Superoxide-based Approach to Electrochemical Oxygen Concentration PDF Download

Author: Bryce Alan Pech
Publisher:
ISBN:
Category : Superoxides
Languages : en
Pages : 124

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Author: Iromie A. Gunasekara
Publisher:
ISBN:
Category : Carbonates
Languages : en
Pages : 174

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High energy density portable power solutions have been of utmost importance for the advancement of modern day necessities such as data and voice communication, vehicular transportation, distributed power generation and storage of energy produced by sustainable power sources. Progress made in fuel cell and lithium-ion battery technologies over the past decade have opened opportunities to power electric and hybrid electric vehicles for long distance transportation. Alkaline membrane fuel cells (AEMFCs) are the new alternatives to proton exchange membrane fuel cells (PEMFCs), which require generous amounts of noble metal-based catalysts on their electrodes. Facile electrode kinetics on non-precious group metal catalysts in alkaline environments is the key factor which has promoted AEMFCs over PEMFCs. While the research on AEMFCs is vastly expanding, high energy density batteries are praiseworthy considering the high cost of hydrogen fuel. The state-of-the-art Li-ion batteries cannot reach the desirable capacity density to power electric vehicles capable of >300 miles on a single charge whereas Li-O2 batteries with a theoretical capacity more than ten times larger than that of Li-ion have become very promising for this application. Chapter 1 of this thesis provides a discussion of the background behind the fuel cell and battery technologies beyond Li-ion along with the electrochemical and analytical techniques employed throughout this investigation. The major deterrent to AEMFC technology is its performance decrease by means of carbonate exchange of the membrane when exposed to carbon dioxide. The second Chapter deals with a quantitative determination of the influence of carbonate ions in the alkaline membrane on interfacial electrode reactions and reactant transport through the membrane. A Pt microelectrode investigation conducted on a commercial anion exchange membrane (AEM) (Tokuyama, A201) showed rather close kinetics for oxygen reduction reaction (ORR) with and without carbonate exchange as well as with a perfluorinated proton exchange membrane analog such as Nafion®. Resolution of the mass transport into constituent components (diffusion coefficient and solubility) showed that the oxygen diffusion coefficient in the AEM exchanged with carbonate ions (CO32−) is lowered while the solubility remained unaffected. These results show remarkable agreement with polarization corrected fuel cell data, thus enabling a method to better resolve interfacial performance of an AEM fuel cell. We have also investigated the kinetics of hydrogen oxidation reaction (HOR) and methanol oxidation reaction (MOR) at the Tokuyama (A201/A901) anion exchange membrane /Pt microelectrode interfaces using solid state electrochemical cells. Diffusion of hydrogen molecules through the membrane was not influenced by the carbonate ions due to the smaller size of the gaseous molecule. However, hydrogen concentration in the anion exchange membrane is low in the presence of carbonate ions. Methanol diffusion is facilitated in the anion exchange polymer electrolyte due to its high water content. A change of the diffusion path length in carbonate polymer electrolytes caused methanol permeability to drop significantly. The kinetic parameters obtained for the AEM in the carbonate form suggests that both hydrogen and methanol oxidation reactions proceed through the carbonate pathway. Therefore, the kinetic parameters obtained are significantly lower than what were observed at the AEM in the hydroxide form. In the third Chapter I demonstrate that a microelectrode can be used as a diagnostic tool to determine O2 transport properties and redox kinetics in dimethyl sulfoxide (DMSO)–based electrolytes for non-aqueous Li-air batteries, and to elucidate the influence of ion-conducting salts on the O2 reduction reaction mechanism. Oxygen reduction/evolution reactions on a carbon microelectrode have been studied in dimethyl sulfoxide-based electrolytes containing Li+ and tetrabutylammonium ((C4H9)4N+) ions. Analysis of chronoamperometric current-time transients of the oxygen reduction reactions in the series of tetrabutylammmonium (TBA) salt-containing electrolytes of TBAPF6, TBAClO4, TBACF3SO3, or TBAN(CF3SO2)2 in DMSO revealed that the anion of the salt exerts little influence on O2 transport. Whereas steady-state ORR currents (with sigmoidal-shaped current-potential curves) were observed in TBA-based electrolytes, peak-shaped current-voltage profiles were seen in the electrolytes containing their Li salt counterparts. The latter response results from the combined effects of the electrostatic repulsion of the superoxide (O2−-) intermediate as it is reduced further to peroxide (O22−) low potentials and the formation of passivation films of the O2 reduction products at the electrode. Raman spectroscopic data confirmed the formation of non-conducting Li2O2 and Li2O on the electrode surface at different reduction potentials in Li salt solutions. Out of the four lithium salt-containing electrolytes studied, namely LiPF6, LiClO4, LiCF3SO3, or LiN(CF3SO2)2 in DMSO, the LiCF3SO3/DMSO solution revealed the most favorable ORR kinetics and the least passivation of the electrode by ORR products. The influence of lithium salts on O2 reduction reactions (ORR) in 1, 2-dimethoxyethane (DME) and tetraethylene glycol dimethyl ether (TEGDME) has been investigated in Chapter 4. Microelectrode studies in a series of tetrabutylammonium salt (TBA salt)/DME-based electrolytes showed that O2 solubility and diffusion coefficient are not significantly affected by the electrolyte anion. The ORR voltammograms on microelectrodes in these electrolytes exhibited steady-state limiting current behavior. In contrast, peak-shaped voltammograms were observed in Li+-conducting electrolytes suggesting a reduction of the effective electrode area by passivating ORR products as well as migration-diffusion control of the reactants at the microelectrode as observed in DMSO-based electrolytes. FT-IR spectra have revealed that Li+ ions are solvated to form solvent separated ion pairs of the type Li+(DME)nPF6− and Li+(TEGDME)PF6− in LiPF6-based electrolytes. On the other hand, the contact ion pairs (DME)mLi+(CF3SO3−) and (TEGDME)Li+(CF3SO3−) appear to form in LiSO3CF3-ontaining electrolytes. In the LiSO3CF3-based electrolytes, the initial ORR product, superoxide (O2−), is stabilized in solution by forming [(DME)m−1(O2−)]Li+(CF3SO3−) and [(TEGDME)(O2−)]Li+(CF3SO3−) complexes. These soluble superoxide complexes are able to diffuse away from the electrode surface reaction sites to the bulk electrolyte in the electrode pores where they decompose to form Li2O2. This explains the higher capacity obtained in Li/O2 cells utilizing LiCF3SO3/TEGDME electrolytes. In Chapter 5 the synthesis of iron(II) phathlaocyanine (FePC)-based catalysts is presented. FePC embedded in a carbon support was heat-treated at a series of temperatures (300oC, 600oC and 800oC) and characterized by means of several spectroscopic and electrochemical techniques. Catalytic oxygen reduction recorded in the low Donor Number acetonitrile (MeCN)-based electrolytes have shown that the oxygen reduction reaction (ORR) mechanism is modified at the catalyst surface. Redox electrochemistry of FePC recorded in argon saturated electrolytes has confirmed that the iron is in the Fe(I) state at the O2 reduction potential in these electrolytes which is capable of stabilizing the superoxide leading to an inner[nil]Helmholtz plane electron transfer reaction. In high Donor Number DMSO[nil]based electrolytes the ORR was not influenced by the catalyst and this has been attributed to the oxidation state of iron being Fe(II) at the superoxide forming potential. The superoxide formed in such conditions are stabilized by the DMSO solvated softer Lewis acid Li+ as the Li+(DMSO)n-O2− ion pair in solution. The ORR reaction in this electrolyte proceeds through an outer Helmholtz plane electron transfer process despite the presence of the FePC catalyst in the electrode. Catalyzed carbon electrodes treated at 300 and 600oC were successfully employed in the low Donor Number tetra ethylene glycol dimethyl ether (TEGDME)[nil]based electrolyte-containing Li-O2

Author: Pei Kang Shen
Publisher: Springer Nature
ISBN: 9813360771
Category : Science
Languages : en
Pages : 259

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This book discusses systematically the theoretical research and the applications of electrochemical oxygen reduction. Oxygen reduction reaction is a common issue in electrochemistry, but is also an important process involved in the field of energy, cryogenic fuel cells, metal–air cells, oxygen sensors and hydrogen peroxide preparation. This book is divided into 6 chapters; it starts with a description of dynamic mechanisms, followed by a detailed introduction on the related experimental methods and related catalyst preparation technology. By providing the basic methods and testing techniques, and by demonstrating their applications, it helps readers gain a better understanding of oxygen reduction reactions, making it a valuable resource for the industrialization of scientific research achievements. Accordingly, the book appeals to a broad readership, particularly graduate students, those working at universities and research organizations, and industrial researchers.

Author: Adrian C. Michael
Publisher: CRC Press
ISBN: 1420005863
Category : Medical
Languages : en
Pages : 540

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Since the first implant of a carbon microelectrode in a rat 35 years ago, there have been substantial advances in the sensitivity, selectivity and temporal resolution of electrochemical techniques. Today, these methods provide neurochemical information that is not accessible by other means. The growing recognition of the versatility of electrochemi

Author: Vladimir M. Mirsky
Publisher: Springer Science & Business Media
ISBN: 3662052040
Category : Science
Languages : en
Pages : 367

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Traditional biological sensors, based on enzymatic receptors and potentiometric or amperometric transducers are well reviewed and are nowadays even included extensively in many textbooks. The editors of this volume, the 2nd in the new Springer Series on Chemical and Biosensors, have focussed exclusively on alternative types of chemical and biological sensors or sensor-like structures. Special attention is given to sensor principles based on the use of linear or non-linear impedance spectroscopy. After self-assembled monolayers have become a viable technology for the immobilization of organic molecules on electrodes and for the formation of covalently stabilized receptor layers and even more sophisticated organic nano- and microstructures, this has led to the development of numerous analytical applications of impedometric sensor methods. These new and very promising types of sensors, their technology and performance in real world applications form the main topic of this book written by leading experts from around the world.

Author: Xueji Zhang
Publisher: Academic Press
ISBN: 008055489X
Category : Science
Languages : en
Pages : 625

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This book broadly reviews the modem techniques and significant applications of chemical sensors and biosensors. Chapters are written by experts in the field – including Professor Joseph Wang, the most cited scientist in the world and renowned expert on sensor science who is also co-editor. Each chapter provides technical details beyond the level found in typical journal articles, and explores the application of chemical sensors and biosensors to a significant problem in biomedical science, also providing a prospectus for the future.This book compiles the expert knowledge of many specialists in the construction and use of chemical sensors and biosensors including nitric oxide sensors, glucose sensors, DNA sensors, hydrogen sulfide sensors, oxygen sensors, superoxide sensors, immuno sensors, lab on chip, implatable microsensors, et al. Emphasis is laid on practical problems, ranging from chemical application to biomedical monitoring and from in vitro to in vivo, from single cell to animal to human measurement. This provides the unique opportunity of exchanging and combining the expertise of otherwise apparently unrelated disciplines of chemistry, biological engineering, and electronic engineering, medical, physiological. Provides user-oriented guidelines for the proper choice and application of new chemical sensors and biosensors Details new methodological advancements related to and correlated with the measurement of interested species in biomedical samples Contains many case studies to illustrate the range of application and importance of the chemical sensors and biosensors

Author: Jonathan R. Strobl
Publisher:
ISBN:
Category : Chemistry
Languages : en
Pages : 200

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A 3-mercapto-1-propanol-modified Au ring electrode has been employed to monitor solution phase superoxide, generated at the surface of a glassy carbon disk of a rotating ring-disk electrode (RRDE) during oxygen reduction in 0.1 M NaOH aqueous solutions. The measurements afforded evidence that maximum yields for superoxide are attained during a current minimum in the polarization curve at Edisk = 0.3 V vs the reversible hydrogen electrode (RHE), with ca. 18% faradaic efficiency. Independent experiments with a Au-disk RRDE revealed no evidence of superoxide escaping the disk, in spite of evidence that ORR rates are determined by transfer of a single electron to oxygen. A mechanism was proposed wherein electron transfer to oxygen generates superoxide, which is rapidly consumed in another electron transfer step, generating hydrogen peroxide, which can undergo slow reduction thereafter. Current measurements with a bare Au ring and disk in oxygen and peroxide-containing solution allowed quantitative detection of the hydrogen peroxide intermediate. Quantitative analysis of the ORR mass balance yielded expressions for the rate constants in terms of ring and disk currents. The rate constants for oxygen / peroxide interconversion agreed closely with a Butler-Volmer equation assuming kinetically controlled oxygen / superoxide and reversible superoxide / peroxide interconversion. Voltammetry was employed to show that underpotential deposited Cu (UPD Cu) on polycrystalline Au electrodes in aqueous 0.1 M HClO4 catalyzes the reduction of selenate, to yield a layer of adsorbed copper selenide, CuxSe. This was exploited for detection of nM levels of selenate, as the amount of accumulated Se in the CuxSe deposit is linearly correlated to the selenate concentration in the electrolyte. Cu-UPD has been found to induce adsorption of selenate on Au at more reducing potentials than usually found on bare Au electrodes, determined by electrochemical quartz crystal microbalance, surface enhanced Raman spectroscopy and normal incidence differential reflectance. At these potentials, selenate reduction kinetics have been investigated to determine the effects of Cu coverages, potential, and selenate concentrations on the reaction rate. It has been concluded that selenate reduction to CuxSe proceeds via sequential first order reductions of an adsorbed selenate and then a soluble selenite intermediate, which can be captured during RRDE experiments.

Author: Jiujun Zhang
Publisher: Springer Science & Business Media
ISBN: 1848009364
Category : Technology & Engineering
Languages : en
Pages : 1147

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Proton exchange membrane (PEM) fuel cells are promising clean energy converting devices with high efficiency and low to zero emissions. Such power sources can be used in transportation, stationary, portable and micro power applications. The key components of these fuel cells are catalysts and catalyst layers. “PEM Fuel Cell Electrocatalysts and Catalyst Layers” provides a comprehensive, in-depth survey of the field, presented by internationally renowned fuel cell scientists. The opening chapters introduce the fundamentals of electrochemical theory and fuel cell catalysis. Later chapters investigate the synthesis, characterization, and activity validation of PEM fuel cell catalysts. Further chapters describe in detail the integration of the electrocatalyst/catalyst layers into the fuel cell, and their performance validation. Researchers and engineers in the fuel cell industry will find this book a valuable resource, as will students of electrochemical engineering and catalyst synthesis.

Author:
Publisher:
ISBN:
Category : Chemistry
Languages : en
Pages : 442

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Author: Kaido Tammeveski
Publisher:
ISBN:
Category : Electrochemistry
Languages : en
Pages : 148

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