C e TiO2/C não foi observada nenhuma diminuição significativa na atividade eletrocatalítica destes materiais na presença dos filmes de quitosana, assim como no mecanismo da reação na presença dos filmes (inclusive no número de elétrons envolvidos na reação), apesar de se notar um pequeno aumento nos valores dos coeficientes de Tafel. Foram também realizados testes de alguns dos materiais como cátodos em células a combustível alcalinas unitárias alimentadas com hidrogênio/oxigênio, tendo sido verificado que o desempenho é promissor, apesar de ser inferior ao de células com eletrólito de membrana ácidas.The oxygen reduction reaction was studied on smooth platinum and silver electrodes recovered with chitosan films and on Pt/C, Ag/C, MnyOx/C e TiO2/C porous electrodes in the presence or absence of chitosan-based films in alkaline electrolyte. These studies were carried out using steady state polarization measurement, obtained in a rotating disc electrode (RDE) and in alkaline fuel cells (AFC) (single cell), from which the corresponding Tafel curves and Levich plots were built. The studies carried out using the RDE had allowed establishing a good understanding of the catalytic activity and of the involved RRO mechanisms. A reduction in the electrocatalytic activity of the metallic electrodes and a change in the reaction mechanism (Pt and Ag smooth and porous) were caused by the presence of the chitosan films Thus, the RDE experiments showed that at high current densities the rate determining step of the ORR is the oxygen adsorption, in contrast to the electrodes without the film for which the rate determining step is the oxygen diffusion. In these cases it was not possible to calculate the number of electrons involved in the reaction. In the cases of the MnyOx/C and TiO2/C electrodes no significant change in the electrocatalytic activity, as well as in the reaction mechanism were caused due to the presence of the films (also in the number of electrons involved in the reaction), although a small increase in the Tafel coefficient values was noted. Also, tests of some of the materials as cathodes in AFC single cells with hydrogen/oxygen were carried out. These results showed that the performance is promising, although inferior to those of acid membrane electrolyte fuel cells.
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ANNAMALAI, ABINAYA. "Electrochemical Energy Conversion Catalysts for Water Oxidation and CO2 Reduction." Doctoral thesis, Università degli studi di Genova, 2022. http://hdl.handle.net/11567/1086344.
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Numerous efforts have been made for the development of renewable energies to replace fossil fuels and thus reduce greenhouse gas emissions. Renewable energy has the advantage of having a limitless supply over time and is clean. This thesis reports on novel transition metal-based electrocatalysts for acidic water splitting and CO2 reduction, which are two significant technologies to produce chemical fuels (i.e. H2 and C-based compounds) from renewable electricity. The target is to develop and investigate cost-effective, stable, and efficient electrocatalysts for acidic water splitting and CO2 reduction, replacing noble metals and achieving performances above the current state of the art.
In the first part, the preparation and oxygen evolution properties of the oxygen plasma-treated and acid-activated carbon paper are investigated. This part also presents the Ru incorporated Carbon paper, as an efficient, stable, and self-standing catalyst for OER in acid. This catalyst shows an overpotential of 230 mV vs. RHE at 1 mA cm−2, comparable to the other carbon-based materials. It shows a small Tafel slope of 74 mV dec-1 and 20 hours of stability at 10 mA cm−2.
In the second part, the template-assisted wet synthesis and electrochemical OER studies of yolk-shell Co3O4/Co1−xRuxO2 hollow microspheres (MSs) are discussed. It demonstrates a lower overpotential of 240 mV at 10 mA cm-2 and a small Tafel slope of 70 mV dec−1. Also, the MSs exhibit high mass activity of 600 A g−1 and show high stability for 24 hours Chronopotentiometry tests at constant current densities of 10 and 20 mA cm−2 in 0.5 M H2SO4.
Finally, nanostructured CdSe/Cu3P/CdSe heterostructures (in the form of nanocoral and sandwiches), obtained through colloidal synthesis, were used as efficient electrocatalysts for CO2 reduction. The nanocoral and Sandwich structured catalyst demonstrated higher CO2-to- HCOO– conversion giving a FEHCOO– of about 60% and 40% at –1.4 V vs RHE, respectively in 0.5 M KCl.
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Lepesant, Mathieu. "Catalyseurs multimétalliques nano-organisés pour pile à combustible PEM." Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENI052/document.
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La diminution du coût des catalyseurs est l'une des conditions nécessaires pour rendre la technologie PEMFC économiquement viable au grand public. Ces catalyseurs, habituellement composés de nanoparticules de platine, sont limités par leur coût, leur performance et leur durabilité. La nanostructuration est une des solutions envisageables pour ces catalyseurs car elle permet d'augmenter considérablement la surface spécifique, de diminuer le chargement en platine et d'augmenter les performances pour la réaction de réduction de l'oxygène, la plus limitante dans la technologie PEMFC.Les travaux présentés dans ce mémoire, ont été réalisés autour de deux types de particules nanostructurées (particules coeur-coquille et particules creuses) à base de platine ou d'alliage de platine. Ces particules ont été étudiées, caractérisées en électrochimie à 3 électrodes (électrode tournante disque-anneau et montage demi-pile) puis intégrées dans des systèmes pile à combustible. Nous avons observé les améliorations de performances offertes par ce type de particules électro-catalytiques vis-à-vis de la réaction de réduction de l'oxygène. Puis nous avons commencé à étudier et à optimiser leur intégration dans les piles à combustible en conditions réelles de fonctionnementThe decrease in cost of catalysts is one of the conditions necessary to make economically viable PEMFC technology to the general public. These catalysts, usually composed of platinum nanoparticles, are limited by cost, performance and durability. Nanostructuring is one of the possible solutions for these catalysts because it greatly increases the surface area, reducing the platinum loading and increase performance for the reaction of oxygen reduction, the most limiting in PEMFC technology.The works presented in this thesis were performed on two types of nanostructured particles (core-shell particles, hollow particles) based on platinum or platinum alloy. These particles have been studied, characterize in electrochemistry to 3 electrodes (rotating ring-disk electrode and half-cell assembly) and then integrated in fuel cell systems. We observed performance improvements offered by this type of electro-catalytic particles towards the reduction reaction of oxygen and then we started studying and optimize their integration into fuel cells and actual conditions of operation
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Phuakkong, Oranit. "Design of carbon based structures for electrochemical applications." Thesis, Bordeaux, 2016. http://www.theses.fr/2016BORD0305/document.
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Dans cette thèse nous avons étudié la mise en forme de matériaux carbonés par des méthodes électrochimiques pour des applications dans les domaines des capteurs et de l’énergie. Dans la première partie, l’électrochimie bipolaire, qui permet de réaliser des réactions électrochimiques sur un objet conducteur présent dans une solution et soumise à un champ électrique, a été utilisée pour générer des objets de type Janus. Ces objets asymétriques ont été modifiés à une extrémité par du poly(N-isopropylacrylamide (pNIPAM), un hydrogel sensible à la température, et par une peinture électrophorétique à l’autre extrémité. En contrôlant l’intensité du champ électrique ainsi que son temps d’application il a été possible de varier la longueur ainsi que l’épaisseur de l’hydrogel. Ces objets sensibles à la température, émettant de la lumière, ont des applications potentielles dans le domaine des capteurs ou dans le milieu médical.Dans la seconde partie, la mise en forme de carbone poreux pour des applications électrochimiques a été étudiée. La carbonisation de polymères contenant du zinc a été utilisé pour synthétiser du carbone micro/mésoporeux possédant ainsi une grande surface spécifique. Les polymères contenant du zinc ont été préparés à partir de différents types de ligands d’acide dicarboxylique par une méthode solvothermique. Ils ont ensuite été carbonisés pour obtenir des matériaux poreux avec des caractéristiques et des propriétés particulières. Ils ont été utilisés comme matériaux d’électrode pour des supercondensateurs, montrant des capacités élevées. De plus ils possèdent également une activité électrocatalytique à la réaction de réduction de l’oxygèneIn this thesis, the design of advanced carbon materials via electrochemical techniques and for electrochemical applications have been studied. In the first part, the concept of bipolar electrochemistry, which allows carrying out electrochemical reactions on a free-standing conductive object in an electric field, was employed to generate Janus-type objects. These objects are modified with a thermoresponsive hydrogel of poly(N-isopropylacrylamide) (pNIPAM) on one side and an electrophoretic deposition paint (EDP) on the other side. The results show that the length and the thickness of the hydrogel can be controlled by varying the electric field and the time of the experiment. The concept can be further generalized to other micro- and nanometer-sized objects, thus opening up perspectives for various applications.In the second part, the design of porous carbon structures for electrochemical applications was studied. The direct carbonization of non-porous zinc containing polymers was used to synthesize micro/mesoporous carbons with high surface area, pore volume. Non-porous zinc containing polymers with various types of dicarboxylic acid ligands prepared by solvothermal method were used as templates and starting materials. After carbonization porous carbons with various characteristics and properties were obtained. The synthesized porous carbon samples showed good electrochemical performance with high capacitance values. In addition, the derived materials exhibit excellent electrocatalytic activity with respect to the oxygen reduction reaction (ORR)
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Ekström, Henrik. "Evaluating Cathode Catalysts in the Polymer Electrolyte Fuel Cell." Doctoral thesis, KTH, Tillämpad elektrokemi, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4413.
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The polymer electrolyte membrane fuel cell (PEMFC) converts the chemical energy of hydrogen and oxygen (air) into usable electrical energy. At the cathode (the positive electrode), a considerable amount of platinum is generally required to catalyse the sluggish oxygen reduction reaction (ORR). This has implications regarding the cost in high-power applications, and for making a broad commercialisation of the PEMFC technology possible, it would be desirable to lower the amount of Pt used to catalyse the ORR. In this thesis a number of techniques are described that have been developed in order to investigate catalytic activity at the cathode of the PEMFC. These methodologies resemble traditional three-electrode research in liquid electrolytes, including cyclic voltammetry in inert gas, but with the advantage of performing the experiments in the true PEMFC environment. From the porous electrode studies it was seen that it is possible to reach mass activities close to 0.2 gPt/kW at potentials above 0.65 V at 60 ◦C, but that the mass activities may become considerably lower when raising the temperature to 80 ◦C and changing the measurement methodology regarding potential cycling limits and electrode manufacturing. The model electrode studies rendered some interesting results regarding the ORR at the Pt/Nafion interface. Using a novel measurement setup for measuring on catalysed planar glassy carbon disks, it was seen that humidity has a considerable effect on the ORR kinetics of Pt. The Tafel slopes become steeper and the activity decreases when the humidity level of the inlet gases decreases. Since no change in the the electrochemical area of the Pt/Nafion interface could be seen, these kinetic phenomena were ascribed to a lowered Pt oxide coverage at the lower humidity level, in combination with a lower proton activity. Using bi-layered nm-thick model electrodes deposited directly on Nafion membranes, the behaviour of TiO2 and other metal oxides in combination with Pt in the PEMFC environment was investigated. Kinetically, no intrinsic effect could be seen for the model electrodes when adding a metal oxide, but compared to porous electrodes, the surface (specific) activity of a 3 nm film of Pt deposited on Nafion seems to be higher than for a porous electrode using ∼4 nm Pt grains deposited on a carbon support. Comparing the cyclic voltammograms in N2, this higher activity could be ascribed to less Pt oxide formation, possibly due to a particle size effect. For these bi-layered films it was also seen that TiO2 may operate as a proton-conducting electrolyte in the PEMFC.I polymerelektrolytbränslecellen (PEMFC) omvandlas den kemiska energin hos vätgas och syrgas (luft) direkt till användbar elektrisk energi. På katoden (den positiva elektroden) krävs betydande mängder platina för att katalysera den tröga syrereduktionsreaktionen (ORR). Detta inverkar på kostnaden för högeffektsapplikationer, och för att göra en bred kommersialisering av PEMFC-teknologin möjlig skulle det vara önskvärt att minska den Pt-mängd som används för att katalysera ORR. I denna avhandling beskrivs ett antal tekniker som utvecklats för att undersöka katalytisk aktivitet på katoden i PEMFC. Metodiken liknar traditionella treelektrodexperiment i vätskeformig elektrolyt, med cyklisk voltammetri i inert gas, men med fördelen att försöken utförs i den riktiga PEMFC-miljön. I försök med porösa elektroder visades att det är möjligt att nå massaktiviteter nära 0.2 gPt/kW för potentialer över 0.65 V vid 60 ◦C, men massaktiviteterna kan bli betydligt lägre om temperaturen höjs till 80 ◦C, och om potentialsvepgränser och elektrodentillverkningsmetod ändras. Försök med modellelektroder resulterade i intressanta resultat rörande ORR i gränsskiktet Pt/Nafion. Genom att använda en ny metodik för att mäta på katalyserade plana elektroder av vitröst kol (glassy carbon), var det möjligt att se att gasernas fuktighet har en betydande inverkan på ORR-kinetiken hos Pt. Tafellutningarna blir brantare och aktiviteten minskar när inloppsgasernas fuktighetsgrad minskar. Eftersom den elektrokemiska arean hos Pt/Nafion-gränsskiktet inte ändrades, ansågs dessa kinetiska effekter bero på en lägre täckningsgrad av Ptoxider vid lägre fuktigheter, i kombination med lägre protonaktivitet. Genom att använda Nafionmembran belagda med nm-tjocka tvåskiktsmodellelektroder undersöktes hur Pt i kombination med TiO2 och andra metalloxider verkar i PEMFC-miljön. Kinetiskt sett hade tillsatsen av metalloxider ingen inre påverkan på aktiviteten, men vid jämförelse med porösa elektroder tycks den specifika ytaktiviteten vara högre hos en 3 nm film av Pt på Nafion än för en porös elektrod baserad på ∼4 nm Pt-korn belagda på ett kolbärarmaterial. Jämför man de cykliska voltammogrammen i N2, kan den högre aktiviteten tillskrivas en lägre grad av Pt-oxidbildning, vilket i sin tur kan bero på en storlekseffekt hos Pt-partiklarna. Försöken med dessa tvåskiktselektroder visade också att TiO2 kan verka som protonledande elektrolyt i PEMFC.
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Pearce, Paul-Emile. "AxIrO3 (A = Li, Na ou H) pour le stockage et la conversion électrochimique de l’énergie." Electronic Thesis or Diss., Sorbonne université, 2019. http://www.theses.fr/2019SORUS313.
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Cette thèse est centrée sur l'étude du composé AxIrO3 en tant qu'hôte polyvalent pour Li+, Na+ et H+. Sa structure tridimensionnelle représente un terrain intéressant pour l’étude fondamentale de l’oxydoréduction du réseau anionique dans les oxydes pour les batteries à ions Li+ et Na+. La phase lithiée peut être obtenue par synthèse céramique à haute température selon deux étapes alors que la phase sodiée n’a pu être obtenue que par voie électrochimique en passant par IrO3. La phase protonée peut être obtenue par échange cationique de la phase lithiée ou par réaction de l’eau avec IrO3. Ces deux dernières phases n’avaient encore pas été reportées auparavant. Les processus d’insertion ont été caractérisés par diverses techniques telles que la diffraction des rayons X et des neutrons et par spectroscopies d’absorption et de photoémission X afin de déterminer les changements structuraux associés aux processus d’oxydoréduction cationique et anionique. Les résultats obtenus permettent d’approfondir notre compréhension d’un mécanisme de compensation de charge encore mal compris. De plus, l’étude de la réactivité d’IrO3 avec un milieu aqueux acide a permis de décrire un mécanisme de catalyse de la réaction d’oxydation de l’eau à la surface des oxydes d’iridium et apporte des pistes pour le développement de nouveaux électrocatalyseurs à base d’iridiumThis thesis focuses on the study of the compound AxIrO3 as a versatile host for Li+, Na+ and H+. Its three-dimensional structure represents an interesting playing field for the fundamental study of the redox activity of the anionic network in oxides for Li+ and Na+ ion batteries. The lithiated phase can be obtained by high temperature ceramic synthesis in two stages whereas the sodiated phase could only be obtained electrochemically via IrO3. The protonated phase can be obtained by cation exchange of the lithiated phase or by reaction of water with IrO3. These last two phases had not been previously reported. The insertion processes were characterized by various techniques such as X-ray and neutron diffraction as well as X-ray absorption and photoemission spectroscopies to determine the structural changes associated with cationic and anionic oxidation processes. The results obtained allow us to deepen our understanding of a charge compensation mechanism that is still poorly understood. In addition, the study of the reactivity of IrO3 with an acidic aqueous media has made it possible to describe a mechanism for the electrocatalysis of the oxygen evolution reaction on the surface of iridium oxides and provides avenues for the development of new electrocatalysts based on iridium