Operando X-ray Photoelectron Spectroscopy Investigation of Ceria/gas Electrochemical Interfaces PDF Download
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Author: Zhuoluo Albert Feng
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
At solid-gas electrochemical interfaces, gas molecules interact dynamically with surface ions and electrons. A fundamental understanding of the technologically important interfaces can lead to better fuel cells and electrolyzers. In the bulk of typical oxygen-ion-conducting solids, oxygen vacancies and mobile electrons migrate under the influence of concentration and electrostatic potential gradients. Similarly, at gas-solid interfaces, these charge carriers migrate across an electrochemical double layer. The two-way traffic of ions and electrons contrasts sharply with conventional metal-based electrocatalysis, in which only electrons are transferred. This type of ion insertion reaction is ubiquitous in energy conversion and storage devices, such as lithium ion batteries, water-splitting membranes and solid oxide fuel cells. CeO2-[delta] (ceria) is a model oxygen-ion-conducting electrode, which is commonly employed to catalyze H2 oxidation and H2O dissociation reactions, as well as CO oxidation and CO2 dissociation reactions. In my thesis studies, I developed synchrotron-based ambient pressure X-ray photoelectron spectroscopy to characterize the electrochemical double layer under reaction conditions. Concentrations and binding energy of oxygen ions, localized electrons, and surface reaction intermediates were quantified using core level and valence band X-ray photoelectron spectroscopy as a function of electrochemical overpotentials. These measurements reveal that localized electrons and oxygen vacancies segregate persistently from the bulk to the surface, resulting in concentrations up to four orders of magnitude greater on the surface than in the bulk. Under water splitting conditions, H2O molecules incorporate rapidly into surface oxygen vacancies. Spectroscopy and electrochemistry results suggest that the electron transfer between Ce 4f states and OH adsorbates is rate determining. Under CO oxidation and CO2 dissociation conditions, on the other hand, carbonate is the stable adsorbate. The larger footprint of carbonate relative to hydroxyl adsorbate gives rise to adsorbate-adsorbate interactions, resulting in a coverage-dependent reaction pathway. Lastly, measurement of surface dipole potential energy in both cases reveals intrinsic dipole moments of adsorbates as the origin of electrostatic potential gradient near the surface. Combined, these in-situ investigations unravel the electrochemical reaction pathway, particularly the role of point defects at ceria/gas interfaces, and establish a rational path towards enhancing the efficacy of oxide electrocatalysts.
Author: Zhuoluo Albert Feng
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
At solid-gas electrochemical interfaces, gas molecules interact dynamically with surface ions and electrons. A fundamental understanding of the technologically important interfaces can lead to better fuel cells and electrolyzers. In the bulk of typical oxygen-ion-conducting solids, oxygen vacancies and mobile electrons migrate under the influence of concentration and electrostatic potential gradients. Similarly, at gas-solid interfaces, these charge carriers migrate across an electrochemical double layer. The two-way traffic of ions and electrons contrasts sharply with conventional metal-based electrocatalysis, in which only electrons are transferred. This type of ion insertion reaction is ubiquitous in energy conversion and storage devices, such as lithium ion batteries, water-splitting membranes and solid oxide fuel cells. CeO2-[delta] (ceria) is a model oxygen-ion-conducting electrode, which is commonly employed to catalyze H2 oxidation and H2O dissociation reactions, as well as CO oxidation and CO2 dissociation reactions. In my thesis studies, I developed synchrotron-based ambient pressure X-ray photoelectron spectroscopy to characterize the electrochemical double layer under reaction conditions. Concentrations and binding energy of oxygen ions, localized electrons, and surface reaction intermediates were quantified using core level and valence band X-ray photoelectron spectroscopy as a function of electrochemical overpotentials. These measurements reveal that localized electrons and oxygen vacancies segregate persistently from the bulk to the surface, resulting in concentrations up to four orders of magnitude greater on the surface than in the bulk. Under water splitting conditions, H2O molecules incorporate rapidly into surface oxygen vacancies. Spectroscopy and electrochemistry results suggest that the electron transfer between Ce 4f states and OH adsorbates is rate determining. Under CO oxidation and CO2 dissociation conditions, on the other hand, carbonate is the stable adsorbate. The larger footprint of carbonate relative to hydroxyl adsorbate gives rise to adsorbate-adsorbate interactions, resulting in a coverage-dependent reaction pathway. Lastly, measurement of surface dipole potential energy in both cases reveals intrinsic dipole moments of adsorbates as the origin of electrostatic potential gradient near the surface. Combined, these in-situ investigations unravel the electrochemical reaction pathway, particularly the role of point defects at ceria/gas interfaces, and establish a rational path towards enhancing the efficacy of oxide electrocatalysts.
Author: Chenghao Wu
Publisher:
ISBN:
Category :
Languages : en
Pages : 90
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Book Description
Gas-phase catalytic reactions and electrochemical reactions are two important categories of heterogeneous reactions. In order to determine the reaction mechanisms and potentially improve the technologies based on these reactions, it is essential to understand what happens at relevant solid/gas or solid/liquid interfaces under reaction conditions. X-ray photoelectron spectroscopy (XPS) and x-ray absorption spectroscopy (XAS) are two element-specific and chemical-state-specific characterization techniques. Recently, researchers have demonstrated that with proper modifications, these vacuum-requiring techniques can also be used to characterize various solid/gas or solid/liquid interface systems under ambient conditions, which opens the way towards in situ and operando characterization of many heterogeneous reaction systems. In this dissertation, the studies on two solid/gas interface systems and two solid/liquid interface systems are presented. The solid/gas interface systems were characterized by ambient-pressure XPS (AP-XPS). In the study regarding Co catalyst for Fischer-Tropsch (F-T) synthesis, it was found that CO adsorbs strongly on Co surface; but small amount of sulfur substantially weakens the CO adsorption and consequently poisons the F-T reaction. Under reaction conditions, Co surface remains metallic. At lower temperatures, water molecules in the reaction products can potentially oxidize the Co surface and thereby hinder the catalytic reaction. When the reaction temperature is above 250°C, H2 is responsible for reducing Co to its metallic phase and keeping the catalyst active. In the study of CoxPdy alloy nanoparticles for catalyzing CO oxidation reaction, a clear dependence of catalytic activities on nanoparticle composition was observed. AP-XPS results revealed that Co segregates to the surface and stays in the oxide form after the pretreatment process. Small amount of Co coexisting with Pd on the surface can promote the CO oxidation reaction synergistically and the synergetic effect becomes more prominent with increasing Co content. However, when Co/Pd ratio is too high, after the cleaning processes, the surface of the nanoparticles is fully covered by thin layers of CoOx, preventing CO molecules from binding with Pd, which leads to significant drop in catalytic activity of the alloy nanoparticles. The solid/liquid interface systems were characterized by our newly developed in situ and operando XAS technique. Total electrode yield (TEY) signal collected through the working electrode can provide information that is sensitive to the solid/liquid interfaces. At Au/H2O interfaces, the hydrogen-bonding network is greatly disrupted by the interface, leaving more broken hydrogen bonds than in bulk water. But the delocalization of the LUMO orbitals of water molecules into the gold substrate, greatly suppresses the pre-edge feature in O1s XAS spectrum that is typically associated with broken hydrogen bonds. These polar molecules can respond to external electrical field and reorient at the interface, producing potential-dependent O1s TEY XAS spectra. At Pt/H2SO4(aq) or Au/H2SO4(aq) interfaces, similar water reorientation behaviors were observed in the negative potential region. In the positive potential regions, the evolution of O1s XAS spectra is different from that of Au/H2O system. The changes in the spectra are possibly related to the adsorption of sulfate ions at the interface, contradicting many reports that proposed an oxide formation or oxygen/ hydroxyl adsorption processes. The studies on four interface systems presented in this dissertation illustrate the capabilities and great potentials of these two in situ x-ray spectroscopy techniques, i.e., AP-XPS and in situ/operando XAS, in the investigation of interfacial phenomena and reaction mechanisms in various heterogeneous reactions. Such mechanistic information can potentially provide insightful guidance for better designs of catalysts and electrode materials.
Author: Jens Rostrup-Nielsen
Publisher: World Scientific
ISBN: 1848165676
Category : Science
Languages : en
Pages : 390
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Book Description
This book provides a general overview of syngas technologies as well as an in-depth analysis of the steam reforming process. Syngas is a mixture of hydrogen and carbon oxides which can be made from hydrocarbons, coal and biomass. It is an important intermediate in the chemical industry for manufacture of ammonia, methanol and other petrochemicals as well as hydrogen for refineries and fuel cells. Syngas is playing a growing role in the energy sector, because it can be converted into a number of important energy carriers and fuels. Syngas catalysis creates new options and flexibility in the complex energy network. The steam reforming process is the main technology today for manufacture of syngas. It is a complex intern-mingling of catalysis and heat transfer with restrictions caused by secondary phenomena such as carbon formation. Many of the principles are applicable for other gasification technologies of growing importance. Concepts of Syngas Preparation aims to provide a comprehensive introduction to this complex field of growing importance and gives a detailed analysis of the catalyst and process problems. This book also serves as an important link between science and industry by illustrating how the basic principles can be applied to solve design issues and operational problems.
Author: Li-chyong Chen
Publisher: World Scientific
ISBN: 9811284652
Category : Science
Languages : en
Pages : 298
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Book Description
Nanomaterials have become a key component for energy-related applications. Their design principle, synthesis and applications are well discussed in various scientific and engineering books, but a gap remains in discussions regarding the application of cutting-edge X-ray techniques to these materials. This volume provides insights from the latest development of X-ray techniques to investigate nanomaterials in specific energy fields, bridging the gap between X-ray analytical scientists and material researchers.We aim to provide researchers with a tool to choose suitable X-ray techniques, carry them out with the right procedure, and analyze the data to give the best reliable results. The approach is microscopic and specific. Among the applications emphasized by the chapters in this book are x-ray techniques in heterogeneous catalysis, electrocatalysis for fuel cells, photocatalysis for water splitting and carbon dioxide reduction, organic photovoltaics, and other energy-related applications.
Author: Jacob Stahl
Publisher:
ISBN:
Category : Copper oxide
Languages : en
Pages : 60
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Book Description
Author: Misook Kang
Publisher: MDPI
ISBN: 3039363107
Category : Technology & Engineering
Languages : en
Pages : 136
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Book Description
Energy crises and global warming pose serious challenges to researchers in their attempt to develop a sustainable society for the future. Solar energy conversion is a remarkable, clean, and sustainable way to nullify the effects of fossil fuels. The findings of photocatalytic hydrogen production (PCHP) by Fujishima and Honda propose that “water will be the coal for the future”. Hydrogen is a carbon-free clean fuel with a high specific energy of combustion. Titanium oxide (TiO2), graphitic-carbon nitride (g-C3N4) and cadmium sulfide (CdS) are three pillars of water splitting photocatalysts owing to their superior electronic and optical properties. Tremendous research efforts have been made in recent years to fabricate visible or solar-light, active photocatalysts. The significant features of various oxide, sulfide, and carbon based photocatalysts for cost-effective hydrogen production are presented in this Special Issue. The insights of sacrificial agents on the hydrogen production efficiency of catalysts are also presented in this issue.
Author: Stephen Skinner
Publisher: Royal Society of Chemistry
ISBN: 1839160055
Category : Technology & Engineering
Languages : en
Pages : 262
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Book Description
Showcasing recent developments in inorganic materials in an area of societal interest and importance, this book provides an up-to-date introduction to the contemporary use of functional solids in emerging technologies. Energy Storage and Conversion Materials describes the application of inorganic materials in the storage and conversion of energy, with an emphasis on how solid-state chemistry allows development of new functional solids for energy applications. Dedicated chapters cover co-electrolysis, low temperature fuel cells, oxide thermoelectric devices for energy conversion, solid-state Li batteries and thermochemical energy conversion. Edited and written by world-renowned scientists, this book will provide a comprehensive introduction for advanced undergraduates, postgraduates and researchers wishing to learn about the topic.
Author: R.E. White
Publisher: Springer Science & Business Media
ISBN: 1461327954
Category : Mathematics
Languages : en
Pages : 397
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Book Description
Author: Yaobing Wang
Publisher: John Wiley & Sons
ISBN: 3527349138
Category : Science
Languages : en
Pages : 60
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Book Description
Electrocatalysis in Balancing the Natural Carbon Cycle Explore the potential of electrocatalysis to balance an off-kilter natural carbon cycle In Electrocatalysis in Balancing the Natural Carbon Cycle, accomplished researcher and author, Yaobing Wang, delivers a focused examination of why and how to solve the unbalance of the natural carbon cycle with electrocatalysis. The book introduces the natural carbon cycle and analyzes current bottlenecks being caused by human activities. It then examines fundamental topics, including CO2 reduction, water splitting, and small molecule (alcohols and acid) oxidation to prove the feasibility and advantages of using electrocatalysis to tune the unbalanced carbon cycle. You’ll realize modern aspects of electrocatalysis through the operando diagnostic and predictable mechanistic investigations. Further, you will be able to evaluate and manage the efficiency of the electrocatalytic reactions. The distinguished author presents a holistic view of solving an unbalanced natural carbon cycle with electrocatalysis. Readers will also benefit from the inclusion of: A thorough introduction to the natural carbon cycle and the anthropogenic carbon cycle, including inorganic carbon to organic carbon and vice versa An exploration of electrochemical catalysis processes, including water splitting and the electrochemistry CO2 reduction reaction (ECO2RR) A practical discussion of water and fuel basic redox parameters, including electrocatalytic materials and their performance evaluation in different electrocatalytic cells A perspective of the operando approaches and computational fundamentals and advances of different electrocatalytic redox reactions Perfect for electrochemists, catalytic chemists, environmental and physical chemists, and inorganic chemists, Electrocatalysis in Balancing the Natural Carbon Cycle will also earn a place in the libraries of solid state and theoretical chemists seeking a one-stop reference for all aspects of electrocatalysis in carbon cycle-related reactions.
Author: S.C. Singhal
Publisher: Elsevier
ISBN: 0080508081
Category : Technology & Engineering
Languages : en
Pages : 423
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Book Description
High Temperature Solid Oxide Fuel Cells: Fundamentals, Design and Applications provides a comprehensive discussion of solid oxide fuel cells (SOFCs). SOFCs are the most efficient devices for the electrochemical conversion of chemical energy of hydrocarbon fuels into electricity, and have been gaining increasing attention for clean and efficient distributed power generation. The book explains the operating principle, cell component materials, cell and stack designs and fabrication processes, cell and stack performance, and applications of SOFCs. Individual chapters are written by internationally renowned authors in their respective fields, and the text is supplemented by a large number of references for further information. The book is primarily intended for use by researchers, engineers, and other technical people working in the field of SOFCs. Even though the technology is advancing at a very rapid pace, the information contained in most of the chapters is fundamental enough for the book to be useful even as a text for SOFC technology at the graduate level.
