>Magister Scientiae - MSc / The objective of the thesis is to develop highly efficient catalysts for solid polymer electrolyte (SPE) electrolyser anodes.The anode is the primary cause of the large overpotential of SPE electrolysers and also adds significantly to the cost of the electrolysers. Currently, unsupported IrO2 is a widely used anode catalyst as it exhibits the best stability during the oxygen evolution reaction. The activity of IrO2 needs to be improved significantly to address the high cost and efficiency issues of the SPE electrolyser. Developments aimed at improving the activity of unsupported IrO2 are however limited due to the limitations of the wellknown supports under the operating conditions of electrolysers, leading to their oxidation.In this study binary metal oxides based on IrO2 were developed and optimized as anode catalysts for the SPE electrolyser and compared to the ‘state-of-art’ commercial IrO2 catalyst. The Adams fusion method was adapted and used to synthesize the catalysts.The activities of the catalysts were determined using half-cell studies. Optimum conditions for the preparation of unsupported IrO2 catalysts were found to be 350 oC and 2 hours. The resulting catalysts had twice the activity of the ‘state-of-art’ commercial IrO2 catalyst. Secondary metals were carefully selected, after carrying out both a literature study and an experimental study. Binary metal oxides were then developed using the optimum synthesis conditions. Four binary metal oxides were studied to identify the best/most efficient catalyst for electrolysis. The catalysts were characterized using XRD, TEM, SEM and EDS analyses, in efforts to understand and correlate the activity of the catalysts to its physical properties and obtain information that could be useful for the further development of efficient catalysts.Although all the binary metal oxides studied showed improved activity compared to IrO2, the catalytic activity of Ir0.7Ru0.3O2 was found to be significantly better than the commercial catalyst: it was over 5 times more active than the ‘state-of-art’ commercial IrO2 catalyst. Ir-Pd mixed oxides also proved to be highly efficient as anode catalysts for SPE electrolysers.

The effects of actively pulsing reactant flow rates into solid polymer electrolyte fuel cells were investigated in this thesis. First, work was conducted to determine the magnitude of voltage response to pulsed reactant flow on a direct hydrogen proton exchange membrane (PEM) cell. The effects of pulsed reactant flow into a direct methanol fuel cell (DMFC) were then considered. The PEM work showed substantially greater response to pulsed air flow than to pulsed fuel flow. It was found that several parameters affect the magnitude of cell response to active flow control (AFC). Increasing current load, increasing the magnitude of flow oscillation, decreasing the frequency of oscillation, and decreasing the average level of excess reactant supplied were found to maximize both the level of voltage oscillations and the decrease in cell power from steady state performance. Greater response to pulsed oxidant flow is believed to have been observed due to effects brought about by changes in membrane humidity. In contrast, pulsed fuel flow showed the greatest response in the study of DMFC technology. In this case, time averaged cell voltage was found to increase as the time averaged fuel flow rate was reduced. The increase in average cell power is the result of a reduction in methanol crossover; sustainable increases of up to 6% in power output were measured. The parameters found to effect the increase in cell power observed include the frequency of oscillation and the time-averaged NOSfuel. Pulsed air flow on the DMFC did not show any such rise in voltage, supporting the hypothesis that a reduction in methanol crossover is the phenomenon which brings about enhanced performance.

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Submitted by Jos? Henrique Henrique (jose.neves@ufvjm.edu.br) on 2018-03-08T18:31:35Z No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) jose_geraldo_mendes_castro_junior.pdf: 20723597 bytes, checksum: f867ab4f1cb9235c24c8c6d16d42c22c (MD5) / Approved for entry into archive by Rodrigo Martins Cruz (rodrigo.cruz@ufvjm.edu.br) on 2018-03-09T18:46:17Z (GMT) No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) jose_geraldo_mendes_castro_junior.pdf: 20723597 bytes, checksum: f867ab4f1cb9235c24c8c6d16d42c22c (MD5) / Made available in DSpace on 2018-03-09T18:46:17Z (GMT). No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) jose_geraldo_mendes_castro_junior.pdf: 20723597 bytes, checksum: f867ab4f1cb9235c24c8c6d16d42c22c (MD5) Previous issue date: 2017 / Eletrodos de di?xido de chumbo (PbO2) suportados sobre tecido de carbono e tela de a?o inoxid?vel foram utilizados na degrada??o eletroqu?mica dos f?rmacos paracetamol (PCT) e dipirona (DPN), utilizando-se uma c?lula eletroqu?mica do tipo eletr?lito polim?rico s?lido (EPS) munida de eletrodos perme?veis a fluidos (EPFs). Todos os estudos foram conduzidos na condi??o de batelada empregando-se a ?gua livre de eletr?litos. Os estudos eletroqu?micos de degrada??o dos f?rmacos foram conduzidos em fun??o da densidade de corrente aparente (jap) (ex., 5, 10, 20, 100, 150 e 200 mA cm-2) e da concentra??o inicial (ex., 10, 30 e 50 mg L 1). As amostras tratadas foram analisadas pelas t?cnicas de espectrofotometria na regi?o do UVVis, cromatografia l?quida de alta efici?ncia (CLAE) e demanda qu?mica de oxig?nio (DQO). Verificou-se para os diferentes casos envolvendo as baixas densidades de corrente que a remo??o das bandas de absor??o no UV-Vis, a remo??o da concentra??o dos f?rmacos (CLAE) e a redu??o da DQO (grau de mineraliza??o) n?o foram significativos. Contrariamente, no caso das elevadas densidades de corrente evidenciou-se uma significante melhora na degrada??o dos f?rmacos em decorr?ncia da atua??o do oz?nio gerado eletroquimicamente. Os melhores resultados foram obtidos para baixas concentra??es dos f?rmacos. Redu??es superiores a 95 % de DQO para o PCT e superiores a 75 % para a DPN foram obtidas. Eletrodos de PbO2 dopados com n?quel (ex., Ni-PbO2) suportados sobre tecido de carbono e tela de a?o inoxid?vel foram confeccionados e caracterizados. A an?lise de microscopia eletr?nica de varredura (MEV) revelou o aparecimento de defeitos superficiais, com a varia??o da concentra??o nominal do Ni no banho eletrol?tico utilizado no preparo do eletrodo por eletrodeposi??o. An?lises de difratometria de raios-X (DRX) corroboraram os resultados de MEV revelando, em alguns casos, picos mais alargados e de menor intensidade (ex., redu??o no tamanho m?dio dos cristalitos) com a varia??o da concentra??o nominal do Ni, indicando assim uma interfer?ncia no processo de eletrodeposi??o do PbO2. Curvas de polariza??o em condi??es quaseestacion?rias foram obtidas para o processo eletr?dico da rea??o de desprendimento de oxig?nio (RDO) sendo verificado que n?o houve influ?ncia significativa do dopante sobre esta rea??o, a qual ocorre em paralelo ao processo de degrada??o oxidativa dos f?rmacos. Verificou-se que a produ??o de oz?nio foi ligeiramente favorecida em algumas concentra??es do dopante e em altas densidades de corrente. No entanto, n?o foi verificada influ?ncia significativa sobre o grau de mineraliza??o dos f?rmacos PCT e DPN mediante uso de eletrodos dopados com Ni. / Disserta??o (Mestrado) ? Programa de P?s-Gradua??o em Qu?mica, Universidade Federal dos Vales do Jequitinhonha e Mucuri, 2017. / Lead dioxide (PbO2) electrodes supported on carbon cloth and stainless-steel mesh substrates were used in the electrochemical degradation of the drugs paracetamol (PCT) and dipyrone (DPN), using a solid polymer electrolyte electrochemical cell (SPE) having fluid-permeable electrodes (FPEs). All studies were conducted in batch condition using the electrolyte-free water. The electrochemical degradation of the drugs was accomplished as a function of the apparent current density (ex., 5, 10, 20, 100, 150 and 200 mA cm-2) and the initial concentration (ex., 10, 30 and 50 mg L-1). The treated samples were analyzed using the UV-Vis spectrophotometry technique, the high-performance liquid chromatography (HPLC), as well as the chemical oxygen demand (COD). For the different cases involving the application of low current density values, it was not verified significant changes accounting for the removal of the UV-Vis absorption band, the drug concentration (HPLC), and the COD decrease (ex., the degree of mineralization). In contrast, in the case of high current densities, a significant improvement in the degradation of the drugs was evidenced as a result of the influence of the electrochemically generated ozone. The best findings were obtained for low drug concentrations. Reductions of above 95% COD for PCT and above 75% for DPN were obtained. Nickel-doped PbO2 electrodes (ex., Ni-PbO2) supported on carbon cloth and stainlesssteel mesh were fabricated and characterized. Scanning electron microscopy (SEM) revealed the appearance of surface defects with a reduction in crystal size with the different Ni concentration in the electrolytic bath used to prepare the electrode by electrodeposition. X-ray diffraction (XRD) analyzes corroborated with the SEM results revealing the formation of broader peaks with lower intensity, in some cases, (ex., reduction in the average crystallite size) with the variation of the nominal dopant concentration in the electrolytic bath, thus indicating an interference in the electrodeposition process for PbO2. Quasi-stationary polarization curves were obtained for the electrode process of the oxygen evolution reaction (OER) and it was verified that there was no significant influence of the dopant on this reaction, which occurs in parallel to the process comprising the oxidative degradation of the drugs. It was found that the ozone generation was slightly favored in some concentrations of the dopant and in higher current densities. However, no significant influence was verified on the degree of mineralization of PCT and DPN by the use of Ni-PbO2 electrodes.

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Die Energieversorgung unbemannter Flugobjekte (UAV) erfolgt gegenwärtig über Batterie-Module. Diese sind als zusätzliche Bauteile in die Struktur eingebracht. Daher erhöht sich das Gesamtgewicht der Struktur deutlich. Im Sinne der Energiespeicherung existieren verschiedene multifunktionale Konzeptansätze. Hierunter zählen strukturelle, elektrische Energiespeicherungssysteme (SEES). Bei diesen Konzepten erfolgt die Energiespeicherung in den Bauteilen bei gleichzeitiger Erfüllung struktureller Eigenschaften. Somit gelten diese als masselose Energiespeicherungssysteme. Im Rahmen dieser Thesis erfolgt eine Betrachtung verschiedener SEES. Schließlich werden strukturelle Superkondensatoren (SSC) zur Integration in ein UAV ausgewählt. Als Integrationsobjekt dient die Drohne DJI Matrice 600 Pro. Ein SSC mit besten Eigenschaften wird anhand einer systematischen Methode aus der aktuellen Literatur ermittelt. Dieser Favorit wird konzeptionell in die Drohne integriert. Diesbezüglich erfolgen verschiedene, physikalische Berechnungen zu elektrischen Eigenschaften und anliegenden Kräften, sodass Rückschlüsse zur Leistungsfähigkeit getroffen werden können. Im weiteren Verlauf wird eine Mehrkörpersimulation mit der Finite-Elemente-Methode (FEM) am Untersuchungsobjekt durchgeführt. Mit der Kenntnis über die anliegenden Beanspruchungen erfolgt weiterführend eine detailgetreue, strukturmechanische Analyse des SSC unter Verwendung der FEM an repräsentativen Volumenelementen. Fortan wird das multiphysikalische Kopplungsphänomen im strukturellen Elektrolyten simuliert. Hierfür werden mathematische Abhängigkeiten von mechanischen Einwirkungen auf geometrisch, veränderliche Größen ermittelt. Diese werden in eine elektrochemische Simulation überführt, sodass das multiphysikalische Kopplungsphänomen berechnet wird. Als Ergebnis zeigt sich, dass die Kompression des Elektrolyten negative Auswirkungen auf die elektrochemischen Eigenschaften hat...:Symbol- und Abkürzungsverzeichnis Abbildungsverzeichnis Tabellenverzeichnis 1 Einleitung 2 Grundlagen 2.1 Strukturelle elektrische Energiespeicherungssysteme 2.2 Superkondensatoren – Aufbau und Funktionsweise 2.3 Berechnungsgrößen am strukturellen Superkondensator 3 Stand der Forschung 3.1 Literaturrecherche – Strukturelle Superkondensatoren 3.2 Festlegung von Parametern und Auswahl des SSC 4 Anwendungsfall: DJI Matrice 600 Pro 4.1 Produktanalyse DJI Matrice 600 Pro 4.2 Integration des strukturellen Superkondensators in die Struktur 4.3 Berechnung elektrischer Eigenschaften 4.4 Analyse und Berechnung der wirkenden Kräfte 4.5 FEM-Mehrkörpersimulation am UAV-Anwendungsfall 5 Strukturmechanische Simulation am SSC 5.1 SSC-Bereichsanalyse und Simulationsaufgabe 5.2 Repräsentative Volumenelemente und Einheitszelle 5.3 Simulation Bereich 1: Poröse Faser in der Matrix 5.4 Simulation Bereich 2: Fasern in der Matrix 5.5 Simulation Bereich 3: Poröser Elektrolyt 6 Multiphysikalische SSC-Simulation 6.1 Multiphysikalischer Kopplungseffekt 6.2 Analyse der geometrischen Größen Porosität und Tortuosität 6.3 Multiphysikalische Simulation mit COMSOL Multiphysics Zusammenfassung und Ausblick Literatur / Unmanned aerial vehicles (UAV) are currently powered by batteries, which are integrated as additional components within their structure. However, the substantial weight of these batteries leads to increased energy consumption and reduced flight time. In addition to battery-based energy systems, there are alternative concepts that serve multifunctional roles. Structural electrical energy storage systems (SEES) for example carry loads and offer electrical energy storage functions at the same time. In this work, structural Supercapacitors (SSC) are selected as SEES candidates. A systematic approach is employed to integrate an SSC into the DJI Matrice 600 Pro done as an UAV use case. The efficiency of the integrated system is assessed through various physical calculations. Subsequently, a multi-body simulation using the finite element method is conducted on the chosen UAV model. Furthermore, representative volume elements are defined within the structural supercapacitor, and simulations are performed to comprehend the underlying processes. During the exploration of multiphysical coupling effects between mechanical stresses and electrochemical behaviors, certain geometric parameters are identified as influential factors. Regression analysis is employed to formulate mathematical equations representing these dependencies for simulation purposes. A multiphysical simulation is executed, considering compression as a representative load case. The results are evaluated using cyclic voltammetry. The study concludes that mechanical compression loads have an adverse effect on the electrochemical properties of the structural supercapacitor:Symbol- und Abkürzungsverzeichnis Abbildungsverzeichnis Tabellenverzeichnis 1 Einleitung 2 Grundlagen 2.1 Strukturelle elektrische Energiespeicherungssysteme 2.2 Superkondensatoren – Aufbau und Funktionsweise 2.3 Berechnungsgrößen am strukturellen Superkondensator 3 Stand der Forschung 3.1 Literaturrecherche – Strukturelle Superkondensatoren 3.2 Festlegung von Parametern und Auswahl des SSC 4 Anwendungsfall: DJI Matrice 600 Pro 4.1 Produktanalyse DJI Matrice 600 Pro 4.2 Integration des strukturellen Superkondensators in die Struktur 4.3 Berechnung elektrischer Eigenschaften 4.4 Analyse und Berechnung der wirkenden Kräfte 4.5 FEM-Mehrkörpersimulation am UAV-Anwendungsfall 5 Strukturmechanische Simulation am SSC 5.1 SSC-Bereichsanalyse und Simulationsaufgabe 5.2 Repräsentative Volumenelemente und Einheitszelle 5.3 Simulation Bereich 1: Poröse Faser in der Matrix 5.4 Simulation Bereich 2: Fasern in der Matrix 5.5 Simulation Bereich 3: Poröser Elektrolyt 6 Multiphysikalische SSC-Simulation 6.1 Multiphysikalischer Kopplungseffekt 6.2 Analyse der geometrischen Größen Porosität und Tortuosität 6.3 Multiphysikalische Simulation mit COMSOL Multiphysics Zusammenfassung und Ausblick Literatur