Academic literature on the topic 'Limiting factors for fuel cell'
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Journal articles on the topic "Limiting factors for fuel cell"
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FRENI, S., S. CAVALLARO, M. AQUINO, D. RAVIDA, and N. GIORDANO. "Lifetime-limiting factors for a molten carbonate fuel cell." International Journal of Hydrogen Energy 19, no. 4 (April 1994): 337–41. http://dx.doi.org/10.1016/0360-3199(94)90065-5.
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Fry, M. R., H. Watson, and J. C. Hatchman. "Design of a prototype fuel cell/composite cycle power station." Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy 211, no. 2 (March 1, 1997): 171–80. http://dx.doi.org/10.1243/0957650971537088.
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The aspiration for fuel cells, in a public utility context, is that they are envisaged in the developed world as a means of significantly increasing the overall efficiency of power plants and of utilizing poor-quality fuel supplies. The thermodynamic and practical aspects in the design of a prototype power station consisting of a composite cycle of fuel cells, a gas turbine expander and a steam plant, or a steam plant only, are reported. The design was based on tubular fuel cell development. Overall efficiencies are estimated and limiting factors in the design are identified. Performance and emission characteristics are compared with existing plant.
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Papurello, Davide, Andrea Lanzini, Davide Drago, Pierluigi Leone, and Massimo Santarelli. "Limiting factors for planar solid oxide fuel cells under different trace compound concentrations." Energy 95 (January 2016): 67–78. http://dx.doi.org/10.1016/j.energy.2015.11.070.
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Yurova, Polina A., Viktoria R. Malakhova, Ekaterina V. Gerasimova, Irina A. Stenina, and Andrey B. Yaroslavtsev. "Nafion/Surface Modified Ceria Hybrid Membranes for Fuel Cell Application." Polymers 13, no. 15 (July 30, 2021): 2513. http://dx.doi.org/10.3390/polym13152513.
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Low chemical durability of proton exchange membranes is one the main factors limiting their lifetime in fuel cells. Ceria nanoparticles are the most common free radical scavengers. In this work, hybrid membranes based on Nafion-117 membrane and sulfonic or phosphoric acid functionalized ceria synthesized from various precursors were prepared by the in situ method for the first time. Ceria introduction led to a slight decrease in conductivity of hybrid membranes in contact with water. At the same time, conductivity of membranes containing sulfonic acid modified ceria exceeded that of the pristine Nafion-117 membrane at 30% relative humidity (RH). Hydrogen permeability decreased for composite membranes with ceria synthesized from cerium (III) nitrate, which correlates with their water uptake. In hydrogen-air fuel cells, membrane electrode assembly fabricated with the hybrid membrane containing ceria synthesized from cerium (IV) sulfate exhibited a peak power density of 433 mW/cm2 at a current density of 1080 mA/cm2, while operating at 60 °C and 70% RH. It was 1.5 times higher than for the pristine Nafion-117 membrane (287 mW/cm2 at a current density of 714 mA/cm2).
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Yim, Chae-Ho, and Yaser Abu-Lebdeh. "Understanding Key Limiting Factors of Electrode and Cell Designs in Solid-State Lithium Batteries." ECS Meeting Abstracts MA2022-01, no. 2 (July 7, 2022): 213. http://dx.doi.org/10.1149/ma2022-012213mtgabs.
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Solid-state batteries (SSBs) use solid electrolytes (SE) to replace flammable liquid electrolytes that result in safer batteries with increased energy density enabled by lithium metal as an anode. Even though there have been recent major breakthroughs at the material level and some at the cell level, there are still many more challenges to overcome that are mostly related to the solid-solid interfaces besides the grand challenge of manufacturing these type of batteries with or without existing manufacturing processes with the promised energy density ( > 400Wh/Kg) at targeted low costs (< 100$/KWh). For this to happen, it is important to look into all the changes that need to be made at the material, electrode and cell levels compared to what is currently used in Li-ion cells and critically evaluate their impact on the cell energy density. In this work, we have first used an equation that we have previously modified and used to calculate the impact of Si content in Si-graphite composite on the full-cell energy density (2) to evaluate the impact of the following parameters (type of anode-or no anode- and cathode materials. N/P ratio, thickness of SE and most importantly the composite cathode formulation on the full-cell energy density. In the latter, we have evaluated the thickness of two electrodes, amount and volume of cathode active material, and amount of catholyte). We will present the impact of each of the above-mentioned factors on the cell energy density supported by data from half and full cells using composite cathodes coupled with and without lithium metal as an anode. References: (1) Mauro Pasta et al 2020 J. Phys. Energy 2 032008. (2) Chae-Ho Yim, Svetlana Niketic, Nuha Salem, Olga Naboka and Yaser Abu-Lebdeh, 2017, J. Electrochem. Soc. 164 A6294.
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Jahan, Sarowar, Md Tarikul Islam, and Suman Chowdhury. "Investigation of Power Performance of a PEM Fuel Cell Using MATLAB Simulation." Malaysian Journal of Applied Sciences 5, no. 1 (April 30, 2020): 83–94. http://dx.doi.org/10.37231/myjas.2020.5.1.230.
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Fuel cell based power generation systems have gained remarkable interest in this modern age, due to its high conversion efficiency and reliability. Among the different types of fuel cells, PEM fuel cells are achieving more significance due to its fast start up time and low operating temperature. This paper studies the mathematical model of proton exchange membrane of fuel cell (PEMFC) using Matlab/SIMULINK software. The paper consists of the calculation of cell voltage, stack current, ohmic loss, activation loss. This model is used to research the fuel cell behavior and the characteristic of output values at different parameters. The model consists of the cathode gas channel, gas diffuser, catalyst layer, and the membrane. In order to composite shape of the gas diffuser and for its gradient in liquid water content, the gas diffuser is modeled as a series of parallel layers with different porosity. It represents in terms of the physical and thermodynamic parameters of the fuel cell. The curve of polarization is expressed parametrically as a function of the surface over potential. This paper expresses for cathode internal as well as overall effectiveness factors, active fraction of the catalyst layer resistance, catalyst layer, limiting current density, and the slope of the polarization curve.
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Chick, Larry A., Kerry D. Meinhardt, Steve P. Simner, Brent W. Kirby, Mike R. Powell, and Nathan L. Canfield. "Factors affecting limiting current in solid oxide fuel cells or debunking the myth of anode diffusion polarization." Journal of Power Sources 196, no. 10 (May 2011): 4475–82. http://dx.doi.org/10.1016/j.jpowsour.2011.01.035.
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Stöver, Detlev, Hans Peter Buchkremer, Andreas Mai, Norbert H. Menzler, and Mohsine Zahid. "Processing and Properties of Advanced Solid Oxide Fuel Cells." Materials Science Forum 539-543 (March 2007): 1367–72. http://dx.doi.org/10.4028/www.scientific.net/msf.539-543.1367.
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Up to now, Solid Oxide Fuel Cell (SOFC) materials and processing does not meet the cost goals for commercialization. This resulted in a worldwide increase in R&D activities dealing with advanced materials and effective manufacturing methods. The present paper describes efforts to process novel SOFC materials as well as optimization of well known ones. The R&D trends are explained for key components such as anode, electrolyte, cathode, contact- and protective layers. Typical SOFC manufacturing methods include tape casting, extrusion, calendaring and axial pressing. Each of these techniques has advantages and limitations. Examples for the highly efficient use of these methods are given for electrolyte supported cells as well as anode and cathode supported designs. An evaluation in reference to automation, process complexity and costs is given under the present limiting factors. Exemplary the processing by tape casting and the micro structural fine tuning of an advanced anode-supported system is discussed in detail. To produce the layered components of an SOFC, techniques like screen printing, wet powder spraying, PVD and CVD are under development. While the layer properties are excellent, PVD and CVD are nowadays too expensive in some cases, due to the low deposition rates. If thin layers are required, these techniques become interesting under cost considerations. The effectiveness of a PVD interlayer between electrolyte and high power density cathodes is shown in comparison to a sintered layer. In thin electrolyte concepts, the cathode becomes the power limiting component at operating temperatures below around 750°C. Thus new cathode materials and adjusted processing parameters are under development. The possibilities to manufacture advanced cathode layers by screen printing, wet powder spraying and other wet chemical methods are discussed. As an example screen printing of LSCF is described which results in a high power density cathode layer for low temperature SOFC operation. Finally, future needs to achieve the technical and economic goals are summarized.
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Vlachopoulos, Nick, and Anders Hagfeldt. "Photoelectrochemical Cells Based on Dye Sensitization for Electricity and Fuel Production." CHIMIA International Journal for Chemistry 73, no. 11 (November 1, 2019): 894–905. http://dx.doi.org/10.2533/chimia.2019.894.
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Dye-sensitized semiconductor oxide photoelectrodes in which light is absorbed by a monomolecular layer of dye chemisorbed on a porous oxide substrate have attracted considerable interest in the last 35 years, mainly for the conversion of sunlight to electricity, in dye-sensitized solar cells (DSSCs) with maximal efficiencies in the range 10–15%, and, most recently, as dye-sensitized photoelectrochemical cells (DSPECs) for the generation of solar fuels. In the latter direction, considerable progress has been achieved but the efficiency is notably lower than for electricity generation. In the present review, the basic physicochemical principles of the DSSC and DSPEC operation are described, several keynote results reported, and the factors limiting the performance and necessitating further research highlighted.
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Cai, Wenfang, and Yunhai Wang. "Investigation of a two-dimensional model on Cu2+ recovery in bioemectrochemical system." IOP Conference Series: Earth and Environmental Science 1135, no. 1 (January 1, 2023): 012013. http://dx.doi.org/10.1088/1755-1315/1135/1/012013.
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Abstract A novel microbial fuel cell (MFC) was designed to recover Cu2+ from simulated electroplating wastewater. The BES has two chambers separated by a bipolar membrane and two cathodes. To explore the rate controlling step affecting Cu2+ deposition rate, spatial mass distribution and its deposition process during Cu2+ deposition on MFC cathode. A two-dimensional, transient model was built to study the factors that limiting Cu2+ deposition in MFC. We found that the formation of ion scarcity zone would decrease Cu2+ deposition rate, which leading to mass transfer limiting Cu2+ reduction on cathode surface (x=0 m). While near the cathode tip (x=0.02 m), the highest deposition rate and thickness was obtained. Furthermore, diffusion and electro-migration of Cu2+ were synergistic to improve Cu2+ reduction efficiency, and electro-migration of Cu2+ had a great impact on Cu2+ transferring from electrolyte domain to electrode surface. This research provided a new studying direction for heavy metal wastewater treatment and metal separation and recovery in the electroplating industry to improve metal ions deposition rate.
Dissertations / Theses on the topic "Limiting factors for fuel cell"
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Khadke, Prashant Subhas [Verfasser], and Ulrike [Akademischer Betreuer] Krewer. "Analysis of Performance Limiting factors in H2-O2 Alkaline Membrane Fuel Cell / Prashant Subhas Khadke ; Betreuer: Ulrike Krewer." Braunschweig : Technische Universität Braunschweig, 2016. http://d-nb.info/1175818275/34.
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Khadke, Prashant Subhas Verfasser], and Ulrike [Akademischer Betreuer] [Krewer. "Analysis of Performance Limiting factors in H2-O2 Alkaline Membrane Fuel Cell / Prashant Subhas Khadke ; Betreuer: Ulrike Krewer." Braunschweig : Technische Universität Braunschweig, 2016. http://nbn-resolving.de/urn:nbn:de:gbv:084-16092811020.
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PAPURELLO, DAVIDE. "Biogas from anaerobic digestion of biomass (Organic Fraction of Municipal Solid Waste and sewage sludge): trace compounds characterization through an innovative technique (PTR-MS) and detrimental effects on SOFC energy generators, from single cells to short stacks." Doctoral thesis, Politecnico di Torino, 2014. http://hdl.handle.net/11583/2544741.
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The use of biofuels instead of conventional fossil derived fuels is becoming an increasingly crucial topic for future energy systems where environmental issues are also taken into account. Biomass exploitation, including biowaste, appears as a promising means for the energy production and also it contributes to the carbon dioxide emissions reduction. Among the different techniques for biomass exploitation, interesting aspects are covered by the dry anaerobic fermentation of organic waste (OFMSW). In addition also interesting aspects can be achieved by the anaerobic digestion of sewage sludge in waste water treatment plants (WWTPs). Organic waste collection from local municipal areas or from sewage sludge exploitation with subsequent energy valorization through CHP systems allows to reduce the amount of waste disposed into landfills and the pollutant emissions into the atmosphere. Solid Oxide Fuel Cell (SOFC) systems are among the most promising energy generator respect to traditional power generating systems due to their higher electrical conversion values, even at partial loads. This is due to the direct conversion of chemical energy to electrical energy. Hence, fuel cells are very appealing from both energy and environmental point of view.
In this work, the main goal was to demonstrate the real feasibility of a SOFC stack system fed by real biogas. This main goal has to be achieved considering three main sub-goals. The first one related to the biogas aspects, mainly on trace compounds investigation followed by the VOCs cleaning for SOFC requirements and then testing the main and the most dangerous VOCs on single cells and on short stacks. These information have been fundamentals for the SOFC generator directly fed by biogas. A 500 We SOFC stack by SOFCpower (Italy) was operated for more than 400 hrs in conjunction with a biogas feeding system.
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Uría, Moltó Naroa. "Microbial fuel cell performance: design, operation and biological factors." Doctoral thesis, Universitat Autònoma de Barcelona, 2012. http://hdl.handle.net/10803/284032.
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Una pila microbiana de combustible es un sistema bioelectroquímico en el cual las bacterias oxidan materia orgánica y transfieren los electrones a un electrodo produciendo electricidad. La eficiencia de este sistema depende de la actividad metabólica de los microorganismos creciendo en el ánodo, pero también de un gran número de factores relacionados con el diseño y la operación del sistema. El objetivo de esta tesis es contribuir al análisis y control de algunos de estos factores, así como ayudar a determinar el papel de los diferentes mecanismos de transferencia de electrones en el funcionamiento de estos dispositivos.
En primer lugar, este trabajo analiza factores relacionados con el diseño que afectan al rendimiento de una pila microbiana. Así, se centra en el efecto de diferentes catalizadores abióticos así como en la relación entre las áreas del cátodo y ánodo necesarias para no afectar la potencia obtenida. Los resultados revelan que catalizadores solubles permiten potencias mucho mayores, y por tanto necesitan menor relación entre las áreas de cátodo y ánodo que en el caso de las pilas con cátodos de platino. No obstante, a largo plazo, las pilas con catalizadores solubles de hierro muestran un descenso progresivo del rendimiento de la celda de combustible que las hace poco adecuadas para aplicaciones que requieren operaciones de larga duración. Recientemente, la búsqueda de catalizadores adecuados para el cátodo ha llevado a los investigadores a explorar el posible uso de biocátodos. En esta tesis se demuestra la capacidad de Shewanella oneidensis MR-1 para catalizar la reacción del cátodo tanto en condiciones aeróbicas como anaeróbicas, siendo capaz de aceptar la corriente proporcionada por las bacterias presentes en el ánodo.
El potencial de las bacterias que se encuentran en el ánodo para la producción de corriente no sólo depende de los niveles de actividad microbiana y de la supresión de las limitaciones producidas por el cátodo, sino que es afectada también por factores relacionados con el funcionamiento del sistema. Nosotros mostramos la importancia de una operación ininterrumpida como otro factor relevante para determinadas aplicaciones. Periodos de interrupción del circuito producen una alteración en los valores de corriente en forma de picos, que aparecen cuando el circuito es cerrado tras un periodo de interrupción y que caen lentamente hasta alcanzar valores normales de corriente. Mediante análisis más exhaustivos de este fenómeno se demuestra la capacidad de Shewanella oneidensis MR-1 para almacenar carga eléctrica en ausencia de aceptores de electrones.
Finalmente, se estudió la contribución en la producción de corriente de los diferentes mecanismos de transferencia de electrones en pilas con comunidades microbianas complejas. La pila con el ánodo descubierto muestra que los mecanismos de transferencia directa son responsables de la mayor parte de la corriente generada. La comunidad microbiana formada se encuentra relacionada con la vía de transferencia de electrones disponible con especies microbianas como Shewanella, Aeromonas, Pseudomonas o Propionibacterium. Los mecanismos de transferencia mediante mediadores le siguen en importancia, siendo los responsables del 40% de la corriente producida. Esta pila cuya corriente depende de la producción de mediadores muestra una gran cantidad de especies redox en el anolito, algunas de ellas no relacionadas con mediadores ya descritos. Por último, en la pila con el electrodo cubierto de nafion, la única especie química capaz de llegar a la superficie del ánodo es el hidrógeno. En este caso, la producción de corriente es sostenida gracias a la relación entre algunos organismos como Comamonas, Alicycliphilus, Diaphorobacter o la archaea Methanosaeta y el ánodo. La oxidación de acetato mediante estos microorganismos resulta en la producción de hidrógeno, el cual es oxidado en la superficie del ánodo tras cruzar el nafion.A Microbial Fuel Cell (MFC) is a bioelectrochemical system, in which bacteria oxidize organic matter and transfer the electrons through their electron transport chains onto an electrode surface producing electricity. The efficiency of the system depends on the metabolic activity of the microorganisms growing at the anode but also on a large number of factors related to the design and operation of the MFC. The purpose of this work is to contribute to the analysis and control of some of these factors as well as to throw some light on the role of different electron transfer mechanisms in MFC operation. To achieve this goal different experiments using the electrogenic bacterium Shewanella oneidensis MR-1 have been carried out. First of all, this works analyses the role of several design factors in MFC performance. This part of the research focuses on the effect of different abiotic catalysts as well as the cathode to anode ratio required for unhindered power output. The results indicate that soluble catalysts such as ferricyanide allow much higher power values, and therefore need smaller cathode/anode ratios than platinum-based cathodes. In the long term, however, MFCs containing soluble iron catalysts show a progressive degradation of fuel cell performance make them unfit for applications requiring extended operations. In recent years, the search for a suitable catalyst at the cathode has led researchers to explore the possible use of biocathodes. In this work, we demonstrate the capacity of Shewanella oneidensis MR-1 to catalyse the cathode reaction both under aerobic and anaerobic conditions, being able to sustain the current provided by bacteria present in the anode. The potential of anode bacteria for current production does not only depend on the levels of microbial activity and on the removal of cathodic limitations but seems to be also affected by factors related to the operation of the system. We have shown the importance of continuous MFC operation as another important factor to take into account for some applications. Periods of circuit interruption produce an alteration of the normal current output in the form of defined current peaks that appear when closing the circuit after a short period of current interruption and that decay slowly back to the original stable values. In depth analysis of this response demonstrates the capacity of Shewanella oneidensis MR-1 to store charge when no electron acceptors are present. Finally, we intended to determine the contribution of the different electron transfer mechanisms to current production in MFCs harbouring complex microbial communities. The MFC with a naked anode shows that direct electron transfer mechanisms are responsible for most of the current generated. The microbial community formed agrees with the electron transfer pathways available. So, this MFC presents species able of direct and mediated electron transfer as Shewanella, Aeromonas, Pseudomonas or Propionibacterium. The MFC sustained by shuttle-dependent electron transfer follows in importance being responsible for as much as 40% of current output. This reactor shows a great quantity of different redox species in the anolyte bulk, some of them not related to mediators currently described in the literature. Finally, in the MFC with a nafion-coated anode, the only chemical species able to diffuse to the anode surface is hydrogen. In this case, current production is sustained by the interaction between some organisms, such as Comamonas, Alicycliphilus, Diaphorobacter or the archaea Methanosaeta and the anode. Oxidation of acetate by these microorganisms results in hydrogen production that is therefore oxidised at the anode surface after crossing the nafion barrier. Current production by this mechanism would account for not more than 5% of the total current evolved in an unrestricted MFC.
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BONA, DENIS. "Study on the key factors allowing the PEM fuel cell systems large commercialization: fuel cell degradation and components integration." Doctoral thesis, Politecnico di Torino, 2014. http://hdl.handle.net/11583/2537914.
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PEM Fuel Cells are expected to gradually substitute internal combustion engines as electrical and co-generation power sources thanks to high efficiency, low operating temperature, fast startup time and favourable power-to-weight ratio.
However, while PEMFCs have achieved significant progresses in the last decade, their short lifetime and high cost still continue to impede large-scale commercialization.
The first subject of the present work had been the study of the PEM fuel cells degradation mechanisms with the aim of: a) find out the most relevant phenomena concerning the fuel cell lifetime, b) testing some methods able to promptly detect the degradation mechanisms and, mostly, c) find out the mitigation strategies able to increase the fuel cells lifetime.
At the end of the research three mitigation strategies had been developed and tested: cell voltage monitoring, the current modulation and the stack shunt. According to the tests results all these mitigation strategies, if adopted all together, can effectively led to doubling the fuel cells lifetime.
In parallel to the fuel cell lifetime increase, a deep investigation on system components integration had been conducted. Following this principle, the system cost has been considerably reduced mostly thanks to the DC-DC converter integration with the stack and the coolant circuit simplification.
The prototypes realized during this work has been taken as example for the production of new fuel cell power systems with increased lifetime at lower cost
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Marcum, Allen McDonald 1961. "Study of factors around automotive fuel cell implementation and market acceptance." Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/8884.
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Thesis (S.M.M.O.T.)--Massachusetts Institute of Technology, Sloan School of Management, Management of Technology Program, 2001.Includes bibliographical references (p. 78-79).
There are data that suggest that the earth's surface temperature has. increased over the past century. Many scientists believe that this rise is due to the emissions of greenhouse gases by anthropogenic sources, while others believe it is due primarily to natural phenomena, such as solar cycles. Regardless of the actual cause, we should be motivated to drastically reduce · emissions of these gases, improve fuel efficiency, and reduce other type of air pollution. This will also reduce the country's reliance on potentially unstable foreign sources of these fuels. There are many technologies currently being developed which promise to reduce our consumption of fossil fuels in automotive applications, including direct injection internal combustion engines, hybrid engines, battery-powered cars, fuel cells, 42-volt electrical systems, and lightweight bodies. When considered on total lifecycle and infrastructure bases, there can be significant downsides associated with any of these technological improvements, but each also offers a potential contribution to lowering fuel consumption. This thesis proposes that there are steps that can be taken to enhance the mainstream acceptance and benefits of these technologies, including early electrification of loads onboard vehicles, incremental reductions in consumption, and use of fleets to implement technologies requiring new infrastructure buildouts. However, automotive emissions are a small part of the overall emission problem, and we should also be concentrating efforts in other areas as well.
by Allen McDonald Marcum.
S.M.M.O.T.
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Colon-Jimenez, Lisandra. "Factors limiting spontaneous repair and their relevance for the efficiency of stem cell therapy of infarcted hearts." The Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1266171874.
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Dyantyi, Noluntu. "Factors influencing fuel cell life and a method of assessment for state of health." University of the Western Cape, 2018. http://hdl.handle.net/11394/6753.
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Philosophiae Doctor - PhDProton 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.
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Biz, Chiara. "Electronic and magnetic factors in the design of optimum catalysts for hydrogen fuel cells." Doctoral thesis, Universitat Jaume I, 2022. http://dx.doi.org/10.6035/14104.2022.709278.
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Fuel cells represent one of the most promising energy storage system nowadays. Nonetheless, several obstacles need to be overcome in order to commercially exploit this technology. One of them lies in the efficiency loss due to the overpotential of the oxygen reduction reaction (ORR). Thus, during the last decades, researchers have mainly focused on finding optimum solid catalyst(s) with the following profile: good ORR activity, good stability under the operating FC conditions, inexpensive, widely available and environmentally friendly. Magnetic catalysts, based on 3d-metals such as Pt-based alloys fit conveniently that profile. The understanding of their outstanding catalytic properties starts with the comprehension of complex physicochemical phenomena in which the spins of the electrons play a significant role. Cooperative ferromagnetic spin-electron interactions are indeed one of the most important energetic contributions in allowing milder chemisorption of reactants onto magnetic catalysts. Accordingly, their study is the focus of this doctoral thesis.Programa de Doctorat en Ciències
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Morgan, Jason. "Towards an Understanding of the Gas Diffusion Layer in Polymer Electrolyte Membrane Fuel Cells." Digital WPI, 2016. https://digitalcommons.wpi.edu/etd-dissertations/555.
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The gas diffusion layer (GDL) is one of the key components in a polymer electrolyte membrane (PEM) fuel cell. It performs several functions including the transport of reactant gases and product water to and from the catalyst layer, conduction of both electrons and heat produced in the catalyst layer, as well as mechanical support for the membrane. The overarching goal of this work is to thoroughly examine the GDL structure and properties for use in PEM fuel cells, and more specifically, to determine how to characterize the GDL experimentally ex-situ, to understand its performance in-situ, and to relate theory to performance through controlled experimentation. Thus, the impact of readily measured effective water vapor diffusivity on the performance of the GDL is investigated and shown to correlate to the wet limiting current density, as a surrogate of the oxygen diffusivity to which it is more directly related. The influence of microporous layer (MPL) design and construction on the fuel cell performance is studied and recommendations are made for optimal MPL designs for different operating conditions. A method for modifying the PTFE (Teflon) distribution within the GDL is proposed and the impact of distribution of PTFE in the GDL on fuel cell performance is studied. A method for characterizing the surface roughness of the GDL is developed and the impact of surface roughness on various ex-situ GDL properties is investigated. Finally, a detailed analysis of the physical structure and permeability of the GDL is provided and a theoretical model is proposed to predict both dry and wet gas flow within a GDL based on mercury intrusion porosimetry and porometry data. It is hoped that this work will contribute to an improved understanding of the functioning and structure of the GDL and hence advance PEM fuel cell technology.
Books on the topic "Limiting factors for fuel cell"
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Tsai, Ching-Wei, Sanjeev Noel, and Hamid Rabb. Pathophysiology of Acute Kidney Injury, Repair, and Regeneration. Oxford University Press, 2014. http://dx.doi.org/10.1093/med/9780199653461.003.0030.
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Acute kidney injury (AKI), regardless of its aetiology, can elicit persistent or permanent kidney tissue changes that are associated with progression to end-stage renal disease and a greater risk of chronic kidney disease (CKD). In other cases, AKI may result in complete repair and restoration of normal kidney function. The pathophysiological mechanisms of renal injury and repair include vascular, tubular, and inflammatory factors. The initial injury phase is characterized by rarefaction of peritubular vessels and engagement of the immune response via Toll-like receptor binding, activation of macrophages, dendritic cells, natural killer cells, and T and B lymphocytes. During the recovery phase, cell adhesion molecules as well as cytokines and chemokines may be instrumental by directing the migration, differentiation, and proliferation of renal epithelial cells; recent data also suggest a critical role of M2 macrophage and regulatory T cell in the recovery period. Other processes contributing to renal regeneration include renal stem cells and the expression of growth hormones and trophic factors. Subtle deviations in the normal repair process can lead to maladaptive fibrotic kidney disease. Further elucidation of these mechanisms will help discover new therapeutic interventions aimed at limiting the extent of AKI and halting its progression to CKD or ESRD.
Book chapters on the topic "Limiting factors for fuel cell"
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Kazim, Ayoub. "Determination of an Optimum Performance of a PEM Fuel Cell Based on its Limiting Current Density." In Hydrogen Materials Science and Chemistry of Carbon Nanomaterials, 159–66. Dordrecht: Springer Netherlands, 2004. http://dx.doi.org/10.1007/1-4020-2669-2_16.
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Pedrazzoli, Paolo, and John B. A. G. Haanen. "Developments in Solid Tumours." In The EBMT/EHA CAR-T Cell Handbook, 105–8. Cham: Springer International Publishing, 2022. http://dx.doi.org/10.1007/978-3-030-94353-0_19.
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AbstractChimeric antigen receptor (CAR) T cells have emerged as breakthrough therapies in patients with refractory haematologic malignancies, and the highly encouraging clinical results have fuelled expectations of implementing these strategies in other cancer types. However, a similar success of CAR-T cell treatment has not yet been observed in solid tumours. Various factors, including the immunosuppressive nature of the tumour microenvironment, hinder CAR-T cell trafficking and infiltration into scarcely accessible tumour sites, and difficulties in identifying targetable antigens with optimal expression and a good toxicity profile, limiting CAR-T dose escalation, must be overcome to achieve success in the treatment of solid cancers (Comoli et al. 2019).
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Golz, Julia Carolin, and Kerstin Stingl. "Natural Competence and Horizontal Gene Transfer in Campylobacter." In Current Topics in Microbiology and Immunology, 265–92. Cham: Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-65481-8_10.
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AbstractThermophilic Campylobacter, in particular Campylobacter jejuni, C. coli and C. lari are the main relevant Campylobacter species for human infections. Due to their high capacity of genetic exchange by horizontal gene transfer (HGT), rapid adaptation to changing environmental and host conditions contribute to successful spreading and persistence of these foodborne pathogens. However, extensive HGT can exert dangerous side effects for the bacterium, such as the incorporation of gene fragments leading to disturbed gene functions. Here we discuss mechanisms of HGT, notably natural transformation, conjugation and bacteriophage transduction and limiting regulatory strategies of gene transfer. In particular, we summarize the current knowledge on how the DNA macromolecule is exchanged between single cells. Mechanisms to stimulate and to limit HGT obviously coevolved and maintained an optimal balance. Chromosomal rearrangements and incorporation of harmful mutations are risk factors for survival and can result in drastic loss of fitness. In Campylobacter, the restricted recognition and preferential uptake of free DNA from relatives are mediated by a short methylated DNA pattern and not by a classical DNA uptake sequence as found in other bacteria. A class two CRISPR-Cas system is present but also other DNases and restriction–modification systems appear to be important for Campylobacter genome integrity. Several lytic and integrated bacteriophages have been identified, which contribute to genome diversity. Furthermore, we focus on the impact of gene transfer on the spread of antibiotic resistance genes (resistome) and persistence factors. We discuss remaining open questions in the HGT field, supposed to be answered in the future by current technologies like whole-genome sequencing and single-cell approaches.
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Salminen, Justin, and Tanja Kallio. "Battery and Fuel Cell Materials." In Materials for a Sustainable Future, 537–57. The Royal Society of Chemistry, 2012. http://dx.doi.org/10.1039/bk9781849734073-00537.
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Lithium ion battery-powered applications are rapidly increasing, especially for larger systems which include energy storage and some types of vehicles. Mass production capability exists for batteries but fuel cells are still made on a small scale. The global capacity for the industrial-scale production of large lithium ion battery cells or fuel cell systems is more likely to be the limiting factor than the shortage of natural resources if current plans for even partial electrification of vehicles or energy storage visions are to be realized. Strategic metals such as lithium, cobalt, platinum and rare earth metals are still readily available and current activities use relative small amounts. The recycling of valuable metals from both batteries and fuel cells is essential and opens up possibilities for the development of new technologies.
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Jung, Sokhee P., and Soumya Pandit. "Important Factors Influencing Microbial Fuel Cell Performance." In Microbial Electrochemical Technology, 377–406. Elsevier, 2019. http://dx.doi.org/10.1016/b978-0-444-64052-9.00015-7.
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Atkinson, Alan. "Solid Oxide Fuel Cell Electrolytes—Factors Influencing Lifetime." In Solid Oxide Fuel Cell Lifetime and Reliability, 19–35. Elsevier, 2017. http://dx.doi.org/10.1016/b978-0-08-101102-7.00002-7.
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Guo, Ting, Kankan Wang, Huikai Chang, Fang Wang, Rongliang Liang, Shiyu Wu, Zhenyu Nie, Zhijun Wang, and Guozhuo Wang. "Fuel Cell Engine Fault Analysis." In Advances in Transdisciplinary Engineering. IOS Press, 2022. http://dx.doi.org/10.3233/atde220282.
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In view of the current development status and structural characteristics of fuel cells, the typical structure of fuel cells is introduced, the faults of fuel cell are classified and summarized, which are divided into mechanical failures, electrical failures, equipment factor failures, subjective factor failures, environmental failures, etc., the factors of fuel cell failures are analyzed, and effective methods for avoiding fuel cell failures are proposed. The workload of fault diagnosis is greatly reduced, and the safety and reliability of fuel cell engines are guaranteed.
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Sterlich, Katharina, and Milen Minkov. "Childhood Langerhans Cell Histiocytosis: Epidemiology, Clinical Presentations, Prognostic Factors, and Therapeutic Approaches." In Rare Diseases [Working Title]. IntechOpen, 2021. http://dx.doi.org/10.5772/intechopen.96543.
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Childhood LCH is a rare disease, affecting 4–9 per 1,000,000 children below the age of 15 years. It is driven by somatic mutations in the MAPK pathway, arising in myeloid marrow progenitors. Both genders are affected by a slight male preponderance. The clinical spectrum of LCH varies from a single lesion affecting one organ system to severe multisystem disease with dysfunction of vital organs. Likewise, variable and unpredictable is its course, spanning from self-limiting course to progression with lethal outcome. Recognized unfavorable prognostic factors are the involvement of hematopoiesis, liver, and spleen, as well as non-response to systemic treatment. Recent studies suggest that patients carrying the BRAFV600E mutation may have a more severe clinical phenotype and less favorable prognosis. The combination of prednisolone and vinblastine is the standard first-line treatment for disseminated disease. Second-line options used in clinical practice are not well evidenced. Inhibitors of the MAPK pathway are a promising alternative option.
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Yeetsorn, Rungsima, and Yaowaret Maiket. "Hydrogen Fuel Cell Implementation for the Transportation Sector." In Hydrogen Implementation in Transportation Sector [Working Title]. IntechOpen, 2020. http://dx.doi.org/10.5772/intechopen.95291.
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Global transportation possesses have compelling rationales for reducing the consumption of oil, emissions of carbon dioxide, and noise pollution. Transitions to alternative transportation technologies such as electric vehicles (EVs) have gained increased attention from the automotive industries. A fuel cell electric vehicle (FCEV) occupying a hydrogen engine is one of the most stupendous technologies, since it is suitable for a large-scale transportation. However, its performance limitations are in question due to voltage degradation in long term operations through steady conditions under constant load and dynamic working conditions. Other drawbacks of using fuel cells in EVs are energy balances and management issues necessary for vehicle power and energy requirements. An efficient solution to accommodate driving behavior like dynamic loads comprises of hybridizing PEMFCs with energy storage devices like supercapacitors and batteries. This opening chapter reviews the projected gist of FCEV status; considers the factors that are going to affect how FCEVs could enter commercialization, including the importance of fuel cells for EV technologies; the degradation diagnoses using accelerated stress test (AST) procedures; FCEV hybridization; and the contribution of an energy storage device for charging EVs. The article also addresses case studies relating to material degradation occurring from driving behavior. Information about material degradation can be compiled into a database for the improvement of cell component performance and durability, leading to the creation of new materials and new fuel cell hybridization designs. To support the growth of EV technologies, an energy storage is required for the integrated alternative electricity generations. A redox flow battery is considered as a promising candidate in terms of attractive charging station for EVs or HEVs.
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Shaukat, Syed, and Cheng-Lung Wu. "Impact of Hydrogen Fuel Cell Technology on Aircraft Maintenance." In Challenges and Opportunities for Aviation Stakeholders in a Post-Pandemic World, 49–63. IGI Global, 2023. http://dx.doi.org/10.4018/978-1-6684-6835-7.ch003.
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The aviation industry is adopting a promising approach to decarbonize the aviation sector dramatically by incorporating hydrogen fuel cell technology and expects to start some commercial services as early as 2035. The authors estimate the aircraft operating cost to become less expensive eventually with this forthcoming fuel cell technology, and the total maintenance cost of hydrogen-powered aircraft to come down in the long run for all segments of the aviation sector, from short haul to long haul services. With the possible incorporation of a new superconducting electrical system, a pneumatic power system, and a fully integrated electrical drive train system, additional maintenance will be required due to their cryogenic factors and associated safety issues. This chapter focuses on the potential impacts of hydrogen fuel cell technology on aircraft maintenance reliability, cost, and safety across the wide range of commuter, regional, short, medium, and long-haul segments of the aviation industry.
Conference papers on the topic "Limiting factors for fuel cell"
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Wang, Yun. "Dynamic Characteristics of Polymer Electrolyte Fuel Cell and Hydrogen Tank." In 2010 14th International Heat Transfer Conference. ASMEDC, 2010. http://dx.doi.org/10.1115/ihtc14-23005.
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In this paper, we develop 3D dynamic models for polymer electrolyte fuel cells (PEFCs) and hydrogen tanks, respectively. The PEFC model considers the key components of a single PEFC and couples the various mechanisms that govern fuel cell transient including the electrochemical double-layer behavior, species transport, heat transfer, liquid water dynamics, and membrane water uptake. The hydrogen tank model includes a 3D description of the hydrogen discharging kinetics coupled with mass/heat transport in a LaNi5–based hydrogen tank. Efforts are made to discuss the dynamic characteristics of the PEFC and hydrogen tank together with the possible coupling of the two systems. Local electrochemical and hydride reaction rates, transport processes and associated limiting factors are investigated.
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Shiomi, Daisuke, Hiroshi Iwai, Kenjiro Suzuki, and Hideo Yoshida. "Numerical Study on Transient Characteristics of a Tubular SOFC Cell." In ASME 2005 3rd International Conference on Fuel Cell Science, Engineering and Technology. ASMEDC, 2005. http://dx.doi.org/10.1115/fuelcell2005-74171.
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Fundamental performance and the transient characteristics of a small tubular SOFC were numerically investigated. The model simultaneously treats momentum, heat and mass transfer, electrochemical phenomena and an electric circuit. Transient characteristics of a cell upon a sudden change of the cell terminal voltage or the air flow rate were examined. During its process, a steady simulation was first conducted and its result was used as the initial condition for the transient calculation. The transient calculation continued until a steady state under the new boundary condition was obtained. Discussions on the time response of the cell performance and thermal field were made in order to find the key factors mainly affecting the transient characteristics. To confirm what factors affect on the transient behavior, calculations were conducted for two different cell geometries, which have different cell diameters, but have same ratios of cell heat capacity to the heat generating area. As a result, it was found that the transient characteristics of a cell are primarily governed by the balance between the heat capacity of a cell and the heat generation by electrochemical reactions. The large heat capacity of the cell is one of the key problems affecting the transient behavior, limiting its quick response. A numerical demonstration is shown in which a rapid cell status change was achieved by controlling its operation conditions.
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Mukherjee, Partha P., and Chao-Yang Wang. "A Catalyst Layer Flooding Model for Polymer Electrolyte Fuel Cells." In ASME 2008 6th International Conference on Fuel Cell Science, Engineering and Technology. ASMEDC, 2008. http://dx.doi.org/10.1115/fuelcell2008-65021.
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It is widely recognized that the performance degradation and the limiting current behavior in polymer electrolyte fuel cells (PEFC) are mainly attributed to the excessive build up of liquid water in the cathode side and the resulting flooding phenomena. Liquid water blocks the open pore space in the catalyst layer (CL) and the gas diffusion layer (GDL) leading to hindered oxygen transport and covers the electrochemically active sites in the CL thereby rendering reduced catalytic activity. The CL flooding therefore plays a crucial role in the overall PEFC performance limitation. In order to elucidate the primary mechanisms of liquid water removal out of the CL, the factors affecting CL flooding and to discern the role and contribution of CL flooding on the overall PEFC voltage loss, a CL flooding model has been developed. The flooding model is based on a simplified structure-wettability representation of the PEFC CL and a physical description of water and heat balance along with electrochemical performance analysis. The model shows that the evaporation mechanism, depending upon the cell operating temperature and the GDL thermal conductivity, plays a crucial role in the CL flooding behavior and the cell performance.
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Barbir, Frano, Bhaskar Balasubramanian, and Jay Neutzler. "Trade-Off Design Analysis of Operating Pressure and Temperature in PEM Fuel Cell Systems." In ASME 1999 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 1999. http://dx.doi.org/10.1115/imece1999-0840.
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Abstract The paper presents the results of an optimization study of an automotive fuel cell propulsion system equipped with a fuel reformer. Based on a set of fuel cell polarization curves determined experimentally by running a prototype fuel cell stack at a variety of operating pressures and temperatures, a numerical steady state model was used to determine the optimal operating pressure and temperature. The optimization criteria were the size of individual components and the entire propulsion system as well as its total efficiency at both full power and partial load. The results suggested that an automotive system should be operated at relatively high pressure (308 kPa), but an expander must be used to recover most of the power used for compression. A surprising result of this analysis is that a relatively low temperature (∼60°C) results in smallest heat rejection equipment if neutral water balance is mandated. The efficiency of the system is about 33% at full power and about 38% at 25% of the load. Higher efficiencies may be achieved by selecting a higher fuel cell operating voltage, but that would result in larger fuel cell stacks, which may be a limiting factor for automotive application with the state-of-the-art fuel cells.
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Nelson, George J., Comas Haynes, and William Wepfer. "Performance Metrics for Solid Oxide Fuel Cell Cross-Section Design." In ASME 2009 7th International Conference on Fuel Cell Science, Engineering and Technology. ASMEDC, 2009. http://dx.doi.org/10.1115/fuelcell2009-85087.
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Analytical models have been developed to describe the partial pressure distributions of reactants within solid oxide fuel cell (SOFC) electrodes and introduce the concept of a reactant depletion current density. These existing analytical expressions for two-dimensional reactant partial pressure distributions and the reactant depletion current density are presented in non-dimensional form. Performance metrics for SOFC electrodes are developed including a correction factor that can be applied to button-cell predictions of pressure distribution and two forms of dimensionless reactant depletion current density. Performance predictions based on these metrics are compared to numerical predictions of partial pressure and depletion current density based on a finite element solution of the dusty-gas model (DGM) within SOFC electrodes. It is shown that the pressure correction factor developed provides a reasonable prediction of interconnect geometry effects. Thus, it is presented as a modeling tool that can be applied to translate component level fidelity to cell and stack level models. The depletion current density metrics developed are used to present basic design maps for SOFC unit cell cross-sections. These dimensionless forms of the depletion current density quantify the influence of sheet resistance effects on reactant depletion and can predict the deviation from the limiting current behavior predicted using a button-cell model.
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Share, Dylan, Lakshmi Krishnan, Dan Walczyk, David Lesperence, and Raymond Puffer. "Thermal Sealing of Membrane Electrode Assemblies for High-Temperature PEM Fuel Cells." In ASME 2010 8th International Conference on Fuel Cell Science, Engineering and Technology. ASMEDC, 2010. http://dx.doi.org/10.1115/fuelcell2010-33227.
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The main challenges of low temperature (80–120°C) Nafion-based PEM technology are (1) low cathode performance due to slow kinetics of the oxygen reduction reaction (2) high material costs (3) considerable system design and operation for water management (4) low tolerance to impurities in fuel stream and (5) low quality heat resulting in low overall system efficiency. Furthermore, Nafion membranes achieve maximum conductivity only when hydrated, limiting their operation to <100 C. Operating the fuel cell >100 C is desirable to overcome the aforementioned limitations. Though several high temperature membranes for PEMFC have been developed, polybenzimidazole (PBI) membranes with high Phosphoric acid content (>90%) developed by BASF Fuel cell are currently seeing commercial interest. The most vital step in MEA manufacturing is the sealing of the membrane in between the electrode-substrate assembly to form a five-layer architecture. Currently, MEA sealing is done by a thermal seal process. This paper examines the effect of thermal sealing process parameters, namely (1) sealing temperature (2) percent compression (3) sealing time and (4) manufacturer-specified post-processing after sealing on the fuel cell performance. A design of experiments was developed with these input process parameters and the polarization behavior during single cell operation, as well as internal cell resistance, were analyzed as performance parameters. ANOVA analysis revealed the statistically significant input factors for the thermal sealing process, which are essential for the rapid and high-quality manufacturing of membrane electrode assemblies for high temperature fuel cells. Furthermore, a multiphysics model has been developed to allow for further refinement of the MEA sealing process.
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Nelson, George, and Comas Haynes. "Parametric Studies of Constriction Resistance Effects Upon Solid Oxide Cell Transport Phenomena." In ASME 2006 International Mechanical Engineering Congress and Exposition. ASMEDC, 2006. http://dx.doi.org/10.1115/imece2006-15100.
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The competition between mass transfer and electronic resistance effects arising from solid oxide cell interconnect geometry has been initially explored through parametric studies based on a design of experiments (DOE) approach. These studies have demonstrated the advantages of smaller interconnect-fuel stream total width and the increased dominance of mass transport as a limiting factor at low fuel stream hydrogen compositions. In addition to the direct effects of solid oxide fuel cell (SOFC) interconnect geometry on mass and electronic transport phenomena, the compounded effects of fuel stream concentration and cell current loading are considered. Finally, the parametric studies conducted for SOFC operation have been applied to the operation of solid oxide electrolysis cells (SOECs). These additional studies have demonstrated that interconnect designs that benefit SOFC performance are mutually beneficial for SOEC performance.
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Kno¨ri, T., M. Schulze, and K. A. Friedrich. "Determination of Local Conditions in PEFCs by Combining Spatially Resolved Current Density Measurements With Real-Time Modelling." In ASME 2008 6th International Conference on Fuel Cell Science, Engineering and Technology. ASMEDC, 2008. http://dx.doi.org/10.1115/fuelcell2008-65225.
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In this contribution a simplified, isothermal, two-phase, one-dimensional model for the calculation of the cathodic gas flow along the flow field channels of a polymer electrolyte fuel cell (PEFC) are presented. The composition of the humidified oxidant gas, average gas velocity, pressure drop, and other quantities can be calculated for different gas distributor structures. Thereby, the model requires several input parameters determined solely by experiment and operation conditions, e.g. the water content of the feed gas, local current densities, and gas flow rates. In contrast to other models, the cross-section reduction has been taken into account which results from the penetration of the gas diffusion layer (GDL) into the flow field channels due to the mounting pressure. Beyond this, the model needs no fit-parameters for further adjustment. For investigating the factors limiting the performance of a PEFC, the DLR has developed several techniques for measuring the spatially resolved current density distribution [1–5]. In order to investigate the origin of the corresponding effects, one of these techniques has been improved by implementing the model of the cathodic gas flow as an on-line feature. The combination of a spatially resolved measurement technique with a real-time simulation gives a better understanding of the local processes within the cell and represents a helpful tool for the development of fuel cell components as well as for the optimization of the operating conditions. In the presentation the results for a 25 cm2 serpentine flow field at different operation modes are shown.
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Shiomi, Takeshi, Richard S. Fu, Ugur Pasaogullari, Yuichiro Tabuchi, Shinichi Miyazaki, Norio Kubo, Kazuhiko Shinohara, Daniel S. Hussey, and David L. Jacobson. "Effect of Liquid Water Saturation on Oxygen Transport in Gas Diffusion Layers of Polymer Electrolyte Fuel Cells." In ASME 2010 8th International Conference on Fuel Cell Science, Engineering and Technology. ASMEDC, 2010. http://dx.doi.org/10.1115/fuelcell2010-33225.
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Improved oxygen diffusivity is essential for reducing mass transport losses in polymer electrolyte fuel cells (PEFCs). In this work, effective oxygen diffusivity in the presence of liquid water inside a gas diffusion layer (GDL) was investigated by means of coupled experimental and numerical analyses. In order to control the liquid water content inside the GDL, a temperature gradient method was developed. In a separate experiment liquid water content inside the GDL was measured by neutron radiography (NR) and analyzed by using a two-phase, non-isothermal numerical model. The model accurately reproduced the total liquid water content and was in qualitative agreement with the liquid saturation trend as obtained from the NR experiments, which was utilized to estimate the liquid saturation in the limiting current experiment. Based on the predicted liquid water profile, the dependence of effective oxygen diffusivity on the liquid water saturation is deduced. It is found that the Bruggeman exponent factor is much larger than the predictions from network models and this suggests that the understanding of the relationship between liquid water transport and the GDL local structure is important.
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Tahseen, Siddiq Husain, Abbas S. Milani, and Mina Hoorfar. "Sensitivity Analysis of Mass Transport Properties of Gas Diffusion Layers of Polymer Electrolyte Membrane Fuel Cells." In ASME 2012 10th International Conference on Nanochannels, Microchannels, and Minichannels collocated with the ASME 2012 Heat Transfer Summer Conference and the ASME 2012 Fluids Engineering Division Summer Meeting. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/icnmm2012-73107.
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A prodigious amount of research has been conducted to study and measure the different properties associated with the mass transfer phenomenon inside the GDL like diffusivity, permeability, porosity, thickness. However, the functional relationship of these parameters with the limiting current; the effect of the individual factor over others; and the interaction, correlation and interdependence of these factors have been subject of little work. Using the experimental data presented in the literature, this paper presents a methodology developed based on a regression model to predict the limiting current from GDL properties. Statistical techniques like factorial design and response surface methodology are used to perform the sensitivity analysis of relevant parameters. The emphasis will be on factor screening to identify efficiently the parameters with most dominant effects. The results obtained will then be used to select the most effective GDL (among those characterized) based on multi criteria decision making tools like weighting sum method (WSM) and TOPSIS with entropy weight. The final goal is to elucidate the impact of each property, and hence to identify the most important parameters that need to be studied and characterized to engineer a better GDL with enhanced water management capabilities.
Reports on the topic "Limiting factors for fuel cell"
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Or, Dani, Shmulik Friedman, and Jeanette Norton. Physical processes affecting microbial habitats and activity in unsaturated agricultural soils. United States Department of Agriculture, October 2002. http://dx.doi.org/10.32747/2002.7587239.bard.
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experimental methods for quantifying effects of water content and other dynamic environmental factors on bacterial growth in partially-saturated soils. Towards this end we reviewed critically the relevant scientific literature and performed theoretical and experimental studies of bacterial growth and activity in modeled, idealized and real unsaturated soils. The natural wetting-drying cycles common to agricultural soils affect water content and liquid organization resulting in fragmentation of aquatic habitats and limit hydraulic connections. Consequently, substrate diffusion pathways to soil microbial communities become limiting and reduce nutrient fluxes, microbial growth, and mobility. Key elements that govern the extent and manifestation of such ubiquitous interactions include characteristics of diffusion pathways and pore space, the timing, duration, and extent of environmental perturbations, the nature of microbiological adjustments (short-term and longterm), and spatial distribution and properties of EPS clusters (microcolonies). Of these key elements we have chosen to focus on a manageable subset namely on modeling microbial growth and coexistence on simple rough surfaces, and experiments on bacterial growth in variably saturated sand samples and columns. Our extensive review paper providing a definitive “snap-shot” of present scientific understanding of microbial behavior in unsaturated soils revealed a lack of modeling tools that are essential for enhanced predictability of microbial processes in soils. We therefore embarked on two pronged approach of development of simple microbial growth models based on diffusion-reaction principles to incorporate key controls for microbial activity in soils such as diffusion coefficients and temporal variations in soil water content (and related substrate diffusion rates), and development of new methodologies in support of experiments on microbial growth in simple and observable porous media under controlled water status conditions. Experimental efforts led to a series of microbial growth experiments in granular media under variable saturation and ambient conditions, and introduction of atomic force microscopy (AFM) and confocal scanning laser microscopy (CSLM) to study cell size, morphology and multi-cell arrangement at a high resolution from growth experiments in various porous media. The modeling efforts elucidated important links between unsaturated conditions and microbial coexistence which is believed to support the unparallel diversity found in soils. We examined the role of spatial and temporal variation in hydration conditions (such as exist in agricultural soils) on local growth rates and on interactions between two competing microbial species. Interestingly, the complexity of soil spaces and aquatic niches are necessary for supporting a rich microbial diversity and the wide array of microbial functions in unsaturated soils. This project supported collaboration between soil physicists and soil microbiologist that is absolutely essential for making progress in both disciplines. It provided a few basic tools (models, parameterization) for guiding future experiments and for gathering key information necessary for prediction of biological processes in agricultural soils. The project sparked a series of ongoing studies (at DTU and EPFL and in the ARO) into effects of soil hydration dynamics on microbial survival strategy under short term and prolonged desiccation (important for general scientific and agricultural applications).
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Meidan, Rina, and Robert Milvae. Regulation of Bovine Corpus Luteum Function. United States Department of Agriculture, March 1995. http://dx.doi.org/10.32747/1995.7604935.bard.
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The main goal of this research plan was to elucidate regulatory mechanisms controlling the development, function of the bovine corpus luteum (CL). The CL contains two different sterodigenic cell types and therefore it was necessary to obtain pure cell population. A system was developed in which granulosa and theca interna cells, isolated from a preovulatory follicle, acquired characteristics typical of large (LL) and small (SL) luteal cells, respectively, as judged by several biochemical and morphological criteria. Experiments were conducted to determine the effects of granulosa cells removal on subsequent CL function, the results obtained support the concept that granulosa cells make a substaintial contribution to the output of progesterone by the cyclic CL but may have a limited role in determining the functional lifespan of the CL. This experimental model was also used to better understand the contribution of follicular granulosa cells to subsequent luteal SCC mRNA expression. The mitochondrial cytochrome side-chain cleavage enzyme (SCC), which converts cholesterol to pregnenolone, is the first and rate-limiting enzyme of the steroidogenic pathway. Experiments were conducted to characterize the gene expression of P450scc in bovine CL. Levels of P450scc mRNA were higher during mid-luteal phase than in either the early or late luteal phases. PGF 2a injection decreased luteal P450scc mRNA in a time-dependent manner; levels were significantly reduced by 2h after treatment. CLs obtained from heifers on day 8 of the estrous cycle which had granulosa cells removed had a 45% reduction in the levels of mRNA for SCC enzymes as well as a 78% reduction in the numbers of LL cells. To characterize SCC expression in each steroidogenic cell type we utilized pure cell populations. Upon luteinization, LL expressed 2-3 fold higher amounts of both SCC enzymes mRNAs than SL. Moreover, eight days after stimulant removal, LL retained their P4 production capacity, expressed P450scc mRNA and contained this protein. In our attempts to establish the in vitro luteinization model, we had to select the prevulatory and pre-gonadotropin surge follicles. The ratio of estradiol:P4 which is often used was unreliable since P4 levels are high in atretic follicles and also in preovulatory post-gonadotropin follicles. We have therefore examined whether oxytocin (OT) levels in follicular fluids could enhance our ability to correctly and easily define follicular status. Based on E2 and OT concentrations in follicular fluids we could more accurately identify follicles that are preovulatory and post gonadotropin surge. Next we studied OT biosynthesis in granulosa cells, cells which were incubated with forskolin contained stores of the precursor indicating that forskolin (which mimics gonadotropin action) is an effective stimulator of OT biosynthesis and release. While studying in vitro luteinization, we noticed that IGF-I induced effects were not identical to those induced by insulin despite the fact that megadoses of insulin were used. This was the first indication that the cells may secrete IGF binding protein(s) which regonize IGFs and not insulin. In a detailed study involving several techniques, we characterized the species of IGF binding proteins secreted by luteal cells. The effects of exogenous polyunsaturated fatty acids and arachidonic acid on the production of P4 and prostanoids by dispersed bovine luteal cells was examined. The addition of eicosapentaenoic acid and arachidonic acid resulted in a dose-dependent reduction in basal and LH-stimulated biosynthesis of P4 and PGI2 and an increase in production of PGF 2a and 5-HETE production. Indomethacin, an inhibitor of arachidonic acid metabolism via the production of 5-HETE was unaffected. Results of these experiments suggest that the inhibitory effect of arachidonic acid on the biosynthesis of luteal P4 is due to either a direct action of arachidonic acid, or its conversion to 5-HETE via the lipoxgenase pathway of metabolism. The detailed and important information gained by the two labs elucidated the mode of action of factors crucially important to the function of the bovine CL. The data indicate that follicular granulosa cells make a major contribution to numbers of large luteal cells, OT and basal P4 production, as well as the content of cytochrome P450 scc. Granulosa-derived large luteal cells have distinct features: when luteinized, the cell no longer possesses LH receptors, its cAMP response is diminished yet P4 synthesis is sustained. This may imply that maintenance of P4 (even in the absence of a Luteotropic signal) during critical periods such as pregnancy recognition, is dependent on the proper luteinization and function of the large luteal cell.
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Analysis of environmental factors impacting the life cycle cost analysis of conventional and fuel cell/battery-powered passenger vehicles. Final report. Office of Scientific and Technical Information (OSTI), January 1995. http://dx.doi.org/10.2172/366490.
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