Dissertations / Theses on the topic 'Metal oxide electrocatalyst'
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GUZMAN, MEDINA HILMAR DEL CARMEN. "Electrocatalytic reduction of CO2 to value-added products." Doctoral thesis, Politecnico di Torino, 2021. http://hdl.handle.net/11583/2907030.
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Gu, Yanjuan. "Nanostructure of transition metal and metal oxide for electrocatalysis." Click to view the E-thesis via HKUTO, 2006. http://sunzi.lib.hku.hk/hkuto/record/B37774396.
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Chen, Youjiang. "Fundamental Aspects of Electrocatalysis at Metal and Metal Oxide Electrodes." Case Western Reserve University School of Graduate Studies / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=case1284390270.
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Baez, Baez Victor Antonio. "Metal oxide coated electrodes for oxygen reduction." Thesis, University of Southampton, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.241271.
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Chen, Junsheng. "Ternary Metal Oxide/(Oxy)Hydroxide for Efficient Oxygen Evolution Reaction." Thesis, The University of Sydney, 2021. https://hdl.handle.net/2123/25536.
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Novel clean energy conversion and storage technologies, such as electrochemical water splitting and metal-air battery, play significant roles in the future clean energy society. Oxygen evolution reaction (OER), as the fundamental reaction of these technologies, is crucial for their practical application. However, OER process is sluggish since the complex reaction process (multi-electron and multi-intermediate involved reaction). Developing efficient and affordable OER electrocatalysts remains a great challenge. Recently, the multimetal incorporation strategy has aroused extensive research interest since it can effectively enhance the catalytic performance of the catalysts. Nevertheless, there are still many scientific questions to be answered for such materials systems, such as the reaction mechanism and the optimum element composition. In this thesis, earth-abundant transition metals Cobalt and iron were selected as the basic elements. Cheap and abundant metals Vanadium, Chromium, and Tungsten were chosen as the incorporation elements respectively because of their unique d orbital structure in oxidation state. Their oxides/(oxy)hydroxides were elaborately designed and synthesised. The OER performance of the incorporated materials display a huge improvement. A variety of characterisations were employed to investigate the electrochemical properties of the materials. Theoretical calculations were also applied and combined with the characterisation observation to explain the reaction mechanism and the role of the incorporation element. Practical electrical water electrolyser devices were built up to determine the synthesised OER electrocatalysts in a real situation. Specifically, a facile electrodeposition catalysts synthesis method was developed, which can rapidly manufacture electrodes with efficient OER electrocatalysts on a large scale.
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Gu, Yanjuan, and 谷艳娟. "Nanostructure of transition metal and metal oxide forelectrocatalysis." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2006. http://hub.hku.hk/bib/B37774396.
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Bateni, Fazel. "Development of Non-precious Metal and Metal Oxide Electrocatalysts for an Alkaline Lignin Electrolysis Process." Ohio University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1562674707447307.
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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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Xing, Shihui. "Rational design of bi-transition metal oxide electrocatalysts for hydrogen and oxygen evolutions." Thesis, Queensland University of Technology, 2021. https://eprints.qut.edu.au/209307/1/Shihui_Xing_Thesis.pdf.
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This thesis mainly focuses on the rational design and preparation of bi-transition metal oxide materials for high-performance electrochemical catalysis, such as hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). To address the challenges of sluggish kinetics and large overpotentials in HER and OER, the effective strategy of morphology engineering, introducing a secondary metal element and supporting on carbon-based materials were carried out and discussed.
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Wu, Ziyang. "Rational design of two-dimensional architectures for efficient electrocatalysis." Thesis, Queensland University of Technology, 2022. https://eprints.qut.edu.au/235888/1/ziyang%2Bwu%2Bthesis%284%29.pdf.
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In this thesis, the principal focus is the rational design and fabrication of two-dimensional (2D) nanoarchitectures, e.g., low-cost metal oxide nanosheets and earth-abundant transition metal layered double hydroxides (LDHs) for enhanced electrocatalysis. The related hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performance not only demonstrated the advances of 2D nanomaterials, such as unique physical and mechanical properties, unprecedented electronic features, and ultrahigh surface areas but also indicated the possible mechanisms behind boosted activity and stability, e.g., phase engineering function and oxygen vacancies influence.
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Thenuwara, Akila Chathuranga. "Investigations of interlayer chemistry in layered metal oxides for energy conversion and storage." Diss., Temple University Libraries, 2018. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/519285.
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ChemistryPh.D.
The overall goal of this dissertation research was to design, tailor and understand layered metal oxides in the context of electrocatalytic energy conversion and storage processes. To accomplish this goal the thesis research combined electrochemistry, state-of-the-art structural characterization and theoretical calculations. The hypothesis examined in this dissertation is that incorporation of metal atoms or metal ions into the sheets and/or interlayer region of the layered materials will enhance the properties of selected 2D materials for chemistry relevant to electrochemical energy conversion (i.e. electrochemical water splitting catalysis; H2O ® H2 + 1/2O2) and energy storage (i.e., as pseudocapacitors). The primary 2D layered materials investigated in this thesis research were birnessite (nominally MnO2) and Fe:Ni double hydroxide materials. Metals (cations) used to modify the geometric and electronic structure of the layered materials include Cu, Ni, and Co. Perhaps the result with broadest impact to result from the integration of experimental and theoretical studies in the thesis research was that the confinement of solvated redox active metals within the interlayer region of 2D layered materials can be used to facilitate their electron transfer reaction rates (relative to the respective unconfined metal) and energy related electrochemistry. This new paradigm for electron transfer has implications for the development of novel electrocatalytic materials for energy conversion. Research showed that the electrocatalytic activity of birnessite toward water oxidation (2H2O® 4H+ + 4e- + O2) was increased by intercalating zero valent copper into the interlayer region of the layered manganese oxide. Electrocatalytic studies showed that the Cu-modified birnessite exhibited an overpotential for water oxidation of ∼490 mV (at a current density of 10 mA cm 2) and a Tafel slope of 126 mV/decade compared to ∼700 mV (at 10 mA cm-2) and 240 mV/decade, respectively, for birnessite without copper. Impedance spectroscopy results suggested that the charge transfer resistivity of the Cu-modified sample was significantly lower than Cu-free birnessite, suggesting that Cu in the interlayer increased the conductivity of birnessite leading to an enhancement of water oxidation kinetics. It was experimentally shown that the oxygen evolution reaction (OER; water oxidation) catalysis of redox active transition metal ions (Ni2+ and Co2+) can be enhanced by individually confining them in the interlayer region of birnessite. It was demonstrated that the metal confined electrocatalyst reached a current density of 10 mA cm−2 at much lower overpotentials than pure Ni and Co oxides, and pristine birnessite. For example, with interlayer nickel and cobalt, overpotentials of 400 and 360 mV, respectively, were achieved for the OER. Molecular dynamics (MD) simulations suggested that electron transfer reaction rates relevant to OER and involving Ni or Co were enhanced when the metal cations were confined in the interlayer of birnessite. The strategy of metal confinement, which was successfully applied to layered manganese oxide to improve OER activity was extended to Ni-Fe based layered double hydroxide. It was demonstrated that the electrocatalytic activity of NiFe layered double hydroxides (NiFe LDHs) for the OER could be significantly enhanced by systematic cobalt incorporation using coprecipitation and/or intercalation. Electrochemical measurements showed that cobalt modified NiFe LDH possessed an enhanced activity for the OER relative to pristine NiFe LDH. The cobalt doped NiFe LDH exhibited overpotentials in the range of 290−322 mV (at 10 mA cm−2), depending on the degree of cobalt content. The cobalt intercalated NiFe LDH achieved a current density of 10 mA cm−2 at a much lower overpotential of ∼265 mV (compared to 310 mV for NiFe LDH). With regard to energy storage, it was shown that the pseudocapacitive charge storage in layered manganese oxide was a sensitive function of interlayer composition and distance. Even though pristine layered manganese oxide shows a 7 Å interlayer spacing, the interlayer engineering via metal (Mg2+) intercalation and thermal annealing led to layered manganese oxide materials with variable interlayer spacings of 10 and 5.6 Å respectively. The interlayer expanded layered manganese oxide (10 Å interlayer spacing) exhibited an improved specific capacitance of 380 Fg-1, in comparison to synthetic Na-birnessite (specific capacitance of 200 F g-1). Dehydrated Na-birnessite (~5.6 Å spacing) produced by annealing to expel interlayer water, showed the lowest specific capacitance of 50 Fg-1. Experimental results showed that interlayer expanded manganese oxide (with intercalated Mg2+) was unstable if exposed to a solution containing only Na+ cation electrolyte. In this circumstance, the interlayer distance decreased from the expanded 10 Å value back to an interlayer distance of 7 Å and a specific capacitance of ~200 F g-1; values associated with synthetic Na-birnessite. Finally, a highly active alkaline medium hydrogen evolving electrocatalyst based on earth abundant materials (Co, Mo and P) was developed and the catalyst exhibited a ~0 V onset for the hydrogen evolution reaction (HER; 2H+ + 2e- ® H2). This value was comparable to that of the precious metal platinum. The Co-Mo-P catalyst was prepared by room temperature electrodeposition and it exhibited an overpotential of ~ 25-30 mV for HER at a geometrical current density of 10 mA cm-2 in an alkaline medium. A DFT theoretical investigation revealed that a Co-Mo center acts as the water-dissociation site enhancing the alkaline medium HER.
Temple University--Theses
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Fugate, Elizabeth Anne. "Investigation of Electronic Structure Effects of Transition Metal Oxides toward Water Oxidation and CO2 Reduction Catalysis." The Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1462868623.
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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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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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Perera, Reshani H. "Nitric Oxide Synthase in Confined Environments: Detection and Quantification of Nitric Oxide Released From Cells and Modified Liposomes Using a Sensitive Metal Catalyst-PEDOT Modified Carbon Fiber Electrode." Cleveland State University / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=csu1297142093.
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Watzele, Sebastian Anselm [Verfasser], Aliaksandr S. [Akademischer Betreuer] Bandarenka, Ifan E. L. [Gutachter] Stephens, and Aliaksandr S. [Gutachter] Bandarenka. "Methodological Aspects of In-Depth Electrochemical Characterization of Metal and Metal Oxide Electrocatalysts / Sebastian Anselm Watzele ; Gutachter: Ifan E. L. Stephens, Aliaksandr S. Bandarenka ; Betreuer: Aliaksandr S. Bandarenka." München : Universitätsbibliothek der TU München, 2020. http://d-nb.info/1206337753/34.
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Xue, Song [Verfasser], Aliaksandr S. [Akademischer Betreuer] Bandarenka, Egill [Gutachter] Skulason, and Aliaksandr S. [Gutachter] Bandarenka. "The role of electrolyte composition in the activity and selectivity of metal and metal oxide electrocatalysts / Song Xue ; Gutachter: Egill Skulason, Aliaksandr S. Bandarenka ; Betreuer: Aliaksandr S. Bandarenka." München : Universitätsbibliothek der TU München, 2020. http://d-nb.info/1204200289/34.
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Colombo, A. "PREPARATION AND PERFORMANCE EVALUATION OF MATERIALS FOR ELECTROCATALYTIC APPLICATIONS." Doctoral thesis, Università degli Studi di Milano, 2010. http://hdl.handle.net/2434/150125.
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This PhD thesis is devoted to the preparation and characterization of materials for electrocatalytic applications. The focus has been on the surface of electrodes. The physical and chemical structure of surfaces is one of the main variables of electrocatalytic properties. In particular, the physical structure of a surface (amorphous vs. crystalline) is often claimed to affect the surface activity of electrocatalysts. Also, the chemical structure (active sites on flat vs. stepped facets) has been claimed to be an essential variable influencing catalysis as well as electrocatalysis. Scrutiny of both situations was performed in our laboratory by preparing a series of transition metals oxides (e.g. Ir, Ru, Ni, Co) used in electrochemically activate electrodes, for the reactions of hydrogen and oxygen evolution.
A number of techniques have been used: i) electrochemical (CV, polarization); ii) non electrochemical (XRD, TGA, SEM, EDX). Two novel synthetic methods for the production of metal oxides nanoparticles have been implemented.
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Naidoo, Qiling Ying. "Multicomponent catalysts for methanol electro-oxidation processes synthesized using organometallic chemical vapourde position technique." Thesis, University of the Western Cape, 2011. http://etd.uwc.ac.za/index.php?module=etd&action=viewtitle&id=gen8Srv25Nme4_7491_1320654024.
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In this study, the OMCVD method is demonstrated as a powerful, fast, economic and environmental friendly method to produce a set of PGMelectrocatalysts with different supports, metal content and metal alloys in one step and without the multiple processing stages of impregnation, washing, drying, calcinationsand activation.
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Hammouche, Abderrezak. "Contribution à l'étude de La(1-x)Sr(x)MnO3 comme matériau d'électrode à oxygène à haute température." Grenoble INPG, 1989. http://www.theses.fr/1989INPG0075.
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Les composes la#1##xsr#xmno#3 sont utilises comme materiau d'electrode a oxygene utilisables dans les cellules galvaniques mettant en jeu un oxyde d'electrolytes solides. Leur caracterisation physicochimique a porte sur la determination de la structure cristalline et l'etude des proprietes thermiques et electriques
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Favaro, Marco. "A rational approach to the optimization of efficient electrocatalysts for the next generation Fuel Cells." Doctoral thesis, Università degli studi di Padova, 2014. http://hdl.handle.net/11577/3424667.
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The PhD project has been performed in the Surfaces and Catalysts group active in the Department of Chemical Sciences, within the frame of the grant “A rational approach to the optimization of efficient electrocatalysts for the next generation Fuel Cells”, funded by CARIPARO foundation. The project has been focused on the preparation and characterization of new carbon-based materials for applications in Polymer Electrolyte Membrane Fuel Cells (PEMFCs), also known as oxygen-hydrogen FCs. The preparation of the materials has been performed using different techniques, depending on the type of the target material and on the possible applications that these materials can offer. With reference to the studied model systems (Highly Oriented Pyrolytic Graphite (HOPG) and Glassy Carbon (GC)), the introduction of doping heteroatoms has been performed by ion implantation, while the study of new chemical functionalities has been allowed by the use of Wet Chemistry techniques, in particular derived from the electrochemical synthesis.
The deposition of thin films or nanoparticles (metal or oxides of transition metals) on the ion-modified materials has been carried out in-situ by using advanced techniques under Ultra High Vacuum conditions (UHV), such as Physical Vapor Deposition (PVD). Within the study of the model systems, PVD was chosen because of its ability to provide an atomic scale control of the metal deposition. In a second time, conventional deposition techniques such as chemical or electrochemical reduction of suitable metal precursors have been performed, in a synergistic combination between Surface Science and Electrochemistry-derived techniques.
The characterization of these materials has been performed using the facilities of the Surface Science group, such as the X-ray and Ultraviolet Photoelectron Spectroscopy (XPS - UPS), Scanning Tunneling and Atomic Force Microscopy (STM - AFM), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray spectroscopy (EDX) and Low Energy Electron Diffraction (LEED). To get a deeper insight in the chemistry/structure/properties of the prepared systems, synchrotron light-based techniques such as HR-XPS, NEXAFS, ARPES, ResPES and PEEM have been extensively used. The study of the electro-catalytic activity has been performed using conventional Electrochemistry techniques, in particular Cyclic and Linear Sweep Voltammetry (CV - LSV), as well as electro-dynamic techniques such as Rotating Disk Electrode (RDE). Finally, in order to support the experimental data or to bring their understanding at a deeper level, simulations using Density Functional Theory (DFT) have been performed in collaboration with the group coordinated by Prof. Cristiana Di Valentin (University of Milano Bicocca). During the course of the doctorate, several collaborations have been pursued with other research groups operating in the Department of Chemical Sciences or abroad, such as the "Interfaces and Energy Conversion E19" research unit, Technical University of Munich (TUM, Germany), coordinated by Profs. O. Schneider and J. Kunze-Liebhäuser.Il progetto di dottorato nasce all’interno del gruppo di ricerca di Superfici e Catalizzatori operante nel dipartimento di Scienze Chimiche, nell’ambito della borsa a titolo vincolato “Un approccio razionale alla ottimizzazione di elettrocatalizzatori efficienti per le celle a combustibile di nuova generazione”, finanziata da fondazione CARIPARO. Le tematica è stata focalizzata sulla preparazione e caratterizzazione di nuovi materiali a base di carbonio utilizzabili per applicazioni in celle a combustibile di tipo PEMFCs (Polymer Electrolyte Membrane Fuel Cells) ad ossigeno-idrogeno. La preparazione dei materiali è avvenuta facendo uso di differenti tecniche, in relazione al tipo di materiale oggetto di studio ed alle applicazioni che tali materiali possono offrire. Con riferimento allo studio dei sistemi modello (grafite pirolitica altamente orientata, HOPG, e carbonio vetroso, GC), il drogaggio degli stessi mediante l’introduzione di eteroatomi (in particolare azoto) è avvenuto ricorrendo alla tecnica dell’impiantazione ionica, mentre lo studio di nuove funzionalità chimiche è stato permesso dall’utilizzo di tecniche di Wet Chemistry, in particolare mutuate dalla sintesi elettrochimica. La deposizione di film sottili o di nanoparticelle (metalliche o a base di ossidi di metalli di transizione) su tali materiali modificati è stata effettuata facendo uso di tecniche avanzate come la deposizione fisica da fase vapore (PVD) in condizioni controllate di Ultra Alto Vuoto (UHV), in grado di offrire un controllo su scala atomica della deposizione di tali film. Sono state utilizzate anche tecniche di deposizione tradizionali quali la riduzione chimica o elettrochimica di opportuni precursori metallici: l‘utilizzazione di una siffatta combinazione sinergica tra tali differenti tecniche di preparazione ha permesso di ottenere materiali caratterizzati da strutture e proprietà peculiari. La caratterizzazione di tali materiali è svolta utilizzando le facilities del gruppo di Scienza delle Superfici, come la spettroscopia di fotoelettroni (XPS) o della banda di valenza (UPS), la microscopia ad effetto tunnel o a forza atomica (STM - AFM), la microscopia elettronica e la dispersione energetica dei raggi X indotta dagli elettroni (SEM-EDX), la diffrazione di elettroni lenti (LEED). Allo scopo di caratterizzare maggiormente in dettaglio la struttura e le proprietà chimiche dei materiali preparati sono state usate estensivamente le tecniche di indagine offerte dalla luce di sincrotrone (HR-XPS, NEXAFS, ARPES, ResPES, PEEM), mentre lo studio della reattività catalitica si basa su tecniche derivate dall’analisi elettrochimica, in particolare la voltammetria ciclica ed a scansione lineare del potenziale applicato, nonchè tecniche elettro-dinamiche come la voltammetria su elettrodo rotante. Infine, allo scopo di supportare i dati sperimentali o portare la comprensione delle proprietà dei materiali ad un livello più profondo, simulazioni mediante teoria del funzionale densità (DFT) sono state adottate per un approccio critico allo studio dei materiali preparati (in collaborazione con il gruppo coordinato dalla prof. Cristiana Di Valentin, Università di Milano Bicocca). Durante il corso del dottorato, diverse collaborazioni sono state perseguite con gruppi interni al Dipartimento di Scienze Chimiche o anche Esteri, come l’unità di ricerca “Interfaces and Energy Conversion E19”, dell’università tecnica di Monaco di Baviera (TUM, Technische Universität München, Germania), coordinata dai proff. O. Schneider e J. Kunze-Liebhäuser.
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Jain, Deeksha. "Development of Alternative Materials to Replace Precious Metals in Sustainable Catalytic Technologies." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1566176607919202.
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Queiroz, Adriana Coêlho. "Síntese e estudo da atividade eletrocatalítica de óxidos de metais de transição e de nanopartículas de prata e ouro para a reação de redução de oxigênio." Universidade de São Paulo, 2011. http://www.teses.usp.br/teses/disponiveis/75/75131/tde-25102011-170304/.
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A reação de redução de oxigênio (RRO) foi estudada em eletrocatalisadores formados por nanopartículas de óxidos puros e mistos de metais de transição de Mn, Co e Ni, além de estrutura tipo espinel, e por nanopartículas de Ag, Au e Ag3M (M= Au, Pt, Pd e Cu) suportadas em carbono Vulcan, em eletrólito alcalino. Os óxidos de metais de transição foram sintetizados por decomposição térmica de seus respectivos nitratos e as nanopartículas a base de prata e ouro foram sintetizadas por redução química com borohidreto. Os eletrocatalisadores foram caracterizados por Difratometria e Espectroscopia de Absorção de Raios X (somente para os óxidos de transição). Os materiais a base de óxidos de manganês, mostraram-se com alta atividade para a RRO, para os quais os resultados espectroscópicos in situ evidenciaram a ocorrência da redução do Mn(IV) para Mn(III), na região de início da RRO. Assim, as atividades eletrocatalíticas foram associadas à ocorrência da transferência de elétrons do Mn(III) para o O2. Entretanto, apresentaram forte desativação após ciclagem potenciodinâmica, o que foi associado à formação da fase Mn3O4, conforme indicado por difratometria de Raios X, após os experimentos eletroquímicos, que é eletroquimicamente inativa. Já o material formado pela estrutura do tipo espinel de MnCo2O4 apresentou alta atividade e estabilidade frente à ciclagem e à RRO. A alta atividade eletrocatalítica foi relacionada a ocorrência do par redox CoII/CoIII em maiores valores de potencial em relação ao CoOx e MnOx, devido a interações entre os átomos de Co e Mn no reticulo espinélico. Contrariamente ao observado nos óxidos com maior quantidade de manganês, o espinel mostrou-se altamente estável, o que foi associada à não alteração de sua estrutura no intervalo de potenciais que a RRO ocorre. Para os materiais bimetálicos a base de prata e ouro, os experimentos eletroquímicos indicaram maior atividade eletrocatalítica para o material de Ag3Au/C. Neste caso, a alta atividade foi associada a dois efeitos principais: (i) a um efeito sinergético, no qual os átomos de ouro atuam na região de ativação, favorecendo a adição de hidrogênio e os átomos vizinhos de prata proporcionam a quebra da ligação O-O, conduzindo a RRO pelo caminho de quatro elétrons por molécula de O2; (ii) ao aumento força da ligação Ag-O, devido à interação da Ag com o Au, resultando em maior atividade para a quebra da ligação O-O, aumentando a atividade da Ag para a RRO, em relação à atividade da Ag pura. Assim, a RRO apresentou menor sobrepotencial e maior número de elétrons em Ag3Au/C, quando comparado com as demais nanopartículas bimetálicas.The oxygen reduction reaction (ORR) was studied on electrocatalysts composed by pure and mixed transition metal oxides of Mn, Co, and Ni, including spinel-like structures, and by Ag, Au, and Ag3M/C (M= Au, Pt, Pd e Cu) bimetallic nanoparticles, in alkaline electrolyte. The transition metal oxides were synthesized by thermal decomposition of their nitrates, and the silver and gold-based nanoparticles by chemical reduction using borohydride. The electrocatalysts were characterized by X-Ray Diffraction and X-Ray Absorption Spectroscopy (in the case of the metal oxides). The manganese-based oxide materials showed high activity for the ORR, in which the in situ spectroscopic results evidenced the Mn(IV) to Mn(III) reduction, in the range of the ORR onset. In this case, the electrocatalytic activities were correlated to the transfer of electron from Mn(III) to O2. However, they presented strong deactivation after several potentiodynamic cycles, which was ascribed to the formation of the electrochemically inactive phase of Mn3O4, as indicated by the XRD results, after the electrochemical experiments. On the other hand, the MnCo2O4 spinel-like material showed high activity and stability for the ORR. Its high electocatalytic activity was attributed to the CoII/CoIII redox pair, taking place at higher potentials, in relation to that of the CoOx e MnOx pure phases, due to the Co and Mn interactions in the spinel lattice. Contrarily to the behavior observed for the manganese-based materials, the spinel oxide presented high stability, which was ascribed to the non alteration of its crystallographic structure in the range of potentials tha the ORR takes place. For the Au and Ag-based materials, the electrochemical experiments indicated higher electrocatalytic activities for Ag3Au/C. In this case, its higher activity as associated to two main aspects: (i) to a synergetic effect, in which the gold atoms act in the activation region, facilitating the hydrogen addition, and the neighboring Ag atoms promoting the O-O bond breaking, leading the ORR to the 4-electrons pathway; (ii) to the increased Ag-O bond strength, due to the electronic interaction between Ag and the Au atoms, resulting in a faster O-O bond breaking, enhancing the electrocatalytic activity of the Ag atoms in the Ag3Au/C nanoparticle, in relation to that on the pure Ag. Therefore, the ORR presented lower overpotential and higher number of electrons in the Ag3Au/C electrocatalyst, when compared to the other investigated bimetallic nanoparticles.
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ANTONIASSI, RODOLFO M. "Preparação de nanopartículas de platina com diferentes morfologias nos materiais Pt/C e PtSnO2/C para aplicação como ânodo em células a combústível de etanol direto." reponame:Repositório Institucional do IPEN, 2017. http://repositorio.ipen.br:8080/xmlui/handle/123456789/28036.
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Neste trabalho foi estudado o efeito da adição de íons haletos (Cl-, Br- e I-) sobre a morfologia das nanopartículas de Pt na produção de catalisadores de Pt/C e PtSnO2/C. Foi desenvolvida uma metodologia de síntese simples capaz de produzir nanopartículas de Pt predominantemente cúbicas com orientação preferencial Pt(100), diretamente suportadas em carbono sem o uso de agentes estabilizantes. Brometo de potássio foi utilizado como agente direcionador de superfície para obtenção do material preferencialmente orientado. O controle de adição do precursor de Pt e de KBr foi crucial para obter nanocubos de Pt de 8 nm bem dispersos sobre o suporte. Na preparação dos catalisadores de PtSnO2/C, o processo de adição do SnCl2 também foi decisivo na obtenção das nanopartículas de Pt com tamanho e morfologia de interesse. Nanocubos de Pt coexistindo com SnO2 disperso foram exclusivamente obtidos ao adicionar o SnCl2 na etapa final da síntese, quando as nanopartículas cúbicas de Pt já estavam formadas. Enriquecidos de domínios Pt(100), os materiais em forma cúbica de Pt/C e PtSnO2/C se mostraram menos afetados pelo acúmulo dos intermediários indesejados provenientes da reação de eletro-oxidação de etanol e foram mais tolerantes ao envenenamento por monóxido de carbono. Resultados similares foram observados para a oxidação de CO e metanol, utilizados como apoio para compreensão da eletro-oxidação de etanol. O efeito morfológico destes materiais no desempenho elétrico em célula a combustível de etanol direto foi avaliado. Pt/C e PtSnO2/C contendo nanopartículas de Pt com orientação preferencial Pt(100) forneceram maiores valores de densidade de potência e de seletividade para CO2 comparados aos catalisadores de Pt/C e PtSnO2/C com nanopartículas de Pt sem orientação preferencial.
Tese (Doutorado em Tecnologia Nuclear)
IPEN/T
Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP
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Creazzo, Fabrizio. "Oxygen evolution reaction at cobalt oxides/water interfaces : heterogeneous electrocatalysis by DFT-MD simulations & metadynamics Ab initio molecular dynamics study of an aqueous NaCl solution under an electric field Ionic diffusion and proton transfer in aqueous solutions of alkali metal salts Ionic Diffusion and Proton Transfer in Aqueous Solutions under an Electric Field: State-of-The-Art Ionic diffusion and proton transfer of MgCl2 and CaCl2 aqueous solutions: an ab initio study under electric field DFT-MD of the (110)-Co 3 O 4 cobalt oxide semiconductor in contact with liquid water, preliminary chemical and physical insights into the electrochemical environment Enhanced conductivity of water at the electrified air–water interface: a DFT-MD characterization Ions tune interfacial water structure and modulate hydrophobic interactions at silica surfaces." Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPASE012.
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Dans cette thèse, des simulations DFT-MD couplées à des techniques inno-vantes de métadynamique, sont appliquées pour acquérir une compréhensionglobale des interfaces aqueuses d'oxyde de cobalt Co3O4 et CoO(OH) dansla catalyse de la réaction d'évolution de l'oxygène (OER), et ainsi éventuellement aider à la conception de nouveaux catalyseurs basés sur des matériaux non précieux, un domaine clé de la recherche scientifique et technologique, particulièrement important pour l'économie de l'hydrogène, pour les technologies vertes dans une période de temps avec une demande toujours plus croissanteen énergie verte. Dans cette thèse, nous révélons étape par étape les mécanismes de l'OER sur les électrocatalyseurs aqueux d'oxyde de cobalt Co3O4 etCoO(OH) via de nouvelles techniques de métadynamique.Jusqu'à présent, la littérature n'a jamais pris en compte les modificationsau niveau atomique de la structure des électrodes ainsi que de l'eau interfaciale dans leur modélisation des processus OER. Ce manque de connaissances représente clairement un obstacle important au développement de catalyseurs améliorés, qui pourrait être surmonté en utilisant des méthodes capables de suivre les caractéristiques catalytiques de l'OER à l'échelle atomique. Pour la première fois, nous montrons combien il est important de prendre en considération la présence de l'environnement aqueux dans la caractérisation structurale des surfaces du catalyseur, c'est-à-dire (110)-Co3O4 et (0001)-CoO(OH) dans ce travail. Une caractérisation détaillée des propriétés chimiques et physiques des interfaces aqueuses est fournie (la structure, la dynamique, la spectroscopie, le champ électrique), pour les surfaces (110)-Co3O4 et (0001)-CoO(OH) en contact avec l'eau liquide.Une étude détaillée de l'OER est présentée non seulement du point de vue descatalyseurs, mais aussi en abordant le rôle de l'environnement de l'eau dans leprocessus catalytique, ce qui n'a pas été fait auparavant dans la littérature. En conséquence, l'OER en phase gazeuse et en phase liquide sont étudiés ici auxinterfaces aqueuses (110)-Co3O4 et (0001)-CoO(OH) en adoptant une nouvelleapproche de métadynamique d'échantillonnage amélioré, capable d'identifieret caractériser les mécanismes de réaction chimique et d'intégrer pleinement lerôle des degrés de liberté du solvant, permettant ainsi de dévoiler des réactivités chimiques d'une complexité remarquable. L'énergétique, la cinétique et la thermodynamique derrière l'OER sont donc trouvées à ces surfaces d'oxyde de cobalt à l'interface avec l'eauIn this thesis, DFT-MD simulations, coupled with state-of-the-art metadynamics techniques, are applied to gain a global understanding of Co3O4 and CoO(OH) cobalt oxide aqueous interfaces in catalyzing the oxygen evolution reaction (OER), and hence possibly help in the design of novel catalysts basedon non-precious materials, a current key field of research in science and technology, especially of importance for the hydrogen economy, for green technology in a period of time with an ever more growing demand in green-energy. In this thesis, we step-by-step reveal the OER mechanisms on spinel Co3O4 andCoO(OH) cobalt aqueous electrocatalysts carefully and rationally via novelmetadynamics techniques.Up to now, the literature has never taken into account the atomistic modifications on the electrode structure as well as on the interfacial water into their modeling of OER processes. Such lack of knowledge clearly represents a significant hurdle toward the development of improved catalysts, which couldbe overcome by employing methods able to track the catalytic features of theOER at the atomistic scale. For the first time, we show how important itis to take into consideration the presence of the liquid water environment inthe structural characterization of catalyst surfaces, i.e. for (110)-Co3O4 and(0001)-CoO(OH) in this work. A detailed characterization of chemical andphysical properties of the aqueous interfaces is provided (i.e. structure, dynamics, spectroscopy, electric field), for the (110)-Co3O4 and (0001)-CoO(OH)aqueous surfaces.A study of the OER is presented not only by looking at the catalysts, butalso by addressing the role of the water environment in the catalytic process,not done before in literature. Accordingly, both gas-phase and liquid-phaseOER are here investigated at the (110)-Co3O4 and (0001)-CoO(OH) adoptinga novel enhanced sampling metadynamics approach able to address a widerange of chemical reaction mechanisms and to fully include the role of thesolvent degrees of freedom, allowing to unveil reaction networks of remarkablecomplexity. The energetics, kinetics and thermodynamics behind the OER aretherefore found at these cobalt oxide surfaces
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Berglund, Sean Patrick. "Mixed metal oxide semiconductors and electrocatalyst materials for solar energy conversion." 2013. http://hdl.handle.net/2152/22903.
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The sun is a vast source of renewable energy, which can potentially be used to satisfy the world's increasing energy demand. Yet many material challenges need to be overcome before solar energy conversion can be implemented on a larger scale. This dissertation focuses on materials used for solar energy conversion through photo-electrochemical (PEC) processes. It discusses methods for improving PEC materials, namely mixed metal oxide semiconductors, by nanostructuring, incorporation of additional elements, and application surface electrocatalysts. In this dissertation several material synthesis techniques are detailed. A high vacuum synthesis process known as reactive ballistic deposition (RBD) is used to synthesize nanostructured bismuth vanadate (BiVO₄), which is studied for PEC water oxidation. Additionally, ballistic deposition (BD) is used to incorporate Mo and W into nanostructured BiVO₄ to improve the PEC activity. An array dispenser and scanner system is used to incorporate metals into copper oxide (CuO) and copper bismuth oxide (CuBi₂O₄) and over 3,000 unique material compositions are tested for cathodic photoactivity. The system is also used to test 35 elements as single component metal oxides, mixed metal oxides, and dopants for titanium dioxide (TiO₂) for use in dye-sensitized solar cells (DSCs). Lastly, RBD is used to deposit tungsten semicarbide (W₂C) onto p-type silicon (p-type) substrates as an electrocatalyst for PEC proton reduction. In many cases, the synthesis techniques and new material combinations presented in this dissertation result in improved PEC performance. The materials are thoroughly assessed and characterized to gain insights into their nanostructure, chemical composition, light absorption, charge transport properties, catalytic activity, and stability.text
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Tovide, Oluwakemi Omotunde. "Graphenated polyaniline nanocomposite for the determination of polyaromatic hydrocarbons (pahs) in water." 2013. http://hdl.handle.net/11394/3851.
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Philosophiae Doctor - PhDThe thesis presents a simple, sensitive, low cost and a novel graphenated polyaniline doped tungsten trioxide nanocomposite, as an electrochemical sensor for the detection and quantitative and determination of PAHs, which are ubiquitous, toxic, as well as dangerous organic pollutant compounds in the environment. The selected PAHs (anthracene, phenanthrene and pyrene) in wastewater were given priority as a result of their threat to human nature and that of the environment. In order for a healthy, non-polluted and well sustainable environment, there is need for an instrument that is capable of detecting and quantifying these organic pollutants onsite and also for constant monitoring. The nanocomposites were developed by chemical and electrochemical methods of preparations, exploiting the intrinsic properties of polyaniline, graphene and tungsten trioxide semiconducting materials. Chemically, graphene-polyaniline (GR-PANI) nanocomposite was synthesised by in situ polymerisation method, then casted on a surface of glassy carbon electrode to form GR-PANI modified electrode. The properties of the prepared electrode were investigated through morphological and spectroscopic techniques, which confirmed the formation of the composite. The electroactivity of the prepared modified electrode revealed great improvement in cyclic and square wave voltammetric response on anthracene. A dynamic range of 2.0 × 10-5 to 1.0 × 10-3 M and detection limit of 4.39 x 10-7 M was established.
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黃馨賢. "Screening and characterization of metal oxide electrocatalysts for oxygen evolution reaction." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/dde4xn.
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碩士逢甲大學
化學工程學系
103
In this study, oxygen evolution catalysts was rapidly screened by scanning electrochemical microscopy (SECM). The Ru and Co oxide based arrays were prepared based on the concept of the combinational method. The element including Ir,V,Fe,Ni,Mo and Mn were used as the binary or ternary metal oxide composition. The surface morphology and elemental composition of metal oxide catalysts were characterized by scanning electron microscope (SEM) and energy dispersive spectrometer (EDX), respectively. Catalyst arrays were screened with SG-TC mode by SECM for oxygen evolution reaction. Linear sweep voltammetry, polarization curves and Tafel curves analyses were used to determine the initial potential, electron transfer coefficient, Tafel slope, and standard rate constant of the catalyst. The results show V1Ru3Co1Ox and V2Ru2Co1Ox catalysts have the better initial potential of 0.42±0.02 V and the larger standard rate constant (k0A) of 1.14×10-5 cm/s.
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Thangaraju, Mahadevan. "Study of precious metal-oxide based electrocatalysts for the oxidation of methanol." Thesis, 1996. http://hdl.handle.net/1957/34264.
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Slanac, Daniel Adam. "Design of nanocomposites for electrocatalysis and energy storage : metal/metal oxide nanoparticles on carbon supports." Thesis, 2012. http://hdl.handle.net/2152/ETD-UT-2012-08-6060.
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Controlling catalyst morphology and composition are required to make meaningful structure-activity/stability relationships for the design of future catalysts. Herein, we have employed strategies of presynthesis and infusion or electroless deposition to achieve exquisite control over catalyst composite morphology. The oxygen reduction (ORR) and the oxygen evolution reactions (OER) were chosen as model systems, as their slow kinetics is a major limiting factor preventing the commercialization of fuel cells and rechargeable metal air batteries. In acid, bimetallic (Pt-Cu, Pd-Pt) and monometallic (Pt) catalysts were presynthesized in the presence of capping ligands. Well alloyed Pt-Cu nanoparticles (3-5 nm) adsorbed on graphitic mesoporous carbon (GMC) displayed an ORR activity >4x that of commercial Pt. For both presynthesized Pt and Pt-Cu nanocrystals on GMC, no activity loss was also observed during degradation cycling due to strong metal-support interactions and the oxidation resistance of graphitic carbon. Similar strong metal-support interactions were achieved on non-graphitic carbon for Pd3Pt2 (<4 nm) nanoparticles due to disorder in the metal surface This led to enhanced mass activity 1.8x versus pure Pt, as well as improved stability. For basic electrolytes, we developed an electroless co-deposition scheme to deposit Ag (3 nm) next to MnOx nanodomains on carbon. We achieved a mass activity for Ag-MnOx/VC, 3x beyond the linear combination of pure component activities due to ensemble effects, where Ag and MnOx domains catalyze different ORR steps, and ligand effects from the unique electronic interaction at the Ag-MnOx interface. Activity synergy was also shown for Ag-Pd alloys (~5 nm), achieving up to 5x activity on a Pd basis, resulting from the unique alloy surface of single Pd atoms surrounded by Ag. Lastly, we combined arrested growth of amorphous nanoparticles with thin film freezing to create a high surface area, pure phase perovskite aggregate of nanoparticles after calcination. Sintering was mitigated during the high temperature calcination required to form the perovskite crystals. The high surface areas and phase purity led to OER mass activities ~2.5x higher than the benchmark IrO2 catalyst.text
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Anju, V. G. "Electrocatalysis using Ceramic Nitride and Oxide Nanostructures." Thesis, 2016. http://etd.iisc.ernet.in/handle/2005/2919.
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Global warming and depletion in fossil fuels have forced the society to search for alternate, clean sustainable energy sources. An obvious solution to the aforesaid problem lies in electrochemical energy storage systems like fuel cells and batteries. The desirable properties attributed to these devices like quick response, long life cycle, high round trip efficiency, clean source, low maintenance etc. have made them very attractive as energy storage devices. Compared to many advanced battery chemistries like nickel-metal hydride and lithium - ion batteries, metal-air batteries show several advantages like high energy density, ease of operation etc. The notable characteristics of metal - air batteries are the open structure with oxygen gas accessed from ambient air in the cathode compartment. These batteries rely on oxygen reduction and oxygen evolution reactions during discharging and charging processes. The efficiency of these systems is determined by the kinetics of oxygen reduction reaction. Platinum is the most preferred catalyst for many electrochemical reactions. However, high cost and stability issues restrict the use of Pt and hence there is quest for the development of stable, durable and active electrocatalysts for various redox reactions.
The present thesis is directed towards exploring the electrocatalytic aspects of titanium carbonitride. TiCN, a fascinating material, possesses many favorable properties such as extreme hardness, high melting point, good thermal and electrical conductivity. Its metal-like conductivity and extreme corrosion resistance prompted us to use this material for various electrochemical studies. The work function as well as the bonding in the material can be tuned by varying the composition of carbon and nitrogen in the crystal lattice.
The current study explores the versatility of TiCN as electrocatalyst in aqueous and non-aqueous media. One dimensional TiC0.7N0.3 nanowires are prepared by simple one step solvothermal method without use of any template and are characterized using various physicochemical techniques. The 1D nanostructures are of several µm size length
and 40 ± 15 nm diameter (figure 1). Orientation followed by attachment of the primary particles results in the growth along a particular plane (figure 2).
(a) (b)
(c)
Figure 1. (a) SEM images of TiC0.7N0.3 nanowires (b) TEM image and (c) High resolution TEM image showing the lattice fringes.
(a) (b) (d)
Figure 2. Bright field TEM images obtained at different time scales of reaction. (a) 0 h; (b) 12 h; (c) 72 h and (d) 144 h.
The next aspect of the thesis discusses the electrochemical performance of TiC0.7N0.3 especially for oxygen reduction. Electrochemical oxygen reduction reaction (ORR) reveals that the nanowires possess high activity for ORR and involves four electron process leading to water as the product. The catalyst effectively converts oxygen to water with an efficiency of 85%. A comparison of the activity of different (C/N) compositions of TiCN is shown in figure 3. The composition TiC0.7N0.3 shows the maximum activity for the reaction. The catalyst is also very selective for ORR in presence of methanol and thus cross-over issue in fuel cells can be effectively addressed. Density functional theory (DFT) calculations also lead to the same composition as the best for electrocatalysis, supporting the experimental observations.
Figure 3. Linear sweep voltammetric curves observed for different compositions of titanium carbonitride towards ORR.
The next chapter deals with the use of TiC0.7N0.3 as air cathode for aqueous metal
- air batteries. The batteries show remarkable performance in the gel- and in liquid- based electrolytes for zinc - air and magnesium - air batteries. A partial potassium salt of polyacrylic acid (PAAK) is used as the polymer to form a gel electrolyte. The cell is found to perform very well even at very high current densities in the gel electrolyte (figures 4 and 5).
Figure 4 Photographs of different components of the gel - based zinc - air battery.
(a) (b)
Figure 5. a) Discharge curves at different current densities of 5, 20, 50 and 100 mA/cm2 for zinc-air system with TiC0.7N0.3 cathode b) Charge – discharge cycles at 50 mA/cm2 for the three electrode configuration with TiC0.7N0.3 nanowire for ORR and IrO2 for OER and Zn electrode (2h. cycle period).
Similarly, the catalytic activity of TiC0.7N0.3 has also been explored in non-aqueous electrolyte. The material acts as a bifunctional catalyst for oxygen in non-
aqueous medium as well. It shows a stable performance for more than 100 cycles with
high reversibility for ORR and OER (figure 6). Li-O2 battery fabricated with a non-aqueous gel- based electrolyte yields very good output. (a) (b) (c)
Figure 6. Galvanostatic charge –discharge cycles. (a) at 1 mA/cm2 (b) specific capacity as a function of no. of cycles (c) photographs of PAN-based gel polymer electrolyte.
Another reaction of interest in non –aqueous medium is I-/I3-. redox couple. TiC0.7N0.3 nanowires show small peak to peak separation, low charge transfer resistance and hence high activity. The catalyst is used as a counter electrode in dye sensitized a
solar cell that shows efficiencies similar to that of Pt, state of the art catalyst (figure 7). (a) (b)
(c)
Figure 7 (a) Cyclic voltammograms for I-/I3 - redox species on TiC0.7N0.3 nanowires (red), TiC0.7N0.3 particle (black) and Pt (blue). (b) Photocurrent density - voltage characteristics for DSSCs with different counter electrodes. TiC0.7N0.3 nanowire (black), TiC0.7N0.3 particle (blue), Pt (red). (c) Photograph of a sample cell.
(a) (b)
(c) (d)
Figure 8 a) Comparison ORR activity for (i) NiTiO3(black), (ii) N-rGO (red), (iii) NiTiO3 – N-rGO (green) and (iv) Pt/C (blue) (b) Linear sweep voltammograms for OER observed on NiTiO3 – N-rGO composite (black), NiTiO3 (brown), N-rGO (blue), glassy carbon (red) in 0.5 M KOH. (c) Galvanostatic discharge curves of NiTiO3 – N-rGO as air electrode
(d) Charge – discharge cycle at 5 mA/cm2 for the rechargeable battery with 10 min. cycle period.
The last part of the thesis discusses about a ceramic oxide, nickel titanate. The electrocatalytic studies of the material towards ORR and OER reveal that the catalyst shows remarkable performance as a bifunctional electrode. A gel - based zinc - air battery fabricated with nickel titanate – reduced graphene oxide composite shows exceptional performance of 1000 charge-discharge cycles in the rechargeable mode (figure 8). Of course, the primary battery configuration works very well too
The thesis contains seven chapters on the aspects mentioned above with summary and future perspectives given as the last chapter. An appendix based on TiN nanotubes and supercapacitor studies is given at the end.
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Turner, Travis Collin. "Synthesis, characterization, and oxygen evolution reaction catalysis of nickel-rich oxides." Thesis, 2014. http://hdl.handle.net/2152/26198.
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A successful transition from fossil fuels to renewable energies such as wind and solar will require the implementation of high-energy-density storage technologies. Promising energy storage technologies include lithium-ion batteries, metal-air batteries, and hydrogen production via photoelectrochemical water splitting. While these technologies differ substantially in their mode of operation, they often involve transition-metal oxides as a component. Thus, fundamental materials research on metal oxides will continue to provide much needed advances in these technologies. In this thesis, the electrochemical and electrocatalytic properties of Fe- and Mn-substituted layered LiNiO₂ materials were investigated. These materials were prepared by heating mixed nitrate precursors in O₂ atmosphere at 700-850 °C for 12 h with intermediate grindings. The products were chemically delithiated with NO₂BF₄, and the delithiated samples were annealed at moderate temperatures in order to transform them to a spinel-like phase. Samples were characterized by inductively coupled plasma analysis and Rietveld refinement of the X-ray diffraction patterns, which were found to be in reasonably close agreement regarding lithium stoichiometry. Spinel-like materials were found to possess an imperfect spinel structure when heated at lower temperatures and a significant amount of NiO impurity was formed when heated to higher temperatures. This structural disorder was manifested during electrochemical cycling -- only Mn-rich compositions showed reversible capacities at a voltage of around 4.5 V. The layered materials exhibited significant capacity loss upon cycling, and this effect was magnified with increasing Fe content. These materials were further investigated as catalysts for the oxygen evolution reaction (OER). All samples containing Mn exhibited low OER activity. In addition, delithiation degraded catalyst performance and moderate temperature annealing resulted in further degradation. Because delithiation significantly increased surface area, activities were compared to the relative to BET surface area. Li₀.₉₂Ni₀.₉Fe₀.₁O₂ exhibited significantly higher catalytic activity than Li₀.₈₉Ni₀.₇Fe₀.₃O₂. This prompted testing of Li[subscript x]Ni₁₋[subscript y]Fe[subscript y]O₂ (y = 0, 0.05, 0.1, 0.2, and 0.3) samples. It was found that a Fe content of approximately 10% resulted in the highest OER activity, with decreased activities for both larger and smaller Fe contents. These results were found to be consistent with studies of Fe substituted nickel oxides and oxyhydroxides, suggesting a similar activation mechanism.text
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Bayeh, Anteneh Wodaje, and Anteneh Wodaje Bayeh. "Advanced Metal Oxide Electrocatalysts Modified Graphite Felt as High-Performance Electrode for Vanadium Redox Flow Batteries." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/2jf9s4.
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博士國立臺灣科技大學
材料科學與工程系
107
As one of the most promising electrochemical energy storage systems, vanadium redox flow battery (VRFB) has received increasing attention due to its attractive features for large-scale storage applications. However, high production cost and the relatively low energy efficiency still limit their feasibility. Therefore, developments of powerful electrocatalyst and electrode materials with low cost are critical for the design of VRFB. To improve the energy density and overall performance for large scale applications, extensive research has been carried out on the electrode modification methods for VRFB. First, to increase the electrocatalytic activity of graphite felt (GF) electrodes in vanadium redox flow batteries (VRFBs) toward the VO2+/VO2+ redox couple, we prepared stable, high catalytic activity, and uniformly distributed hexagonal Ta2O5 nanoparticles on the surface of GF by varying the Ta2O5 contents. Scanning electron microscopy (SEM) revealed the amount and distribution uniformity of the electrocatalyst on the surface of GF. It was found that the optimum amount and uniformly immobilized Ta2O5 nanoparticles on GF surface provided the active sites, enhanced hydrophilicity and electrolyte accessibility, thus remarkably improved electrochemical performance of GF. In particular, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) results showed that the Ta2O5-GF nanocomposite electrode with weight percentage of Ta2O5 to GF of 0.75 wt% exhibited the best electrochemical activity and reversibility toward the VO2+/VO2+ redox reaction, when compared with the other electrodes. The corresponding energy efficiency was enhanced by ~ 9% at a current density of 80 mA cm−2, as compared with untreated GF. Furthermore, the charge–discharge stability test with 0.75 wt% Ta2O5-GF electrode at 80 mA cm−2 showed that after 50 cycles, there was no obvious attenuation of efficiencies signifying, the best stability of Ta2O5 nanoparticles which strongly adhered on the GF surface. Second, we synthesized simple, inexpensive, and conductive W18O49 nanowires (W18O49NWs) as electrocatalysts on the surface of GF through the one-step solvothermal process. Cyclic voltammetry and electrochemical impedance spectroscopy studies revealed that W18O49NWs exhibit electrocatalytic effects on a VO2+/VO2+ redox couple on the positive side, which enhance the electrochemical kinetics of the redox reactions. To further improve the electrochemical performance of the W18O49NWs, the sample was thermally annealed with a controlled amount of H2/Ar atmosphere to form oxygen-vacancy–rich hydrogen-treated W18O49NWs (H-W18O49NWs). When used as an electrode in a VRFB single cell, this material demonstrated outstanding performance with 9.1% and 12.5% higher energy efficiency than cells assembled with W18O49NWs and treated GF, respectively, at a high current density of 80 mA cm−2. The superior performance of the H-W18O49NW electrocatalyst-based electrode can be attributed to the presence of numerous oxygen vacancies, which were proven to act as active sites for the VO2+/VO2+ redox reaction. Moreover, the uniformly immobilized and 1D nature of the W18O49NWs facilitated the charge-transport process, enhanced hydrophilicity and electrolyte accessibility, and thus remarkably reduced electrochemical polarization during the mass transfer of active species. The long-term cycling performance confirmed the outstanding durability of the as-prepared H-W18O49NWs–based electrode with negligible activity decay after 100 cycles. Third, we use a simple, low-cost, and powerful titanium niobium oxide–reduced graphene oxide (TiNb2O7–rGO) nanocomposite electrocatalyst which was synthesized through dispersion and blending in aqueous solution followed by freeze-drying and annealing for all-vanadium redox flow battery (VRFB). The TiNb2O7 nanoparticles are uniformly anchored between the rGO sheets; simultaneously, the rGO sheets are separated using TiNb2O7 nanoparticles. The synergistic effects between them prevent the agglomeration of the nanoparticles and restacking of the rGO sheets. Cyclic voltammetry and electrochemical impedance spectroscopy results reveal that among all prepared samples, the TiNb2O7–rGO nanocomposite electrocatalyst exhibits the most favorable electrocatalytic activity toward VO2+/VO2+ and V3+/V2+ at the positive electrode and the negative electrode, respectively, to facilitate the electrochemical kinetics of the vanadium redox reactions. The corresponding energy efficiency is improved by ~11.1% and 12.34% at current densities of 80 and 120 mA cm−2, respectively, compared with pristine graphite felt. The superior performance of the TiNb2O7–rGO nanocomposite electrode may have been due to the synergistic effects related to the high electronic conductivity of rGO nanosheets and the interfacial properties created within TiNb2O7 and rGO. Furthermore, the charge-discharge stability test demonstrates the outstanding stability of the TiNb2O7–rGO electrodes. The TiNb2O7–rGO-based VRFB exhibits negligible activity decay after 200 cycles. The remarkable electrocatalytic activity and mechanical stability are achieved due to the TiNb2O7–rGO nanocomposite being strongly anchored on the graphite felt surface for a substantial time during repetitive cycling.
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Muthumariappan, Akilarasan, and Akilarasan Muthumariappan. "Morphologically Tuned Transition Metal Oxide as a High Surface Electrocatalysts for Electrochemical (Bio) Sensors and Supercapacitor Applications." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/h2963c.
Full textAbstract:
博士國立臺北科技大學
能源與光電材料專班(EOMP)
107
The Transition Metal Oxides (TMO) clenches a vast perspective for the expansion of various novel materials with its prospective in medical, energy storage, electrochemical sensor and biosensor applications. However, as the electrode materials, the fabrication of nano-scaled TMO have some theoretical limitations, it can be resolved by current synthesis known protocols and also the carbon (graphite, graphene, reduced graphene oxide, and carbon nanotubes) based matrix were combined with metal oxide to enhance their properties. Nevertheless facilely, tuning the morphology of TMO results in the enhancement of catalytic activity, conductivity, and physical and chemical properties. Nowadays, domestic waste, is an extensive problem in all over the nation. Due to lack of proper maintenance, awareness, and proper disposal systems, the problem is rather more acute in developing nations. When this waste entered into the landfill, it will be hazardous to the environment and cause health risks to human. On the other hand, these waste are considered as a valuable one, because it consists of a massive amount of iv metals, including precious metals. Therefore, the recovery of metals such as gold, silver, tantalum, aluminum, and Iron from waste become an emerging trend. An extensively utilized active component of a glucose sensor, cuprous oxide (Cu2O) is synthesized and dealt with various annealing temperatures at 400, 600, and 800◦C. The impacts of annealing temperatures on morphology, electro-active surface area, and the glucose sensing properties of cuprous oxides are investigated and spotted that, 600◦C is an effective annealing temperature. Then, a comprehensively applied effective material of the dopamine (DA) and uric acid (UA) sensors, Zinc oxide (ZnO) is prepared through the microwave method with the different stoichiometric ratios of urea, such as [C4H6O4Zn ·2H2O: CH4N2O]=[1:1], [1:2], and [1:3], respectively. After that, the DA and UA biosensor over the cost-effective screen-printed carbon electrode (SPCE) adaption method. The functional (mono and binary) microstructures of transition metal oxides (Co and Mn) with different morphologies have been prepared through simple one-step hydrothermal methodology. The (mono and binary) microstructures of transition metal oxides (Co and Mn) such as Co3O4 polyhedrons (PHs), Mn3O4 microcubes (MCs), MnCo2O4 microflowers (MFs) and CoMn2O4 hollow microspheres (HMs) were employed for the specific and sensitive detection of triptan drug Rizatriptan benzoate (RZB), to evaluate the electrocatalytic ability of transition metal oxides towards electrochemical biosensing. Finally, aluminium oxide nanoparticles (Al2O3 NPs) has recovered through a facile one-step sonochemical methodology. The as-recovered Al2O3 NPs were employed for the specific and sensitive detection of omeprazole (OMZ), which comes under the class of protonpump inhibitor. Furthermore, the recovered material was employed as an active participant in supercapacitor application, which exhibited an appreciable specific capacitance value (688 F/g) at 1 A/g current density in 1 M KOH and maintained 86 % capacitance retention even after 3000 GCD cycles.
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Chiou, Yuh-Jing, and 邱郁菁. "Electrocatalysis Applications of Palladium and Gold Catalysts Supported on Metal Oxide Modified Multi-Walled Carbon Nanotubes." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/00347803783944807580.
Full textAbstract:
博士大同大學
材料工程學系(所)
99
For the application of direct formic acid fuel cell, Pd catalyst with some modification attracts the study attention for its electrocatalytic advantages. To benefit the catalytic performance and prevent the catalyst poison problem, this study develops Pd basis catalysts, which have solid solution phase with Au and ceria/ceria-zirconia modified MWCNTs substrate, by impregnation and polyol methods. The composition, structure and morphology are analyzed by ICP, XRD and FETEM, respectively. For Au-Pd bimetal catalysts, the formation of solid solution phase and the compositions of the catalysts are proved to be consistent with the initial designation. For MWCNTs modified by ceria or ceria-zirconia, both mesoporous structure of ceria/ceria-zirconia and the advanced breaking of MWCNTs in the impregnation process may cause the surface area increasing of MWCNTs. Zr doping may decrease the temperature of lattice oxygen desorption. The addition of metal can fill the defect of the substrate and decrease the surface area. Pd is the main dominant to promote the reaction and lower the reaction temperature in the TPD helium process. In electrocatalysis, Au-Pd solid solution can prevent the leaching of Pd in formic acid, while the oxide modified support can prevent catalyst poison. The prepared catalysts can totally convert CO between 150~250oC. More Pd can convert 100% CO at lower temperature. It can be considered that, both the formation of solid solution, Au-Pd, and the oxide modification of MWCNTs can decrease the activation energy of the catalyzing reaction and have better catalytic performance.
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Chin, Chih-Chun, and 金智駿. "Preparation of Mesoporous Metal Oxide Composites as Electrocatalysts by Soft Template Method for Cathode Material of Lithium-Air Batteries." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/31888056569858071372.
Full textAbstract:
碩士國立高雄大學
應用化學系碩士班
103
Oxygen reduction reactions ( ORR ) at the air cathode in non-aqueous electrolytes are well-known to influence the performance of Li-air batteries. In this work, highly ordered mesoporous metal oxide composites were designed as electrocatalysts and porous air cathode material in the Li-air battery. The highly ordered mesoporous MnO2/C and TiO2/C composites were synthesized by soft template method and hydrothermal method, combining solvent-evaporation-induced self-assembly and the in situ carbothermal reduction reaction and using the triblock copolymer F127 as the structure-directing agent and resol as the carbon source. In summary, the XRD patterns show metal oxide can be attributed to a pure and well-crystallized MnO2 and TiO2 phase. The metal oxide composites with large specific surface area 424 m2/g ( MnO2/C ) and 599 m2/g ( TiO2/C ). The porous structure of metal oxide composites provides high electrocatalytic active sites and sufficient transmission paths for O2 and electrolyte. Both ordered metal oxide composites show good elecrcatalytic activity toward Oxygen Reduction Reactions ( ORR ) / Oxygen Evolution Reactions ( OER ) in non-aqueous electrolytes. Employing the ordered mesoporous metal oxides as electrocatalyst in Li-air batteries, the Li-air batteries display lower overpotential and good discharge capacity. This result demonstrates ordered mesoporous metal oxide composites are promising cathode electrocatalysts for non-aqueous Li-air batteries.
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Guo, Mann-Charn, and 郭蔓嬋. "Adding metal oxides in Pt anode electrocatalysts for enhancing CO tolerance in proton exchange membrane fuel cells." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/81445252234693930210.
Full textAbstract:
碩士國立中興大學
環境工程學系所
100
The aim of this study is to discuss the preparation of the membrane-electrode assembly (MEA) by using carbon nanotubes (CNTs) in proton exchange membrane fuel cell (PEMFC). Different pretreatment procedures of carbon supports are also considered to evaluate the catalytic activity with various catalysts. Besides, the addition of metal oxides such as CeO2、ZrO2 and SnO2 are investigated to enhance the electrocatalytic activity and the tolerance of different CO concentrations. All catalysts are characterized by means of FESEM, TEM, XRD, BET and ESCA. The experimental results show that the effects of various preparation methods on the MEA to determine the best operating parameters. The 240 seconds hot-press with temperature is 135 oC has been selected for further experiments. Additionally, the investigation of the catalytic activity compared with different pretreatment procedures for catalyst support indicates that CNTs pretreated with nitric acid at 50 oC for two days (CNTs-50 oC-2d) that are supported active metals has higher catalytic activity than others. It is supposed that CNTs-50oC-2d supports have higher surface area provided more active sites and the gas molecules may easily diffuse into the pores to be reacted. Moreover, the electrocatalytic activities by using several catalysts included 5%SnO2-5%Pt/C, 5%ZrO2-5%Pt/C at the same voltage are higher than those without adding any MOx, and 5%SnO2-5%Pt/C is the effectiveness catalyst found after testing .On the other hand, it was reported that the CO tolerance of electrocatalyst was also enhanced by the addition of SnO2 and ZrO2 under the CO concentration is 100 ppm. The CO tolerance are in the following order as 5%ZrO2-5%Pt/C > 5%SnO2-5%Pt/C > 5%Pt/C > 5%CeO2-5%Pt/C. The effect of various concentrations of CO (0、50 and 100 ppm) shows that 5%ZrO2-5%Pt/C catalyst displays a better CO tolerance than the others. Consequently, the electrocatalytic activity and CO tolerance of catalysts are both enhanced while MOx added with Pt.
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Alves, Ana Catarina Gomes Moreira. "Synthesis and characterization of abiotic electrocatalysts based on reduced graphene oxide for oxygen reduction reaction." Master's thesis, 2019. http://hdl.handle.net/10451/40629.
Full textAbstract:
Tese de mestrado, Química (Química) Universidade de Lisboa, Faculdade de Ciências, 2019The use of low-temperature fuel cells as power supplies of energy conversion devices is attracting considerable interest because of the direct electrochemical conversion of a fuel, e.g. hydrogen and glucose, and an oxidant, such as oxygen, producing electrical current. The sluggish kinetic of the oxygen reduction reaction (ORR) on the cathode half-reaction is particularly investigated since its acceleration relies on the development of efficient electrocatalysts. Unfortunately, the most promising catalysts for ORR are platinum-based materials that exhibit poor durability, limited resource and high cost. Under such circumstances, the development of non-noble, efficient and low-cost electrocatalysts has attracted a great deal of attention. The present dissertation focuses on the synthesis and physicochemical characterization of graphene-based materials doped with nitrogen and 2 and 10 wt % transition metals (Fe, Co, Mn, Cu, Ni and Rh), denoted as rGO/M 2 and 10 %, capable of reducing molecular oxygen. Firstly, nitrogen-doped reduced graphene oxide with atomically dispersed transition metal materials were synthesized using commercial graphene as precursor. A sequential extra-exfoliation and oxidation of the graphene increased the d-spacing between carbon layers and created porosity on the structure, which is essential for the diffusion of reactants on the material. Further simultaneous N doping and reduction of graphene oxide using thermal and low-temperature plasma treatment allowed the formation of M-Nx active sites that contribute greatly on the ORR activity. The obtained carbon structure exhibited a large specific surface area (c.a. 800 m2 g-1) doped with c.a. 1.98 wt % of nitrogen. The incorporation of atomically dispersed metal reached 21 % of 2 wt %, 3 % and 0.46 % of 10 wt % using different reduction methods. The engagement of aromatic macrocycle molecules, particularly iron and cobalt metalloporphyrins, in the graphene oxide structure was also studied. The synthesis of these hybrid materials was based on a procedure described previously, relying on the addition of the metalloporphyrin to the graphene structure, followed by its pyrolysis under N2 atmosphere. The ORR electrochemical characterization of the materials was performed using hydrodynamic convective systems: the rotating disk electrode (RDE) and the rotating ring-disk electrode (RRDE), in acidic, alkaline and neutral media. Among all the synthesized materials, iron- and cobalt-based materials showed the highest performance towards ORR. In particular rGO/Fe 2 % exhibited a remarkable activity in acidic (Eonset 0.76 V vs. RHE), alkaline (Eonset 0.91 V vs. RHE) and neutral (Eonset 0.78 V vs. RHE) media, comparable to Pt/C catalysts. A mixed 2- and 4-electron pathway was observed for rGO/Fe 2 % in acidic and alkaline media due to the contributions of several functional groups in the structure. The remaining materials displayed lower onset potential in acidic (0.44 to 0.71 V vs. RHE), alkaline (0.80 to 0.87 V vs. RHE) and neutral (0.64 to 0.74 V vs. RHE) media. The outstanding ORR performance of these materials is attributed to the presence of M-Nx actives sites dispersed in the carbon structure and intrinsic ORR activity of metalloporphyrins.
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Chien-JuiLo and 羅建睿. "Fabrication of Co-based metal-organic frameworks/ N-doped reduced graphene oxide nanocomposites as bifunctional electrocatalysts for Zn-air batteries." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/cxkg4p.
Full text
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Leelavati, A. "Nanostructured Hybrids with Engineered Interfaces for Efficient Electro, Photo and Gas Phase Catalytic Reactions." Thesis, 2015. http://etd.iisc.ernet.in/2005/3849.
Full textAbstract:
Catalysis using nanostructures has been a topic of substantial interest for fundamental studies and for practical applications in energy and environmental sectors. The growing demand for production of energy and in the cleaning of polluting hazardous vehicles/industrial wastes has led to several studies in catalysis. Despite the substantial growth of heterogeneous catalytic technologies in last decade, they are still far from reaching their full potential in terms of efficiency, selectivity as well as durability. It is often difficult to simultaneously tackle all the mentioned issues with single component catalysts. Most of these challenges are being overcome with heterostructures/supported hybrid catalysts by modifying their interfaces.
The properties of heterostructures hybrids arises not only from the individual contributions of the individual components but also from strong synergetic effect arising from the interface. Engineering the interfaces provides pathways to promote the catalytic performance and hence has been explored. In this regard, we have focused on the progress in investigating the active interfaces that affect the performance of metal oxide-metal, semiconductor-metal and coupled semiconductor nanocatalyst hybrids. We explored a wide spectrum of their applications in photo catalytic, electrocatalytic as well as gas-phase reactions and highlighted the importance of the interface for overall performance.
The entire study reported in the thesis is organized as follows:
Chapter 1 is a general introduction of hybrid nanocatalyst and their role in wide spectra of catalytic reactions in photo/electro catalysis as well as gas-phase reactions. This chapter describes the motivation behind modulating the interface between two or more nanostructures to obtain multifunctional nanocatalysts. Nan catalysts to achieve high throughput with active interfaces are elaborated while indicating the role of morphology, internal induced state, charge transfer, geometric, support, as well as electronic effect for enhanced performance. Motivation behind specific nanocatalyst hybrid, synthesis routes as well as characterization techniques are detailed in the respective chapters. Specific details for different hybrids are described in the following chapters.
Chapter 2 describes the synthesis of high dense ultrathin Au wires on ZnO nanorods for electrocatalytic oxidation of ethanol, where the prerequisite step is the formation of amine-modified support. Oleylamine modification not only serves to anchor Au nanowires on ZnO but also passivates surface defects of ZnO, which in turn enhances the photocurrent. In addition to the stability, the support induces electronic effect on Au nanowires, which facilitates redox process at low potential. Most importantly, the support promotes the activity of Au nanowires upon photoirradiation, and thus leading to synergy between electro and photooxidation current. This is of immense importance for photofuel cell technologies. Moreover, the method enabled the first time electrocatalysis on these nanowires that revealed ultrathin nanowires are potentially interesting systems for catalysis applications provided they are stabilized by a suitable support.
Chapter 3 deals with the growth of ultrathin Au nanowires on metal oxide (TiO2) coupled with graphene hybrid support in order to overcome the low conductivity of metal oxide. Oleylamine, used for growth of Au nanowires simultaneously functionalizes the support and leads to room temperature GO reduction. With respect to catalytic activity, we also synthesized the binary counterparts (rGO/Au, TiO2/Au ultrathin nanowires) to delineate the contribution of each of the components to the overall electrocatalytic oxidation of ethanol. Comparative analysis of photo and electrocatalytic activity between the different binary and ternary hybrids provides interesting information. Both, electronic effect of TiO2 and electrical conductivity of rGO add their specific beneficial to the nanowires, leading to superior ternary system.
Chapter 4 rGO supported ultrathin Au nanowires exhibits high electrocatalytic performance for oxidation of borohydride with a lower onset potential compared to rGO/Au nanoparticles. Electrochemical impedance spectroscopy measurements display abnormal inductive behavior of the synthesized hybrids, indicative of Au surface reactivation. DFT calculations indicate that the origin of the high activity stems from the shift in the position of the Au d-band center.
Chapter 5 Different aspect ratio ZnO nanostructures are obtained by varying the solvothermal reaction time. We observed a direct correlation between observed photocatalytic activity, measured photocurrent and length of the ZnO nanorods. Furthermore, photoresponse of the high aspect ratio ZnO nanorods are improved by
attaching Au nanoparticles, intimate contact of two components leads to band bending. Thus, the synthesized ZnO/Au heterostructure favors for prominent separation of photogenerated charge carriers.
Chapter 6 TiO2 and PbO/TiO2 hybrids are synthesized via non–hydrolytic sol–gel combustion method. Hybrid exhibits higher photocatalytic activity for the degradation of dye than TiO2. The estimated photogenerated species reveals that the origin of enhanced activity stems from the direct oxidization of dye via photogenerated hole rather than radicals.
The semiconductors are matched based on their band edge positions, for the formation of energetic radicals to degrade the pollutants. Based on this study, we infer that semiconductors should not neglected (for example Si) based on calculated mismatch of their valence band edges position for photooxidation reaction via radicals.
Chapter 7 describes the Pd dopant associated band engineering, a strategy for tuning the optoelectronic properties of ZnO towards enhanced photocatalytic activity. Incorporated Pd heterocation induces internal energy states within the ZnO band gap. The created energy level leads to trends mismatch between photocatalytic activity and measured photocurrent. Formed energy level arrests the photogenerated electrons, which make them not contribute for the photocurrent generation. Hence, the isolated photogenerated hole efficiently oxidizes the pollutants through hydroxyl radicals, and thus leads to enhanced photocatalytic activity.
Chapter 8 employed Pd-substituted zinc stannate for CO oxidation as heterogeneous catalyst for the first time. Compared with SnO2 support, zinc stannate based materials exhibits abnormal sudden light-off profiles at selective temperatures. On the basis of DRIFT studies under relevant conditions, we find that the initially formed product gets adsorbed over the catalyst surface. It leads to the accumulation of carbonates as a consequence, both lattice oxygen mobility and further CO interactions are disabled. As soon as Sn redox nature dominates over the accumulated carbonates, this leads to sudden release of lattice oxygen, and thus leads to a sudden full conversion. Therefore, choosing the suitable support material greatly influences the nature of the light-off CO oxidation profile.
Chapter 9 Although, reducible oxide supported gold nanostructures exhibits the highest CO oxidation activity; they still suffer from problems such as limited selectivity towards CO in the presence of H2. Both ex-situ and in-situ experiments demonstrate that, Au nanoparticles supported on Zn2SnO4 matrix selectively oxidizes CO. DRIFT experiments revealed that the involvement of OH groups leads to the formation of hydroxycarbonyl under PROX conditions.
Chapter 10 This chapter discusses the conclusions for the previous chapters and highlights the possibilities for future scope for the developed nanocatalysts hybrids for energy and environmental applications.
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Sarkar, Sujoy. "Electrocatalytic Studies on Layer-type Ternary Phosphochalcogenides and on the Formation of Nitride Phases." Thesis, 2014. http://hdl.handle.net/2005/3027.
Full textAbstract:
Research on new, environment-friendly, clean and efficient energy sources have contributed immensely to the development of new technologies for the generation and storage of electrical energy. Heterogeneous ‘electrocatalysis’ involves catalysis of redox reactions where the electrode material, termed as ‘electrocatalyst’ reduces the overpotential and maximizes the current for the processes occurring at the electrode/electrolyte interface. Efficient catalysts for hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR) are of paramount importance for electrochemical energy generation and storage applications in water splitting, fuel cells and batteries. However, high cost of Pt catalysts that are commonly used for such applications restricts their commercial viability. In addition, there are issues related to poisoning of the surface under certain conditions. One particular case of direct methanol fuel cells involves problems of methanol tolerance as well. Hence, the on-going search in this direction, is to search for alternate catalysts that can match the performance of Pt. There is a quest for the development of stable and durable electrocatalysts/ supports for various electrochemical redox reactions particularly based on energy storage and conversion.
The present thesis is structured in exploring the multi-functional aspects of ternary palladium phosphochalcogenides (PdPS and PdPSe) that possess layer-type structure with high crystallinity. They are semiconducting in nature and possess favorable electrochemical, electrical and optical properties. The chalcogenide compounds crystallize in orthorhombic symmetry with an indirect band gap close to 1.5 eV. The current study shows the versatility of ternary phosphochalcogenides in the bulk phase as well as in small sizes. The electrocatalytic activities of the chalcoenides are found to be dramatically improved by increasing the electrical conductivity by way of forming composites with reduced graphene oxide (rGO). The average crystallite size of the PdPS and PdPSe are 30 μm ±10 μm (figure 1). The composites are prepared by simple hydrothermal methods without use of any reducing agent and are characterized using various physico-chemical techniques.
Figure 1. FESEM images of (a) PdPSe and (b) PdPS.
In the present investigations, PdPS and its reduced graphene oxide composite (rGO-PdPS) are shown to be very efficient hydrogen evolution electrocatalysts (figure 2a). The bulk form of PdPS is found to be very active and the composite of PdPS with reduced graphene oxide improves the hydrogen evolution performance dramatically, even superior to state of the art, MoS2-based catalysts.
Figure 2. (a) Linear sweep voltammograms of rGO, bulk PdPS, rGO-PdPS composite and 40 % Pt-C in 0.5 M H2SO4 solution (pH 0.8). Scan rate used is 1 mV s-1. (b) Tafel plots for PdPS, rGO, rGO-PdPS and 40 wt% Pt-C in 0.5 M H2SO4 at 1 mVs-1 scan rate.
The Tafel slope and the exchange current density values associated with hydrogen evolution reaction are 46 mV dec-1 and 1.4 x 10-4 A cm-2 respectively (figure 2b). The stability of the PdPS-based catalyst is found to be excellent retaining same current densities even after thousand cycles. Moreover, post-HER characterization reveals the durability of the material even after cycling for a long time. Preliminary spectroelectrochemical investigations are attempted to gain further insight in to the HER.
Subsequently, the PdPS and its composite are explored as ORR catalysts in alkaline medium. The composite of PdPS with rGO is formed to enhance the catalytic activity of pure PdPS and the electron transfer kinetics is found to be very favorable. The kinetics of the oxygen reduction reactions are followed by RDE/RRDE measurements. It is experimentally verified that the composite eletrocatalyst is very stable, efficient and methanol tolerant in alkaline medium. The characteristics of the composite catalyst are comparable with widely used standard Pt-C for ORR (figure 3a). Moreover, ternary phophochalcogenide, PdPS, combined with rGO shows good catalytic activity towards OER and it affords a current density of 10 mA cm-2 at an overpotential of η = 570 mV (figure 3b).
Figure 3. (a) Comparative voltammograms for rGO, bulk PdPS, rGO-PdPS and 40 % Pt-C in 1M KOH at 1600 rpm. The potential is swept at a rate of 5 mVs-1. (b) Linear sweep voltammograms of oxygen evolution reaction on rGO-PdPS, PdPS and 40 % Pt-C in 1 M KOH electrolyte. Scan rate 5 mV s-1.
Apart from its tri-functional electrocatalytic behavior, PdPS and its rGO composite act as an anode material for Li-ion batteries showing high storage capacity of lithium (figure 4). The capacity fading of bulk PdPS is analyzed using XRD and SEM. The introduction of rGO, a well-known conducting matrix, improves the performance.
Palladium phosphorous selenide (PdPSe) and its composite with rGO (rGO-PdPSe) are also explored as electrocatalysts for HER, ORR and OER. They show the tri¬functional electrocatalytic behavior as well.
Figure 4. Discharge capacity as a function of number of cycles for PdPS, rGO rGO-PdPS electrode at current density of 35 mAg-1 in rechargeable lithium ion battery.
The next chapter deals with single or few layer PdPS where layer-type PdPS is exfoliated by several methods such as ultra-sonication and solvent exfoliation. Various microscopic and spectroscopic techniques have been used to characterize the material. These sheets show significantly improved electrocatalytic activity towards ORR and HER with notably low onset potential and low Tafel slopes. The charge storage capacity also increases by an order from its bulk counterpart. The catalyst shows excellent stability for HER and good methanol tolerance behavior towards ORR is also observed. This opens up possibilities for applications of few-layer ternary phosphosulphides in energy conversion and storage. However, one should be cautious since the exfoliation results in a slightly different composition of the material.
Different aspects of electrodeposition of gallium nanoparticles on exfoliated graphite surfaces from aqueous acidic solution forms part of the next study. The electrodeposited surface is characterized by various microscopic and spectroscopic techniques. The presence of surface plasmon peak in the visible region has led us to explore the use of Ga on EG for SERS studies. This preliminary work shows that the Raman signal of R6G is enhanced in the presence of Ga deposited on EG surface.
The research work presented in the next part of the thesis deals with the preparation, physicochemical, spectroscopic characterization of room temperature molten electrolytes based on amides. Room temperature ternary molten electrolyte involving a combination of acetamide, urea and gallium nitrate salt is prepared and the molten eutectic is characterized. An electrochemical process is developed for depositing gallium nitride from the ternary molten electrolyte on Au electrode. Gallium ion is reduced at low potentials while nitrate ion is reduced to produce atomic nitrogen, forming gallium nitride under certain conditions. Au coated TEM grid is used for patterning gallium nitride (figure 5). The deposited gallium nitride is further annealed at high temperature to increase the crystalinity and improve the stoichiometry of gallium nitride.
Figure 5. The FESEM image of patterned gallium nitride deposited on Au coated TEM grid. Elemental mapping of Ga and N from the same region is given.
The last chapter explores the prepration and uses of textured GaN tubes synthesized from GaOOH rod-like morphology. The precursor material is prepared by simple hydrothermal technique, maintaining certain value for the pH of the solution. The thermal treatment under ammonia atmosphere leads to highly crystalline, single phase textured tube- like morphology. The as-prepared material is explored as photoanodes in photoelectrochemical water splitting, dye sensitized solar cells and active substrate for SERS. The appendix-I discusses the Na-ion storage capacity by rGO-PdPS composite whereas appendix-II deals with the synthesis of InN and FeN from ternary molten electrolyte.
(For figures pl refer the abstract pdf file)