Author: Elaine M. Petrach
Publisher:
ISBN:
Category : Composite materials
Languages : en
Pages : 238

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Author: Taylor Jacob Mali
Publisher:
ISBN:
Category :
Languages : en
Pages :

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Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 4

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Polymer electrolyte fuel cells (PEFCS) are under widespread development to produce electrical power for a variety of stationary and transportation applications. To date, the bipolar plate remains the most problematic and costly component of PEFC stacks (1). In addition to meeting cost constraints, bipolar plates must possess a host of other properties, the most important of which are listed in Table 1. The most commonly used material for single cell testing is machined graphite, which is expensive and costly to machine. The brittle nature of graphite also precludes the use of thin components for reducing stack size and weight, which is particularly important for transportation applications. Other stack designs consider the use of metal hardware such as stainless steel (2,3). But a number of disadvantages are associated with stainless steel, including high density, high cost of machining, and possible corrosion in the fuel cell environment. In light of these difficulties, much of the recent work on fuel cell bipolar plate materials has concentrated on graphite/polymer composites (4--8). Composite materials offer the potential advantages of lower cost, lower weight, and greater ease of manufacture than traditional graphite and metal plates. For instance, flow fields can be molded directly into these composites, thereby eliminating the costly and difficult machining step required for graphite or metal hardware.

Author: Rungsima Yeetsorn
Publisher:
ISBN:
Category :
Languages : en
Pages : 248

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Polymer electrolyte membrane fuel cells (PEMFCs) have the potential to play a major role as energy generators for transportation and portable applications. One of the current barriers to their commercialization is the cost of the components and manufacturing, specifically the bipolar plates. One approach to preparing PEMFCs for commercialization is to develop new bipolar plate materials, related to mass production of fuel cells. Thermoplastic/carbon filler composites with low filler loading have a major advantage in that they can be produced by a conventional low-cost injection molding technique. In addition, the materials used are inexpensive, easy to shape, and lightweight. An optimal bipolar plate must possess high surface and bulk electronic conductivity, sufficient mechanical integrity, low permeability, and corrosion resistance. However, it is difficult to achieve high electrical conductivity from a low-cost thermoplastic composite with low conductive filler loading. Concerns over electrical conductivity improvement and the injection processability of composites have brought forth the idea of producing a polypropylene/three-carbon-filler composite for bipolar plate application. The thesis addresses the development of synergistic effects of filler combinations, investigating composite conductive materials and using composite bipolar plate testing in PEMFCs. One significant effect of conductive network formation is the synergetic effects of different carbon filler sizes, shapes, and multiple filler ratios on the electrical conductivity of bipolar plate materials. A polypropylene resin combined with low-cost conductive fillers (graphite, conductive carbon black, and carbon fibers with 55 wt% of filler loading) compose the main composite for all investigations in this research. Numerous composite formulations, based on single-, two-, and three-filler systems, have been created to investigate the characteristics and synergistic effects of multiple fillers on composite conductivity. Electrical conductivity measurements corresponding to PEMFC performance and processing characteristics were investigated. Experimental work also involved other ex-situ testing for the physical requirements of commercial bipolar plates. All combinations of fillers were found to have a significant synergistic effect that increased the composite electrical conductivity. Carbon black was found to have the highest influence on the increase of electrical conductivity compared to the other fillers. The use of conjugated conducting polymers such as polypyrrole (PPy) to help the composite blends gain desirable conductivities was also studied. Electrical conductivity was significantly improved conductivity by enriching the conducting paths on the interfaces between fillers and the PP matrix with PPy. The conductive network was found to have a linkage of carbon fibers following the respective size distributions of fibers. The combination of Fortafil and Asbury carbon fiber mixture ameliorated the structure of conductive paths, especially in the through-plane direction. However, using small fibers such as carbon nanofibers did not significantly improve in electrical conductivity. The useful characteristics of an individual filler and filler supportive functions were combined to create a novel formula that significantly improved electrical conductivity. Other properties, such as mechanical and rheological ones, demonstrate the potential to use the composites in bipolar plate applications. This research contributes a direction for further improvement of marketable thermoplastic bipolar plate composite materials.

Author: Atul Kumar
Publisher:
ISBN:
Category :
Languages : en
Pages : 414

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Author: Atul Kumar
Publisher:
ISBN:
Category :
Languages : en
Pages : 232

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Author: Ahmed Saib Naji Al-alawi
Publisher:
ISBN:
Category : Fuel cells
Languages : en
Pages : 211

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Using unclean fuels such as fossil fuel has many consequences including global warming and environmental pollution. Nowadays, searching for the clean, sustainable and cheap energy source is increasing. Many suggestions have been put on the table; among them, fuel cell technology represents the most promising one. Polymer electrolyte membrane fuel cells (PEMFC) are the most common ones used widely in various applications ranging from portable batteries to the fuel cell power plants. PEMFC is still expensive, heavy and not efficient enough to be available in the markets in a cost-effective manner. The main part of the fuel cell which is involved with these problems is the bipolar plate (BPP). Therefore, the US Department of Energy (DOE) has suggested a list of requirements for the BPP to commercialize the PEMFC. Up-to-date, different types of BPP have been developed using several material types. Among these materials, conductive polymer composites (CPCs) have shown great promises owing to their outstanding combination of the required proportions.In this study, CPC materials based on polycarbonate and hybrid carbon-based fillers were manufactured using three different technologies: solution casting, melt mixing with singular polymer and melt mixing with a blend of polymers. The results showed that the dispersion and distribution of the conductive filler play an important role in controlling the morphological, electrical, thermal, and mechanical properties. Moreover, the percolation threshold of the singular and hybrid filler systems and the localization of the fillers within the matrix are important factors governing various properties. The results showed that the solution casting can yield light CPCs but they do not still qualify to manufacture BPP, because of their low conductivities and poor mechanical properties. The melt mixing approach for singular polymer matrix provided a significant improvement in the conductivities and the mechanical properties over the solution casting CPCs. However, the melt mixing of the singular polymer is still challenging due to the required high filler loads. Using a plasticizer with this technology proved an effective solution toward increasing filler load and enhancing various properties. Finally, CPCs fabricated using melt mixing of polymer blends exhibited the best combination of various physical and mechanical properties suitable for BPP performance.

Author: Nannan Guo
Publisher:
ISBN:
Category : Biomimetics
Languages : en
Pages : 173

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"The flow field of a bipolar plate distributes reactants for polymer electrolyte membrane (PEM) fuel cells and removes the produced water from the fuel cells. It greatly influences the performance of fuel cells, especially the concentration losses. Two approaches were developed to improve flow field designs in this dissertation. One is inspired by the biological circulatory structures and called bio-inspired designs, which have great potential to transport reactant efficiently and hence improve fuel cell performance. Another way is using a network-based optimization model to optimize the conventional flow field configurations, i.e., pin-type, parallel and serpentine designs, to improve flow distributions within the channels. A three-dimensional, two-phase numerical model was developed to investigate the mass, velocity and pressure distributions within the different flow fields and also the final fuel cell performance. Selective Laser Sintering, which provides a cost- and time-efficient way to build parts with complicated geometries, was used to fabricate graphite composite bipolar plates with these developed designs. Different graphite materials, including natural graphite, synthetic graphite, carbon black, and carbon fiber, were investigated in order to achieve higher electrical conductivity and flexural strength of the fabricated bipolar plates. Experimental testing of the PEM fuel cells with these fabricated bipolar plates was carried out to verify the numerical model and compare the performance for different flow field designs. Both the numerical and experimental results demonstrated that the bio-inspired designs and the optimized designs could substantially improve the fuel cell performance compared to the traditional designs"--Abstract, page iv.

Author: Yuhua Wang
Publisher:
ISBN:
Category :
Languages : en
Pages :

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Author: Cabir Turan
Publisher:
ISBN:
Category : Fuel cells
Languages : en
Pages :

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Polymer electrolyte membrane fuel cells (PEMFCs) have emerged as a strong and promising candidate to replace internal combustion engines (ICE) due their high efficiency, high power density and near-zero hazardous emissions. However, their commercialization waits for solutions to bring about significant cost-reductions and significant durability for given power densities. Bipolar plate (BPP) with its multi-faceted functions is one of the essential components of the PEMFC stacks. Stainless steel alloys are considered promising materials of choice for bipolar plate (BPP) applications in polymer electrolyte membrane fuel cells (PEMFC) due to their relatively low cost and commercial availability in thin sheets. Stainless steel materials build a protective passive metal oxide layer on their surface against corrosion attack. This passive layer does not demonstrate good electrical conductivity and increases interfacial electric contact resistance (ICR) between BPP and gas diffusion layer GDL in PEMFC. Lower ICR values are desired to reduce parasitic power losses and increase current density in order to improve efficiency and power density of PEMFC. This study aimed to bring about a broader understanding of manufacturing effects on the BPP contact resistance. In first stage, BPP samples manufactured with stamping and hydroforming under different process conditions were tested for their electrical contact resistance characteristics to reveal the effect of manufacturing type and conditions. As a general conclusion, stamped BPPs showed higher contact conductivity than the hydroformed BPPs. Moreover, pressure in hydroforming and geometry had significant effects on the contact resistance behavior of BPPs. Short term corrosion exposure was found to decrease the contact resistance of bipolar plates. Results also indicated that contact resistance values of uncoated stainless steel BPPs are significantly higher than the respective target set by U.S. Department of Energy. Proper coating or surface treatments were found to be necessary to satisfy the requirements. In the second stage, physical vapor deposition technique was used to coat bipolar plates with CrN, TiN and ZrN coatings at 0.1, 0.5 and 1 [micro]m coating thicknesses. Effects of different coatings and coating thickness parameters were studied as manufactured BPPs. Interfacial contact resistance tests indicated that CrN coating increased the contact resistance of the samples. 1 [micro]m TiN coated samples showed the best performance in terms of low ICR; however, ICR increased dramatically after short term exposure to corrosion under PEMFC working conditions. ZrN coating also improved conductivity of the SS316L BPP samples. It was found that the effect of coating material and coating thickness was significant whereas the manufacturing method and BPP channel size slightly affected the ICR of the metallic BPP samples. Finally, effect of process sequence on coated BPPs was investigated. In terms of ICR, BPP samples which were coated prior to forming exhibited similar or even better performance than coated after forming samples. Thus, continuous coating of unformed stripes, then, applying forming process seemed to be favorable and worth further investigation in the quest of making cost effective BPPs for mass production of PEMFC.