The work presented in this thesis centers on the application of atomic-resolution transmission electron microscopy to study Platinum-alloy nanoparticles. In particular, the thesis focusses on the platinum-iron and platinum-gold systems. Additionally, few other complementary structures based on Pt thin films and nanowires are also characterized. These materials are studied in the context of their catalytic application towards the oxygen reduction reaction in polymer electrolyte membrane fuel cells (PEMFCs). Here we report on the detailed investigation of many structural and compositional aspects of these catalyst nanoparticles including lattice strain, the surface and bulk atomic-structure, the surface/bulk chemical composition, surface segregation, and atomic ordering. In some cases we have even looked beyond the traditional characterization approaches. For instance, instead of observing the particle structures before and after a particular treatment (e.g., heating and degradation tests), we have captured the dynamics of structural evolution over the entire course of such treatments. These investigations were useful in interpreting their catalytic performances, which opened new perspectives towards further optimization of their material structure on the atomic-level. / Thesis / Doctor of Philosophy (PhD)

Hydrogen, nature’s simple and the most abundant element has been in the limelight for the past few decades from the stand point of the so-called hydrogen economy. With a high calorific value (142 MJ/kg) that is three times as large as the liquid hydrocarbons, hydrogen has emerged as a promising and environmentally friendly source of energy for the future generations. However, on-board hydrogen storage is one of the bottlenecks for its widespread usage for mobile applications. Storing hydrogen in liquid or compressed form is extremely difficult because of its low density. One of the best alternatives is to store hydrogen in a chemical form. Despite extensive work in this area, none of the materials seem to satisfy the essential criteria of reversible hydrogen storage with high gravimetric content. With regard to chemical hydrogen storage, apart from metal hydrides, ammonia borane (H3N•BH3, AB) is a promising prospect with a very high gravimetric storage of 19.6 wt% of hydrogen. Objectives 1) Develop cost-effective and active first-row transition metal based catalysts for the generation of hydrogen from AB in protic solvents 2) Study the dehydrogenation of AB in fluorinated alcohols and acids in order to realize compounds that are suitable for regeneration. 3) Study the interaction of Cu2+ with AB in non-aqueous medium using 11B NMR spectroscopy and powder XRD techniques. 4) Generation of highly pure hydrogen from ammonia borane in the solid state under mild conditions in the presence of late first row transition metal salts. 5) Synthesis of highly monodisperse ultrasmall colloidal Mg nanoparticles using the Solvated Metal Atom Dispersion (SMAD) method and digestive ripening technique; study the effect of size on the desorption temperature of MgH2. 6) Synthesize Cu/ZnO and Cu/MgO nanocomposites from the individual metal nanoparticles using co-digestive ripening technique and establish the structure of the composites using TEM, EF-TEM, and powder XRD techniques. Significant results Hydrogen generation from AB in protic solvents was realized using first-row transition metal catalysts. Initial studies were carried out using Cu nanocatalyst synthesized by the solvated metal atom dispersion method (SMAD). The activity order was found to be Cu2O > Cu@Cu2O > Cu. In addition, the late first-row transition metal ions, Co2+, Ni2+, and Cu2+ ions were also found to be highly active towards AB hydrolysis. These ions assisted AB hydrolysis via in-situ formation of metal atoms/clusters. Cu2+ assisted the hydrolysis of AB via the in-situ generation of both H+ and Cu clusters. At higher concentrations of AB, hydrolysis resulted in the evolution of NH3 in addition to H2 whereas, methanolysis afforded pure H2. In the case of methanolysis, for catalyst/AB = 0.2, three equiv of H2 were liberated in 2.5, 4.2, and 1.5 min when Co-Co2B, Ni-Ni3B, and Co-Ni-B nanopowders were used as catalysts, respectively. Dehydrogenation of ammonia borane (AB) was carried out in 2,2,2-trifluoroethanol and trifluoroacetic acid in order to realize compounds that are suitable for regeneration. The final byproduct obtained after the catalytic dehydrogenation of AB in 2,2,2-trifluoroethanol was NH4+B(OCH2CF3)4–. The FTIR data showed that the B-O bond in NH4+B(OCH2CF3)4 is slightly weaker compared to that in boric acid. Dehydrogenation of AB in trifluoroacetic acid in a controlled manner resulted in the formation of [CF3COO]–[BH2NH3]+ as the final by-product. Ammonia-borane was regenerated from [CF3COO]–[BH2NH3]+ by its reaction with LiAlH4, which served as the hydride source. Dehydrogenation of AB in non-aqueous medium and in the solid state were studied in hydrogen storage point of view. Cu2+ was found to activate the B–H bond in amine boranes in non-aqueous medium even at room temperature. As a result of the B–H bond cleavage in AB, [H3N•BH2]Cl species is formed. This compound reacts with unreacted AB via 3 separate pathways one involving hydrogen evolution, a second involving formation of a stable diammoniate of diborane cation [(NH3)2BH2]Cl without hydrogen evolution, and the third involving the formation of [H2NBH2]n and BNHx polymers accompanied by the generation of H2. Mechanisms of these pathways have been elaborated using 11B NMR spectroscopy and powder X-ray diffraction methods. These studies demonstrate that Cu(II) salts can be used as effective initiators for the dehydrogenation of amine boranes. Copper-induced hydrogen generation from AB in the solid state was also studied: for Cu2+/AB = 0.05, two equiv of H2 were liberated in 6.5 h at 333 K, which is equal to 9 wt% of the system. The 11B MAS NMR studies showed that the reaction proceeds through the intermediacy of [NH4]+[BCl4]– which eliminates the formation of borazine impurity, thereby affording pure H2. The cost effectiveness of CuCl2 makes this reaction scheme extremely attractive for real time applications. In the context of hydrogen storage in metal hydrides, highly monodisperse colloidal Mg nanoparticles with a size regime of 2–4 nm were synthesized by using the SMAD method followed by digestive ripening technique. The Mg-HDA nanopowder was fully hydrided at 33 bar and 391 K. Onset of hydrogen desorption from MgH2 nanoparticles was observed at a remarkably low temperature, 388 K compared to > 623 K in the case of bulk MgH2. The present study is a step towards realizing hydrogen storage materials that could operate close to ambient conditions. Colloids of Cu and Zn nanoparticles stabilized by 2-butanone have been prepared by the SMAD method. The as-prepared colloids which are polydisperse in nature have been transformed into highly monodisperse colloids by the digestive ripening process in the presence of hexadecylamine. Using this process, copper nanoparticles of 2.1 ± 0.3 nm and zinc nanoparticles of 3.91 ± 0.3 nm diameters have been obtained. Co-digestive ripening of Cu, Zn and Cu, Mg colloids resulted in the formation of Cu/ZnO and Cu/MgO nanocomposites, respectively. The structures of these nanocomposites were established using UV-visible spectroscopy, TEM, EF-TEM, and powder XRD techniques.

Hydrogen is under the spotlight due to its ability to decarbonize the hard-to-abate sector. Sweden, which aims to achieve net zero emissions by 2025, has incorporated hydrogen as an instrument to reach a decarbonization pathway. The Swedish Energy Agency announced that the hydrogen target covers a 5 GW electrolyzer installation needing an enormous electricity supply of around 22-42 TWh in phase 1. However, generating fossil-free hydrogen on a large scale is relatively new in Sweden’s history. There is an urgency to identify the current state of production, distribution, storage, and application of fossil-free hydrogen in Sweden. Comprehending the potential direction using a system thinking approach is also mainly absent. Thus, the study aims to fill those knowledge gaps and provide insight into hydrogen’s current state and future direction. The thesis evaluates materials through the qualitative research design with quantitative data supplementation. The system thinking approach is implemented to investigate the leverage points that can influence the system. The findings showed that various actors had proposed a total of 3.85 GW of electrolyzer installation, implying that 17-32 TWh of electricity should be available. The projects are primarily used to meet industrial demand in the electrofuel, iron and steel, and refinery sectors. However, insufficient electricity supply and investment could inhibit growth. Storage and pipeline infrastructure development is also lagging. Those elements should be resolved to achieve the hydrogen target. The study suggested that reducing production costs, increasing government support, and pursuing disruptive technology will accelerate the transition to a fossil-free hydrogen society.

No description available.

<p>The aim of my work is to model a segment of a unit cell of a fuel cell stack using numerical methods which is classified as computational fluid dynamics and implementing the work in a commercial computational fluid dynamics package, FLUENT. The focus of my work is to study the thermal distribution within this segment. The results of the work aid in a better understanding of the fuel cell operation in this temperature range. At the time of my investigation experimental results were unavailable for validation and therefore my results are compared to previously published results published. The outcome of the results corresponds to this, where the current flux density increases with the increasing of operating temperature and fixed operating voltage and the temperature variation across the fuel cell at varying operating voltages. It is in the anticipation of determining actual and or unique material input parameters that this work is done and at which point this studies results would contribute to the understanding high temperature PEM fuel cell thermal behaviour, significantly.</p>

<p>The aim of my work is to model a segment of a unit cell of a fuel cell stack using numerical methods which is classified as computational fluid dynamics and implementing the work in a commercial computational fluid dynamics package, FLUENT. The focus of my work is to study the thermal distribution within this segment. The results of the work aid in a better understanding of the fuel cell operation in this temperature range. At the time of my investigation experimental results were unavailable for validation and therefore my results are compared to previously published results published. The outcome of the results corresponds to this, where the current flux density increases with the increasing of operating temperature and fixed operating voltage and the temperature variation across the fuel cell at varying operating voltages. It is in the anticipation of determining actual and or unique material input parameters that this work is done and at which point this studies results would contribute to the understanding high temperature PEM fuel cell thermal behaviour, significantly.</p>

Sodium borohydride is stable in alkaline solution, however, it hydrolyses and generates hydrogen gas in the presence of suitable catalyst. By this way hydrogen can be generated safely for the fuel cells. All of the catalyst having been used in the hydrolysis of sodium borohydride, with one exception, are heterogeneous. The limited surface area of the heterogeneous and therefore, have limited activity because of the surface area. Thus, the use of metal nanoclusters as catalyst with large surface area is expected to provide a potential route to increase the catalytic activity. In this dissertation we report for the first time the use of ruthenium(0) nanoparticles as catalyst in the hydrolysis of sodium borohydride. The water dispersible ruthenium(0) nanoparticles were prepared by the reduction of RuCl3.xH2O with sodium borohydride and were stabilized by three different ligands dodecanethiol, ethylenediamine and acetate. Among these three colloidal materials the acetate stabilized ruthenium(0) nanoparticles were found to have the highest catalytic activity in catalyzing the hydrolysis of sodium borohydride. The acetate stabilized ruthenium(0) nanoparticles were characterized by tranmission electron microscopy (TEM), X-ray photoelectron spectroscopy and FT-IR spectroscopy. The particle size of the acetate stabilized ruthenium(0) nanoparticles was determined to be 2.62&plusmn / 1.18 nm from the TEM analysis. The kinetic of the ruthenium(0) nanoparticles catalyzed hydrolysis of sodium borohydride was studied depending on the catalyst concentration, substrate concentration and temperature. The activation parameters of this reaction were also determined from the evaluation of the kinetic data. This catalyst provides the lowest activation energy ever found for the hydrolysis of sodium borohydride.

Magister Scientiae - MSc / The aim of my work is to model a segment of a unit cell of a fuel cell stack using numerical methods which is classified as computational fluid dynamics and implementing the work in a commercial computational fluid dynamics package, FLUENT. The focus of my work is to study the thermal distribution within this segment. The results of the work aid in a better understanding of the fuel cell operation in this temperature range. At the time of my investigation experimental results were unavailable for validation and therefore my results are compared to previously published results published. The outcome of the results corresponds to this, where the current flux density increases with the increasing of operating temperature and fixed operating voltage and the temperature variation across the fuel cell at varying operating voltages. It is in the anticipation of determining actual and or unique material input parameters that this work is done and at which point this studies results would contribute to the understanding high temperature PEM fuel cell thermal behaviour, significantly. / South Africa

This dissertation thesis revolves around hydrogen economy and energy-storage electrochemical systems. More specifically, it investigates the possibility of using magnetron sputtering for deposition of efficient thin-film anode catalysts with low noble metal content for proton exchange membrane water electrolyzers (PEM-WEs) and unitized regenerative fuel cells (PEM-URFCs). The motivation for this research derives from the urgent need of minimizing the price of mentioned electrochemical devices should they enter mass production. Numerous experiments were carried out, correlating the actual in-cell performance with the varying position of thin-film catalyst within the membrane electrode assembly, with the composition of high-surface support sublayer and with the chemical structure of the catalyst itself. The wide arsenal of analytical methods ranging from electrochemical impedance spectroscopy through scanning electron microscopy to photoelectron spectroscopy allowed us to describe complex phenomena behind different obtained efficiencies. Consequent systematic optimizations led to the design of novel PEM-WE anode thin-film iridium catalyst with thickness of just 50 nm, supported on optimized TiC-based sublayer which performed similarly to standard counterparts despite using just a fraction of their noble metal...

Il concetto di rete dell'informazione può diventare uno schema logico con cui descrivere l'evoluzione delle politiche sulle energie rinnovabili e sulla sostenibilità? La ricerca è stata svolta analizzando l'architettura delle due reti (internet e reti energetiche) e l'evoluzione del bene prodotto e distribuito nella rete energetica, l'energia, esplicitando l'accessibilità da parte della distribuzione mondiale delle risorse petrolifere tradizionali e delle risorse rinnovabili. La struttura metodologica del progetto di ricerca si basa due tipi di analisi teorica: 1) l'analisi della nascita delle società in rete attraverso le teorie di Manuel Castells (concetto di spazio di flussi) e di Saskia Sassen e l'evoluzione delle città (cap.2 e cap.5) 2) le analisi dei flussi dei materiali e delle energie avendo come riferimento metodologico l'approccio ecologico ideato dai ricercatori dell'istituto per il Clima, l'Ambiente e l'Energia di Wuppertal, Germania (cap.3 e cap.4) La contraddizione tra città innovative e città che sono ai livelli di enormi discariche o di baraccopoli è esposta nel cap.6 attraverso casi studio e progetto dei Programmi Europei. Nell'ultimo capitolo (cap.7) si riassumono le ipotesi di partenza e i risultati della ricerca e si espongono le questioni aperte. / Can internet logic scheme be used as a basis to describe public policies evolution on renewable energies production and sharing in urban areas all over the world? The research project analyses the two networks (internet and energetic grids) architectures in actual and future urban areas. This analysis is connected with present and future forecasts energy productions from traditional fuels and from renewable sources. Theoretical analysis is conducted following a double conceptual pathway: - societal networks (Manuel Castells theory) and urban areas evolution (Saskia Sassen and Mike Davis) in order to picture the evolution of cities and towns in modern economies and in developing countries (Chapters 2 and 5); - Material and Energy Flow Analysis (approach by Wuppertal Institute for Climate, Environment and Energy) applied to renewable energy (Chapters 3 and 4) In Chapter 6 case studies are exposed on the deep cleavage between two different worlds: innovative, rich towns on a side and the landfills cities, slums on the other side. In the last part hypothesis and thesis are put together and open questions are explained (Chapter 7).