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1
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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Mamtani, Kuldeep. "Carbon-based Materials for Oxygen Reduction Reaction (ORR) and Oxygen Evolution Reaction (OER) in Acidic Media." The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu149376896628355.
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Wu, Qi-Long. "Defect Based Three-Dimensional Hierarchical Porous Carbons for Efficient Oxygen Reduction Reaction." Thesis, Griffith University, 2022. http://hdl.handle.net/10072/419073.
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The energy crisis and environmental pollution are the two major global issues caused by the excessive utilization of fossil fuels. In recent decades, developing renewable energy via electrocatalytic conversion technology has been considered as a feasible approach to replace fossil fuels. However, the scarcity and high price of commercial catalysts (e.g., Pt/C catalyst for oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER); RuO2 for oxygen evolution reaction (OER)) seriously hinder the industrialization of the electrocatalytic technology. Therefore, it is highly urgent to develop efficient and cost-effective electrocatalysts to accelerate the further development of renewable energy technologies.
Defective carbon-based materials (DCMs) have recently been considered as one of the most promising alternatives to replace precious metal electrocatalysts with the merits of high-performance, abundance and low-cost. However, structural tailoring of carbon defects at atomic scales poses great challenges in regulating defect types and density to maximize the activity.
In this thesis, we aim to develop new synthetic strategies to precisely control the structural reconstruction and surface modification of carbons, which involves a series of intensive thermal redox reactions and oxygen atom modification.
Specifically,
For the first research work, an interfacial self-corrosion strategy was developed to control the removal and reconstruction of carbon atoms via a series of thermal redox reactions of ZnO quantum dots and formed CO2 gas in confined carbon cavity, which results an ultra-dense carbon defects on carbons (HDPC). Such ultra-dense carbon defects (2.46 × 1013 cm-2) were served as efficient active sites for oxygen reduction, resulting in an excellent catalyst in both base and acid media (half-wave potentials of 0.90 or 0.75 V in 0.1 M KOH or HClO4).
For the second research work, in consideration of the difficulty of identification of active sites on hierarchical porous carbon, we employed graphene as a model catalyst to control carbon defect density and surface oxygen groups (O-groups) on graphene. Firstly, the as-synthesized catalyst with the highest defect density (DG-30) shows the best four electronic pathway oxygen reduction reaction (4e-ORR) performance. After modifying O-groups (named as O-DG-30), the ORR of the catalyst turns into a 2e- pathway. Moreover, the dynamic evolution processes and catalytic mechanisms were revealed through multiple in-situ technologies and theoretical simulations. This work further demonstrated the significance of defect density towards ORR performance.
In summary, we develop a new synthetic strategy to fabricate ultra-dense defect density on carbon, emphasizing the importance of defect density towards ORR. Based on this knowledge, we further control defect density and surface chemical environment on graphene to identify the real active sites of DCMs. This thesis provides new knowledge and perspectives in materials synthesis and electrocatalytic mechanisms via 1) developing a new synthetic methodology for ultra-dense defects construction and 2) identifying the real active site and catalytic mechanism of DCMs.Thesis (Masters)
Master of Philosophy (MPhil)
School of Eng & Built Env
Science, Environment, Engineering and Technology
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Zou, Yu. "Supported Composite Electrocatalysts for Energy Conversion Applications." Thesis, Griffith University, 2022. http://hdl.handle.net/10072/417198.
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Increasing energy demand and environmental awareness have promoted the development of efficient and environment-friendly hydrogen technologies. Water electrolysis (2𝐻2𝑂→2𝐻2+𝑂2) is a promising way to store renewable electricity generated by solar or wind energy into chemical fuel in the form of H2. Water electrolysis is comprised of a hydrogen evolution reaction (HER) on the cathode and an oxygen evolution reaction (OER) on the anode. For both HER and OER, highly catalytic active electrocatalysts are required to lower the overpotentials and to speed up the sluggish kinetics. To date, noble metal catalysts are still the most efficient electrocatalysts for these two reactions, but their high cost and low abundance on Earth limit the scalable application of water electrolysis. Therefore, investigation of alternative catalysts with low cost and high electrocatalytic activity is urgently needed.
This thesis focuses on alkaline electrocatalytic HER, as well as related reactions such as OER, and hydrazine oxidation(HzOR)-assistant HER. In terms of material design, the components are introduced to improve conductivity and mass transfer, as well as boost the intrinsic catalytic activity. Moreover, the mechanism was investigated through exploring the link between structure and performance, as well using density functional theory (DFT) calculations.
The first two experimental chapters employed a two-dimensional (2D) material, MXene, as support. In Chapter 2, ruthenium single atoms were incorporated onto ultrathin Ti3C2Tx MXene nanosheets to unlock its electrocatalytic activity. The RuSA@Ti3C2Tx presented a 1 A cm−2 HER current density with an over potential of 425.7 mV, outperforming the commercial Pt/C benchmark. Operando Raman test under HER potential showed the different protonation level between RuSA@Ti3C2Tx and Ti3C2Tx, suggesting the different hydrogen absorption energy of the oxygen terminal on the Ti3C2Tx basal plane. Finally, the theoretical calculations confirmed that the RuSA not only facilitates water dissociation, but also modulates the hydrogen After increasing the Ru content and conducting electroreduction, RuTi alloy nanoclusters were constructed on the surface of Ti3C2Tx. Surprisingly, the RuTi@Ti3C2Tx showed better performance in HER, and excellent hydrazine oxidation reaction (HzOR) performance. The overpotential to attain a current density of 10 mA cm−2 for HER was only 14 mV, lower than that of the commercial Pt/C. The HzOR catalytic activity also outperformed most reported work. In addition, the overall hydrazine spitting was conducted in an H-type electrolytic cell, demonstrating superior thermodynamic advantage and good stability.
Defect-abundant active carbon (AC-DCD) as support was prepared by the hydrothermal reaction with dicyanamide. Then, the Ru nanoparticles were grown on the surface. Compared to the catalyst with pristine AC as support prepared under same conditions, Ru600@AC-DCD presented a larger electrochemical special area with strain-abundant Ru nanoparticles. Ru600@AC-DCD delivered excellent HER performance in alkaline media, and good catalytic properties in acidic and neutral media.
Finally, another novel metal@carbon composite, Ni nanoparticles encapsulated in graphite carbon layers, was synthesized by directly annealing the Ni-imidazole framework precursors at 350 °C in H2/Ar. By tuning the annealing time under H2/Ar flow, Ni nanoparticles with different crystalline phases were synthesized. These Ni@C samples are di-function electrocatalysts for HER and OER in alkaline condition. The mixed-phase catalyst mix2-Ni@C delivered the highest activity to catalyze HER, while the pure hcp phase catalyst hcp-Ni@C showed best OER activity. This work provided a practical method to prepare low-cost difunctional electrocatalysts for overall water electrolysis.
In summary, the thesis innovatively contributes to the knowledge in material science and water electrolysis in the aspects of: (i) designing novel supported composite electrocatalysts with high catalytic activity for HER, OER, and HzOR; (ii) monitoring the changing of surface terminal by operando Raman spectroscopy to verify the HER mechanism; (iii) development of metal nanostructures, like RuTi alloy, hcp phase Ni and mixed-phase Ni, via facile methods, and investigation of their unique properties; and (iv) application of large current HER and exploration of the kinetics under different potentials.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Environment and Sc
Science, Environment, Engineering and Technology
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Stevens, Michaela. "Fundamentals and Industrial Applications: Understanding First Row Transition Metal (Oxy)Hydroxides as Oxygen Evolution Reaction Catalysts." Thesis, University of Oregon, 2017. http://hdl.handle.net/1794/22633.
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Intermittent renewable energy sources, such as solar and wind, will only be viable if the electrical energy can be stored efficiently. It is possible to store electrical energy cleanly by splitting the water into oxygen (a clean byproduct) and hydrogen (an energy dense fuel) via water electrolysis. The efficiency of hydrogen production is limited, in part, by the high kinetic overpotential of the oxygen evolution reaction (OER). OER catalysts have been extensively studied for the last several decades. However, no new highly active catalyst has been developed in decades. One reason that breakthroughs in this research are limited is because there have been many conflicting activity trends. Without a clear understanding of intrinsic catalyst activity it is difficult to identify what makes catalysts active and design accordingly. To find commercially viable catalysts it is imperative that electrochemical activity studies consider and define the catalyst’s morphology, loading, conductivity, composition, and structure.
The research goal of this dissertation is twofold and encompasses 1) fundamentally understanding how catalysis is occurring and 2) designing and developing a highly active, abundant, and stable OER catalyst to increase the efficiency of the OER. Specifically, this dissertation focuses on developing methods to compare catalyst materials (Chapter II), understanding the structure-compositional relationships that make Co-Fe (oxy)hydroxide materials active (Chapter III), re-defining activity trends of first row transition metal (oxy)hydroxide materials (Chapter IV), and studying the role of local geometric structure on active sites in Ni-Fe (oxy)hydroxides (Chapter V). As part of a collaboration with Proton OnSite, the catalysts studied are to be integrated into an anion exchange membrane water electrolyzer in the future.
This dissertation includes previously published and unpublished co-authored material.10000-01-01
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Bernicke, Michael [Verfasser], Ralph [Akademischer Betreuer] Krähnert, Peter [Gutachter] Strasser, and Michael [Gutachter] Bron. "Mesoporous oxides as efficient catalysts for the electrocatalytic oxygen evolution reaction (OER) / Michael Bernicke ; Gutachter: Peter Strasser, Michael Bron ; Betreuer: Ralph Krähnert." Berlin : Technische Universität Berlin, 2016. http://d-nb.info/1156010195/34.
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Al-Mamun, Mohammad. "Rational Design of Nanostructured Earth-Abundant Electrocatalysts for Energy Conversion Applications." Thesis, Griffith University, 2016. http://hdl.handle.net/10072/365651.
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Electrocatalysis contributes to a huge extent in a large array of research fields and applications, including corrosion science, electroanalytical sensors, wastewater treatment, electro-organic synthesis and more importantly, energy conversion applications. Of the many electrocatalytic processes, the oxygen evolution reaction (OER) and triiodide reduction reaction (IRR) are of widespread importance in electrochemical cells and dye-sensitised solar cells (DSSCs). OER is a key half reaction in electrochemical water splitting, direct solar-to-electricity driven water splitting and metal-air batteries. The high cost of efficient benchmark electrocatalysts, such as RuO2 or IrO2, however, is a major drawback of OERs. While, IRR plays a significant role in DSSCs, which must be electrocatalysed at the counter electrode to complete the external circuit in real devices and thereby successfully convert solar energy to electricity. Traditionally, Pt is accepted as an ideal benchmark electrocatalyst for IRR, but its high cost and scarcity limits broad application of DSSCs. Thus, extensive effort has been made to find active alternative electrocatalysts with low-cost, high electrocatalytic activity and excellent stability for OER and IRR to the noble metals (Ru, Ir and Pt). Therefore, a rational design of earth-abundant and low-cost electrocatalysts for OER and IRR maintains a paramount significance for energy conversion applications to meet the constantly growing demand for energy supply.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
Griffith School of Environment
Science, Environment, Engineering and Technology
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Kumar, Kavita. "Catalyseurs sans métaux nobles pour pile à combustible régénérative." Thesis, Poitiers, 2017. http://www.theses.fr/2017POIT2284/document.
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Le dihydrogène (H2) se présente comme le futur vecteur énergétique pour une économie basée sur des ressources propres et respectueuses de l'environnement. Il est le combustible idéal de la pile à combustible régénérative constituée de deux entités : un électrolyseur pour sa production, et une pile à combustible pour sa conversion directe en énergie électrique. Ce système présente l'avantage d'être compact et autonome. Cependant, l'amélioration de l'activité catalytique des matériaux, leur stabilité et l'élimination de métaux nobles dans leur composition sont nécessaires. Des catalyseurs bifonctionnels à base de métaux de transition associés au graphène ont alors été synthétisés. L'interaction oxyde-graphène a été étudiée sur un catalyseur Co3O4/NRGO. À faible teneur en cobalt, l'interaction entre les atomes de cobalt de l'oxyde et les atomes d'azote greffés sur les plans de graphène a été observée par voltammétrie cyclique. Cette interaction est responsable d'une diminution de la taille des nanoparticules de cobaltite et de l'activité de celles-ci vis-à-vis de la réaction de réduction du dioxygène (RRO). La substitution du cobalt par le nickel dans des structures de type spinelle (NiCo2O4/RGO) obtenu par voie solvothermale, a permis d'améliorer les performances électrocatalytiques vis-à-vis de la RRO et de la RDO. Ce matériau et un autre de type Fe-N-C préparé en collaboration avec un laboratoire de l'Université Technique de Berlin ont servi de cathode dans des études préliminaires réalisées en configuration pile à combustible alcaline à membrane échangeuse d'anion (SAFC)Hydrogen, as an environmentally friendly future energy vector, is a non-toxic and convenient molecule for regenerative fuel cell, which connects two different technologies: an electrolyzer for H2 production, and a fuel cell for its direct conversion to electric energy. This kind of system possesses many advantages, such as lightness, compactness and more autonomy. However, improvement of activity and durability of electrode materials free from noble metals in their composition is needed. Thereby, bifunctional catalysts composed of transition metals deposited onto graphene-based materials were synthesized. The interaction between the metal atom of the oxide and the graphene doped heteroatom in the Co3O4/NRGO catalyst was investigated physicochemically. With a low cobalt loading, the interaction between cobalt and nitrogen was characterized by cyclic voltammetry, which revealed that it was responsible for decreasing the oxide nanoparticle size, as well as increasing the material activity towards the oxygen reduction reaction (ORR). The substitution of Co by Ni in the spinel structure (NiCo2O4/RGO) obtained by solvothermal synthesis, allowed the enhancement of the electrocatalytic performances towards the ORR and OER. Moreover, this catalyst as well as another material prepared in collaborative program with a lab from Technical University of Berlin were used as cathode in preliminary studies undertaken on solid alkaline fuel cell (SAFC)
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Filimonenkov, Ivan. "Electrocatalyse de la réduction de l’oxygène et de l’oxydation de l’eau par des oxydes de métaux de transition : cas des pérovskites de Mn et Co." Thesis, Strasbourg, 2019. http://www.theses.fr/2019STRAF072.
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L’étude de l'électrocatalyse des réactions de réduction de l'oxygène (RRO) et de dégagement de l'oxygène (RDO) est étroitement reliée au développement de matériaux cathodiques et anodiques pour les piles à combustible et les électrolyseurs. L’objectif de cette thèse est de développer et d’étudier des matériaux d’électrodes à base d’oxydes de Mn et de Co, actifs et stables, à la fois pour la RRO et la RDO. Les relations entre les caractéristiques électrochimiques des compositions pérovskite / carbone et les propriétés de leurs composants sont établies et étayées expérimentalement dans la thèse. Il a été constaté que la résistance des matériaux carbonés à la corrosion dans les conditions de la RDO est influencée non seulement par leur ordre cristallin, mais également par leur activité intrinsèque pour la RDO. Il a été démontré que les activités des pérovskites à base de Mn et de Co dépendent linéairement du nombre de cations de Mn et de Co rechargeables, respectivement pour la RRO et la RDO. Il a été découvert qu'une intercalation réversible de l'oxygène dans la structure cristalline des pérovskites à base de Co se produit dans les conditions de la RDO, ainsi qu'à des potentiels plus faiblesA study of electrocatalysis of oxygen reduction (ORR) and oxygen evolution (OER) reactions is closely related with a development of cathodic and anodic materials for fuel cells and elec-trolyzers. An objective of this thesis is to develop and investigate Mn, Co-oxide-based elec-trode materials active and stable in both the ORR and OER. Relationships between electro-chemical characteristics of perovskite/carbon compositions and properties of their compo-nents are stated and experimentally substantiated in the thesis. It is found a corrosion re-sistance of carbon materials under OER conditions is influenced not only by their crystalline order, but also by their intrinsic OER activity. It is shown the ORR and OER activity of Mn, Co-based perovskites linearly depends on the number of rechargeable Mn and Co cations, respectively. It is revealed a reversible oxygen intercalation through a crystal structure of Co-based perovskites occurs under OER conditions as well as at lower potentials
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Saveleva, Viktoriia. "Investigation of the anodes of PEM water electrolyzers by operando synchrotron-based photoemission spectroscopy." Thesis, Strasbourg, 2018. http://www.theses.fr/2018STRAF002/document.
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Le développement de catalyseurs de la réaction de dégagement de l’oxygène (OER) pour les électrolyseurs à membrane échangeuse de protons (PEM) dépend de la compréhension du mécanisme de cette réaction. Cette thèse est consacrée à l'application de la spectroscopie d’émission de photoélectrons induits par rayons X (XPS) et de la spectroscopie de structure près du front d'absorption de rayons X (NEXAFS) operando sous une pression proche de l'ambiante (NAP) dans le but d’étudier les mécanismes de la réaction d’oxydation de l’eau sur des anodes à base d’iridium et de ruthénium et leurs dégradation dans les conditions de la réaction. Cette thèse montre les mécanismes différents de la réaction OER pour les anodes à base d’Ir et de Ru impliquant respectivement des transitions anioniques (formation d’espèce OI- électrophile) ou cationiques (formation des espèces de Ru avec l’état d'oxydation supérieur à IV) quelle que soit la nature (thermique ou électrochimique) des oxydesDevelopment of oxygen evolution reaction (OER) catalysts for proton exchange membrane water electrolysis technology depends on the understanding of the OER mechanism. This thesis is devoted to the application of near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) and near edge X-ray absorption fine structure (NEXAFS) techniques for operando investigation of the Ir, Ru - based anodes. For Ru-based systems, we observe the potential-induced irreversible transition of Ru (IV) from an anhydrous to a hydrated form, while the former is stabilized in the presence of Ir. Regarding single Ir-based anodes, the analysis of O K edge spectra reveals formation of electrophilic oxygen OI- as an OER intermediate. Higher stability of Ir catalysts supported on antimony-doped tin oxide (ATO) is related to their lower oxidation. This work demonstrates different OER mechanisms on Ir, Ru-based anodes involving anion and cation red-ox chemistry, correspondingly, regardless the oxide nature
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Pandey, Kadel Usha. "Metal-free electrocatalysts for oxygen evolution reaction and photocatalysts for carbon dioxide reduction reaction." Bowling Green State University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1513279535028305.
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Zhou, Leyao. "Electroless Deposited Transitional Metal Phosphide for Oxygen/Hydrogen Evolution Reactions." University of Akron / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=akron1522333083629295.
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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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Luo, Lin. "Novel Nanostructure Electrocatalysts for Oxygen Reduction and Hydrogen Evolution Reactions." University of the Western Cape, 2019. http://hdl.handle.net/11394/7315.
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Philosophiae Doctor - PhDThe widespread use of fossil energy has been most convenient to the world, while they also cause environmental pollution and global warming. Therefore, it is necessary to develop clean and renewable energy sources, among which, hydrogen is considered to be the most ideal choice, which forms the foundation of the hydrogen energy economy, and the research on hydrogen production and fuel cells involved in its production and utilization are naturally a vital research endeavor in the world. Electrocatalysts are one of the key materials for proton exchange member fuel cells (PEMFCs) and water splitting. The use of electrocatalysts can effectively reduce the reaction energy barriers and improve the energy conversion efficiency.
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Demeter, Ethan L. "The Promotion of Base Metal Catalysts for the Electrochemical Oxygen Evolution Reaction." Research Showcase @ CMU, 2013. http://repository.cmu.edu/dissertations/236.
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As the energy needs of society continue to grow, and pressure to produce fewer emissions continues to mount, clean alternatives will be utilized to meet these demands. Conventional renewable technologies (wind and solar, etc.) have great potential, but cannot be used as base-load power, at least not in the traditional sense. Rather, these technologies would require the further adoption of energy storage technologies, such as water splitting, to convert the energy produced into chemical bonds for later use to match demand.
Water splitting currently suffers from large energetic barriers, on the oxygen side, that create a need for catalysts, and high costs associated with the best available catalysts, ruthenium and iridium. This work focuses on developing and understanding ways to promote the catalysis of the oxygen evolution reaction on earth-abundant base metal catalysts. We utilize a combination of electrochemical and in situ surface characterization techniques to correlate changes in the surface chemistry to changes in catalyst activity.
Three systems are examined for their potential effect on the OER. The first two focus on the promotion of NiO materials, examining the effect of changing the alkali cation present in the hydroxide electrolyte, and adding iron to the NiO materials. For the cations, the electrochemical activity is found to increase by a factor of two, switching from a LiOH solution to a CsOH solution of the same concentration. The use of in situ Raman spectroscopy suggests that different phases of the oxidized Ni oxyhydroxides are promoted in the presence of the different cations, with γ-NiOOH promoted in CsOH while β-NiOOH is observed in LiOH. The addition of Fe results in large increases in OER activity up to a loading of 10 mol% Fe, where the further addition of Fe decreases activity. Raman spectra of the electrodes suggest at low Fe loadings, the Ni oxidation to γ- NiOOH is promoted, while further addition of Fe blocks access to active catalyst sites. Finally, we demonstrate the use of Fe-TAML molecular complex as an electrocatalyst for the OER. Fe-TAML is shown to be electrochemically active, and through immobilization, much higher catalyst utilization is achieved.
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Eychmüller, Alexander, Chengzhou Zhu, Dan Wen, Susanne Leubner, Martin Oschatz, Wei Liu, Matthias Holzschuh, Frank Simon, and Stefan Kaskel. "Nickel cobalt oxide hollow nanosponges as advanced electrocatalysts for the oxygen evolution reaction." Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-188848.
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A class of novel nickel cobalt oxide hollow nanosponges were synthesized through a sodium borohydride reduction strategy. Due to their porous and hollow nanostructures, and synergetic effects between their components, the optimized nickel cobalt oxide nanosponges exhibited excellent catalytic activity towards oxygen evolution reaction.
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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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Wang, Zhiyuan Verfasser], Rüdiger-A. [Akademischer Betreuer] [Eichel, and Marcel [Akademischer Betreuer] Liauw. "Oxygen reduction reaction and oxygen evolution reaction mechanisms investigation of the non-noble bifunctional electrocatalysts in alkaline electrolyte / Zhiyuan Wang ; Rüdiger-Albert Eichel, Marcel Liauw." Aachen : Universitätsbibliothek der RWTH Aachen, 2018. http://d-nb.info/1169915191/34.
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Wang, Zhiyuan [Verfasser], Rüdiger-A. [Akademischer Betreuer] Eichel, and Marcel [Akademischer Betreuer] Liauw. "Oxygen reduction reaction and oxygen evolution reaction mechanisms investigation of the non-noble bifunctional electrocatalysts in alkaline electrolyte / Zhiyuan Wang ; Rüdiger-Albert Eichel, Marcel Liauw." Aachen : Universitätsbibliothek der RWTH Aachen, 2018. http://d-nb.info/1169915191/34.
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Miyahara, Yuto. "Studies on Bifunctional Oxygen Electrocatalysts with Perovskite Structures." 京都大学 (Kyoto University), 2017. http://hdl.handle.net/2433/225622.
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Kim, Sohae. "Nanoscale heterojunctions of transition metal oxide and silicon for high-efficiency oxygen evolution reaction." Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/119347.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2018.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 118-126).
Hydrogen fuel, storing solar energy by splitting water, is of great potential as efficient energy storage due to its sustainability, carbon-neutrality and high energy density per mass. One of major bottlenecks for the solar-driven energy storage into hydrogen, however, is oxygen evolution reaction (OER) because of its high overpoential and the complexity of surface structures and reaction mechanisms. To overcome these obstacles, researchers have approached in two ways: (i) searching for the best materials with the highest efficiency and (ii) devising schemes that can yield a higher efficiency, given materials. Considering that the efficiency improvement with inexpensive materials would be ultimately beneficial for future global energy requirements, we pursue the second approach and examine nanoscale heterojunctions of earth abundant materials. In this thesis, we employ density functional theory (DFT) calculations to investigate nanoscale heterojunctions of transition metal oxide and silicon (Si), which are commonly used for photo/photoelectocatalytic and photovoltaic materials, respectively. In particular, the heterojunction of anatase titanium dioxide (TiO₂) and Si is of our best interest. The heterojunctions of TiO₂ and Si have not only exhibit great synergies based on the bulk properties, but also have improved the photoelectrocatalytic efficiency experimentally. However, the mechanism for this improvement is unclear. Optimizing the catalytic activity of such systems requires a deeper understanding of the detailed atomic and electronic structure of the TiO₂/Si interface, the OER mechanism on TiO₂ surface, and how the TiO₂/Si interface affects the active TiO₂ surface, thus changing the OER overpotential. This thesis examines mainly four aspects of the heterojunctions of anatase TiO₂(001) and Si: (i) the thermodynamic stability of different local stoichiometry at the TiO₂/Si interface, (ii) the electronic structures induced by the different TiO₂/Si interface, (iii) how the TiO₂/Si interface influences OER on TiO₂ surface and its rate-limiting overpotential, and (iv) whether this scheme is transferrable to other oxides such as strontium titanate (SrTiO₃ perovskite) to improve the OER efficiency. We also propose a new OER pathway on anatase (001) surface that is plausible under realistic experimental conditions and compare it with the OER pathways that have been proposed earlier. This work, thus, has potential to deepen our understanding and insights of interface physics, surface chemistry and energy conversion.
by Sohae Kim.
Ph. D.
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Wahl, Sebastian. "Shed Light on Cobalt Oxides for the Oxygen Evolution Reaction – An Operando Spectroelectrochemical Study." Doctoral thesis, Humboldt-Universität zu Berlin, 2020. http://dx.doi.org/10.18452/21108.
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In dieser Dissertation wird der Einfluss unterschiedlicher Sauerstoff-Koordinationsgeometrien um ein zentrales Kobaltatom evaluiert. Genauer werden Oxide, die tetraedrisch und oktaedrisch koordiniertes Kobalt enthalten, synthetisiert und charakterisiert. Zudem wird ihre Aktivität in Hinblick auf die Sauerstoffentwicklungsreaktion (OER) unter alkalischen Bedingungen untersucht. Die elektrochemischen Analysen zeigen dabei, dass Materialien, die Kobalt in tetraedrischer Sauerstoffkoordination enthalten, die besseren Katalysatorvorläufer für die OER sind. Weiterhin kann demonstriert werden, dass das Herauslösen von inaktiven Metallen aus einer Struktur die Aktivität erhöht. Darauf basierend wird das neue Material Zn0.35Co0.65O vorgeschlagen. Es kristallisiert in der Wurtzitstruktur und enthält nur tetraedrisch koordinierte Atome. In alkalischen Lösungen wandelt sich die Wurtzitstruktur über die Zwischenstufe Co(OH)2 zum gamma-Co(O)OH um, und nahezu alles Zink wird aus der Struktur herausgelöst. Dadurch wird ein Material mit einer großen elektrochemisch aktiven Oberfläche gewonnen, das unterkoordinierte CoO(6-x) Oktaeder als aktive Zentren für die OER enthält. Hierdurch wird eine herausragende katalytische Leistung erreicht. Um weitere Einblicke in die OER zu generieren, wird Diffuse Reflexions UV/Vis (DRUV) Spektroskopie verwendet. Es werden neuartige Durchflusszellendesigns vorgeschlagen, die es erlauben, DRUV Spektren während der Katalyse aufzunehmen, d.h. operando. Durch diesen spektroelektrochemischen Ansatz werden Veränderungen der Katalysatoren während der OER beobachtet. So kann die Phasenumwandlung von Zn0.35Co0.65O erfolgreich verfolgt werden. Ebenso kann gezeigt werden, dass CoAl2O4 und Co2SnO4 nur an ihrer Oberfläche katalytische Aktivität aufweisen. Durch den Vergleich mit ex situ Analysen werden eindeutige Struktur-Eigenschaftsbeziehungen vorgeschlagen und tiefere Einsichten in die katalytisch aktiven Strukturmotive erhalten.In this PhD thesis, the influence of different coordination geometries of oxygen atoms around a central cobalt atom is evaluated. Specifically, oxides containing tetrahedral and octahedral coordinated cobalt are synthesized, characterized and their activity towards the OER under alkaline conditions is evaluated. The electrochemical analyses reveal, that materials containing cobalt in tetrahedral oxygen coordination are better precatalysts for the OER. Furthermore, it is demonstrated that leaching of inactive metals from a structure increases the activity as well. Based on the previous mentioned, the new material Zn0.35Co0.65O is proposed. It crystallizes in the wurtzite structure and contains solely tetrahedrally coordinated atoms. In alkaline solutions, it transforms from wurtzite structure via a hydroxide to gamma-Co(O)OH, and nearly all Zn is leached from the structure. By this, a material with a large electrochemically active surface area is generated, that contains under-coordinated CoO(6-x) octahedra as active centers for the OER. Thus, outstanding catalytic performance is achieved. To generate further insights into the OER, diffuse reflectance ultraviolet visible (DRUV) spectroscopy is facilitated. Novel flow-cell designs are proposed, that allow to record DRUV spectra of catalysts under working conditions, i.e. operando. By this spectroelectrochemical approach, changes the catalysts undergo during the OER are observed. The phase transitions of Zn0.35Co0.65O are successfully followed, and it can be further shown, that CoAl2O4 and Co2SnO4 are only active at their surface. By comparison to ex situ analyses, clear structure-activity correlations are proposed, and deeper insights in the catalytically active structural motifs are obtained.
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Zhang, Tianhou. "Theoretical Studies of Fuel Cell Reaction Mechanisms: Water and Oxygen on Platinum Electrodes." Case Western Reserve University School of Graduate Studies / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=case1215456813.
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Gao, Guoping. "Computational design of catalysts for clean energy conversion and storage." Thesis, Queensland University of Technology, 2017. https://eprints.qut.edu.au/109443/1/Guoping_Gao_Thesis.pdf.
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This project focuses on the computational design of novel catalyst for artificial synthesis: converting sunlight into fuels. With the atomic-scale insight of catalysts obtained by theoretical calculations, many efficient and optimum catalysts for these processes have been designed and engineered. The outcomes of this thesis are expected to provide theoretical solutions for current global energy and environmental challenges.
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Heras, Domingo Javier. "Modeling of RuO2 surfaces and nanoparticles. Their potential use as catalysts for the oxygen evolution reaction." Doctoral thesis, Universitat Autònoma de Barcelona, 2020. http://hdl.handle.net/10803/669578.
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Avui dia, el subministrament d'energia mundial prové principalment de combustibles basats en carboni, que estan involucrats en problemes mediambientals. Estudis científics sobre la fotosíntesi declaren la capacitat de les plantes per a oxidar l'aigua en oxigen, emmagatzemant energia en forma d'enllaços químics. Inspirant-nos en la naturalesa, la ruptura de la molècula d'aigua sembla ser el procés més adequat per a produir energia neta, amb la reacció d'oxidació de l'aigua com a pas crític.
En aquesta tesi, mètodes de DFT periòdics han estat utilitzats per a comprendre els factors clau que controlen l'adsorció de l'aigua i el rendiment catalític del RuO2 en la reacció d'evolució de l'oxigen. Per primera vegada, no sols s'ha tingut en compte la superfície més estable, sinó totes les superfícies que constitueixen la forma Wulff tant per a la interfase de l'aigua com per a la seva activitat catalítica. El teorema de Wulff s'ha utilitzat per a construir models atomístics de nanopartícules de RuO2 de diferents grandàries. El rendiment de la reacció d'evolució de l'oxigen en RuO2 ha estat explorat a través de dos mecanismes, el de l'atac nucleòfil de l'aigua (WNA) i el d'acoblament entre grups oxo (I2M) tant per a superfícies com per a models de nanopartícules. Finalment, s'han proposat dos mecanismes de (WNA) per a un catalitzador d'Iridi ancorat en un suport d'òxid d'indi i estany (ITO) com el treball realitzat durant una estada predoctoral en l'institut ETH-Zuric (Suïssa).
Els resultats mostren que la dissociació de l'aigua en les superfícies principals de RuO2 està controlada per l'acidesa del metall, la basicitat dels grups Obr de la superfície i els efectes cooperatius entre les molècules d'aigua adsorbides. Quant al mecanisme de la reacció d'evolució de l'oxigen, el WNA és el mecanisme principal tant per a les superfícies com per a les nanopartícules. No obstant això, el mecanisme I2M sobre nanopartícules sembla ser significativament més favorable, a causa de la flexibilitat de la superfície de les nanopartícules. A més, els resultats del catalitzador d'Iridi indiquen que el bis-oxo Ir(VI) és un intermedi clau en el mecanisme de la reacció d'evolució de l'oxigen.Hoy en día, el suministro de energía mundial proviene principalmente de combustibles basados en carbono, que están involucrados en problemas medioambientales. Estudios científicos sobre la fotosíntesis declaran la capacidad de las plantas para oxidar el agua en oxígeno, almacenando energía en forma de enlaces químicos. Inspirándonos en la naturaleza, la ruptura de la molécula de agua parece ser el proceso más adecuado para producir energía limpia, con la reacción de oxidación del agua como paso crítico. En esta tesis, métodos de DFT periódicos han sido utilizados para comprender los factores clave que controlan la adsorción del agua y el rendimiento catalítico del RuO2 en la reacción de evolución del oxígeno. Por primera vez, no solo se ha tenido en cuenta la superficie más estable, sino todas las superficies que constituyen la forma Wulff tanto para la interface del agua como para su actividad catalítica. El teorema de Wulff se ha utilizado para construir modelos atomísticos de nanopartículas de RuO2 de diferentes tamaños. El rendimiento de la reacción de evolución del oxígeno en RuO2 ha sido explorado a través de dos mecanismos, el del ataque nucleófilo del agua (WNA) y el de acoplamiento entre grupos oxo (I2M) tanto para superficies como para modelos de nanopartículas. Por último, se han propuesto dos mecanismos de (WNA) para un catalizador de Iridio anclado en un soporte de óxido de indio y estaño (ITO) como el trabajo realizado durante una estancia predoctoral en el instituto ETH-Zúrich (Suiza). Los resultados muestran que la disociación del agua en las superficies principales de RuO2 está controlada por la acidez del metal, la basicidad de los grupos Obr de la superficie y los efectos cooperativos entre las moléculas de agua adsorbidas. En cuanto al mecanismo de la reacción de evolución del oxígeno, el WNA es el mecanismo principal tanto para las superficies como para las nanopartículas. Sin embargo, el mecanismo I2M sobre nanopartículas parece ser significativamente más favorable, debido a la flexibilidad de la superficie de las nanopartículas. Además, los resultados del catalizador de Iridio indican que el bis-oxo Ir(VI) es un intermedio clave en el mecanismo de la reacción de evolución del oxígeno.
Nowadays, the world energy supply comes mainly from carbon-based fuels, which is highly involved with environmental issues. Several decades ago, scientific studies about photosynthesis stated the ability of plants to oxidize water into oxygen powered by sunlight, storing energy as chemical bonds. Taking nature as inspiration, water splitting appears to be the most suitable process to produce clean energy from water, with the water oxidation reaction as the critical step. In this thesis, state-of-the-art periodic DFT methods are used to understand the key factors that control water adsorption and the catalytic performance of RuO2 on the oxygen evolution reaction (OER). For the first time, not only the most stable surface, but also all the surfaces that constitute the Wulff shape were taken into account for both the water interface and their catalytic activity. Wulff theorem was employed to build atomistic models of RuO2 nanoparticles of different sizes. The OER performance of RuO2 has been explored through the water nucleophilic attack (WNA) and oxo-coupling (I2M) mechanisms for both surfaces and nanoparticle models. Finally, two OER mechanisms have been proposed for an Iridium single site catalyst grafted on an Indium Tin Oxide (ITO) support as the work done during a predoctoral stay in ETH-Zürich (Switzerland). Results show that water dissociation onto the RuO2 main surfaces is controlled by the intrinsic Ru site acidity, the basicity of the Obr groups coming from the surface and cooperative effects between adsorbed water molecules. Concerning the OER mechanism, the WNA is the applying mechanism for both the main surfaces and nanoparticles. However, the I2M mechanism on nanoparticles seems to be significantly more favorable, because of the higher flexibility of the nanoparticle surface. Consequently, the I2M mechanism could be competitive on small clusters. Furthermore, results for the Iridium supported catalyst indicate that the highly oxidized Ir(VI) bis-oxo is a key intermediate in the OER mechanism.
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Rajan, Ziba Shabir Hussein Somjee. "Iridium oxide supported on antimony-doped tin oxide as an electrocatalyst for the oxygen evolution reaction." Master's thesis, University of Cape Town, 2020. http://hdl.handle.net/11427/32528.
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The generation of high purity hydrogen by renewable, sustainable means is a crucial building block towards the realisation of a carbon-free energy economy. Proton exchange membrane water electrolysis (PEMWE) offers a promising route for the generation of clean hydrogen, using renewable energy, for both stationary and mobile energy storage applications, and as a feedstock for the chemical industry. As water electrolysis is an electrochemical redox reaction, cathodic hydrogen evolution cannot occur without an efficient, and rapid anodic oxygen evolution reaction (OER). While both iridium and ruthenium oxides are state-of-the-art OER catalysts in acidic environment, the latter undergoes dissolution under anodic OER conditions much more rapidly than the former, and this makes iridium oxide the most suitable catalytic material for electrolyser anodes. Several strategies have been explored as a means to lower the iridium content in OER catalysts, and of these, the use of cheap, stable support materials has been seen as a promising means to produce highly active, durable catalysts, by enhancement of the electrocatalytically active surface area. In this thesis, the viability of an organometallic chemical deposition method for the deposition of IrOₓ nanoparticles on antimony-doped tin oxide (ATO) support is investigated. The effect of the gas environment (oxygen or argon) and the temperature used for the deposition was examined. The ex-situ OER performance of the synthesised electrocatalysts was evaluated using the rotating disk electrode technique. Using X-ray photoelectron spectroscopy (XPS) and high-resolution transmission scanning electron microscopy (HR-STEM), the physical properties of the synthesised IrOₓ/ATO catalysts were elucidated, in order to understand the observed oxygen evolution activity and stability of IrOₓ/ATO in relation to the OMCD technique. In addition to developing an understanding towards the physical and electrochemical properties of the synthesised materials, strategies to optimise the Ir yield achieved by the organometallic chemical deposition process were explored.
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Hjelm, Vivien. "Optimizing a Single Atom Catalyst for theOxygen Evolution Reaction using DensityFunctional Theory." Thesis, KTH, Skolan för kemi, bioteknologi och hälsa (CBH), 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-259703.
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The growing interest of renewable fuel and energy sources has steadily increased over time due to climate changes. Research is being made around the world to find solutions for the different problems; one possible solution is to produce hydrogen gas to help phase out the usage of fossil fuels. So far, the technology for the hydrogen gas production is expensive for various reasons, one of the challenges is to minimize the energy usage for the production. Hydrogen could be used in fuel cells which can be used to fuel an electric car. In a fuel cell, hydrogen and oxygen gas are mixed to produce electrical energy as the main product, but it also forms thermal energy and water. Hydrogen gas can be produced from the reversed reaction; by electrolysis of water. This reaction requires energy and one way to minimize the energy usage for this is by using acatalyst. The goal with this master thesis was to see how the reaction rate of the oxygen evolution reaction can be affected by different single atom catalyst systems. The main structure for this catalyst in this thesis is aporphyrin molecule where different transition metals were tried as the active site. Different modifications on the structure were also made by exchanging some of the structures atoms and by adding different ligands.The purpose of this is to see how these modifications change the activity of the catalyst. The catalysts were optimized and calculated in a computational chemistry program called Gaussian 16. The calculations was made by using the DFT functional PBE0 and the basis sets Def2svp and Def2tzvpp. The results show that different modifications do affect the activity of the catalyst. The biggest variations in activity are from placing ligands under the active site while exchanging hydrogens to other substituents on the outer radial position can fine tune the results. The best active sites for this system came by using iridium, rhodium and cobalt which are all elements in group 9 of the periodic table. The lowest overpotential of 0.513 V was given by an iridium based system with four hydrogens exchanged by fluorides.Runt om i världen finns ett ökat intresse för förnyelsebara energi och bränslekällor för att tackla klimat förändringarna. Stor del av forskningen som görs idag har i syfte att hitta nya lösningar för att minska klimatpåverkan i olika områden. Ett av forskningsområderna är hitta vägar till en miljövänligare vätgasproduktion där vätgasen skulle kunna användas i bränsleceller. Dessa celler kan sättas i elbilar och på så sätt fasa ut användingen av fossila bränslen. En av utmaningarna för vätgasproduktionen är att den idag är kostsam och kräver mycket energi. Forskare försöker hitta olika katalysatorer som kan minska energiåtgången som krävs vid elektrolys av vatten där syrgas och vätgas produceras. Målet med det här examensarbetet är att se hur en single atom catalyst kan påverka reaktionskinitiken för den syrgasbildande reaktionen vid elektrolys av vatten. Huvudstrukturen för katalysatorn som beräkningarna är gjorda på är en porphyrinmolekyl där olika övergångsmetaller kommer testas som det aktiva sätet i katalysatorn. Olika ligander kommer även tillsättas systemet samt utbyte av några väteatomer till olika substituenter i porfyrinstrukturen. Katalysatorn optimerades i det kvantkemiska beräkningsprogrammet Gaussian 16 med funktionalen PBE0 med basset Def2svp och Def2tzvpp. Resultaten visade att olika modifikationer på systemet hade en påverkan på katalysatorns aktivitet. Den största påverkan hade de olika liganderna som placerades under det aktiva sätet jämfört med de olika substituenterna. De bästa metallerna för katalysatorn var iridium, rhodium och kobolt vilket alla ligger i grupp nio i det periodiska systemet. Den lägsta överpotentialen på 0.513 V gavs av iridium systemet med fyra utbyta väten till fluor.
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He, Tianwei. "Computational discovery and design of nanocatalysts for high efficiency electrochemical reactions." Thesis, Queensland University of Technology, 2020. https://eprints.qut.edu.au/203969/1/Tianwei_He_Thesis.pdf.
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This thesis reports a computational discovery and design of highly efficient electrocatalysts for various of electrochemical reactions. The method is based on the Density Functional Theory (DFT) by using Vienna ab initio simulation package (VASP). This project is a step forward in developing the low-cost, high activity, selectivity, stability and scalability for the electrochemical reactions, which could make a contribution to the global-scale green energy system for a clean and sustainable energy future.
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González, Forero Danilo. "Automatized Nanoparticle Models Generation and Application to the Oxygen Evolution Reaction Catalyzed by IrO2. Slab vs Nanoparticle Models." Doctoral thesis, Universitat Autònoma de Barcelona, 2020. http://hdl.handle.net/10803/671127.
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Les nanopartícules tenen un gran impacte en múltiples camps científics principalment a causa d’i) la seva gran superfície específica i ii) la possibilitat d’ajustar l’estructura electrònica del material modificant la seva grandària i forma. Això és especialment rellevant en el camp de la catàlisi amb metalls de transició. Per a caracteritzar les propietats catalítiques de les nanopartícules s’han desenvolupat diverses tècniques experimentals i computacionals. No obstant això, la majoria dels esforços computacionals dedicats a comprendre l’activitat catalítica de les nanopartícules empren superfícies esteses per a representar el material. De fet, fins on sabem, hi ha pocs exemples de reaccions catalitzades per nanopartícules d’òxid metàl·lic utilitzant models de nanopartícules. Això limita l’exploració de llocs particulars sol presents en les superfícies de les nanopartícules i, per tant, és desitjable l’ús de models més realistes. Un dels colls d’ampolla en l’ús de models de nanopartícules realistes és el fet que la construcció del model no és senzilla, particularment per a materials multicomponent com els òxids de metalls de transició.
Aquesta tesi té dues parts principals. En primer lloc, desenvolupem una eina computacional capaç de construir models de nanopartícules per a compostos multicomponent amb estequiometria controlada i terminació de superfície de manera automatitzada, la qual cosa elimina la subjectivitat i el biaix humà. En segon lloc, utilitzem models de *slabs i nanopartícules per a avaluar els factors clau que determinen l’adsorció d’aigua i el rendiment catalític de *IrO2 per a la reacció d’evolució d’oxigen (*OER) mitjançant l’ús de simulacions DFT. El rendiment OER catalitzat per IrO2 s’ha explorat a través dels mecanismes d’atac nucleofílico d’aigua (WNA) i de oxoacoblament (I2M) tant per a superfícies com per a models de nanopartícules.
Hem trobat que la dissociació de l’aigua està controlada per les propietats intrínseques del material com l’acidesa de l’Anar, la basicitat Obr, la naturalesa del lloc vacant i els efectes cooperatius entre les molècules d’aigua adsorbidas. Respecte al mecanisme de la OER, els nostres resultats suggereixen que tant el mecanisme WNA com l’I2M requereixen intermediaris radicals per a ser factibles. A més, el mecanisme WNA sembla ser el més favorable per a gairebé tots els llocs estudiats en superfícies i nanopartícules. De fet, el mecanisme I2M només sembla ser el preferit en la superfície (011), on el caràcter oxil dels àtoms d’O en la superfície és major i la distància interatómica entre els grups oxil és bastant curta. A més, i de manera bastant notable, el lloc de la punta de la nanopartícula exhibeix un sobrepotencial lleugerament més gran que l’ideal, la qual cosa suggereix que els llocs tetracoordinats han d’explorar-se per a millorar el rendiment catalític del IrO2 per a la OER.Las nanopartículas tienen un gran impacto en múltiples campos científicos principalmente debido a i) su gran superficie específica y ii) la posibilidad de ajustar la estructura electrónica del material modificando su tamaño y forma. Esto es especialmente relevante en el campo de la catálisis con metales de transición. Para caracterizar las propiedades catalíticas de las nanopartículas se han desarrollado varias técnicas experimentales y computacionales. Sin embargo, la mayoría de los esfuerzos computacionales dedicados a comprender la actividad catalítica de las nanopartículas emplean superficies extendidas para representar el material. De hecho, hasta donde sabemos, hay pocos ejemplos de reacciones catalizadas por nanopartículas de óxido metálico utilizando modelos de nanopartículas. Esto limita la exploración de sitios particulares solo presentes en las superficies de las nanopartículas y, por lo tanto, es deseable el uso de modelos más realistas. Uno de los cuellos de botella en el uso de modelos de nanopartículas realistas es el hecho que la construcción del modelo no es sencilla, particularmente para materiales multicomponente como los óxidos de metales de transición. Esta tesis tiene dos partes principales. En primer lugar, desarrollamos una herramienta computacional capaz de construir modelos de nanopartículas para compuestos multicomponente con estequiometría controlada y terminación de superficie de manera automatizada, lo que elimina la subjetividad y el sesgo humano. En segundo lugar, utilizamos modelos de slabs y nanopartículas para evaluar los factores clave que determinan la adsorción de agua y el rendimiento catalítico de IrO2 para la reacción de evolución de oxígeno (OER) mediante el uso de simulaciones DFT. El rendimiento OER catalizado por IrO2 se ha explorado a través de los mecanismos de ataque nucleofílico de agua (WNA) y de oxoacoplamiento (I2M) tanto para superficies como para modelos de nanopartículas. Hemos encontrado que la disociación del agua está controlada por las propiedades intrínsecas del material como la acidez del Ir, la basicidad Obr, la naturaleza del sitio vacante y los efectos cooperativos entre las moléculas de agua adsorbidas. Con respecto al mecanismo de la OER, nuestros resultados sugieren que tanto el mecanismo WNA como el I2M requieren intermediarios radicales para ser factibles. Además, el mecanismo WNA parece ser el más favorable para casi todos los sitios estudiados en superficies y nanopartículas. De hecho, el mecanismo I2M solo parece ser el preferido en la superficie (011), donde el carácter oxil de los átomos de O en la superficie es mayor y la distancia interatómica entre los grupos oxil es bastante corta. Además, y de manera bastante notable, el sitio de la punta de la nanopartícula exhibe un sobrepotencial solo un poco más grande que el ideal, lo que sugiere que los sitios tetracoordinados deben explorarse para mejorar el rendimiento catalítico de IrO2 para la OER.
Nanoparticles have a large impact in multiple scientific fields mainly due to i) their large specific surface area and ii) the possibility of tuning the electronic structure of the material by modifying its size and shape. This has been particularly relevant in the field of catalysis with precious transition metals. To characterize the nanoparticle catalytic properties several experimental and computational techniques have been developed. Most of the computational efforts devoted to understand the catalytic activity of nanoparticles, however, employ extended surfaces to represent the material. Indeed, to the best of our knowledge, few examples of reactions catalyzed by metal oxide nanoparticles have been studied by using nanoparticles models. This limits the exploration of particular sites only present in the nanoparticle surfaces and thus, the use of more realistic models is desirable. One of the bottlenecks in the use of realistic nanoparticle models is the fact that model construction is not straightforward, particularly for multicomponent materials such as transition metal oxides. This thesis has two main parts. Firstly, we develop a computational tool able to construct nanoparticle models for multicomponent compounds with controlled stoichiometry and surface termination in an automatized manner, which removes human subjectivity and bias. Secondly, we use slab and nanoparticle models to evaluate the key factors that determine the water adsorption and the catalytic performance of IrO2 for the oxygen evolution reaction (OER) by using DFT simulations. The OER performance of IrO2 has been explored through the water nucleophilic attack (WNA) and oxo-coupling (I2M) mechanisms for both surfaces and nanoparticle models. We have found that the water dissociation is controlled by the intrinsic material properties like the Ir acidity, the Obr basicity, the nature of the vacant site and the cooperative effects between adsorbed water molecules. Concerning the OER mechanism, our results suggest that both the WNA and the I2M mechanisms require radical intermediates to be feasible. Moreover, the WNA mechanism seems to be the most favorable for almost all studied sites on surfaces and nanoparticles. Indeed, the I2M mechanism only seems to be the preferred one on the (011) surface, were the oxyl character of O atoms on the surface is larger and the interatomic distance between the oxyl groups is rather short. Furthermore, and quite remarkably, the tip site of the nanoparticle exhibits an OER potential that is only slightly larger than the ideal one, thereby suggesting that tetracoordinated sites should be explored to improve the catalytic performance of IrO2 for the OER.
Universitat Autònoma de Barcelona. Programa de Doctorat en Química
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Soudens, Franschke A. "A modified Adams fusion method for the synthesis of binary metal oxide catalysts for the oxygen evolution reaction." University of Western Cape, 2020. http://hdl.handle.net/11394/8231.
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>Magister Scientiae - MScThe majority of the global energy is sourced from conventional fossil fuels. The high demand for energy is accelerating along with the depletion of these fossil fuels. Hence, the shift to renewable energy sources and technology becomes indispensable. Hydrogen is considered a promising alternative to fossil fuels. Polymer electrolyte membrane water electrolysers offer an environmentally friendly technique for the production of hydrogen from renewable energy sources. However, the high overpotential and acidic environment at the anode is one of the challenges faced by polymer electrolyte membrane water electrolysers. This harsh environment requires distinct electrocatalysts which currently consist of expensive precious metals such as Ir, Ru and their oxides.
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Sultana, Ummul Khair. "Electrochemical synthesis of water splitting nanomaterials." Thesis, Queensland University of Technology, 2019. https://eprints.qut.edu.au/126972/1/Ummul%20Khair_Sultana_Thesis.pdf.
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This project was a step forward in electrochemically synthesizing nanomaterials for the water splitting reaction which directly produces hydrogen and oxygen. The thesis investigated the performances of newly developed nanomaterials for the energetically demanding water splitting reaction. In order to understand the reaction mechanism, thorough materials characterization was carried out to identify structure-activity relationships. This study also answers some fundamental questions such as "bifunctionality" in the field of water electrolysis. It also presents the modification of a readily available and cheap material, stainless steel, into an efficient water splitting catalyst that operates under industrial conditions.
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Crawford, Jessica F. "Using room-temperature liquid metals as a new reaction environment." Thesis, Queensland University of Technology, 2022. https://eprints.qut.edu.au/232783/1/Jessica_Crawford_Thesis.pdf.
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When conducting a chemistry experiment, reactions are often completed in a liquid solvent. This thesis investigates the outcome of using liquid metals as a new reaction environment. Galinstan is an alloy comprised of 68.5% gallium, 21.5% indium and 10% tin that can remain a liquid at room temperature and is extremely useful due to its flexibility and conductivity. This thesis shows that liquid metals can be used to synthesise new 2D materials that catalyse oxygen production during water splitting, form new materials that can catalyse ammonia production from abundant nitrate sources and facilitate the degradation of organic dye pollutants.
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Wang, Li [Verfasser], and K. Andreas [Akademischer Betreuer] Friedrich. "Development and investigation of oxygen evolution reaction catalysts for proton exchange membrane electrolyzers / Li Wang ; Betreuer: K. Andreas Friedrich." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2018. http://d-nb.info/1185487522/34.
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Zhang, Zhihao. "The Development of Three Dimensional Porous Nickel Materials and their Catalytic Performance towards Oxygen Evolution Reaction in Alkaline Media." Thesis, Université d'Ottawa / University of Ottawa, 2020. http://hdl.handle.net/10393/40636.
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As the global energy crisis and environmental pollution problem continues, there is an increasing demand for clean and sustainable energy storage and conversion technologies, such as water-splitting electrolysis. Water electrolysis is a process of running an electrical current through water in separating the hydrogen and oxygen. Oxygen evolution reaction (OER) is a key reaction in this electrochemical process, and the electrochemical performance of these systems is usually hindered by the slow OER reaction kinetics. In order to achieve high energy conversion efficiency, the development of efficient OER catalysts is the key. To achieve that, abundant research is done by using noble metal oxides as catalyst, such as IrO2 and RuO2. However, considering their high cost, a cheap earth-abundant material with a high OER catalytic activity is required. Accordingly, this study has been focused on the synthesis of three dimensional porous structured Ni-based OER catalysts. First, a 3D porous Ni meso-foam was developed through a facile high-temperature one-pot synthesis method, and its catalytic activity towards OER was explored. Specifically, the as-synthesized Ni meso-foam material, referred to as raw NMF, has a wire-linked structure and high surface area. A reduction procedure was introduced to obtain reduced Ni meso-foam materials, referred to as NMF-H2. It was also oxidized in air at 600 ℃ to form a semi-hollow NiO crosslinking phase and subsequently reduced in H2 at 300℃, forming a regenerated porous Ni foam material, referred to as NMF-O2/H2. The composition and morphology of all materials were investigated by XRD and SEM, respectively. The SEM image reveals that, in the porous NMF-O2/H2, the cross-linked meso-wire structure was maintained, and the average pore size is between 0.5-5 μm. Electrochemical analysis show that the OER activity of the Ni foam catalysts follows NMF-O2/H2 > NMF-H2 > raw NMF. In addition to the NMF-based materials, a Ni/Ni(OH)2 layer-structured electrocatalyst, referred to as NiDHBT, was also developed using a dynamic hydrogen bubble templating (DHBT) method. First, the 3D-porous micro Ni/Zn nanoplatelets were constructed in a two-step DHBT deposition method. The Ni/Zn foil was used as a scaffold, featured with the open porous structure and high surface area, for the subsequent electrodeposition of Ni(OH)2. Then, the Zn was etched from the as-prepared Ni/Zn/Ni(OH)2 nanocomposite to obtain the NiDHBT. The catalytic performance of the NiDHBT toward OER reaction was evaluated, and the optimal catalysts developed from different electro deposition potentials were determined. On the recognition of the high catalytic activity of NMF-O2/H2 and NiDHBT, porous structured FeOx-Nickel meso-foam, referred to as Fe@NMF-O2/H2, and FeOx- Ni/Ni(OH)2 layered-structure materials, referred to as Fe@NiDHBT, was further developed to explore the benefits of FeOx deposition for its OER catalytic performance. The deposition of FeOx is achieved by physical mixing FeOx colloid with NMF-O2/H2 and NiDHBT, and the electrochemical performance of these materials was examined in 1 M KOH. Among the developed materials, the best performing catalyst is Fe@NiDHBT synthesized by loading FeOx colloid onto the NiDHBT support. The overpotential for Fe@NiDHBT to reach 10 mA·cm-2 is 247mV, and the corresponding Tafel slope is 48.10mV·dec-1. Therefore, it was concluded that the FeOx¬¬ loading modification is an effective strategy to improve the OER activity of Ni foam-based catalysts.
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Weidler, Natascha [Verfasser], Ulrike [Akademischer Betreuer] Kramm, and Wolfram [Akademischer Betreuer] Jaegermann. "Plasma-enhanced chemical vapor deposition of cobalt-based catalysts for the oxygen evolution reaction / Natascha Weidler ; Wolfram Jaegermann, Ulrike Kramm." Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2017. http://d-nb.info/1134865961/34.
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Zhao, Zhenghang. "Design Principle on Carbon Nanomaterials Electrocatalysts for Energy Storage and Conversion." Thesis, University of North Texas, 2017. https://digital.library.unt.edu/ark:/67531/metadc984279/.
Full textAbstract:
We are facing an energy crisis because of the limitation of the fossil fuel and the pollution caused by burning it. Clean energy technologies, such as fuel cells and metal-air batteries, are studied extensively because of this high efficiency and less pollution. Oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are essential in the process of energy storage and conversion, and noble metals (e.g. Pt) are needed to catalyze the critical chemical reactions in these devices. Functionalized carbon nanomaterials such as heteroatom-doped and molecule-adsorbed graphene can be used as metal-free catalysts to replace the expensive and scarce platinum-based catalysts for the energy storage and conversion. Traditionally, experimental studies on the catalytic performance of carbon nanomaterials have been conducted extensively, however, there is a lack of computational studies to guide the experiments for rapid search for the best catalysts. In addition, theoretical mechanism and the rational design principle towards ORR and OER also need to be fully understood.
In this dissertation, density functional theory calculations are performed to calculate the thermodynamic and electrochemical properties of heteroatom-doped graphene and molecule-adsorbed graphene for ORR and OER. Gibb's free energy, overpotential, charge transfer and edge effect are evaluated. The charge transfer analysis show the positive charges on the graphene surface caused by the heteroatom, hetero-edges and the adsorbed organic molecules play an essential role in improving the electrochemical properties of the carbon nanomaterials. Based on the calculations, design principles are introduced to rationally design and predict the electrochemical properties of doped graphene and molecule-adsorbed graphene as metal-free catalysts for ORR and OER. An intrinsic descriptor is discovered for the first time, which can be used as a materials parameter for rational design of the metal-free catalysts with carbon nanomaterials for energy storage and conversion. The success of the design principle provides a better understanding of the mechanism behind ORR and OER and a screening approach for the best catalyst for energy storage and conversion.
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Öztürk, Secil [Verfasser], Christoph [Gutachter] Janiak, and Christian [Gutachter] Ganter. "Metal-Organic Framework and Covalent Triazine Framework Based Electrocatalysts for the Oxygen Evolution Reaction / Secil Öztürk ; Gutachter: Christoph Janiak, Christian Ganter." Düsseldorf : Universitäts- und Landesbibliothek der Heinrich-Heine-Universität Düsseldorf, 2021. http://d-nb.info/1236399560/34.
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Massué, Cyriac [Verfasser], Robert [Akademischer Betreuer] Schlögl, Peter [Akademischer Betreuer] Strasser, Robert [Gutachter] Schlögl, Peter [Gutachter] Strasser, and Martin [Gutachter] Muhler. "Iridium oxohydroxide electrocatalysts for the oxygen evolution reaction / Cyriac Massué ; Gutachter: Robert Schlögl, Peter Strasser, Martin Muhler ; Robert Schlögl, Peter Strasser." Berlin : Technische Universität Berlin, 2016. http://d-nb.info/1156014514/34.
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Shi, Zhangsheng. "Strain engineering of Co-N-C catalyst toward enhancing the HER and ORR electrocatalytic activities." Thesis, Queensland University of Technology, 2020. https://eprints.qut.edu.au/207078/8/Zhangsheng_Shi_Thesis.pdf.
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This thesis presents a comprehensive review of practical strategies to enhance the catalytic activity of M-N-C materials. The practical strategies can be extended to engineer external factors to break the linear scaling relationships and to further enhance the catalytic performances. In order to design the next-generation higher-performance catalysts, this project was a step forward in developing strain and heterostructure method to achieve a superior HER performance and a ORR performance beyond the limit.
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Ho, Chi Keung (Jimmy). "Effects of elevated temperatures on electrochemical processes and electrocatalysis and adsorption in the oxygen evolution reaction at alpha and beta lead dioxides." Thesis, University of Ottawa (Canada), 1993. http://hdl.handle.net/10393/6573.
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The first part of the thesis is concerned with the problem of temperature dependence of the Tafel slope for various electrochemical processes including the cathodic H$\sb2$ and anodic O$\sb2$ evolution reactions at Au, Pt and Ni in 0.2 N NaOH aqueous solutions at elevated temperatures up to 473 K by means of steady-state polarization experiments. It is found that the commonly assumed representation of the Tafel slope, b, as b = RT/$\beta$F with $\beta$ a constant, often equal to 0.5, is not followed, i.e. $\beta$ is dependent on T. Several examples of this unconventional behaviour of b on temperature are provided in this thesis. The effect of temperature on the surface processes of oxide film formation and reduction in both acid and alkaline aqueous solutions is also examined by means of cyclic voltammetry experiments at temperatures as high as 529 K. In addition to the expected behaviour, such as the higher is the temperature the larger is the rate of reaction, the processes also become more reversible. Experimental examples are provided in this thesis. The second part of the thesis is about the anodic O$\sb2$ evolution reaction at the two "allotropic" forms of lead dioxide, $\alpha$- and $\beta$-PbO$\sb2$ in 1 N HClO$\sb4$ aqueous solutions. The existence of these two forms of PbO$\sb2$ provides a rare opportunity of examining the structural effect in electrocatalysis and kinetics of the O$\sb2$ evolution process. Significant differences between the dimorphs are observed both in the kinetics and the adsorption behaviour of the O and OH intermediates of the reaction. Both potential-relaxation transients, following prior current interruption, and a.c. frequency-response spectroscopy are used in deriving the adsorption behaviour of the reaction intermediates, both H and O/OH species.
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Zhang, Xinyu, Li An, Jie Yin, Pinxian Xi, Zhiping Zheng, and Yaping Du. "Effective Construction of High-quality Iron Oxy-hydroxides and Co-doped Iron Oxy-hydroxides Nanostructures: Towards the Promising Oxygen Evolution Reaction Application." NATURE PUBLISHING GROUP, 2017. http://hdl.handle.net/10150/623197.
Full textAbstract:
Rational design of high efficient and low cost electrocatalysts for oxygen evolution reaction (OER) plays an important role in water splitting. Herein, a general gelatin-assisted wet chemistry method is employed to fabricate well-defined iron oxy-hydroxides and transitional metal doped iron oxyhydroxides nanomaterials, which show good catalytic performances for OER. Specifically, the Co-doped iron oxy-hydroxides (Co0.54Fe0.46OOH) show the excellent electrocatalytic performance for OER with an onset potential of 1.52 V, tafel slope of 47 mV/dec and outstanding stability. The ultrahigh oxygen evolution activity and strong durability, with superior performance in comparison to the pure iron oxyhydroxide (FeOOH) catalysts, originate from the branch structure of Co0.54Fe0.46OOH on its surface so as to provide many active edge sites, enhanced mass/ charge transport capability, easy release oxygen gas bubbles, and strong structural stability, which are advantageous for OER. Meanwhile, Co-doping in FeOOH nanostructures constitutes a desirable four-electron pathway for reversible oxygen evolution and reduction, which is potentially useful for rechargeable metal-air batteries, regenerative fuel cells, and other important clean energy devices. This work may provide a new insight into constructing the promising water oxidation catalysts for practical clean energy application.
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Heese-Gärtlein, Justus [Verfasser], and Malte [Akademischer Betreuer] Behrens. "Manganese oxides as electrocatalysts in water oxidation : synthesis, characterization and their activity in the oxygen evolution reaction / Justus Heese-Gärtlein ; Betreuer: Malte Behrens." Duisburg, 2018. http://d-nb.info/119169433X/34.
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Liu, Zhibin [Verfasser], Kristina [Gutachter] Tschulik, Malte [Gutachter] Behrens, and Tong [Gutachter] Li. "Electrocatalytic oxygen evolution reaction at single Co3O4-based nanoparticles / Zhibin Liu ; Gutachter: Kristina Tschulik, Malte Behrens, Tong Li ; Fakultät für Chemie und Biochemie." Bochum : Ruhr-Universität Bochum, 2021. http://d-nb.info/1233484133/34.
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Wahl, Sebastian [Verfasser], Nicola [Gutachter] Pinna, Klaus [Gutachter] Rademann, and Holger [Gutachter] Dau. "Shed Light on Cobalt Oxides for the Oxygen Evolution Reaction – An Operando Spectroelectrochemical Study / Sebastian Wahl ; Gutachter: Nicola Pinna, Klaus Rademann, Holger Dau." Berlin : Humboldt-Universität zu Berlin, 2020. http://d-nb.info/1204424772/34.
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Rodríguez, Hernández Fermín. "Theoretical description of water splitting on TiO2 and combined Mo2C-graphene based materials." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-227530.
Full textAbstract:
The electrocatalytic water decomposition has been investigated in this thesis by means of its two half standard reactions: the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER). These reactions occur in different locations in a typical electrochemical cell: the anode and the cathode, respectively. Motivated by the lack of understanding about the reaction mechanisms occurring at the anodes and cathodes, we have proposed first: novel representations of typical TiO2 surfaces, based on small cluster systems, which can be used for a quick and more detailed assessment of the OER activities at modified TiO2 surfaces, and secondly we investigated the HER in two sets of model surfaces which represent recently synthesized materials, based on Mo2C and graphene with promising activities toward the HER. We have employed Density Functional Theory (DFT) based methods within both localized and extended basis sets, as implemented in GAMESS and VASP packages, respectively, to examine the structural, electronic and vibrational properties of the proposed models.
We propose new reaction mechanisms for the OER on a number of molecular representations of TiO2 electrodes. For each reaction pathway, the free energy profile is computed, at different biases, from the DFT energies, the entropic and the zero-point energy contributions. The mechanisms explored in this thesis are found to be energetically more feasible than alternative reaction pathways considered in previous theoretical works based on molecular representations of the TiO2 surfaces. The representation of the surface of specific, commonly occurring, titanium dioxide crystals (e.g., rutile and anatase) within the small cluster approximation is able to reproduce qualitatively the rutile (110) outperforming of the anatase (001) surface.
We subsequently investigate the influence of doping TiO2 surfaces with transition metals (TMs) on the performance of TiO2 -based electrodes for the water splitting electrochemical reaction. Two cluster models of the TM-doped active sites which resemble both the TiO2 anatase (001) and rutile (110) surfaces, respectively, are considered for the evaluation of the water decomposition reaction when a Ti is replaced by a TM atom. A set of TMs spanning from Vanadium to Nickel is considered. The late TMs explored here: Fe, Co and Ni are found to reproduce the observed experimental trends for the overpotentials in TiO2-doped electrodes. In the case of Cr and Mn, the present study predicts an enhancement of the OER activity for the anatase-like clusters while a reduction of this activity is found for the rutile-like ones. The vanadium-doped structures do not show relevant influence in the OER activity compared to pure TiO2-based cluster models.
The last part of this work is devoted to the theoretical study of the HER on recently found materials based on the synergistic combination of molybdenum carbide and graphene layers. We propose two major structural models to describe the HER mechanism within the framework of DFT: Mo2C-based clusters adsorbed on carbon nanosheets and the Mo2C (001) surface covered by pure and nitrogen-doped graphene layers. The former system evaluates the influence of Mo2C nanoparticles adsorbed on carbon nanosheets towards the HER. The second one is employed to gain insight about the high HER activity observed in molybdenum carbide anchored on nitrogen-doped porous carbon nanosheets (Mo2C@2D-NPC), recently synthesized. The H-adsorption free energy has been used as a principal descriptor to asses the HER activity at the proposed model active sites. It resembles the value for the best state of the art catalyst for the HER (i.e., platinum at carbon substrate Pt@C) in some of the proposed structural models. Furthermore, a pH-correction is added within a simplified model, to the H-adsorption free energy barrier in every proposed structure. The pH dependence of the H-adsorption free energy barriers allows the assessment of the HER at acidic and alkaline conditions simultaneously. An overall agreement with experimental results is found and further predictions, promoting the development of better HER catalysts, have been done.
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Wang, Teng. "Nickel based nanomaterials for renewable energy conversion and storage application." Thesis, Queensland University of Technology, 2018. https://eprints.qut.edu.au/119163/8/Teng_Wang_Thesis.pdf.
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This research focuses on the synthesis and development of new functional nanomaterials with tailored morphology for high performance supercapacitors and hydrogen generation through electrolysis of water splitting in order to alleviate the energy crisis and environmental problems. A series of nickel based nanomaterials have been synthesized and their electrochemical properties were thoroughly studied. Ultrafine amorphous barium nickel phosphate nanofibers, and Ni-Co and NiCu layered double hydroxide (LDH) nanosheet arrays directly grown on carbon fibre clothes (CFC) demonstrated excellent performance for supercapacitors while NiCoFe LDH nanosheet arrays on CFC showed high catalytic activity for oxygen evolution reaction for water splitting.
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Bôas, Naiza Vilas. "Síntese e caracterização de óxidos de manganês puros e dopados com cátions metálicos utilizados como materiais aplicados em dispositivos eletroquímicos de conversão de energia." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/75/75135/tde-25012018-164925/.
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O dióxido de manganês (MnO2) é um catalisador eficiente de baixo custo utilizado no cátodo de baterias do tipo metal-ar e células a combustível alcalinas, sendo capaz de promover a redução completa de oxigênio pela rota 4e-. No entanto, o dióxido de manganês é um semicondutor e só pode ser utilizado como material eletródico nos dispositivos mencionados se combinado com algum suporte condutor. O suporte condutor mais utilizado para este fim é o carbono em pó. Entretanto, este material não possui estabilidade suficiente nas condições operacionais das células alcalinas, sendo convertido gradativamente em CO2. Uma das possíveis estratégias para tentar minimizar esta deficiência é incrementar a condutividade eletrônica do óxido puro pela dopagem com alguns cátions metálicos. Sendo assim, este trabalho tem como objetivo geral pesquisar de maneira sistemática o efeito da dopagem de dióxido de manganês com alguns cátions metálicos, como o Bi3+e Ce4+ nas propriedades físico-químicas e eletrocatalíticas deste óxido, visando o uso dos mesmos como em cátodos de baterias recarregáveis do tipo Zn-ar. As análises das características morfológicas dos catalisadores por meio de MEV e TEM mostram que os óxidos de manganês são gerados na forma de nano-bastões de 50 a 100 nm de comprimento. Os óxidos puros e dopados com bismuto e cério apresentam estruturas tetragonais típicas, ocorrendo expansão da célula unitária dos óxidos dopados pela troca de íons manganês pelos correspondentes dopantes na rede cristalina de MnO2. Os resultados eletroquímicos sugerem um aumento de condutividade do óxido dopado que possibilita seu uso sem mistura com carbono. Além disso, observa-se que a RRO é catalisada por um mecanismo que envolve a transferência de 4e- nestes materiais com participação de peróxido como intermediário. O óxido de manganês dopado com Bi apresentou promissor desempenho catalítico para a RDO, o que junto com os demais resultados apresentados para a RRO o qualificou a funcionar como o catalisador bifuncional mais promissor de todos os estudados em baterias do tipo metal-ar. Experimentos realizados em mini baterias do tipo Zn-ar demonstraram a total capacidade do catalisador dopado com bismuto operar como catalisador do eletrodo de ar, resultando num desempenho superior ao de um catalisador convencional de MnO2/C.Manganese dioxide is at the same time an efficient and low-cost material used as cathode catalyst in the air electrode of metal-air and alkaline fuel cells, capable to promote the complete reduction of oxygen thru the 4e- mechanism. However, manganese dioxide is a semiconductor and can be used as electrodic material in the mentioned devices only combined with a conductor support. High surface area carbon powder is the most commonly used material for such purpose. The problem is that carbon suffers from severe instabilities in the experimental conditions that fuel cells and metal-air batteries operates, being gradually converted into CO2. A possible strategy to overcome or at least minimize the low oxide conductivity is by doping this material with some metallic cations. In this sense, the main purpose of this work was the systematic investigation of the physicochemical and electrocatalytic properties of Bi3+ and Ce4+ doped manganese dioxide materials used as cathode catalysts in the air electrode of alkaline type Zn-air batteries. The morphologic characterization performed SEM and TEM revealed that pure as well cation doped MnO2 are formed as poly dispersed nanorods with 50-100 nm length. Both pure and doped materials presented typical tetragonal structures, although a cell expansion was observed in the doped oxides caused by the exchange of some manganese cations by the doping counter parts. Electrochemical results suggest that a material with increased conductivity results from the doping process, allowing it to operate as air catalyst without the use of a carbon support. Besides, it is observed that the oxygen reduction reaction proceeds thru the 4e- mechanism on the doped oxides involving hydrogen peroxide as intermediate. The Bi doped oxide presented the best performance for the oxygen evolution reaction among all catalysts investigated. This result together with the superior performance for the oxygen reduction reaction presented by this material suggest that Bi doped MnO2 is a potential candidate to operate as an air catalyst of rechargeable alkaline metal-air batteries. Experiments conducted in a mini Zn-air battery using Bi doped MnO2 as air catalyst corroborated this observation.
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Ying, Qiling. "Preparation and characterization of highly active nano pt/c electrocatalyst for proton exchange membrane fuel cell." Thesis, University of the Western Cape, 2006. http://etd.uwc.ac.za/index.php?module=etd&action=viewtitle&id=gen8Srv25Nme4_3791_1188474883.
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Catalysts play an essential role in nearly every chemical production process. Platinum supported on high surface area carbon substrates (Pt/C) is one of the promising candidates as an electrocatalyst in low temperature polymer electrolyte fuel cells. Developing the activity of the Pt/C catalyst with narrow Pt particle size distribution and good dispersion has been a main concern in current research.
In this study, the main objective was the development and characterization of inexpensive and effective nanophase Pt/C electrocatalysts. A set of modified Pt/C electrocatalysts with high electrochemical activity and low loading of noble metal was prepared by the impregnation-reduction method in this research. The four home-made catalysts synthesized by different treatments conditions were characterized by several techniques such as EDS, TEM, XRD, AAS, TGA, BET and CV.
Pt electrocatalysts supported on acid treatment Vulcan XC-72 electrocatalysts were produced successfully. The results showed that Pt particle sizes of Pt/C (PrOH)x catalysts between 2.45 and 2.81nm were obtained with homogeneous dispersion, which were more uniform than the commercial Pt/C (JM) catalyst. In the electrochemical activity tests, ORR was confirmed as a structure-sensitive reaction. The Pt/C (PrOH/pH2.5) showed promising results during chemically-active surface area investigation, which compared well with that of the commercial standard Johnson Matthey Pt/C catalyst. The active surface area of Pt/C (PrOH/pH2.5) at 17.98m2/g, was higher than that of the commercial catalyst (17.22 m2/g ) under the conditions applied. In a CV electrochemical activity test of Pt/C catalysts using a Fe2+/Fe3+ mediator system study, Pt/C (PrOH/pH2.5) (67mA/cm2) also showed promise as a catalyst as the current density is comparable to that of the commercial Pt/C (JM) (62mA/cm2).
A remarkable achievement was attained in this study: the electrocatalyst Pt supported on CNTs was synthesized effectively. This method resulted in the smallest Pt particle size 2.15nm. In the electrochemically-active surface area study, the Pt/CNT exhibited a significantly greater active surface area (27.03 m2/g) and higher current density (100 mA/cm2) in the Fe2+/Fe3+ electrochemical mediator system than the other home-made Pt/C catalysts, as well as being significantly higher than the commercial Pt/C (JM) catalysts. Pt/CNT catalyst produced the best electrochemical activities in both H2SO4 and K4[Fe(CN)6] electrolytes. As a result of the characteristics of Pt/CNTï¼it can be deduced that the Pt/CNT is the best electrocatalyst prepared in this study and has great potential for use in fuel cell applications.
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French, Katherine L. (Katherine Louise). "Testing the ancient marine redox record from oxygenic photosynthesis to photic zone euxina." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/97336.
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Thesis: Ph. D., Joint Program in Chemical Oceanography (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2015.Cataloged from PDF version of thesis.
Includes bibliographical references.
Tracing the evolution of Earth's redox history is one of the great challenges of geobiology and geochemistry. The accumulation of photosynthetically derived oxygen transformed the redox state of Earth's surface environments, setting the stage for the subsequent evolution of complex life. However, the timing of the advent of oxygenic photosynthesis relative to the Great Oxidation Event (GOE; -2.4 Ga) is poorly constrained. After the deep ocean became oxygenated in the early Phanerozoic, hydrogen sulfide, which is toxic to most aerobes, may have transiently accumulated in the marine photic zone (i.e. photic zone euxinia; PZE) during mass extinctions and oceanic anoxic events. Here, the molecular fossil evidence for oxygenic photosynthesis and eukaryotes is reevaluated, where the results imply that currently existing lipid biomarkers are contaminants. Next, the stratigraphic distribution of green and purple sulfur bacteria biomarkers through geologic time is evaluated to test whether these compounds reflect a water column sulfide signal, which is implicit in their utility as PZE paleoredox proxies. Results from a modern case study underscore the need to consider allochthonous and microbial mat sources and the role of basin restriction as alternative explanations for these biomarkers in the geologic record, in addition to an autochthonous planktonic source.
by Katherine L. French.
Ph. D.
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Moureaux, Florian. "Etude des réactions mettant en jeu l'oxygène dans un système électrochimique lithium-air aqueux rechargeable électriquement." Phd thesis, Université de Grenoble, 2011. http://tel.archives-ouvertes.fr/tel-00947541.
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Les systèmes électrochimiques lithium-air sont des concepts naissants mais exhibent des performances théoriques intéressantes qui laissent espérer une rupture technologique dans le domaine des batteries pour véhicule électrique. La possibilité d'atteindre une densité d'énergie supérieure à 500 Wh kg-1 est effectivement en ligne de mire. A contrario de la technologie lithium-air anhydre, les systèmes lithium-air aqueux n'ont, jusqu'à présent, fait l'objet d'aucune étude approfondie. Ce travail concerne donc le développement d'un système lithium-air aqueux, à trois électrodes, et vise également à améliorer nos connaissances fondamentales dans le domaine. La présente étude se focalise sur le compartiment positif de la cellule, dans lequel les réactions de l'oxygène sont mises en jeu. Dans un premier temps, une électrode spécifiquement dédiée à la réaction de dégagement d'oxygène a été élaborée à partir d'un acier 316L. L'étude de son comportement a révélé une bonne propension à catalyser la réaction de dégagement d'oxygène ainsi qu'une bonne stabilité sur 3 000 heures de fonctionnement. Néanmoins, d'importants problèmes de catalyse ont pu être observés et attribués à la présence des ions lithium dans l'électrolyte de la batterie. Les ions Li+ bloquent les transitions électrochimiques des sites actifs à l'origine des propriétés d'électrocatalyse. Le comportement d'une électrode à air, composée de carbone et d'oxydes de manganèse, a par la suite été caractérisé dans ce milieu. L'étude révèle deux phénomènes importants réduisant la performance de l'électrode et dont l'origine a également été attribuée aux ions lithium : un blocage des transitions (MnIII/MnIV), et une stabilisation des groupements oxygénés à la surface du carbone. Pour finir, il a été proposé d'optimiser le système électrolytique en limitant l'activité des ions Li+ en solution et ainsi d'améliorer le rendement en potentiel de charge/décharge de la batterie.