Fuel cells are expected to play a major role in the economy of this century and for the foreseeable future. The use of hydrogen and fuel cells can address critical challenges in all energy sectors like commercial, residential, industrial, and transportation. Fuel cells are electrochemical devices that convert energy of a chemical reaction directly into electrical energy by combining hydrogen fuel with oxygen from air. If hydrogen is used as fuel, only byproducts are heat and water. The objective of this thesis is to investigate the effect of operating temperature and relative humidity (RH) of reactant gases on proton exchange membrane (PEM) fuel cell performance by adjusting the operation temperature of the fuel cell and humidification temperature of the reactant gases. In this study, the effect of the different operating parameters on the performance of single proton exchange membrane (PEM) fuel cell have been studied experimentally using pure hydrogen on the anode side and air on the cathode side. Experiments with different fuel cell operating temperatures, different air and hydrogen humidification temperatures have been carried out. The experimental results are presented in the form of polarization curves, which show the effects of the various operating parameters on the performance of the PEM fuel cell. The polarization curves data have been fit to a zero dimensional model, and the effect of the fuel cell operation and humidification temperatures on the kinetic parameters and the cell resistance have been determined. The fuel cell has been operated with 1.2 and 2 stoichiometry ratio for hydrogen and air, respectively. Fuel cell performance was detected at different fuel cell operation temperatures changing from 60 to 80 &ordm / C, and relative humidity of the entering gases changing from 20 to 100 % for air and 50 % and 100 % for hydrogen. Tests were performed in a PEM fuel cell test station. The highest performance of 275 mA/cm2 at 0.6 V and 650 mA/cm2 at 0.4 V was obtained for 50 % RH air with a constant 100 % relative humidity of hydrogen for working at atmospheric pressure and 60 oC fuel cell temperature. However, the highest performance of 230 mA/cm2 at 0.6 V for 50 % RH of air with a constant 100 % relative humidity of hydrogen and the highest performance of 530 mA/cm2 at 0.4 V for both 70 % RH and 100% RH air with a constant 100 % relative humidity of hydrogen was obtained for working at atmospheric pressure and 70 oC fuel cell temperature. Besides, the highest performance of 200 mA/cm2 at 0.6 V and 530 mA/cm2 at 0.4 V was obtained for 100 % RH air with a constant 100 % RH of hydrogen for working at atmospheric pressure and 80 oC fuel cell temperature.

<p>In this study novel composite electrodes were developed, in which the catalytic components were deposited in nanoparticulate form. The efficiency of the nanophase catalysts and membrane electrodes were tested in an important electrocatalytic process, namely hydrogen production by water electrolysis, for renewable energy systems. The activity of electrocatalytic nanostructured electrodes for hydrogen production by water electrolysis were compared with that of more conventional electrodes. Development of the methodology of preparing nanophase materials in a rapid, efficient and simple manner was investigated for potential application at industrial scale. Comparisons with industry standards were performed and electrodes with incorporated nanophases were characterized and evaluated for activity and durability.</p>

Made available in DSpace on 2014-10-09T12:42:20Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:59:42Z (GMT). No. of bitstreams: 0 / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Made available in DSpace on 2014-10-09T12:42:20Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T13:59:42Z (GMT). No. of bitstreams: 0 / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Sistemas de PEMFC são capazes de gerar energia elétrica com alta eficiência e baixa ou nenhuma emissão de poluentes, porém questões de custo e durabilidade impedem sua ampla comercialização. Nesse trabalho foi desenvolvido um MEA com eletrocatalisadores à base de paládio. Foram sintetizados e caracterizados eletrocatalisadores Pd/C, Pt/C e Ligas PdPt/C com diferentes razões entre metais e carbono. Foi realizado um estudo da razão entre ionômero de Nafion e eletrocatalisador para formação de triplas fases reacionais de máximos desempenhos, criado um modelo matemático para transpor esse ajuste para eletrocatalisadores com diferentes razões entre metal e suporte, considerando os aspectos volumétricos da camada catalisadora, e então realizado um estudo da espessura da camada catalisadora. Para as caracterizações foram utilizadas as técnicas de Difração de Raios-X, Microscopias Eletrônicas de Transmissão e de Varredura, Energia Dispersiva de Raios-X, Picnometria a Gás, Porosimetria por Intrusão de Mercúrio, Adsorção de Gás, segundo as equações de BET e BJH, Análise Termo Gravimétrica e feitas as determinações de diâmetros de partículas, de áreas de superfície específica e de parâmetros de rede. Todos os eletrocatalisadores foram usados no preparo de MEAs que foram avaliados em célula unitária de 5 cm2 entre 25 e 100 °C a 1 atm; e a melhor composição foi avaliada também a 3 atm. No estudo dos metais para as reações, visando reduzir a platina aplicada aos eletrodos, sem perdas de desempenho, foram selecionados Pd/C para ânodos e PdPt/C 1:1 para cátodos. A estrutura de MEA desenvolvida utilizou 0,25 mgPt.cm-2 e resultou em densidades de potência de até 550 mW.cm-2 e potências de até 2,2 kWe por grama de platina. A estimativa realizada mostrou que houve uma redução de até 64,5 % nos custos em relação à estrutura de MEA previamente conhecida. Em função da temperatura e pressão de operação foram obtidos valores a partir de R$ 3.540,73 para o preparo de MEAs para cada quilowatt instalado. Com base em estudos recentes, concluiu-se que o custo do MEA desenvolvido é compatível às aplicações estacionárias de PEMFC. / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP / FAPESP: 10/10028-1

Doctor Scientiae - DSc / In this study novel composite electrodes were developed, in which the catalytic components were deposited in nanoparticulate form. The efficiency of the nanophase catalysts and membrane electrodes were tested in an important electrocatalytic process, namely hydrogen production by water electrolysis, for renewable energy systems. The activity of electrocatalytic nanostructured electrodes for hydrogen production by water electrolysis were compared with that of more conventional electrodes. Development of the methodology of preparing nanophase materials in a rapid, efficient and simple manner was investigated for potential application at industrial scale. Comparisons with industry standards were performed and electrodes with incorporated nanophases were characterized and evaluated for activity and durability. / South Africa

In a previous study, we reported that polymer electrolyte fuel cells prepared by direct membrane deposition (DMD) produced power densities in excess of 4 W/cm2. In this study, the underlying origins that give rise to these high power densities are investigated and reported. The membranes of high power, DMD-fabricated fuel cells are relatively thin (12 μm) compared to typical benchmark, commercially available membranes. Electrochemical impedance spectroscopy, at high current densities (2.2 A/cm2) reveals that mass transport resistance was half that of reference, catalyst-coated-membranes (CCM). This is attributed to an improved oxygen supply in the cathode catalyst layer by way of a reduced propensity of flooding, and which is facilitated by an enhancement in the back diffusion of water from cathode to anode through the thin directly deposited membrane. DMD-fabricated membrane-electrode-assemblies possess 50% reduction in ionic resistance (15 mΩcm2) compared to conventional CCMs, with contributions of 9 mΩcm2 for the membrane resistance and 6 mΩcm2 for the contact resistance of the membrane and catalyst layer ionomer. The improved mass transport is responsible for 90% of the increase in power density of the DMD fuel cell, while the reduced ionic resistance accounts for a 10% of the improvement.

The results described in this dissertation have demonstrated several alternative proton exchange membranes (PEM) for hydrogen-air and direct methanol fuel cells (DMFC) that perform as well or better than the state of the art Nafion perfluorosulfonic acid membrane. Direct aromatic nucleophilic substitution polycondensations of disodium 3,3′ S-disulfonate-4,4′ S-difluorodiphenylsulfone (SDFDPS), 4,4′ S-difluorodiphenylsulfone (DFDPS) (or their chlorinated analogs, SDCDPS, DCDPS) and 4,4′ S-thiobisbenzenethiol (TBBT) in the presence of potassium carbonate were investigated. Electrophilic aromatic substitution was employed to synthesize the SDFDPS or SDCDPS comonomers in high yields and purity. High molecular weight disulfonated poly(arylene thioether sulfone) (PATS) copolymers were easily obtained using the SDFDPS monomers, but in general, slower rates and a lower molecular weight copolymer was obtained using the analogous chlorinated monomers. Tough and ductile membranes were solution cast from N,N-dimethylacetamide for both series of copolymers. The degrees of disulfonation (20-50%, PATS 20-50) were controlled by varying the ratio of disulfonated to unsulfonated comonomers. Composite membranes were prepared by homogeneous solution blending the copolymers with phosphotungstic acid (PTA) in dimethylacetamide (DMAc). The composite PATS membranes exhibited moderate PTA molecule water extraction after acidification treatments performed at either room or boiling temperatures. The membranes containing HPA showed improved conductivity at high temperatures (120 °C) and low relative humidities when compared to the pure copolymers. Molecular weight of the copolymers plays a critical role in the overall copolymer physical behavior. It is well known that molecular weight has an enormous impact on practically all of the physical properties of polymeric systems. This dissertation discusses the influence of molecular weight on the characteristics of a specific family of PEM PATS copolymers. This study elucidated that the lower molecular weight materials did indeed behave differently than the higher molecular weight copolymers. Specifically, the water uptake and permeability to methanol decreased with increasing molecular weight. Furthermore, the fully hydrated mechanical properties also improved with molecular weight. The synthesis and fabrication of 45 mole percent disulfonated poly(arylene ether phenyl phosphine oxide diphenyl sulfone) terpolymer-heteropolyacid (HPA) composite membranes and membrane electrode assemblies were chosen for detailed investigation. A series of 45 mole percent disulfonated biphenol-based poly(arylene ether phenyl phosphine oxide diphenyl sulfone) terpolymers (BPSH45-PPO) were also synthesized by nucleophilic aromatic substitution polymerizations. The level of disulfonation was constant at 45 mole percent providing a compromise between high conductivity at low humidity and reasonable mechanical properties in liquid water. The amounts of 4,4′-difluorodiphenyl phenyl phosphine oxide comonomer incorporated into the terpolymer backbone were precisely controlled from 0-50 mole percent relative to the 4,4′-dihalodiphenyl sulfone. Phosphine oxide moieties were employed to enhance the interactions with the PTA relative to the pure copolymer. The composite BPSH45-PPO membranes exhibited lower HPA molecule water extraction after acidification at room and boiling temperatures, which was ascribed to the strong hydrogen and polar interactions between the phosphine oxide moiety and functional groups on the HPA. The membranes containing HPA displayed improved conductivity at high temperatures and low relative humidities when compared to the pure terpolymer samples. The increase of proton conductivity was attributed to the water retention characteristics of the HPA molecules, which allowed enhanced mobility of the protons even at lower humidification levels, providing superior hydrogen-air fuel cell performance. The effect of hexafluoroisopropylidene bisphenol (6FBP) incorporation into 45 mole percent disulfonated poly(arylene ether sulfone) copolymers was investigated. This novel series of directly disulfonated poly(arylene ether sulfone) copolymers with various mole ratios of the 6FBP were synthesized in high molecular weight. The levels of fluorination within the statistically random copolymer architecture were varied from 0-100 mole percent using 6FBP and the correct stoichiometric amount of 4,4′-biphenol. The 6FBP monomer was introduced to decrease the water swelling and improve bonding characteristics with Nafion-bonded electrodes. Indeed, water uptake decreased with increasing incorporation of the 6FBP monomer into the terpolymer. This suggested that the hydrophobic fluorinated material aided in water repulsion of the system. Proton conductivity decreased slightly as the amount of fluorination increased, which was interpreted to be due to the decrease in the ion-exchange capacity. High temperature hydrogen/air fuel cell experiments indicated better Nafion-bonded electrode adhesion for the partially fluorinated materials, as depicted by high temperature (120 °C) and low humidity (50% RH) hydrogen-air fuel cell performance. Investigations into polymeric electromechanical transducers were based on poly(arylene sulfone) ion-exchange membranes bonded between two conductive metal layer electrodes. Imposed deformations and small electric fields allowed similar explorations of both sensing and actuation applications. These copolymers produced larger sensitivities than the benchmark Nafion systems, which was interpreted as being due to their higher hydrated moduli. Methodologies for better defining the morphology of the electrodes were identified to enhance the capacitance and effective interfacial area of the conductive electrodes. The new procedures afforded major improvements to performance and transduction. Transducer actuation at lower frequencies was improved by employing a new direct assembly electrode fabrication technique that suggested a strong correlation between the capacitance and charge motion. / Ph. D.

Thematic interrelation is an underdeveloped field of inquiry in Lukan studies. The design and elegance of Lukan theology begs for guided investigation into a possible system of organisation that governs history and theology, that is, narrative and theme. Based on the Greimasian Actantial Model, morpho–syntactical structural–critical analysis of Luke and Acts reveals that the covenant concept in its operative aspect of service functions as an organising principle, structuring the narratives and facilitating thematic interrelation. A survey of representative Lukan research consisting of five methodologically determined approaches shows a commonality regarding Lukan purpose. These all share the “plan of God” as a fundamental concept, thus intimating its plausibility as a common organisational principle in the text. This observation encourages further analysis of Lukan narrative and meta–narrative as relevant subject matter. Investigation into the purpose and goals of Ancient Jewish and Ancient Greek literature suggests that the concepts of piety/holiness and justness combined with a notion of divine order and expectation demonstrates organisational capacity. Under the terms and conditions of the Old Covenant three non–exclusive themes/concepts hold organisational functionality and ability to facilitate thematic interrelation: Exodus typology, the covenant concept and the eschaton idea. Exodus typology connects narrative with theme, developing Israel’s story. The covenant idea frames stories using parallelism and gives the meta–story progression. The eschaton idea presents the Day of YHWH as an organisational principle guiding the story of judgment to restoration. It is observed that the covenant concept is the most prevalent of these themes/ideas. Assuming the conceptual unity of Luke and Acts and adopting a morpho–syntactical structuralist approach, it was observed that the covenant concept in its operative aspect of service occurred as Helper at ten places, determining the development and structure of the meta–narrative. According to the Greimasian Actantial Model, Israel failed to fulfil its covenant–based mandate to serve God and shine God’s light of mercy to the nations. Jesus, Israel’s new Helper, becomes the Subject and by his covenant–based ministry, characterised as the greatest service, resolves the problem that prevents Israel from carrying out its divine mandate and sets the stage for its fulfilment. In Jesus Israel is given new leaders, an ethical platform of discipleship and the Holy Spirit. The apostle Paul as the epitomised and exemplary witness and servant of Jesus fulfils what Israel could not. He is vindicated in righteousness and shares in the Isaianic ministry of Jesus, to bear witness to leaders and to shine God’s light to the nations. Paul is unhindered in this ministry. Additionally, in thematic–critical terms, the key placement of the covenant concept in its operative aspect of service at plot–defining junctures features its catalytic dynamic as a “template” concept advancing the re–conceptualising of themes and providing a platform for meaningful relation. The evidence thus suggests that the covenant concept in its operative aspect structures the conjoined narratives of Luke and Acts. It also provides a basis for relation between the divine and humans in the context of the history of God’s salvation, linking history and theology, and makes possible a discernible means to thematic interrelation. The SO2 electrolysis was performed by supplying the anode of the cell with SO2 gas, while the water was fed to the cathode using graphite plates as flow fields. Initial experimental work was done at ambient pressures on the anode (SO2 gas–fed) and cathode (water–fed) after which the water pressure was increased from ambient to 1 bar. Various parameters were evaluated for SO2 electrolysis at ambient conditions, including operating temperature, membrane thickness and catalyst loading. The operating temperature was increased from 50oC to 80oC which resulted in a significant voltage improvement from 0.78V to 0.64V at 300mA/cm2. Operating the cell with thinner membranes (86 vs 170um) also resulted in an improved overall cell performance, while the catalyst loading (1 vs 0.5mgPt/cm2) had a negligible effect on the operating voltage. SEM images and EDX analysis were performed on the best performing MEA (N1135) which showed that no degradation of the MEA had occurred. / Thesis (M.Sc. (Chemistry))--North-West University, Potchefstroom Campus, 2011.

Thematic interrelation is an underdeveloped field of inquiry in Lukan studies. The design and elegance of Lukan theology begs for guided investigation into a possible system of organisation that governs history and theology, that is, narrative and theme. Based on the Greimasian Actantial Model, morpho–syntactical structural–critical analysis of Luke and Acts reveals that the covenant concept in its operative aspect of service functions as an organising principle, structuring the narratives and facilitating thematic interrelation. A survey of representative Lukan research consisting of five methodologically determined approaches shows a commonality regarding Lukan purpose. These all share the “plan of God” as a fundamental concept, thus intimating its plausibility as a common organisational principle in the text. This observation encourages further analysis of Lukan narrative and meta–narrative as relevant subject matter. Investigation into the purpose and goals of Ancient Jewish and Ancient Greek literature suggests that the concepts of piety/holiness and justness combined with a notion of divine order and expectation demonstrates organisational capacity. Under the terms and conditions of the Old Covenant three non–exclusive themes/concepts hold organisational functionality and ability to facilitate thematic interrelation: Exodus typology, the covenant concept and the eschaton idea. Exodus typology connects narrative with theme, developing Israel’s story. The covenant idea frames stories using parallelism and gives the meta–story progression. The eschaton idea presents the Day of YHWH as an organisational principle guiding the story of judgment to restoration. It is observed that the covenant concept is the most prevalent of these themes/ideas. Assuming the conceptual unity of Luke and Acts and adopting a morpho–syntactical structuralist approach, it was observed that the covenant concept in its operative aspect of service occurred as Helper at ten places, determining the development and structure of the meta–narrative. According to the Greimasian Actantial Model, Israel failed to fulfil its covenant–based mandate to serve God and shine God’s light of mercy to the nations. Jesus, Israel’s new Helper, becomes the Subject and by his covenant–based ministry, characterised as the greatest service, resolves the problem that prevents Israel from carrying out its divine mandate and sets the stage for its fulfilment. In Jesus Israel is given new leaders, an ethical platform of discipleship and the Holy Spirit. The apostle Paul as the epitomised and exemplary witness and servant of Jesus fulfils what Israel could not. He is vindicated in righteousness and shares in the Isaianic ministry of Jesus, to bear witness to leaders and to shine God’s light to the nations. Paul is unhindered in this ministry. Additionally, in thematic–critical terms, the key placement of the covenant concept in its operative aspect of service at plot–defining junctures features its catalytic dynamic as a “template” concept advancing the re–conceptualising of themes and providing a platform for meaningful relation. The evidence thus suggests that the covenant concept in its operative aspect structures the conjoined narratives of Luke and Acts. It also provides a basis for relation between the divine and humans in the context of the history of God’s salvation, linking history and theology, and makes possible a discernible means to thematic interrelation. The SO2 electrolysis was performed by supplying the anode of the cell with SO2 gas, while the water was fed to the cathode using graphite plates as flow fields. Initial experimental work was done at ambient pressures on the anode (SO2 gas–fed) and cathode (water–fed) after which the water pressure was increased from ambient to 1 bar. Various parameters were evaluated for SO2 electrolysis at ambient conditions, including operating temperature, membrane thickness and catalyst loading. The operating temperature was increased from 50oC to 80oC which resulted in a significant voltage improvement from 0.78V to 0.64V at 300mA/cm2. Operating the cell with thinner membranes (86 vs 170um) also resulted in an improved overall cell performance, while the catalyst loading (1 vs 0.5mgPt/cm2) had a negligible effect on the operating voltage. SEM images and EDX analysis were performed on the best performing MEA (N1135) which showed that no degradation of the MEA had occurred. / Thesis (M.Sc. (Chemistry))--North-West University, Potchefstroom Campus, 2011.

Diese Dissertation befasst sich mit der industrienahen Herstellung von Katalysatorschichten für Polymer-Elektrolyt-Membran-Brennstoffzellen mit Hilfe des Tiefdrucks als Fertigungsverfahren. Um die Anforderungen an die Katalysatorschicht hinsichtlich der Schichtdicke zu erreichen, wird ein Linienraster für den Tiefdruck entwickelt. Das patentierte und verifizierte Designkonzept des Linienrasters ermöglicht es, trotz Tinten mit geringem Feststoffgehalt hohe Trockenschichtdicken zu erzeugen. Aufgrund des verwendeten Tiefdruckrasters sind Optimierungsschritte an der Fertigungsanlage notwendig, um eine hohe Schichtqualität zu erreichen. Schließlich werden kontinuierlich und industrienah Katalysatorschichten gefertigt, die als Membran-Elektroden-Einheit in einer Polymer-Elektrolyt-Membran-Brennstoffzelle erfolgreich eingesetzt werden. / This work presents an industrial close manufacturing process of active electrodes for Polymer Electrolyte Fuel Cells utilizing an adapted gravure printing process. To meet the requirements of the electrodes regarding the layer thickness (weight) and quality a novel line screen with maximized dipping volume for gravure printing was developed and investigated. A design rule for this kind of screens was realized and verified by a successful manufacturing of electrodes with different dried layer thicknesses. Due to the rough structure and the high dipping volumes of these line screens an adaption and optimization of the machinery and the whole process was necessary to achieve high quality electrodes. Finally, it is shown that it is possible to manufacture continuiously in an industrial close roll-to-roll process platinum loaded electrodes, working successful as cathode in a Membran-Electrode-Assembly.