In this study, two different flow field plates, a serpentine field plate and a perforated filed plate, were produced by LIGA-like formation and micro electroforming technology. The two type field plates were also used to make up three different types of micro proton exchange membrane fuel cells (µPEMFCs), serpentine (anode)-serpentine (cathode), serpentine-perforated, and perforated-perforated, each of whose active area is 1 cm2. In addition to the performance tests under different flow rate, operation temperature, and relative humidity conditions, electrochemical impedance spectroscopy (EIS) and cyclic votammetry (CV) methods were also adapted to measure correspondent EIS and Pt utilization of MEA. Even the fuel cell with serpentine field plates in anode and cathode needs more pressure input, the extra pressure is effective to avoid the water accumulation and to raise the total performance.

The research of a hydrogen proton exchange membrane fuel cell is performed under certain designing and operational conditions. The water management technique is incorperated into the experimental work. The cell voltage vs. the current densities are studied by changing the stack reactive temperatures, the gas inlet temperatures and pressures, and the relative humidities in hydrogen stream. Eventually, we hope that these experimental results can provide the information about the optimizing conditions of fuel cells so that they can be used to design a high power multiple-cell fuel cell stack. A membrane and electrode assembly (called MEA) which contains a proton exchange membrane Nafion 112, anode catalyst Pt 0.4 mg/cm2, and cathode catalyst Pt 1.0 mg/cm2 is used in this experiment. The gas flowing area is about 58% of the total area. A proper heating and humidification equipment is applied in this experimental system. The experimental results show that the cell voltage at low current density is slightly influenced by the hydrogen inlet temperature; however, the cell voltage at high current density is strongly influenced by the humidity ratio of hydrogen stream. Raising the hydrogen pressure and the oxygen pressure at the same time can increases the cell voltage, but it is no obvious effects on the cell voltage when the gas pressure increases to more than 2 atm. When air is used as a oxidizer, increasing the inlet air temperature always reduces the cell voltage. With the hydrogen stream at saturated temperature 80¢XC, the assembly torque of the stack at 4 N-m, and the stack temperature at 80¢XC, the single fuel cell stack can always generate the best cell voltages at most of the current densities. At this time, the cell voltage at current density 1 A/cm2 already can reach a value higher than 0.6 V.

A three dimensional numerical model for a micro proton exchange membrane fuel cell was developed to simulate the concentration distribution of the fuel gas, and analyze the flow field and current field in the fuel cell. Finite control volume scheme with SIMPLEC algorithm was employed in the numerical method. Various operating conditions on the performance of the fuel cell were studied. It was shown that the concentration of oxygen at the cathode can strongly influence the cell performance. Increase the operating temperature and the pressure of the inlet gas can improve the performance of the fuel cell.

Proton exchange membrane (PEM) fuel cell possesses the characteristics of microminiaturization and low temperature operation. For this reason, the proton exchange membrane fuel cell is very suitable to serve as power source of portable electronic products. In this paper, a three-dimensional numerical model to evaluate the voltage and the total current density of a PEM fuel cell stack was developed. The polarization curves of the PEM fuel cell stack under three different operating temperatures were investigated. In this study, the micro PEM fuel cell stack contains two single cells. Pure H2 gas stream was supplied as the anode inlet flow and air as the cathode inlet flow under constant pressure at 97 kPa and constant cell temperate (298K¡B308K¡B323K) conditions. Because the cell temperature may affect the chemical reaction rate on the cathode side, we discussed the influences of different temperatures on the cell performance. Solutions were compared with the experimental data. Both the value of power density and the tendency of polarization curve are in good agreement with the experimental data.

Proton exchange membrane fuel cells (PEMFC) are attractive power sources as they offer high conversion efficiencies with low or no pollution. However, several challenges, especially the sluggish oxygen reduction reaction (ORR) and the high cost of Pt catalysts, impede their commercialization. With an aim to search for more active, less expensive, and more stable ORR catalysts than Pt, this dissertation focuses on the development of non-platinum or low-platinum Pd-based nanostructured electrocatalysts and a fundamental understanding of their structure-property-performance relationships. Carbon-supported Pd–Ni nanoalloy electrocatalysts with different Pd/Ni atomic ratios have been synthesized by a modified polyol reduction method, followed by heat treatment in a reducing atmosphere at 500–900 oC. The Pd–Ni sample with a Pd:Ni atomic ratio of 4:1 after heat treatment at 500 °C exhibits the highest electrochemical surface area and catalytic activity. The enhanced activity of Pd80Ni20 compared to that of Pd is attributed to Pd enrichment on the surface and the consequent lattice-strain effects. To improve the catalytic activity and long-term durability of the Pd–Ni catalysts, Pd–Pt–Ni nanoalloys have been synthesized by the same method and evaluated in PEMFC. The Pt-based mass activity of the Pd–Pt–Ni catalysts exceeds that of commercial Pt by a factor of 2, and its long-term durability is comparable to commercial Pt within the testing duration of 180 h. Both the favorable and detrimental effects of Pd and Ni dissolution on the performance of the membrane-electrode assembly (MEA) have been investigated by compositional analysis by transmission electron microscopy (TEM) of the MEAs before and after the fuel cell test. The MEAs of the Pd–Pt–Ni catalyst have then been characterized in-situ by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) to better understand the performance changes during cell operation. The surface state change from Pd-enrichment to Pt-enrichment and the consequent decrease in the charge transfer resistance during cell operation is believed to contribute to the activity enhancement. To further improve the MEA performance and durability, the as-synthesized Pd–Pt–Ni catalysts have been pre-leached in acid and Pd–Pt alloy catalysts have been synthesized to alleviate contamination from dissolved metal ions. Compared to the pristine Pd–Pt–Ni catalyst, the preleached catalyst shows improved performance and the Pd–Pt catalyst exhibits similar performance in the entire current density range. Finally, the catalytic activities for ORR obtained from the rotating disk electrode (RDE) and PEMFC single-cell measurements of all the catalysts are compared. The improvement in the activities of the Pd-Pt-based catalysts compared to that of Pt measured by the RDE experiments is much lower than that obtained in single cell test. In other words, RDE tests underestimate the value of the Pd-Pt-based electrocatalysts for real fuel cell applications. Also, based on the RDE data, the Pd–Pt–Cu catalyst exhibits the highest catalytic activity among all the Pd–Pt–M (M = Fe, Ni, Cu) catalysts studied. / text

Made available in DSpace on 2018-08-02T00:00:46Z (GMT). No. of bitstreams: 1 tese_11381_Amanda Loureiro Nascimento.pdf: 5566345 bytes, checksum: 5395dbad693189a43064b03b3fb7e88b (MD5) Previous issue date: 2017-09-12 / A dissertação propõe a modelagem de um sistema híbrido isolado composto por arranjo fotovoltaico e conjunto de células a combustível do tipo membrana trocadora de prótons utilizando o software PSCAD. O texto traz a revisão dos principais conceitos relativos à energia fotovoltaica e à célula a combustível, além de apresentar trabalhos relacionados ao tema que motivaram a realização desse estudo. O módulo fotovoltaico é modelado a partir de folha de dados fornecida pelo fabricante, enquanto que a célula a combustível tem seu modelo baseado em estudo realizado anteriormente. Para garantir a potência do sistema, são feitas associações série-paralelo dos módulos fotovoltaicos e das células a combustível. A modelagem do sistema híbrido, que inclui inversores, conversor buck e filtros LCL, assim como o controle utilizado são apresentados de forma detalhada. As fontes atuam em conjunto para suprir as cargas no sistema isolado. Entretanto, o conjunto de células a combustível somente produz potência ativa quando o arranjo fotovoltaico é incapaz de suprir a demanda total, com exceção da partida do sistema. Por se tratar de sistema isolado e pela fonte solar fotovoltaica ter a característica de fonte intermitente, a referência dos sistemas de controle advém do conjunto de PEMFCs. O objetivo das simulações é verificar a dinâmica de funcionamento do sistema isolado mediante variações de radiação solar e de carga. Palavras-chave: Célula a combustível. Arranjo fotovoltaico. PEMFC. PSCAD. Sistema híbrido.

Hydrogen fuel cells have the potential to dramatically reduce emissions from the energy sector, particularly when integrated into an automotive application. However, there are three main hurdles to the commercialisation of this promising technology; one of which is reliability. Cur- rent standards require an automotive fuel cell to last around 5000 h of operation (equivalent to around 150,000 miles), which has proven difficult to achieve to date. This hurdle can be overcome through in-depth reliability analysis including techniques such as Failure Mode and Effect Analysis (FMEA), Fault Tree Analysis (FTA) and Petri-net simulation. This research has found that the reliability field regarding hydrogen fuel cells is still in its infancy, and needs development, if the current standards are to be achieved. In this research, a detailed reliability study of a Polymer Electrolyte Membrane Fuel Cell (PEMFC) is undertaken. The results of which are a qualitative and quantitative analysis of a PEMFC. The FMEA and FTA are the most up to date assessments of failure in fuel cells developed using a comprehensive literature review and expert opinion. Advanced modelling of fuel cell degradation logic was developed using Petri-net modelling techniques. 20 failure modules were identfied that represented the interactions of all failure modes and operational parameters in a PEMFC. Petri-net simulation was used to overcome key pitfalls observed in FTA to provide a verfied degradation model of a PEMFC in an automotive application, undergoing a specific drive cycle, however any drive cycle can be input to this model. Overall results show that the modeled fuel cell's lifetime would reach 34 hours before falling below the industry standard degradation rate of more than 5%. The degradation model has the capability to simulate fuel cell degradation under any drive cycle and with any operating parameters. A fuel cell test rig was also developed that was used to verify the simulated degradation. The rig is capable of testing single cells or stacks from 0-470W power. The results from the verification experimentation agreed strongly with the degradation model, giving confidence in the accuracy of the developed Petri-net degradation model. This research contributes greatly to the field of reliability of PEMFCs through the most up-to-date and comprehensive FMEA and FTA presented. Additionally, a degradation model based upon Petri-nets is the first degradation model to encompass a 1D performance model to predict fuel cell life time under specific drive cycles.

Philosophiae Doctor - PhD / Proton exchange membrane fuel cells (PEMFC) converts chemical energy from the electrochemical reaction of oxygen and hydrogen into electrical while emitting heat, oxygen depleted air (ODA) and water as by-products. The by-products have useful functions in aircrafts, such as heat that can be used for ice prevention, deoxygenated air for fire retardation and drinkable water for use on board. Consequently, the PEMFC is also studied to optimize recovery of the useful products. Despite the progress made, durability and reliability remain key challenges to the fuel cell technology. One of the reasons for this is the limited understanding of PEMFC behaviour in the aeronautic environment. The aim of this thesis was to define a comprehensive non-intrusive diagnostic technique that provides real time diagnostics on the PEMFC State of Health (SoH). The framework of the study involved determining factors that have direct influence on fuel cell life in aeronautic environment through a literature survey, examining the effects of the factors by subjecting the PEMFC to simulated conditions, establishing measurable parameters reflective of the factors and defining the diagnostic tool based on literature review and this thesis finding.

Les préoccupations environnementales actuelles nous amènent à envisager des solutions alternatives, telles que la pile à combustible. Cette dernière malgré ses avantages présente des faiblesses qui ralentissent sa diffusion au sein de l'industrie, entre autres, sa trop courte durée de vie. Face à cette considération, nous proposons d'appliquer le PHM à la PEMFC. Il faut donc développer le pronostic puis considérer son insertion au sein d'un système industriel. Nous choisissons de baser l'approche proposée sur un modèle de comportement, tout en proposant de combler le manque de connaissance concernant le vieillissement de la pile par les données, ce qui nous permet amène à développer une approche hybride. Dans ces travaux, le modèle comportemental est étudié sur des durées de plus en plus grandes pour enfin proposer une prédiction de l'ordre du millier d'heure. Afin de prendre en compte une implantation au sein d'un système réel, une étude sur la généricité et applicabilité de l'approche est réalisée. Ainsi, ces travaux proposent une approche de pronostic hybride basée sur un modèle de comportement et étudie son insertion au sein d'un système réel. / The current environmental concerns lead us to consider alternative solutions. The fuel cell can be one of them with numerous advantages, it presents however weaknesses, especially, its life duration which is too short. Face to this issue, we offer to apply the PHM to the PEMFC. For that, it is necessary to develop the prognostics for this application and the possibility of the on-line implementation on an industrial system. It was chosen to base the approach on a behavioral model in which the knowledge gaps are completed with the use of data. So, the approach proposed here, is hybrid. In this work, the behavioral model is studied on laps of time longer in order to finally introduce a prediction of a thousand of hours. Then, the online implementation on a real system is considered with a genericity and an applicability study. This work proposes a hybrid prognostics approach based on a behavioral model and study its implementation on an industrial system.

Este trabalho teve como objetivo sintetizar eletrólitos híbridos de Nafion-TiO2 e eletrocatalisadores de PtSn/C para a aplicação em células a combustível de oxidação direta de etanol (DEFC) em alta temperatura (130oC). Para tanto, partículas de TiO2 foram incorporadas in-situ em membranas comerciais de Nafion via processo sol-gel. Os materiais resultantes foram caracterizados por análise gravimétrica, absorção de água, DSC, DRX e EDX. Eletrocatalisadores baseados em platina-estanho dispersos em carbono (PtSn/C), de diferentes composições, foram produzidos pelo método de redução por álcool e utilizados como eletrodos anódicos. Os eletrocatalisadores foram caracterizados por DRX, EDX, XPS e MET. A avaliação eletroquímica dos eletrocatalisadores foi realizada por voltametria cíclica, varredura linear anódica de monóxido de carbono (stripping de CO) e cronoamperometria. Ânodos de PtSn/C e cátodos de Pt/C comercial foram dispostos juntamente com os híbridos Nafion-TiO2 para a formação do conjuntos membrana-eletrodos. A avaliação final dos materiais foi realizada por meios de curvas de polarização em células unitárias alimentadas com misturas padrão H2/CO ou etanol no ânodo e com oxigênio no cátodo no intervalo de temperatura de 80 a 130oC. As análises demonstraram que o uso de membranas híbridas diminuiu o crossover de combustível, melhorando o desempenho da célula e que o eletrocatalisador PtSn/C 70:30, produzido pelo método de redução por álcool, foi o que demonstrou melhor desempenho para oxidação de etanol. / In this work, Nafion-TiO2 hybrid electrolytes and PtSn/C electrocatalysts were synthesized for the application in direct ethanol fuel cell operating at high temperature (130oC). For this purpose, TiO2 particles were incorporated in commercial Nafion membranes by an in situ sol gel route. The resulting materials were characterized by gravimetric analysis, water uptake, DSC, XRD and EDX. Electrocatalysts based on carbon dispersed platinum-tin (PtSn/C), with different composition, were produced by alcohol-reduction method and were employed as anodic electrode. The electrocatalysts were characterized by XRD, EDX, XPS and transmission electronic spectroscopy. The electrochemical characterization was conducted by cyclic voltametry, carbon monoxide linear anodic voltammetry (CO stripping), and chronoamperometry. Membrane-electrodes assembly (MEAs) were formed with PtSn/C anodes, Pt/C cathodes and Nafion-TiO2 hybrids. The performance of these MEA was evaluated in single-cell fed with H2/CO mixture or ethanol solution at the anode and oxygen at the cathode in the temperature range of 80-130oC. The analysis showed that the hybrid membranes improved the DEFC performance due to crossover suppression and that PtSn/C 70:30 electrocatalysts, prepared by an alcohol reduction process, showed better performance in ethanol oxidation.