Дисертації з теми "OER reaction"

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.

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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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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Le développement d'électrocatalyseurs efficaces pour la réaction de libération d'oxygène (OER) est important pour améliorer l'efficacité globale du processus d'électrolyse de l'eau. Les oxydes / hydroxydes de métaux de transition présentent une activité et une stabilité raisonnables lorsqu’utilisés dans un milieu alcalin. Ils ont le potentiel de remplacer les oxydes à base d'Ir et de Ru. Comprendre la réaction d’OER pour les oxydes / hydroxydes de métaux de transition dans les électrolytes alcalins aide à la conception d'électrocatalyseurs peu coûteux et très efficaces. Avec trois travaux différents sur les oxydes / hydroxydes à base de Co, cette thèse approfondit la compréhension des propriétés de surface des matériaux et des propriétés interfaciales sur la cinétique de la réaction d’OER. Tout d'abord, la substitution au fer régule par exemple la configuration des cations métalliques dans LaCoO3. Cela ajuste la covalence de la liaison oxygène 2p – métal 3d et améliore les performances. Deuxièmement, la substitution au Ni dans ZnCo2O4 modifie la position relative du centre de la bande O 2p et du centre de la bande métallique dans un environnement octahédrique MOh. Cela modifie la stabilité et la possibilité pour l'oxygène du réseau de participer à la réaction de dégagement d’oxygène. Enfin, en étudiant les séries La1-xSrxCoO3, CoOOH et CoOOH contenant Fe, l'impact de l'électrolyte sur les paramètres de la cinétique de réaction a été exploré. Avec une meilleure compréhension de la façon dont les propriétés des matériaux et l'environnement dynamique influencent l'activité et le mécanisme des OER, nous pouvons obtenir des catalyseurs de OER plus efficaces pour une meilleure infrastructure énergétique
The development of efficient electrocatalysts to lower the overpotential of oxygen evolution reaction (OER) is of fundamental importance in improving the overall efficiency of fuel production by water electrolysis. Among a plethora of catalysts being studied on, transition metal oxides / hydroxides that exhibit reasonable activity and stability in alkaline electrolyte have been identified as catalysts to potentially overpass the activity of expensive Ir- and Ru- based oxides. Understanding the OER for transition metal oxides / hydroxides in alkaline electrolytes paves the way for better design of low cost and highly efficient electrocatalysts. This dissertation, with three different work on Co-based oxides / hydroxides, studies and deepens the understanding of the bulk properties, surface properties of materials and interfacial properties on OER. Firstly, with Fe substitution, it addresses tuning the eg configuration of metal cations in LaCoO3 where adjusting the metal 3d oxygen 2p covalency can bring benefits to the OER performance. Secondly, with Ni substitution in ZnCo2O4, it demonstrates a change in relative position of O p-band and MOh d-band centre which induces a change in stability as well as the possibility for lattice oxygen to participate in the OER. Finally, with La1-xSrxCoO3 series, CoOOH and Fe-containing CoOOH as examples, the impact of the electrolyte has been explored by the study of reaction kinetics parameters. With a better understanding of how material properties and dynamic environment influence the OER activity and mechanism, we can obtain more efficient OER catalysts for better energy infrastructure

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

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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Si l'hydrogène est un vecteur énergétique prometteur pour le stockage durable de l'énergie, sa production doit reposer sur des technologies sans carbone. L’électrolyse de l’eau qui consiste à dissocier l'eau via un courant électrique issu d’énergies renouvelables est idéal pour produire un hydrogène vert. Toutefois, ce processus est entravé par une cinétique lente de la réaction OER (Oxygen Evolution Reaction, 2H2O ⇋ O2 + 4H+ + 4e-) à l'anode, nécessitant un apport d’énergie supplémentaire pour assurer un rendement énergétique satisfaisant. Ainsi, des catalyseurs, généralement des oxydes d'iridium et de ruthénium, sont utilisés pour réduire cette énergie en facilitant le transfert d'électrons et de protons impliqués dans la réaction OER. Toutefois, l’utilisation de ces métaux de plus en plus rares freine l'évolution de cette technologie. Pour y remédier, des catalyseurs à base d'oxydes et d'oxyhydroxydes de métaux de transition 3d, économiques et abondants, ont été mis au point pour l’électrolyse de l’eau en milieu alcalin et présentent des performances élevées. Ce travail de thèse présente la synthèse de nouveaux composés oxyfluorés à base d’éléments éco-compatibles et abordables en utilisant une voie d’élaboration simple et directe en deux étapes pour une application en tant qu'électrocatalyseur anodique dans un électrolyseur alcalin.L'étude initiale porte sur des catalyseurs oxyfluorés enrichis en fer, issus de la décomposition thermique à l'air ambiant de (Co1-xFex)2+Fe3+F5(H2O)7 (0 ≤ x ≤ 0,72). Les résultats montrent que la teneur en cobalt peut être réduite de 20% sans affecter les performances OER, permettant d'atteindre un surpotentiel de 320 mV à 10 mA.cm-2, une activité massique de 110 A.g-1 à 1,55 V vs. RHE et une grande stabilité. La deuxième partie de la thèse vise à améliorer les propriétés catalytiques du composé référence Co0,5Fe0,5O0,5F1,5 en remplaçant le cobalt par du nickel, connu pour son activité OER. La solution solide (Co(1-x)/2Nix/2)2+Fe0,5O0,5F1,5-y(OH)y (y ≤ 0.3) a été obtenue par décomposition thermique (Co1-xNix)2+FeF5(H2O)7 (0 ≤ x ≤ 1). La dernière partie vise à évaluer les performances de ces matériaux ainsi que d’étudier leur mécanisme de réaction. La composition x = 0,5 présente les meilleures performances, avec un faible surpotentiel de 290 mV à 10 mA.cm-2 et une activité spécifique de 3,9 A.m-2 de surface BET à 1,5 V vs. RHE. L'origine des propriétés catalytiques exceptionnelles de (Co0.25Ni0.25)2+Fe3+0.5O0,5F1,3(OH)0,2, mis en évidence via entre autres des analyses in-situ/operando ont été employées, proviendrait de la synergie entre Co et Ni, et l’implication d’oxygènes du réseau dans le mécanisme (LOM), contournant les limites théoriques liées au mécanisme conventionnel
If hydrogen is a promising energy vector for sustainable energy storage, its production must rely on carbon-free technologies. Water splitting powered by green electricity is ideal for producing a decarbonized energy carrier from water. However, this process is hampered by the sluggish kinetics of the oxidation evolution reaction (OER, 2H2O ⇋ O2 + 4H+ + 4e-) at the anode, requiring extra energy to ensure a suitable production rate. Catalysts, usually iridium and ruthenium oxides, are employed to reduce the energy requirement by facilitating electron and proton transfer involved in OER, but these metals are scarce, limiting the scalability of this technology. To overcome this, oxides and oxyhydroxides catalysts based on cost-effective and abundant 3d transition metal-based have been developed for alkaline water splitting, presenting high performance. In this way, this work presents the synthesis of new oxyfluorides with eco-compatible and affordable elements using a simple and straightforward two-step synthetic route for application as OER electrocatalyst in alkaline electrolyte.The initial study focuses on iron-enriched oxyfluoride catalysts from thermal decomposition under ambient air of (Co1-xFex)2+Fe3+F5(H2O)7 (0 ≤ x ≤ 0.72). Results show that cobalt content can be reduced by 20% without affecting OER performance, achieving an overpotential of 320 mV at 10 mA.cm-2, a mass activity of 110 A.g-1 at 1.55 V vs. RHE and high stability. The second part aims to enhanced the catalytic properties of Co0.5Fe0.5O0.5F1.5 reference by substituting cobalt with nickel, known for its OER activity. The (Co(1-x)/2Nix/2)2+Fe0.5O0.5F1.5-y(OH)y (y ≤ 0.3) solid solution have been obtained by thermal decomposition (Co1-xNix)2+FeF5(H2O)7 (0 ≤ x ≤ 1). The final section assesses the performance of these materials and studies their reaction mechanism. The x = 0.5 composition shows the best performance, with a low overpotential of 290 mV at 10 mA.cm-2 and a specific activity of 3.9 A.m-2 of BET surface area at 1.5 V vs. RHE. The origin of the exceptional catalytic properties of (Co0.25Ni0.25)2+Fe3+0.5O0.5F1.3(OH)0.2, highlighted via in-situ/operando analyses, among others, were employed, would stem from the synergy between Co and Ni, and the involvement of lattice oxygens in the mechanism (LOM), circumventing the theoretical limits linked to the conventional mechanism

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)

The exploration of highly active and durable cathodic oxygen reduction reaction (ORR) catalysts with economical production cost is still the bottleneck to realize the large-scale commercialization of some emerging technologies, such as fuel cells and metal-air batteries. At present, the composite that contains expensive platinum (Pt) particles dispersed on a porous carbon support (e.g., activated carbon (AC)) is the most efficient ORR catalyst. In a common sense, the AC itself normally shows very low activity for the ORR, so the Pt particles are vital. Imagine that if we remove all of the Pt particles, can the remaining AC still play the similar role? The current work aims to make the inert AC active for the electrochemical reactions by creating unique defects in the AC. First of all, different porous carbon materials with variable specific surface areas were synthesized by an easy and scalable chemical activation method. It is shown that all the activated samples demonstrate obviously improved ORR activity. Afterwards, the unique defects were introduced into the activated ACs via a facile nitrogen doping and removal approach to further enhance their catalytic performance, based on the defective mechanism that was proposed in our group, in which the nitrogen was incorporated into the ACs under an ammonia atmosphere at 500 °C and subsequently removed at 1050 °C under a nitrogen environment. The results showed that the doped nitrogen did not enhance the ORR performance of the synthesized samples directly, but the produced defects possibly served as the active sites for the ORR, which finally contributed to the catalytic performance improvement. Particularly, the resulting defective carbon (D-AC) derived from the highest surface area AC (3508 m2/g) also exhibits the best ORR performance in alkaline medium with low overpotential. For example, the ORR activity of the D-AC is comparable to the commercial Pt/C (20 wt% Pt) in terms of 4-electron pathway, half-wave potential and limiting current density, namely, 3.6, 0.771 V and 4.4 mA·cm-2 vs 3.9, 0.785 V and 5.0 mA·cm-2, respectively. Meanwhile, the D-AC also exhibits excellent HER activity, which is better than most of the reported metal-free HER catalysts, but with much lower production cost.
School of Natural Sciences
Science, Environment, Engineering and Technology
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This lessons covers the difference between impressionism and expressionism. Post-impressionism is represented through artworks by Vincent Van Gogh, Paul Gauguin, Paul Cèzanne, and Henri de Toulouse-Lautrec. Expressionism is represented through artworks by Edvard Munch, Henri Matisse, Ernst Ludwig Kirchner, and Vassily Kandinsky.

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 faibles
A 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

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 oxydes
Development 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

Este trabajo de Tesis Doctoral se ha centrado en comprender el comportamiento de electrocatalizadores basados en materiales carbonosos para la reacción de reducción de oxígeno. Con el fin de profundizar en el conocimiento de la naturaleza de los sitios activos de catalizadores basados en materiales carbonosos para esta reacción, se han seleccionado o preparado muestras con diferentes composiciones, texturas porosas y estructuras. De estos resultados se han conseguido importantes avances en el conocimiento del papel que los sitios activos de catalizadores basados en materiales carbonosos desempeñan en dicha reacción. Estos conocimientos y los materiales derivados pueden utilizarse en el desarrollo de cátodos para pilas de combustible en medio alcalino.
Heiwa Nakajima Foundation

The first part of this dissertation highlights the contents of the electrochemical characterization of Cu and its electroplating on Ru-based substrates. The growth of Ru native oxide does diminish the efficiency of Cu plating on Ru surface. However, the electrochemical formed irreversible Ru hydrate dioxide (RuOxHy) shows better coverage of Cu UPD. The conductive Ru oxides are directly plateable liner materials as potential diffusion barriers for the IC fabrication. The part II of this dissertation demonstrates the development of a new rapid corrosion screening methodology for effective characterization Cu bimetallic corrosion in CMP and post-CMP environments. The corrosion inhibitors and antioxidants were studied in this dissertation. In part III, a new SEC methodology was developed to study the ORR catalysts. This novel SEC cell can offer cheap, rapid optical screening results, which helps the efficient development of a better ORR catalyst. Also, the SEC method is capable for identifying the poisoning of electrocatalysts. Our data show that the RuOxHy processes several outstanding properties of ORR such as high tolerance of sulfation, high kinetic current limitation and low percentage of hydrogen peroxide.

Magister Scientiae - MSc
Fuel cells convert chemical energy from a fuel into electricity through chemical reaction with oxygen. This possesses some challenges like slow oxygen reduction reaction (ORR), overpotential, and methanol fuel cross over in a direct methanol fuel cell (DMFC). These challenges cause inefficiency and use of higher amounts of the expensive platinum catalyst.Several binary catalysts with better ORR activity have been reported. In this study we investigate the best catalyst with better ORR and MOR performances and lower over-potentials for PEMFC and DMFC applications by comparing the in-house catalysts (10%Pt/C, 20%Pt/C,30%Pt15%Ru/C, 40%Pt20%Ru/C, 30%PtCo/C, 20%Pt20%Cu/C and 20%PtSn/C) with the commercial platinum based catalysts (10%Pt/C, 20%Pt/C, 20%Pt10%Ru/C, 20%PtCo/C,20%PtCu/C and 20%PtSn/C) using the cyclic voltammetry and the rotating disk electrode to determine their oxygen reduction reaction and methanol tolerance. HRTEM and XRD techniques were used to determine their particle size, arrangement and the atomic composition. It was observed that the 20%Pt/C in-house catalyst gave the best ORR activity and higher methanol oxidation current peaks compared to others catalysts followed by 20%Pt10%Ru/C commercial catalyst. The 20%PtCo/C commercial, 30%PtCo/C in-house and 20%PtSn/C in-house catalysts were found to be the most methanol tolerant catalysts making them the best catalysts for ORR in DMFC. It was observed that the ORR activity of 20%PtCo/C commercial and 30%PtCo/C inhouse catalysts were enhanced when heat treated at 350 0C. From XRD and HRTEM studies, the particle sizes were between 2.72nm to 5.02nm with little agglomeration but after the heat treatment, the particles were nicely dispersed on the carbon support.

Developing highly active and durable oxygen reduction reaction (ORR) catalysts is crucial to reduce the cost of polymer electrolyte fuel cells (PEFCs). To meet those requirements, unsupported Pt-Cu alloy nanochains (aerogels) were synthesized by a simple co-reduction route in aqueous solution and their structure was characterized by X-ray absorption spectroscopy and STEM-EDX. These catalysts exceeded the ORR activity of commercial Pt/C catalysts by more than 100 % in RDE experiments and met the US DOE targets, thereby qualifying as very promising materials. The behavior of Pt-Cu aerogels under PEFC operation conditions was mimicked by acid washing experiments which showed that the Cu content in the alloy phase and ORR activity decrease through this step. Comparing composition, structure and ORR activity for various specimens, the Cu content in the alloy phase was identified as the main descriptor of ORR activity. An almost linear correlation was found between those two parameters and complemented by supporting data from the literature.

The present work focuses on mineral reactions and slag formation of LKAB olivine iron ore pellets (MPBO) subjected to reducing conditions in the LKAB experimental blast furnace (EBF). The emphasis is on olivine reactions with surrounding iron oxides. Many factors influence the olivine behaviour. The study was performed by use of micro methods; optical microscopy, micro probe analysis, micro Raman and Mössbuer spectroscopy and thremodynamic modeling. During manufacturing, in oxidising atmosphere at high temperature (1350°C), olivine alterations occur through slag formation and rim reactions with iron oxides and other additives. To be able to describe olivine behaviour in the rather complex blast furnace reduction process one has to consider factors such as reactions kinetics, reduction degree of iron oxides, vertical and horizontal position in the furnace and reactions with alkali. Samples were collected from the EBF both from in shaft probing during operation and from excavation following quenching of the EBF. The initial slag forming olivine consist of primary forsterite – (Mg1.9Fe0.1)SiO4 – with inclusions of hematite and an amorphous silica rich phase, a first corona with lamellae of magnesioferrite, olivine and orthopyroxene, a second corona of amorphous silica and magnesioferrite. During reduction in the upper shaft in the EBF (700-900°C) Fe3+ reduces to Fe2+. The amorphous silica in the second corona absorbs alkali, Al, Fe2+, Mg, and Ca and form glasses of varying compositions. The lamellae in the first corona will merge into a single phase olivine rim. With further reduction the glasses in the second corona will merge with the olivine rim forming an iron rich olivine rim and leaving the elements that do not fit into the olivine crystal lattice as small silicate glass inclusions. Diffusion of magnesium and iron between olivines and iron oxides increase with increasing temperature in the lower shaft of the EBF (750-1100°C). In the cohesive zone of the EBF (1100-1200°C) Fe2+ is not stable any longer and Fe2+ will be expelled from the olivine as metallic iron blebs, and the olivine will form a complex melt with a typical composition of alkali-Al2O3-MgO-SiO2. Alkali plays an important role in this final olivine consumption. The quench time for samples collected with probes and excavation are minutes respectively hours. A study of the quench rate’s effect on the phases showed no differences in the upper shaft. However, in the lower shaft wüstite separates into wüstite and magnetite when wüstite grows out of its stability field during slow cooling of excavated samples. There is also a higher alkali and aluminium deposition in the glass phases surrounding olivines in excavated pellets as a result of alkali and aluminium gas condensing on the burden in the EBF during cooling. Coating applied to olivine pellets was studied in the EBF with the aim to investigate its behaviour, particularly its ability to capture alkali. The coating materials were kaolinite, bauxite, olivine and limestone. No significant reactions were observed in the upper shaft. In the lower shaft a majority of the phases were amorphous and reflecting the original coating compositions. Deposition from the EBF gas phase occurs and kalsilite (KAlSiO4) is found in all samples; coating used for binding alkali is redundant from a quality perspective.

Although the metal oxides are capable of displaying interesting catalytic activity characteristics, the intrinsic activities of these types of systems are found to be largely depending on other parameters such as particle size, morphology, and how well the catalyst particles are dispersed on a conducting substrate and additionally the surface intermediates involved in the process. Herein, we have explored the close relation of particle size, dispersion characteristics of the active particles on a conducting carbon, substitution effect of other metals and controlled interplay of the surface intermediates for the cobalt and iron metal atoms in facilitating the reactions like ORR and OER. Substituting some portion of Fe by Zn in the spinel lattice of cobalt ferrite nanocrystals can favorably influence the overpotential for ORR. However, the substitution of Zr in a cobalt ferrite matrix shows a significant level of improvement for the overpotentials of both ORR and OER, thereby positioning the composite as a potential bifunctional electrocatalyst. Basically, the electrochemical faradaic reactions are controlled by the transition states formed in between the reaction process and the adsorption energies of these states. In acidic and basic media, the stability of the transition states changes significantly with a direct impact on the ORR activity. To understand this and to gain insightful information on the mechanistic aspects, we have studied the variation in the ORR activity with the nature of the medium for cobalt and iron atom incorporated active centers. The functioning of the catalyst is demonstrated in the primary zinc-air battery in correlation of the transition states over the catalyst.
V.K acknowledges University Grant Commission (UGC), New Delhi, India, for research fellowship and K.S acknowledges Council of Scientific and Industrial Research (CSIR), New Delhi, India, for research funding (TLP003526).
AcSIR

This thesis examines the bioleaching of six different Canadian nickel sulphide ores at pH levels above what is generally considered optimum (~ 2). The majority of work discussed in this thesis was conducted with a low-grade metamorphosed ultramafic nickel sulphide ore from Manitoba, Canada (Ore 3), which is not currently exploitable with conventional technologies. The ore contains 21% magnesium and 0.3% nickel. Nickel is the only significant metal value, and is present primarily as pentlandite. A substantial fraction of the magnesium is present as the serpentine mineral lizardite, making processing difficult with conventional pyro- and biohydrometallurgical techniques. The work with this ore has two equally important objectives: to minimize magnesium mobilization and to obtain an acceptable level of nickel extraction. Batch stirred-tank bioleaching experiments were conducted with finely ground ore ( 147 µm) with temperature and pH control. The first phase of experimentation examined the effect of pH (2 to 6) at 30 °C, and the second phase examined all combinations of three pH levels (3, 4 and 5) and five temperatures (5, 15, 22.5, 30, and 45 °C).

Proton Exchange Membrane (PEM) Fuel Cells are a promising technology for the clean energy production, especially in the automotive field. Actually, the main commercial catalysts employed in this system are based on Pt Nanoparticles supported on high surface area Carbon. The main issues associated to PEM Fuel Cells deal with the sluggish kinetic of oxygen reduction (ORR) at Platinum based electrode, with the low stability of both the carbon support and the metal phase, that tend respectively to oxidize and dissolve or diffuse and with the high cost due to rare and expensive Pt. In fact, nowadays high costs and low durability are the two factors that make PEM fuel cells still not competitive with internal combustion engine. For these reasons, research now focuses on obtaining more stable material with higher performances toward ORR. Two strategies are possible to improve catalyst for oxygen reduction. The first one deals with the enhancing of Pt activity modifying its electronic properties by alloying Pt with other transition metal (ligand effect) or by reducing the Pt-Pt distance (geometric effect). In both cases a Pt d-band shift occurs, which is responsible for the modification of adsorption and desorption energies of all species involved in ORR, and has as a direct consequence a modulation in the electrochemical activity. The second strategy deals with with the utilization of supports more stable respect to corrosion, like graphene, carbon nanotubes or mesoporous carbons. Furthermore, doping of carbon support with heteroatoms like N or S, can help to stabilize the metallic nanoparticles. In fact, doping creates homogeneous and narrow dispersion of small metallic nanoparticles, strongly bound to the surface of carbon support and with a higher resistance to agglomeration. Furthermore, doping has as well an influence on the electronic structure of the Pt catalyst, resulting in a modulation of its electrochemical activity. Doping is not beneficial only in noble-metal catalyst, but may also modify properties of the carbon support in which heteroatoms are present. Wettability, electrical conductivity and electrochemical activity are generally boosted when heteroatoms are inserted in carbonaceous substrates such as carbon blacks (CBs). The goal of this Ph.D. project consists in synthesizing nitrogen and sulphur doped and co-doped Mesoporous Carbons. MCs are highly porous materials, which offer high surface area (>1000 m2/g), pore diameter in the range between 2 and 50 nm, controlled pore structure, good mechanical and thermal stability and good mass transport. The syntheses of differently doped MCs is conducted via hard template, a technique which allow to obtain materials with a well-defined structure, originating directly from the used template. The effect of template, pyrolysis temperature and carbon precursor on the final properties of synthesized MCs is evaluated. SEM, TEM, elemental analysis, XPS, BET and TGA are employed to characterize morphology, chemical composition and functional groups, surface are, pore dimension and thermal stability of MCs, respectively. Electrochemical performance toward oxygen reduction are evaluated via cyclic voltammetry in steady state conditions, with rotating disk electrode and with rotating ring disk electrode. Electrochemical stability tests are conducted to highlight stability of differently doped MCs and the modification occurring to functional groups. The synthesized MCs are modified with Pt nanoparticles. An exhaustive deposition investigation is conducted via both chemical reduction and solid state reduction of several Pt salts, in order to find the conditions which allow to have the best Pt distribution on the whole surface of the carbon support. The catalysts made of Pt NPs on doped MCs are characterized by TEM, ICP and TGA techniques. Cyclic Voltammetry in steady conditions and with Rotating Disk Electrode are employed for the determination of electrochemical surface area (ECSA) and catalytic activity toward ORR, respectively, and compared to a commercial Pt/C catalyst. Electrochemical stability tests are conducted in order to assess both Pt degradation and C corrosion. In particular, the comparison of ECSA evolution between doped and reference catalyst determines if there is an enhancement of bounding which can mitigate Ostwald ripening. Finally, Pt on nitrogen and sulphur doped MC are incorporated in a membrane electrode assembly, in order to evaluate their performance and stability during operation as cathode material in a PEM Fuel Cell. Beyond catalytic properties, oxygen transport resistance was evaluated, knowing that all these properties are strongly influenced by the more severe condition of PEMFC environment.
Le celle a combustibile con membrana a scambio protonico (PEMFC) sono una tecnologia molto promettente per la produzione di energia pulita, specialmente nel settore automobilistico. Attualmente, i principali catalizzatori utilizzati in questi sistemi sono basati su nanoparticelle di Pt depositate su supporti carboniosi con elevata area superficiale. I maggiori problemi associati a questi catalizzatori riguardano la bassa velocità con cui avviene la reazione di riduzione dell’ossigeno (ORR), la bassa stabilità sia del supporto carbonioso che del catalizzatore di Pt che danno facilmente fenomeni di ossidazione e dissoluzione/diffusione, e infine il costo elevato del Pt, che è un metallo raro e costoso. Attualmente il costo elevato e la bassa stabilità sono i due fattori che rendono le PEMFC ancora non competitive con i motori a combustione interna, e per questo motivo la ricerca si sta focalizzando sullo studio di nuovi materiali stabili e con performance maggiori verso la ORR. Si possono seguire due strategie principali per migliorare i catalizzatori per le PEMFC. La prima riguarda l’aumento dell’attività del Pt, ottenuto modificando le sue proprietà elettroniche. Questo si può fare formando una lega di Pt con un altro metallo di transizione (effetto legante) o riducendo la distanza Pt-Pt (effetto geometrico). In entrambi i casi avviene uno spostamento del centro della banda d, responsabile della modifica delle energie di adsorbimento e desorbimento di tutte le specie coinvolte nella ORR, e ha come conseguenza la modulazione dell’attività catalitica del Pt stesso. La seconda strategia riguarda l’impiego di supporti carboniosi più stabili rispetto la corrosione, come grafene, nanotubi di carbonio o carboni mesoporosi. Inoltre, il dopaggio dei supporti con eteroatomi quali N o S ha come effetto positivo la stabilizzazione delle nanoparticelle metalliche supportate. In effetti, il dopaggio può determinare una omogenea dispersione di piccole nanoparticelle metalliche, fortemente interagenti con il supporto stesso e con una più elevata resistenza all’agglomerazione. Infine, il doping può pure modificare la struttura elettronica del Pt, risultante in una modulazione della sua attività catalitica verso la reazione di interesse. Gli aspetti positivi del dopaggio di un materiale carbonioso non si realizzano solo nella sua interazione con una fase metallica, ma modificano le proprietà stesse del supporto. La bagnabilità, la conducibilità elettrica e le proprietà elettrocatalitiche sono tendenzialmente migliorate se degli eteroatomi sono inseriti nella struttura chimica di un supporto come il Carbon Black (CB). Lo scopo di questa tesi di dottorato è quello di sintetizzare carboni mesoporosi (MCs) dopati e co-dopati con azoto e zolfo. I MCs sono materiali altamente porosi, con un’elevata area superficiale (>1000 m2/g), diametro dei pori nel range 2-50 nm, struttura porosa controllabile, buona stabilità termica e meccanica e offrono un buon trasporto di massa all’interno della loro struttura. I carboni mesoporosi vengono sintetizzati mediante hard template, una tecnica che consente di ottenere materiali con una struttura ben definita, che deriva direttamente dal templante utilizzato. È stato studiato l’effetto determinato dal templante, temperatura di pirolisi e precursore di carbonio sulle proprietà finali del materiale mesoporoso. Le tecniche utilizzate per la caratterizzazione della morfologia, della composizione chimica, dei gruppi funzionali, dell’area superficiale, della struttura porosa e della stabilità termica dei carboni mesoporosi sintetizzati sono rispettivamente microscopia elettronica a scansione e a trasmissione (SEM e TEM), analisi elementare, spettroscopia fotoelettronica a raggi x (XPS), metodologia Brunauer-Emmett-Teller (BET) e analisi termogravimetrica (TGA). Le proprietà elettrochimiche verso la ORR sono state valutate mediante voltammetria ciclica in condizioni stazionarie, con elettrodo a disco rotante e con elettrodo a disco-anello rotante. Test di stabilità elettrochimica sono stati eseguiti per valutare la stabilità dei carboni mesoporosi diversamente dopati e le modificazioni che occorrono a carico dei gruppi funzionali. I carboni mesoporosi sintetizzati sono stati modificati con nanoparticelle di Pt. È stata condotta una caratterizzazione completa della deposizione di Pt mediante due diverse metodologie (riduzione chimica e allo stato solido) e a partire da diversi sali di Pt, in modo da individuare le condizioni che consentono di ottenere la migliore distribuzione di nanoparticelle sull’intera superficie del supporto di carbonio mesoporoso dopato. I catalizzatori a base di Pt supportato su carbonio sono stati caratterizzati mediante TEM, spettroscopia di massa a plasma accoppiato induttivamente (ICP-MS) e TGA. La voltammetria ciclica in condizioni stazionarie e con elettrodo a disco rotante è stata impiegata rispettivamente per la determinazione dell’area elettrochimica superficiale (ECSA) del Pt e dell’attività catalitica verso la ORR. I risultati sono stati paragonati a quelli ottenuti nelle stesse condizioni per un catalizzatore commerciale sempre a base di Pt su carbonio ad alta area superficiale. Test di stabilità elettrochimica sono stati effettuati anche in questo caso per determinare sia la degradazione del Pt che la corrosione del carbonio. In particolare il confronto dei valori ECSA per i supporti dopati e per il supporto commerciale è stato utile per la determinazione di un eventuale effetto stabilizzante sulle nanoparticelle, che mitiga la maturazione di Ostwald. Infine, i catalizzatori a base di Pt su supporto mesoporoso dopato S e N sono stati incorporati come catodo in una PEMFC. In questo caso, oltre alle proprietà elettrochimiche, sono state valutate anche la resistenza della Membrane Electrode Assembly (MEA) al trasporto di ossigeno e la resistenza ohmica del materiale, dato che le condizioni più severe sperimentate nelle PEMFC hanno un forte impatto anche su queste proprietà.

This thesis’s main focus is a CO2 capture technology known as chemical looping combustion (CLC). The technology is a novel form of combustion and fuel processing that can be applied to gas, solid and liquid fuels. By using two interconnected fluidised-bed reactors, with a bed material capable of transferring oxygen from air to the fuel, a stream of almost pure CO2 can be produced. This stream is undiluted with nitrogen and is produced without any direct process efficiency loss from the overall combustion process. The heart of the process is the oxygen carrier bed material, which transfers oxygen from an air to fuel reactor for the conversion of the fuel. Oxygen carrier materials and their production should be of low relative cost for use in large-scale systems. The first part of this research centres on development and investigative studies conducted to assess the use of low-cost materials as oxygen carriers and as supports. Mixed-oxide oxygen carriers of modified manganese ore and iron ore were produced by impregnation. While copper (II) oxide supported on alumina cement and CaO have been produced by pelletisation. These oxygen carriers were investigated for their ability to convert gaseous fuels in a lab-scale fluidised bed, and characterised for their mechanical and chemical suitability in the CLC process. The modified ores and pelletised copper-based oxygen carriers’ mechanical properties were enhanced by their production methods and in the case of the modified iron ore, significant oxygen uncoupling was observed. The copper-based oxygen carriers particularly those containing alumina cement showed high conversion rates of gaseous fuels and improved mechanical stability. The second part of this research thesis focuses on the design philosophy, commissioning and operation of a dual-fast bed chemical looping pilot reactor. Based on the operational experience, recommendations for modifications to the CLC system are discussed. In support, a parallel hydrodynamic investigation has been conducted to validate control and operational strategies for the newlydesigned reactor system. It was determined that the two fast bed risers share similar density and pressure profiles. Stable global circulation rate is flexible and could be maintained despite being pneumatically controlled. Reactor-reactor leakage via the loop-seals is sensitive to loop seal bed-height, and inlet fluid velocity but can be maintained as such to ensure no leakage is encountered.

The upflow anaerobic sludge blanket (UASB) reactor is widely used around the world to treat variety of domestic andindustrial wastewater with three main advantages: production of biogas as renewable energy, no need of support structure for development of microorganisms and high rate treatment efficiency with low rate of biomass production. This study evaluates the effect of temperature on biogas production and CODtotal removal in Line 4-UASB system treating domestic wastewater in Hammarby Sjöstadsverk. Eight parameters were examined including the following: Influent and effluent temperature, pH, influent CODtotal, influent rate, effluent CODtotal, volatile fatty acids, biogas production rate and methane concentration. There are eight set temperature and each is stabilized for seven days. The biogas production analysis is focus on UASB 1. Temperature rising from 19°C to 35°C achieves a general benefit result in methane yield rate and CODtotal removal efficiency. The best methane yield rate and CODtotal removal rate are 0.167l/gCODtotal and 56.84% respectively at highest working temperature 33.4°C with OLR 3.072gCODtotal/(l*day) and HRT 4.2h.
Den ökande energiförbrukningen i världen och utsläpp av växthusgaser (GHG) gör det nödvändigt att söka nya hållbara energikällor för att matcha efterfrågan på energi i framtiden. Rötningsteknik med organiskt avfall som förnybar energikälla, ger biogas som i genomsnitt består av 78% CH4, 22% av CO2och spår av H2S (<0.5%), är en idealisk kostnadseffektiv metod. Den Uppåt flödande anaeroba slambäddsreaktorn(UASB) med största fördelarna: biogasproduktion som förnybar energi, hög belastning och hög behandlingseffektivitet med låg produktion av biomassa, inget behov av stödstruktur för utveckling av mikroorganismer, är den viktigaste typen för anaerobt reningssystem. Det finns flera faktorer som påverkar UASB-reaktorns prestanda, såsom temperatur, pH, HRT, Uppåtriktat flödeshastighet, OLR, SRT och VFA. I denna studie är huvudsyftet att med fokus på utvärdering av temperaturpåverkan på biogasproduktion och CODtotal avlägsnat i UASB-systemet Linje 4 som behandlar hushållsspillvatten i Hammarby Sjöstadsverk. Analysen avbiogasproduktionen fokuserades på UASB reaktor 1. Åtta parametrar övervakades för att kontrollera skick inklusive inflöde och utflöde, temperatur, pH, CODtotal inflöde, strömningshastighet för inflöde, CODtotal utflöde, flyktiga fettsyror VFA, biogasproduktionstakt och metankoncentration. Försöken utfördes vid åtta inställda temperaturnivåer och varje nivå stabiliserades i sju dagar. pH och VFA-värde var stabilt under hela försöket. Resultatetvisar att temperaturen har en större inverkan på metanavkastningen och CODtotal avlägsnat än belastningen, OLR. Då temperaturen höjs från 19°C till 35°C erhålls en större metanavkastning och större CODtotal avlägsnat. Den största metanavkastningen och CODtotal avlägsnat är 0,167l/g CODtotal respektive 56.84% vid den högsta arbetstemperaturen 33.4°C med OLR 3.072g CODtotal/(l * dag) och HRT 4.2h. Energibalansen vid olika arbetstemperaturer visaratt det finns en stor skillnad i energibehov för uppvärmning och utbyte avenergi i form av biogas. För att minska klimatpåverkan och nå balans mellan input och output av energi måste energibehovet för uppvärmning reduceras. Energiåtervinning från utflöde till inflöde liksom drift av UASB vid låg temperatur är ämnen som kan studeras vid fortsatt arbete.

Thesis (Doctor of Philosophy)--Case Western Reserve University, 2010
Department of Chemical Engineering Title from PDF (viewed on 2010-05-25) Includes abstract Includes bibliographical references and appendices Available online via the OhioLINK ETD Center

En la presente tesis doctoral se realiza un estudio detallado sobre el mecanismo de la reacción de reducción de oxígeno (ORR) en electrodos monocristalinos de platino. Para ello, se han realizado medidas electroquímicas usando la configuración de electrodo rotatorio de menisco colgante (HMRDE) con superficies con distinta estructura superficial y variando condiciones de la disolución de trabajo como el pH, fuerza iónica o la ausencia o presencia de bromuros. La conclusión principal que se extra de estos experimentos es la posibilidad de la existencia de un punto de bifurcación en el mecanismo, implicando el intermedio OOH, antes de la formación de peróxido de hidrógeno. Además, también se estudia la ORR y la reacción de oxidación de ácido fórmico en electrodos monocristalinos de Pt en presencia de acetonitrilo, como estudio previo al estudio de estas reacciones en disolventes orgánicos con pequeñas cantidades de agua. Por último, se estudia la ORR en un Aza-CMP, lo cual permite obtener información fundamental que se puede aplicar en estudios sobre el mecanismo de la ORR en los sitios activos de materiales de carbón funcionalizados con nitrógeno.

Ein Großteil der Lebensmittel wird in der heutigen Zeit vor allem aufgrund ihrer langen Haltbarkeit in Konservendosen verpackt. Zur Qualitätserhaltung des Lebensmittels werden Weißblechdosen im Innenbereich in der Regel mit einer Lackierung versehen. Lackrohstoffe sind dabei u. a. Phenol- und Epoxidharze, die als Basis- oder Vernetzerkomponente eingesetzt werden. Bei der Herstellung und Lagerung dieser Lebensmittel kann jedoch nicht ausgeschlossen werden, dass es zur Migration von Bestandteilen aus der Kunststoffinnenbeschichtung in das Füllgut kommt. Toxikologisch und somit auch analytisch sind dabei vor allem die migrierenden Verbindungen unter 1000 Da von Interesse, da Substanzen mit einer Molmasse von über 1000 Da nur zu weniger als 1 % im Gastrointestinaltrakt absorbiert werden. Analytik von phenolischen Verbindungen Bei Untersuchungen zur Migration phenolischer Verbindungen unter Verwendung verschiedener Modellcoatings und Simulanzlösemittel wurden Konzentrationen an migrierenden phenolischen Substanzen in Summe bis 160 µg/dm² bestimmt, womit dieser Gehalt deutlich unter dem gesetzlichen Grenzwert für die Gesamtmigration von 10 mg/dm² liegt. Die Quantifizierung erfolgte dabei über SEC-FLD-Kalibriergeraden der für diese Coatings verwendeten Phenolharze. Tendenziell steigt dabei die Menge an übergehenden Verbindungen mit abnehmender Polarität der verwendeten Simulanzien. Ebenso abhängig vom Lösungsmittel ist die Molekulargewichts¬verteilung der im Migrat enthaltenen Phenole. So zeigte sich eine deutliche Verschiebung der phenolischen Verbindungen zu höheren Molekulargewichten mit abnehmender Polarität der Simulanzlösemittel. Mit wenigen Ausnahmen besitzen jedoch alle migrierenden Substanzen eine Molmasse von unter 1000 Da. Das beobachtete Migrationsverhalten kann u. a. auf die unterschiedliche Reaktivität der phenolischen Basismonomere der Harze zurückgeführt werden, wodurch die Fähigkeit variiert, unter den Einbrennbedingungen ein ausgeprägtes Netzwerk zu bilden. Zur näheren Charakterisierung der Phenolharze wurden einzelne Hauptverbindungen der RP-HPLC-FLD-Chromatogramme identifiziert. Über Derivatisierungsreaktionen mit Picolinsäure, Essigsäureanhydrid sowie Dansylchlorid konnten Informationen zur Anzahl an alkoholischen und phenolischen Hydroxylgruppen im Molekül erhalten werden. Mit dem Wissen um die eingesetzten Phenolmonomere und einer eventuellen Veretherung konnten Strukturvorschläge erstellt werden. Die Quantifizierung der migrierenden phenolischen Verbindungen in Migraten kommerzieller Coatings in Summe wurde über eine universell anwendbare Kalibrierung angestrebt. Dazu wurden 17 verschiedene Phenolharze bezüglich der Steigung der SEC-FLD-Kalibriergeraden, des mittleren Molekulargewichtes, der Hydroxylzahl und dem Verhältnis OH-Gruppen/Molekül charakterisiert. Wie erwartet steigt mit wenigen Ausnahmen die Anzahl der OH-Gruppen im Molekül tendenziell mit dem mittleren Molekulargewicht. Es zeigte sich zudem, dass die verschiedenen Phenolharze in ihren fluorophoren Eigenschaften stark variieren. Die Steigung der SEC-FLD-Kalibriergeraden konnte zudem in keine Korrelation mit einem anderen ermittelten Parameter gebracht werden. Die Anwendung einer universellen Kalibriergerade zur Quantifizierung war deshalb nicht möglich. Die Größenordnungen der Migratkonzentrationen konnten daher nur über die zwei im Anstieg am stärksten variierenden SEC-FLD-Kalibriergeraden abgeschätzt werden. Bei der Analyse kommerzieller Epoxy-Phenol-Coatings war im Gegensatz zu Polyester-Phenol-Coatings die isolierte Detektion der phenolischen Verbindungen im Migrat mittels Fluoreszenz nicht möglich, da sowohl Epoxide als auch Phenole fluorophorer Eigenschaft besitzen. Es wurde daher eine Methode zur Abtrennung der Phenole von anderen im Migrat enthaltenen Subtanzen auf Basis eines Anionenaustauschermaterials entwickelt. Dabei wurde die Eigenschaft der Phenole genutzt, im basischen Milieu Phenolate zu bilden. Diese, aber auch Säuren adsorbieren am Austauschermaterial, während Epoxide oder Polyester nicht retardiert werden. Für zwei kommerzielle Epoxy-Phenol-Coatings konnte somit der Anteil an phenolischen Verbindungen im Migrat zu 7 und 28 % bestimmt werden. Mittels RP-HPLC/ESI-MS war es möglich, einige der phenolischen Verbindungen in diesen Migraten zu identifizieren. Dabei handelt es sich um nichtepoxidierte BPA-Derivate der Epoxidkomponente des Coatings, die aufgrund des BPA-Grundkörpers eine phenolische Hydroxylgruppe besitzen. Phenolische Vernetzungsprodukte beider Basisharze konnten dagegen nicht identifiziert werden. Die Menge an migrierenden phenolischen Verbindungen der beiden Epoxy-Phenol-Coatings konnte über die Kalibration eines niedermolekularen Epoxidharzes zu 0,1 mg/dm² bzw. 0,27 mg/dm² abgeschätzt werden. Während für einzelne phenolische Verbindungen gesetzliche Grenzwerte für die Migration bestehen, gibt es für Oligomere, mit Ausnahme von BPA keine spezifischen Migrationslimits. Ebenso sind in der Literatur kaum toxikologische Untersuchungen zu Phenololigomeren zu finden. Um einen ersten Einblick in die toxikologische Relevanz migrierender phenolischer Verbindungen zu erhalten, wurden mehrere kommerzielle als auch selbst synthetisierte phenolische Standardsubstanzen und verschiedene Molekulargewichtsfraktionen eines Phenolharzes, im Fischembryotest an Eiern des Zebrabärblings (Brachydanio rerio) nach DIN 38415-T647 und/oder Neutralrottest an Hep-G2 und HT-29 Zellen untersucht. Die stärksten Effekte im Fischembryotest bewirkte das Trimer BPM, hier reichte bereits eine Konzentration von etwa 2 mg/l aus, um 50 % der Fischembryonen letal zu schädigen. Im Gegensatz dazu waren beim Dimer 5-Hydroxymethyl-2,4´-dihydroxydiphenylmethan (M 230) mit einem EC50-Wert von 170 mg/l die geringste toxikologische Wirkung zu beobachten. Für alle anderen Subtanzen konnten EC50-Werte im Bereich 20 - 100 mg/l bestimmt werden. Tendenziell zeichnete sich dabei eine Zunahme der EC50-Werte mit steigender Lipophilie, ausgedrückt über den KOW-Wert ab, was auf den Aufbau der Fischeier zurückzuführen ist. So müssen die zu untersuchenden Xenobiotika mehrere lipophile Membranen durchdringen, um am eigentlichen Wirkungsort Einfluss auf die Embryonalentwicklung nehmen zu können. Im Zelltest konnten tendenziell ähnliche Ergebnisse ermittelt werden wie im Fischembryotest, wobei in der Regel die Hep-G2 Zellen empfindlicher reagieren als die HT-29 Zellen. Während für Phenol im untersuchten Konzentrationsbereich keine toxischen Effekte beobachtet werden konnten, liegen die EC50-Werte für das Trimer BPM, analog zum Fischembryotest deutlich unter 10 mg/l. Für die anderen Verbindungen wurden EC50-Werte zwischen 16 und 100 mg/l bestimmt. Analog zu den Untersuchungen der Einzelsubstanzen zeigte sich auch bei den 5 untersuchten Molekulargewichtsfraktionen zwischen 0 und 1000 Da, dass das toxikologische Potential im niedermolekularen Bereich (0 - 200 Da) gegenüber den Fraktionen 200 400 und 400 600 Da vergleichsweise gering ist. Bereits 25,1 mg/l bzw. 17,3 mg/l der Fraktionen 200 400 Da und 400 600 Da waren in den Tests ausreichend, um alle Embryonen letal zu schädigen. Im Molekulargewichtsbereich über 600 Da konnten dagegen lediglich subletale oder gar keine Missbildungen beobachtet werden. Analytik von Epoxiden In der amtlichen Überwachung beschränkt sich die Analytik von Epoxidverbindungen bisher auf die Bestimmung rechtlich geregelter Einzelsubstanzen. Eine Summenmethode zur Erfassung aller in einem Migrat enthaltenen Substanzen mit reaktionsfähigen Oxirangruppen, wodurch das gesamte Reaktionspotential erfasst werden kann, liegt dagegen nicht vor. Zur selektiven Erfassung aller oxirangruppenhaltigen Verbindungen wurde daher mittels statistischer Versuchsplanung eine Derivatisierung mittels Cysteamin entwickelt. Die Reaktion mit Cysteamin erfolgt dabei nach Abtrennung der Substanzen &gt; 1000 Da mittels Größenausschlusschromatographie. Im Anschluss werden die Derivate durch Zugabe eines Kationenaustauschers aus der Lösung entfernt. Durch den Vergleich der RP-HPLC-FLD Chromatogramme vor und nach der Aufarbeitung können Substanzen mit intakten Oxirangruppen somit einfach erkannt werden. Eine quantitative Abschätzung der enthaltenen Epoxidverbindungen ist bei Lacken auf Basis von BPA-Harzen über die BPA-Chromophorkonzentration möglich. Bei der Untersuchung von 5 kommerziellen Coatings wurden in den einzelnen Migraten recht unterschiedliche Gehalte an Substanzen mit intakten Epoxidgruppen ermittelt. Ebenso ist die Anzahl der oxriangruppenhaltigen Verbindungen, auf die sich dieser Gehalt verteilt sehr unterschiedlich, was möglicherweise an unterschiedlichen Einbrennzeiten, -temperaturen aber auch der Menge an Lack pro m² und an der Art und Menge des Reaktionspartners liegt. Für die Konzentration der epoxidischen Verbindungen in den Coatingmigraten wurden Werte zwischen 18,5 und 835 µg/dm² bestimmt. Dies entspricht einem Anteil der reaktionsfähigen Substanzen an der Fraktion unter 1000 Da berechnet über die Flächen im Chromatogramm zwischen 2,6 und 76,3 %. Neben dem Einsatz als Basismaterial für Konservendoseninnenbeschichtungen werden Epoxidharzsysteme auch in Zubereitungen wie Grundierungen, Füllmassen, Lacken oder Klebstoffen für die Bauchemie vielfach in verschiedenen Mischungen (aromatische, aliphatische oder cycloaliphatische Glycidylether bzw. Siloxanglycidylether) eingesetzt. Durch den Kontakt dieser Materialien mit der Haut kann es zu Kontaktekzemen kommen, deren Ursache durch Epikutantests (Patchtests) mit den potentiell auslösenden Substanzen ermittelt werden kann. Der Umfang der in den Standardtestsystemen enthalten Testsubstanzen entspricht dabei jedoch nicht dem Spektrum der in der Industrie verwendeten Materialien. Über die genaue Zusammensetzung der in den Patchtest´s eingesetzten Materialien ist zudem wenig bekannt. Durch die Analyse einer Vielzahl von Patchtestsubstanzen und industriellen Epoxidkomponenten mittels RP-HPLC/UVD bzw. -ELSD Chromatographie und die Identifizierung der enthaltenen Verbindungen über RP-HPLC/ESI-MSD, konnte ein genaueres Bild über den Charakter dieser Materialen gewonnen werden. Bei den BPA- und BPF-Harzen wurden überwiegend Monomere, die entsprechenden Di- und Trimere aber auch dessen hydrolysierte Verbindungen identifiziert. Im Gegensatz dazu liegen bei den analysierten aliphatischen Produkten z. T. die reinen Glycidylether gar nicht oder nur in geringen prozentualen Anteilen vor. Vielmehr wird durch die sauer geführte Reaktion bei den aliphatischen Verbindungen die Bildung von 1,3 Chlorhydrinen als Nebenreaktion zur 1,2 Chlorhydrinbildung gefördert, wodurch eine beträchtliche Menge an Substanzen, die nicht verseifbares Chlor enthalten, in den Materialien vorhanden ist. Um die enthaltenen Verbindungen von aliphatischen und cycloaliphatischen Epoxidzubereitungen quantifizieren zu können, wurde eine Derivatisierung mit einem selbst synthetisierten Fluorophor (5-(Dimethylamino)-N-(2-mercaptoethyl)-1-naphthalen-sulfonamid) entwickelt. Dadurch konnten auch Verbindungen erfasst werden, die aufgrund ihrer Flüchtigkeit mittels ELSD nicht detektierbar waren. Bei der Analyse von Handelsprodukten zeigte sich, dass die einzelnen Komponenten in ihrer Zusammensetzung gut mit den untersuchten aromatischen und aliphatischen Rohmaterialien vergleichbar sind. Bei entsprechend eingesetzten Patchtestsubstanzen spiegeln diese somit die Produkte gut wieder, mit denen die Patienten in Kontakt kommen.

Les oxydes de manganèse présentent un grand intérêt en raison de leur activité catalytique pour l'ORR (la réaction de réduction de l’oxygène) en milieu alcalin et peuvent être utilisés comme matériaux sans métaux nobles pour la cathode dans les piles à combustible. La présente thèse est consacrée à l’étude de l’activité d'oxydes de manganèse pour l’ORR. Il a été montré que Mn2O3 avec structure bixbyite a une meilleure activité catalytique vers l'ORR en milieu alcalin que les autres oxydes de manganèse étudiés. L'activité spécifique de Mn2O3 est seulement 4 fois inférieure à celle de Pt à une surtension de 0.3 V (ERH). Le lien entre la structure des oxydes de Mn et l'activité ORR est identifié: l'activité spécifique augmente exponentiellement avec le potentiel du couple redox Mn(III)/Mn(IV) de surface. Pour assurer l'activité électrocatalytique élevée de Mn2O3, il est nécessaire d'ajouter du carbone à la composition d'électrode, ainsi que de garder un potentiel supérieur à 0.7 V (ERH)
Manganese oxides are of great interest due to their catalytic activity towards the ORR (the oxygen reduction reaction) in alkaline media and can be used as noble metal-free materials for the cathode in liquid and polymer electrolyte alkaline fuel cells. The present thesis is devoted to the investigation of the ORR activity of manganese oxides. It was shown that Mn2O3 with bixbyite structure has a better catalytic activity toward the ORR in alkaline media than other investigated manganese oxide, the surface activity of Mn2O3 is only 4 times lower than that of Pt at an overvoltage of 0.3 V (RHE). The link between the structure of Mn oxides and the ORR activity is found: the specific ORR activity exponentially increases with the potential of the surface Mn(III)/Mn(IV) red-ox couple. To ensure the high electrocatalytic activity of Mn2O3, it is necessary to add carbon to the electrode composition, as well as to keep potential above 0.7 V (RHE)

Adaptive video streaming is perpetually influenced by unpredictable network conditions, whichcauses playback interruptions like stalling, rebuffering and video bit rate fluctuations. Thisleads to potential degradation of end-user Quality of Experience (QoE) and may make userchurn from the service. Video QoE modelling that precisely predicts the end users QoE underthese unstable conditions is taken into consideration quickly. The root cause analysis for thesedegradations is required for the service provider. These sudden changes in trend are not visiblefrom monitoring the data from the underlying network service. Thus, this is challenging toknow this change and model the instantaneous QoE. For this modelling continuous time, QoEratings are taken into consideration rather than the overall end QoE rating per video. To reducethe user risk of churning the network providers should give the best quality to the users. In this thesis, we proposed the QoE modelling to analyze the user reactions change over timeusing machine learning models. The machine learning models are used to predict the QoEratings and change patterns in ratings. We test the model on video Quality dataset availablepublicly which contains the user subjective QoE ratings for the network distortions. M5P modeltree algorithm is used for the prediction of user ratings over time. M5P model gives themathematical equations and leads to more insights by given equations. Results of the algorithmshow that model tree is a good approach for the prediction of the continuous QoE and to detectchange points of ratings. It is shown that to which extent these algorithms are used to estimatechanges. The analysis of model provides valuable insights by analyzing exponential transitionsbetween different level of predicted ratings. The outcome provided by the analysis explains theuser behavior when the quality decreases the user ratings decrease faster than the increase inquality with time. The earlier work on the exponential transitions of instantaneous QoE overtime is supported by the model tree to the user reaction to sudden changes such as video freezes.

Ce travail apporte de nouvelles contraintes sur les interactions entre déformation et processus d'hydratation et de percolation de magma ou de fluides et leurs implications sur les propriétés sismiques dans le coin mantellique. Il se base sur l'analyse de péridotites à spinelle provenant du massif de Ronda (Espagne) et deux séries de xénolites issues de zones de subduction actives (Kamchatka, Papouasie-Nouvelle-Guinée). L'étude structurale, pétrologique et géochimique de ces échantillons montrent qu'ils ont subi une percolation réactive de magma ou de fluide synchrone d'une déformation de haute température basse contrainte cohérente avec les condition PT de la base de la lithosphère ou de l'asthénosphère. Cette percolation réactive est responsable d'un enrichissement en pyroxènes localisés dans des bandes parallèles aux structures de déformation. Cet enrichissement est associé à la décroissance et à la désorientation des cristaux d'olivine. Le système de glissement dominant dans l'olivine est {0kl}[100], cela implique que la direction de polarisation rapide des ondes S dans la partie supérieure du coin mantellique est parallèle à la direction d'écoulement du manteau. L'enrichissement en pyroxène associé à une décroissance de l'intensité des OPR de l'olivine a pour conséquence une baisse non négligeable de l'anisotropie qui peut induire jusqu'à 33% d'erreur sur l'interprétation de la couche anisotrope. Un enrichissement en orthopyroxène peut entraîner une baisse du rapport Vp/Vs, mais ne peut expliquer des Vp/Vs <1,7 cartés dans certains avant-arcs. Cependant de telles valeurs peuvent être expliquées si l'anisotropie des péridotites du coin mantellique est prise en compte
This work provides new constraints on the interactions between deformation and hydration process and the percolation of melt or fluids, and their implications for seismic properties of the mantle wedge. It is based on the analysis of spinel peridotites from the massif of Ronda (Spain) and two xenolith suites from active subduction zones (Kamchatka, Papua New Guinea). The structural, petrological and geochemical of these samples show that they underwent a reactive percolation of melt or fluid, which was synchronous to a deformation event occuring under high temperature and low stress consistent with the PT conditions of the base of the lithosphere or in the asthenosphere. This reactive percolation is responsible for pyroxenes enrichment localized in bands parallel to the deformation structures. This enrichment is associated with the grain size recuction and the disorientation of the crystals of olivine. The dominant slip system in olivine is {0 kl}[100], which results in fast S-wave polarization parallel to the flow direction in the mantle. The enrichment in pyroxene, associated with a decrease in the intensity of the olivine crystal preferred orientations, results in a significant decrease of the anisotropy that may induce error on the interpretation of the anisotropic layer (up to 33%). The observed orthopyroxene enrichment also lowers the Vp/Vs ratio, but cannot explain Vp/Vs < 1.7 mapped in some fore-arc mantles. Such low Vp/Vs ratios may however be explained by considering the intrinsic anisotropy of the peridotites, which is generally ignored in large-scale Vp/Vs ratio mapping of the mantle wedge

La fabrication de matériaux hybrides, combinant sans les altérer les propriétés de leurs différents constituants, est au cœur de la recherche en nanosciences. Parmi les différents types de nanomatériaux envisagés à cette fin, les nanotubes de carbone sont des objets prometteurs en raison de leurs propriétés optiques, de conductivité et de leur fonctionnalisation, pour la catalyse, l’électronique et l’optoélectronique. Dans la première partie de cette thèse, des structures hybrides supramoléculaires à base de nanotubes de carbone multi-parois et de macrocycles (porphyrines, phtalocyanine ou corrole) de cobalt et/ou de fer ont été formées et testées comme catalyseurs pour la réduction du dioxygène. La méthode de fonctionnalisation non covalente employée (couplage de Hay et click-chemistry) préserve au mieux les propriétés électroniques des nanotubes et assure la stabilité de l’assemblage obtenu. Grâce à leurs propriétés d’émission dans la région proche infrarouge, les nanotubes de carbone mono-paroi présentent un intérêt en optique et en optoélectronique. Cependant, leur extrême sensibilité au milieu les environnant entrave leur utilisation. La fabrication de matériaux hybrides, préservant leur propriété optique et facilitant leur manipulation est alors primordiale. La deuxième partie de cette thèse est consacrée à la fonctionnalisation de nanotubes de carbone mono-paroi en vue de leur utilisation en optoélectronique. A cet effet, une synthèse de coquille, composée de polymères amphiphiles, protégeant les nanotubes de carbone de leur environnement et facilitant leur solubilité en milieu aqueux, sera réalisée
The production of hybrid materials, combining the properties of their different building blocks without altering them, is a central issue of nanoscience. Among the different classes of nanomaterials being considered for this purpose, carbon nanotubes are an outstanding class of materials due to their optical, conductivity and their functionalization properties, that can be used for various applications in catalysis, electronics and optoelectronics. In the first part of this thesis, supramolecular hybrid structures based on multi-walled carbon nanotubes and macrocycles (porphyrins, phthalocyanine or corrole) containing cobalt and/or iron ions have been performed and tested as catalysts for oxygen reduction reaction (ORR). The non-covalent functionalization methods (based on either Hay-coupling or click chemistry) preserve the electronic properties of the nanotubes and enhances the stability of the resulting hybrids. Thanks to their emission properties in the near infrared region, single-walled carbon nanotubes are of peculiar interest in optoelectronics. However, their extreme sensitivity to the surrounding environment hinders their application. The production of hybrid materials that preserve their optical properties and facilitate their handling is therefore a key challenge. The second part of this PhD is dedicated to the functionalization of single-walled carbon nanotubes for optoelectronics. To this end, it is necessary to carry the synthesis of a core-shell structures, composed of amphiphilic copolymers protecting the carbon nanotubes from their environment and facilitating their solubility in aqueous medium

Un des principaux défis lors de l'élaboration des catalyseurs adéquats pour le procédé de déparaffinage catalytique (hydroisomérisation) est de maximiser le rendement en isomères et l'activité du catalyseur, tout en maintenant une faible sélectivité en produits de craquage. En effet, des catalyseurs avec sélectivité de forme à base de zéolithes à taille de pore intermédiaire, par exemple Pt/ZSM-22, sont sélectives en isomères, tandis que les zéolithes à large pore sont plus actifs, mais moins sélectif. L'objectif principal de cette thèse était, alors, d’étudier et de développer un catalyseur à la fois actif et sélectif en isomères. Deux études parallèles ont été realisées: la première basée sur l'impact de la proximité entre les sites actifs sur la réaction (Part I), et la seconde, portant sur le développement d'un catalyseur d'hydroisomérisation de haute performance en utilisant des nanocristaux de zéolithe BEA comme support acide (Part II). La participation de l’épandage d’hydrogène (Hsp) sur le mécanisme de la réaction d'hydroisomérisation a été démontrée. En effet, lorsque les sites actifs sont proches, les espèces Hsp diffusent au voisinage des sites acides provocant l'hydrogénation directe des ions carbénium. Un mécanisme de réaction a, alors, été proposé utilisant ce phénomène comme une alternative au mécanisme classique proposé par Weisz, où la réaction d'hydrogénation a lieu uniquement sur les sites métalliques. Ce phénomène justifie l'activité et la sélectivité plus élevées observées sur les catalyseurs, où les sites actifs sont proches. Sur la deuxième partie de ce manuscrit, des nanocristaux de zéolithe BEA ont été utilisés pour développer un catalyseur d’hy
One of the main challenges when developing adequate catalysts for the catalytic dewaxing process (hydroisomerization) is to maximize the isomerization products yield and the catalyst activity, while maintaining a low selectivity towards light cracking products. Indeed, shape selective catalysts based on medium pore zeolites, e.g. Pt/ZSM-22, were proven to produce high yields of isomerization products, whereas larger pore zeolites were more active but less selective. The main objective of this thesis was, then, to study and develop a catalyst with both high activity and selectivity towards the production of isomerization products. For that two parallel studies were made: the first based on the impact of the proximity between the active sites on the reaction (Part I); and the second, focused on the development of a high performance hydroisomerization catalyst using BEA zeolite nanocrystals as an acid support (Part II). The participation of the spilt-over hydrogen (Hsp) species on the hydroisomerization reaction mechanism played a major role on the study performed on the first part of this manuscript. Indeed, when the active sites were near enough the Hsp species were able to diffuse into the vicinity of the acid sites promoting the direct hydrogenation of the carbenium ions. Due to this fact, a reaction mechanism was proposed using this reaction as an alternative to the classical mechanism proposed by Weisz, where the hydrogenation reaction takes place on the metallic sites. This phenomenon justified the higher activity and selectivity observed on the catalysts where the active sites were sideby side. On the second part of this manuscript nanocrystals of BEA zeolite were

Syfte: Är att ta reda på om man med hjälp av immunhistokemi (IHC) med infärgning avantikroppar mot laminin-5 och C3d kan särskilja mellan slemhinnepemfigoid (MMP) ochorala lichenoida reaktioner (OLR) med epitelsläpp. Vidare undersöks graden inflammation för MMP och OLR för att fastställa om det går att se ett samband mellan grad av inflammation och antikroppsinfärgning.Material och metod: En pilotstudie utfördes på 10 prover med diagnosen MMP respektive 9 prover med OLR, som hämtades från Malmö universitets biobank. Proverna genomgickrutinfärgning respektive antikroppsinfärgning mot laminin-5 och C3d. Granskning av prover skedde i digitalmikroskop. Efteråt delades proverna in i grupper efter var infärgningen sågs. Sammanställning gjordes i Excel med stapeldiagram.Resultat: Ingen tendens till särskiljning ses mellan MMP och OLR avseende infärgning mot laminin-5 och C3d. Positiva utslag för infärgning mot Laminin-5 ses enhetligt på enbart en sida om epitelsläppet hos både snitten för MMP och OLR. Vidare kan det inte ses att snitt med diagnosen OLR har slumpartad infärgning mot laminin-5 på båda sidor om släppet. Det finns en tendens till att MMP-snitt får mer positiva utslag för infärgning mot C3d än för OLR snitt. Graden inflammation var högre i OLR snitt än för MMP snitt.Slutsats: Enligt studien går det inte att, med IHC, med infärgning av antikroppar mot laminin5 och C3d, kunna särskilja MMP och OLR med epitelsläpp. Större urval krävs för definitiva slutsatser. Vidare studier behövs för att utreda om det går att använda IHC för att särskilja MMP och OLR.Nyckelord: C3d, immunhistokemi (IHC), laminin-5, orala lichenoida reaktioner (OLR),slemhinnepemfigoid (MMP)
Aim: To investigate if it is possible to differentiate between the diagnoses mucous membrane pemphigoid (MMP) and oral lichenoid reactions (OLR) with epithelial detachment using immunohistochemistry (IHC) with antibodies against laminin-5 and C3d. Furthermore, the extent of inflammation was examined for MMP and OLR to determine if a correlation between the inflammation and immunostaining is evident.Material and method: A pilot study is conducted using 10 samples diagnosed with MMP and 9 samples diagnosed with OLR, collected from Malmö University’s biobank. H&E staining and immunostaining against laminin-5 and C3d is performed on the samples. Analysis is conducted using a microscope. Samples are then divided into groups depending on the staining. Excel is used to compile the results.Result: No differentiating tendencies are observed between MMP and OLR regardingimmunostaining against laminin-5 and C3d. Immunostaining against laminin-5 is positive for MMP and OLR and is seen continuously on only one side of the epithelial detachment.Furthermore, staining with laminin-5 is not seen as random staining on both sides of theepithelial detachment. Samples with MMP have a higher tendency to stain against C3dcompared to OLR samples. Inflammation is higher in OLR samples than those for MMP.Conclusion: According to this study it is not possible to differentiate between the diagnoses MMP and OLR with epithelial detachment using immunostaining against laminin-5 and C3d. A larger sample size is needed for a definitive conclusion. Additionally, further studies are required to conclude if IHC can be used to differentiate between MMP and OLR.Keywords: C3d, immunohistochemistry (IHC), laminin-5, mucous membrane pemphigoid(MMP), oral lichenoid reactions (OLR)

Background: Obesity-related diseases are arising as a major problem among children. inflammation has recently been identified to play an important role in the relationship between obesity.- as well as stunting-related diseases. Objectives: The aim of this study was to assess the association between serum tumour necrosis factor-alpha (TNF-α), interleukin-6 (IL-6) and C-reactive protein (CRP) concentrations and a variety of cardiometabolic and anthropometric indices of children in a township outside Potchefstroom, South Africa. Methods: Blood samples of 115 girls and 78 boys (mean age 15.6 ± 1.35) in the Physical Activity in the Young (PLAY) study were cross-sectionally analysed. Trained fieldworkers collected the demographic, Tanner growth stage and habitual physical activity information. Physiologists measured the children’s blood pressure. Anthropometric measurements were taken by. trained post-graduate students with level 1 or 2 qualifications in anthropometrics. A standard test battery was administered by trained postgraduate students in Human Movement Science to assess muscular strength. flexibility and endurance of the children. Blood samples were collected, centrifuged and stored frozen until further analyses. Results: Stunted girls had a significantly higher serum TNF-α concentration than the non-stunted girls (p=0.03). The factor analyses showed that the inflammatory. status clustered with the height for age-z-scores (HAZ) scores and the waist-hip-ratio (WHR). The HAZ-score of the over-fat boys (- 1.46) was significantly smaller than the lean boys (- 1.14, p=0.0 1). whereas the over-fat girls had a trend for a smaller HAZ-score (-1.07) than the lean girls (-0.89). No significant differences were found between the over-fat and the lean children-s inflammatory status. TNF-α and CRP levels tended to be higher in the over-fat children than in lean children. The girls' scrum IL-6 and CRP concentrations correlated significantly with their body mass index (BMI) and WHR (p<0.05 )and their TNF-α and IL-6 concentrations correlated significantly with their WHR (p<0.01 and p<0.05, respectively). Conclusion: In comparison to the non-stunted girls, stunted girls had a statistically significantly higher TNF-α concentration. Unusual fat distribution that is found in over-fat and stunted children may be associated with low-grade inflammation in children. More research is needed on these associations with markers of inflammation in a long-term longitudinal study.
Thesis (M.Sc. (Nutrition))--North-West University, Potchefstroom Campus, 2007.

Limited knowledge of the neuromechanical response to use of an ankle foot orthosis-footwear combination (AFO-FC) has created a lack of consensus in understanding orthotic motion control as a therapeutic treatment. Lack of consensus may hinder the clinician’s ability to target the motion control needs of persons with movement impairment (e.g., peripheral nerve injury, stroke, etc.). Some evidence suggests a proportional relationship between joint motion and neuromuscular activity based on the notion that use of lower limb orthoses that constrain joint motion may invoke motor slacking and decreasing levels of muscle activity. Use of AFO-FCs likely alters the biomechanical and neuromuscular output as the central control system gradually forms new movement patterns. If there is proportional relationship between muscle activation and joint motion, then it could be examined by quantifying joint motion and subsequent neuromuscular output. Considering principles of neuromechanical adjustment, my general hypothesis examines whether orthotic control of lower limb motion alters neuromuscular output in proportion to the biomechanical output as a representation of the limb’s dynamics are updated by the neural control system. The rationale for this approach is that reference knowledge of the neuromechanical response is needed to inform clinicians about how a person responds to walking with motion controlling devices such as ankle foot orthoses combined with footwear. In the first line of research, I hypothesize that a newly developed AFO which maximizes leverage and stiffness will constrain the talocrural joint and alter joint kinematics and ground reaction force patterns. To answer the hypothesis, I sampled kinematics and kinetics of healthy subjects’ treadmill walking using an AFO-FC in a STOP condition and confirmed that the AFO substantially limited the range of talocrural plantarflexion and dorsiflexion motion to 3.7° and in a FREE condition maintained talocrural motion to 24.2° compared to 27.7° in a CONTROL (no AFO) condition. A follow up controlled static loading study sampled kinematics of matched healthy subjects limbs and cadaveric limbs in the AFO STOP and FREE conditions. Findings revealed healthy and cadaveric limbs in the AFO STOP condition substantially limited their limb segment motion similar to matched healthy subjects walking in the STOP condition and in the AFO FREE condition healthy and cadaveric limbs maintained similar limb segment motion to matched healthy subjects walking in the FREE condition. In a second line of research, I hypothesize that flexibility of a newly developed footwear system will allow normal walking kinetics due to the shape and flexibility of the footwear. To answer the hypothesis, I utilized a curved-flexible footwear system integrated with an AFO in a STOP condition and sampled kinematics and kinetics of healthy subjects during treadmill walking. Results revealed subjects elicited similar cadence, stance and swing duration and effective leg-ankle-foot roll over radius compared to walking in the curved-flexible footwear integrated with the AFO in a FREE condition and a CONTROL (no AFO) condition. To validate rollover dynamics of the curved-flexible footwear system, a follow up study of healthy subjects’ treadmill walking in newly developed flat-rigid footwear system integrated with the AFO in a STOP condition revealed interrupted leg-ankle-foot rollover compared to walking in curved-flexible footwear in STOP, FREE and CONTROL conditions. In a third line of research, I hypothesize that use of an AFO that limits talocrural motion in a STOP condition will proportionally reduce activation of Tibialis Anterior, Soleus, Medial and Lateral Gastrocnemii muscles compared to a FREE and CONTROL condition due to alterations in length dependent representation of the limb’s dynamics undergoing updates to the central control system that modify the pattern of motor output. To answer the question, the same subjects and AFO-footwear presented in the first two lines of research were used in a treadmill walking protocol in STOP, FREE, and CONTROL conditions. Findings revealed the same subjects and ipsilateral AFO-footwear system presented in Aim 1 exhibited an immediate yet moderate 30% decline in EMG activity of ipsilateral Soleus (SOL), Medial Gastrocnemius (MG) and Lateral Gastrocnemius (LG) muscles in the STOP condition compared to the CONTROL condition. The reduction in EMG activity in ipsilateral SOL, MG and LG muscles continued to gradually decline during 15 minutes of treadmill walking. On the contralateral leg, there was an immediate yet small increase of 1% to 14% in EMG activity in SOL, MG, LG muscles above baseline. After 10 minutes of walking, the EMG activity in contralateral SOL, MG and LG declined to a baseline level similar to the EMG activity in the contralateral CONTROL condition. These collective findings provide compelling evidence that the moderate 30% reduction in muscle activation exhibited by subjects as they experience substantial (85%) constraint of total talocrural motion in the AFO STOP condition is not proportionally equivalent. Further, the immediate decrease in muscle activation may be due to a reactive feedback mechanism whereas the continued decline may in part be explained by a feedforward mechanism. The clinical relevance of these findings suggests that short term use of orthotic constraint of talocrural motion in healthy subjects does not substantially reduce muscle activation. These preliminary findings could be used to inform the development of orthoses and footwear as therapeutic motion control treatments in the development of motor rehabilitation protocols.

Neste trabalho foi estudada a atividade eletrocatalítica dos eletrocatalisadores nanoestruturados de Ru, Ir, Hf ou La suportados em carbono Printex 6L frente à Reação de Redução de Oxigênio (RRO) em meio ácido. Inicialmente analisou-se a influência do Método de Impregnação e dos Precursores Poliméricos (MPP), também conhecido como Pechini para os eletrocatalisadores RuO2/C e IrO2/C. Ficou evidente neste estudo, que os materiais obtidos pelo MPP apresentaram uma maior eficiência de corrente para a eletrogeração de H2O2 quando comparado ao método da Impregnação. Na etapa seguinte, os eletrocatalisadores HfO2/C e LaONO3/C foram preparados apenas pelo MPP. As propriedades estruturais, morfológicas e de superfície foram investigadas por meio das técnicas de caracterização DRX, FRX, MET, XPS e TG. De acordo com os dados de DRX e MET, verificou-se que o método de incorporação do metal no carbono Printex 6L favoreceu a formação dos óxidos nanoestruturados. Ademais, foi verificado que os eletrocatalisadores obtidos pelo método de Pechini apresentam menores tamanho de cristalitos (1 a 5 nm), melhor distribuição dos óxidos sobre a matriz de carbono (menos aglomerados) e menores tamanhos de partículas. O comportamento eletroquímico dos eletrocatalisadores foi avaliado através das voltametrias lineares (curvas de polarização) obtidas pelo eletrodo de disco anel rotatório (RRDE). Os resultados obtidos pelas voltametrias lineares, cálculos de eficiência de corrente de H2O2 (H2O2 %), número total de elétrons trocados (nt) e de Koutecký-Levich mostraram que a incorporação dos eletrocatalisadores (Ru e Ir) no carbono Printex 6L obtidos por ambos os métodos de síntese influenciaram negativamente na eletrogeração de H2O2. Neste caso, os eletrocatalisadores de Ru e Ir apresentaram uma tendência ao mecanismo via 4 elétrons, ou seja, geração de H2O como produto final da RRO. Os resultados mostraram ainda que os eletrocatalisadores contendo maiores teores de Hf, apresentaram maiores eficiência de corrente para H2O2 quando comparado ao carbono Printex 6L, uma vez que o catalisador contendo 15 % de Hf apresentou valores de eficiência de corrente de H2O2 próximos a 80 % e número de elétrons de 2,4. Além disso, foi observado também um deslocamento no potencial de aproximadamente 200 mV para valores mais positivos, o que significa um menor consumo energético em termos de eletrogeração de H2O2. Para os eletrocatalisadores à base de La, a amostra contendo 7% apresentou uma melhor eficiência de corrente de H2O2, com valores próximos a 87% e número de elétrons de 2,3, além de um deslocamento do potencial de aproximadamente 250 mV para valores mais positivos. Pode-se inferir então, que os eletrocatalisadores de Hf e La obtidos pelo método de Pechini são promissores para utilização em Eletrodos de Difusão Gasosa (EDG) visando a eletrogeração in situ de H2O2, visto que apresentam uma tendência a mecanismo via 2 elétrons.
In the present work, the electrocatalytic activity of nanostructured electrocatalysts based on Ru, Ir, Hf or La supported in Printex L6 front of Oxygen Reduction Reaction (ORR) in an acid medium were studied. Initially, the influence of impregnation methods and polymeric precursors (MPP), also known as Pechini for the electrocatalysts RuO2/C and IrO2/C, was analyzed. It was evidenced in this study, that the materials obtained by MPP presented bigger efficiency for H2O2 electrogeneration when compared to the impregnation method. In the following stage, the electrocatalysts HfO2/C and LaONO3/C were prepared only by MPP. The structural properties and surface morphology were investigated by means of the characterization techniques DRX, FRX, TEM, XPS and TG. According to the XRD and TEM data, it was found that the method of metal incorporation in Printex 6L carbon promoted the formation of nanostructured oxides. Moreover, it was verified that the electrocatalysts obtained by Pechini\'s method presented smaller crystallite size (1 to 5 nm), better distribution of the oxides on the carbon matrix (fewer clusters) and smaller particle sizes. The electrochemical behavior of the electrocatalysts were evaluated by linear voltammetry (polarization curves) obtained by rotating ring-disk electrode (RRDE). The results obtained by linear voltammetry, calculations of current efficiency of H2O2 (H2O2 %), total number of exchanged electrons (nt) and of Koutecký-Levich showed that the incorporation of the electrocatalysts (Ru and Ir) in Printex 6L carbon obtained by both methods of synthesis influenced negatively on the electrogeneration of H2O2. In that case, the Ru and Ir electrocatalysts showed a tendency to a 4 electrons mechanism, that is, generation of H2O as final product of the ORR. The results also showed that the electrocatalysts containing higher Hf content, presented higher current efficiency for H2O2 when compared to carbon Printex L6, since that the catalyst containing 15% of Hf presented values of current efficiency for H2O2 around 80% and number of electrons of 2.4. Furthermore, a potential displacement for positive values of approximately 200 mV was also observed which means lower energy consumption in terms of H2O2 electrogeneration. For the La based electrocatalysts, the sample containing 7% showed better current efficiency for H2O2, with values near 87% and number of electrons of 2.3, besides a potential displacement of approximately 250 mV for more values positive. It can be inferred that the Hf and La electrocatalysts obtained by Pechini\'s method are promising for use in Gas Diffusion Electrodes (GDE) aiming in situ electrogeneration of H2O2, since they exhibit a tendency to a mechanism via 2 electrons.

Étude cinétique par thermogravimétrie dans CO-CO::(2) dans une large gamme de température, sur cristaux synthétiques et sur un minerai d'hématite à gangue siliceuse. Rôle de K sur la germination et la croissance de la magnétite interprété par la formation transitoire de KFE::(11)O::(17), dont l'épitaxie sur FE::(2)O::(3) est à priorité facile. Le dopage de K par BA montre que K intervient par sa taille et non par sa charge. Dans le cas du minerai, l'action de K est minimisée par la silice

La batterie zinc-air devient une alternative potentielle à la batterie lithium-ion en raison de son avantage en termes de ressources, de sa densité d'énergie théorique élevée et de son faible potentiel de risque pour la sécurité. Ce travail met l'accent sur les problèmes conventionnels impliquant à la fois l'électrode à zinc et à air, visant à l'application.Pour l'électrode de zinc, deux configurations maison sont utilisées pour étudier la croissance des dendrites de zinc et l'évolution de l'hydrogène pendant le dépôt avec un électrolyte statique et en flux, respectivement. On trouve qu'une concentration élevée de zincate dans un électrolyte avec 7 M KOH (> 0,4 M ZnO) et la présence de circulation de l’électrolyte sont préférables pour réduire la croissance des dendrites. Cependant l'électrolyte en circulation générerait plus de dégagement d'hydrogène. Pour l'électrode à air, une étude de voltampèremètre cyclique détaillée de l'activité catalytique de pérovskites de lanthane- manganèse dopés au strontium (LSMO) vis-à-vis de la réaction de réduction de l'oxygène est menée. Une nouvelle méthodologie est proposée pour la comparaison de l'activité catalytique des LSMO. L'assemblage de la batterie zinc-air est également testé en formulant les électrodes avec un polymère PVDF-HFP prometteur dans les applications d’électrode à air
Zinc-air battery is becoming a potential alternative for lithium-ion battery owing to its resource stock advantage, high theoretical energy density, and low potential of safety risk. This work emphasizes the conventional issues involving both zinc and air electrode, aiming to application.For the zinc electrode, two homemade setups are used to study the zinc dendrite growth and hydrogen evolution during deposition with static and flowing electrolyte, respectively. It is found that high zincate concentration in electrolyte with 7 M KOH (>0.4 M ZnO) and flowing electrolyte are preferable for depressing dendrite growth. While flowing electrolyte would generate more hydrogen evolution. For the air electrode, a detailed cyclic voltametric investigation of the catalytic activity of lanthanum strontium manganese oxides (LSMO) towards oxygen reduction reaction is conducted. A new current normalization method is proposed for comparison of catalytic activity of the LSMOs. Zinc-air battery assembly is also tested, while remaining to be improved. Nevertheless, cost-effective PVDF-HFP is found to be a promising binder for air electrode formulation

Master’s thesis is concerned with maintenance management in manufacturing companies focusing on TPM. The first part of the thesis deals with the topic theoretically and proposes possible solution in company Siemens Electric Machines s.r.o. based on system analysis. The practical part then describes the current state of maintenance management and recommend various measures to improve autonomous, scheduled and reactive maintenance in this company.

Les électrocatalyseurs conventionnels utilisés dans les piles à combustibles à membrane échangeuse de protons (PEMFC) sont composés de nanoparticules de platine supportées sur des noirs de carbone de forte surface spécifique. A la cathode de la PEMFC, siège de la réaction de réduction de l’oxygène (ORR), le potentiel électrochimique peut atteindre des valeurs élevées - notamment lors de phases arrêt-démarrage - engendrant des dégradations irréversibles du support carboné. Une solution « matériaux » consiste à remplacer ce dernier par des supports à base d’oxydes métalliques. Ceux-ci doivent être résistants à la corrosion électrochimique, conducteurs électroniques et posséder une structure poreuse et nano-architecturée (permettant le transport des réactifs et produits et une distribution homogène de l’ionomère et des nanoparticules de platine). Dans ce travail, nous avons donc élaboré et caractérisé des électrocatalyseurs à base de nanoparticules de platine (Pt) déposées sur du dioxyde d’étain (SnO₂) et de titane (TiO₂) texturés (morphologies aérogel, nanofibres ou « loosetubes ») et conducteurs électroniques (dopés au niobium Nb ou à l’antimoine Sb). Le support permettant d’atteindre les meilleures propriétés électrocatalytiques est un aérogel de SnO₂ dopé à l’antimoine, noté ATO. En particulier, l’électrocatalyseur Pt/ATO présente une activité spécifique vis-à-vis de l’ORR supérieure à celle d’un électrocatalyseur Pt/carbone Vulcan® synthétisé dans les mêmes conditions, suggérant des interactions bénéfiques entre les nanoparticules de Pt et le support oxyde métallique (Strong Metal Support Interactions, SMSI).Des tests de durabilité simulant le fonctionnement d’une PEMFC en conditions automobile ont été effectués en électrolyte liquide à 80 °C sur ces deux électrocatalyseurs : cyclage entre 0,60 et 1,00 V vs l’électrode réversible à hydrogène (RHE) ou entre 1,00 et 1,50 V vs RHE. Le catalyseur Pt/ATO présente une durabilité accrue par rapport au catalyseur Pt/carbone Vulcan® de référence. Cependant, de nouveaux mécanismes de dégradation ont été mis en évidence dans cette étude : tout d’abord, l’élément dopant Sb est progressivement dissout au cours du vieillissement électrochimique, ce qui implique une perte de conductivité électronique. Cette perte est en partie liée à des incursions à bas potentiel, notamment durant les caractérisations électrochimiques. De plus, entre 5 000 et 10 000 cycles de vieillissement électrochimique (entre 0,60 et 1,00 V vs RHE ou entre 1,00 et 1,50 V vs RHE à 57 °C), le matériau support perd sa structure poreuse et forme un film amorphe peu conducteur
Conventional electrocatalysts used in proton exchange membrane fuel cells (PEMFC) are composed of platinum nanoparticles supported on high specific surface area carbon blacks. At the cathode side of the PEMFC, where the oxygen reduction reaction (ORR) occurs, the electrochemical potential can reach high values - especially during startup-shutdown operating conditions - resulting in irreversible degradation of the carbon support. A “material” solution consists of replacing the carbon with supports based on metal oxides. The latter have to be resistant to electrochemical corrosion, be electronic conductor and have a porous and nano-architectural structure (for the transport of reagents and products and the homogeneous distribution of the ionomer and platinum nanoparticles).In this work, we have developed and characterized electrocatalysts composed of platinum (Pt) nanoparticles based on tin dioxide (SnO2) and titanium dioxide (TiO2) with optimized textural (aerogel, nanofibres or loosetubes morphologies) and electron-conduction properties (doped with niobium Nb or antimony Sb). The best electrocatalytic properties are reached for an antimony-doped SnO2 aerogel support, denoted ATO. The Pt/ATO electrocatalyst has especially a higher specific activity for the ORR than a Pt/carbon Vulcan® electrocatalyst, synthesized in the same conditions, suggesting beneficial interactions between the Pt nanoparticles and the metal oxide support (Strong Metal Support Interactions SMSI).Durability tests simulating automotive operating conditions of a PEMFC were carried out in liquid electrolyte at 57 °C on these two electrocatalysts by cycling between 0.60 and 1.00 V vs the reversible hydrogen electrode (RHE) or between 1.00 and 1.50 V vs RHE. The Pt/ATO electrocatalyst has an increased stability compared to the reference Pt/carbon Vulcan® electrocatalyst. However, new degradation mechanisms were highlighted in this study: first, the doping element (Sb) is progressively dissolved during electrochemical ageing, which implies a loss of electronic conductivity. This loss is partly due to incursions at low potential, including during electrochemical characterizations. Moreover, between 5,000 and 10,000 cycles of the accelerated stress tests (between 0.60 and 1.00 V vs RHE or between 1.00 and 1.50 V vs RHE at 57 °C), the support loses its porous structure and forms a poorly conductive amorphous film