Water plays an important role in the operation of Fuel Cell. It determines where the electrochemical reactions should or should not occur. The purpose of this study is to investigate the transport characteristics of vapor through all components of an electrode and how they are related to the cell performance. In the transmit experiment of cell produce water which prove the level of water steam transmission characteristics has relative relations with the measurements of water transport in fuel cell. In a sum, the electrode with higher water steam transmission characteristics, the measurement of water transport will also be higher. From cell performance measure experiment, we can found that water steam transmission characteristics have the opposite relation with the concentration loss¡]mass transfer behavior¡^. As cell working on high current density, water will not clog easily under the great quality transmit electrode. Further, catalyst layer that has enough concentration would not cause the cell performance dismiss with the follow up reactions and it represents that cell performs batter with mass transfer. According to the experiment, PTFE in MPL with smaller amount has better performance to fuel cell. What the differences between the presentation of water as liquid state or gaseous state when it transmits in electrode? We can discover the rate of gaseous state water is faster compared to liquid state water when transmitting through MEA in a simple experiment. We assume that gaseous state of water is the first type within the electrode.

Fuel cell performance was obtained as functions of the humidity at the anode and cathode sites, back pressure, flow rate, temperature, and channel depth. The fuel cell used in this work included a membrane and electrode assembly (MEA) which possessed an active area of 25, 50, and 100 cm2 with the Nafion® 117 and 115 membranes. Higher flow rates of inlet gases increase the performance of a fuel cell by increasing the removal of the water vapor, and decrease the mass transportation loss at high current density. Higher flow rates, however, result in low fuel utilization. An important factor, therefore, is to find the appropriate stoichiometric flow coefficient and starting point of stoichiometric flow rate in terms of fuel cell efficiency. Higher air supply leads to have better performance at the constant stoichiometric ratio at the anode, but not much increase after the stoichiometric ratio of 5. The effects of the environmental conditions and the channel depth for an airbreathing polymer electrolyte membrane fuel cell were investigated experimentally. Triple serpentine designs for the flow fields with two different flow depths was used. The shallow flow field deign improves dramatically the performance of the air-breathing fuel cell at low relative humidity, and slightly at high relative humidity. For proton exchange membrane fuel cells, proper water management is important to obtain maximum performance. Water management includes the humidity levels of the inlet gases as well as the understanding of the water process within the fuel cell. Two important processes associated with this understanding are (1) electro-osmotic drag of water molecules, and (2) back diffusion of the water molecules. There must be a neutral water balance over time to avoid the flooding, or drying the membranes. For these reasons, therefore, an investigation of the role of water transport in a PEM fuel cell is of particular importance. In this study, through a water balance experiment, the electro-osmotic drag coefficient was quantified and studied. For the cases where the anode was fully hydrated and the cathode suffered from the drying, when the current density was increased, the electro- osmotic drag coefficient decreased.

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Properties of textiles have great influences on the thermo-physiological and skin sensorial wear comfort of the human body. Sportswear is expected to have good moisture management property, which is key factor to achieve wear comfort. For some sports, they are also expected to have low friction with skin and antibacterial capability. To meet these demands, single-layer fabrics are utterly incompetent. Thus, model dual-layer textiles that consist of a thin hydrophobic electrospun inner layer and a thick hydrophilic electrospun outer layer are designed and fabricated to verify the possibility to simultaneously achieve dual functionalities, including good moisture transport property, with low friction with skin or good antibacterial property. The hydrophobic inner layer ensures low water absorption and transmission of sweat via capillary motion, while the hydrophilic outer layer draws the sweat out from the inner layer and facilitates evaporation to the surrounding environment. In the PhD work presented in this thesis, electrospun nanofibrous mats are used as the model textiles because they have large specific surface area due to a lot of interpenetrating pores between the nanofibers, which could facilitate both the capillary motion and effect of surface modification and incorporation of functional materials. Also, to let the moisture transport away fast, fairly thin hydrophobic inner layers could be achieved by electrospinning because it could control the thickness accurately. To improve the moisture transport property, the capillary motion in the textile is facilitated by decreasing the pore size or increasing the surface hydrophilicity. Dual-layer mats composed of a thick layer of hydrophilic polyacrylonitrile (PAN) nanofibers and a thin layer of hydrophobic polystyrene (PS) nanofibers with and without interpenetrating nanopores are fabricated respectively. Then the mats are coated with polydopamine (PDOPA) to different extents to tailor the water wettability of the PS layer. It is found that with a large quantity of nanochannels, the porous PS nanofibers exhibit a stronger capillary effect than the solid PS nanofibers. The capillary motion in the porous PS nanofibers can be further enhanced by slight surface modification with PDOPA while retaining the large hydrophilicity difference between the two layers, inducing a strong push-pull effect to transport water from the PS to the PAN layer. To lower the friction between the textile and skin, both of the hydration of the skin and the chemical component of textiles are modified. Core-shell nanofibers with a PAN-rich core and a poly (vinylidene fluoride) (PVDF)-rich shell are fabricated by single-spinneret electrospinning and used as the inner layer of the dual-layer mats. The dual-layer textile has good moisture transport property and the inner layer of the textile has lower friction with the skin, because the PAN in the inner layer could increase the wettability of the layer, thus improve the capillary effect, and the PVDF-rich shell could lower the friction between the textile and the skin. The synergistic combination of a considerably hydrophobic PAN/PVDF inner layer and a highly hydrophilic CA outer layer induces a strong push-pull effect, resulting in efficient moisture-wicking. To introduce antibacterial property to the dual-layer textile, zinc oxide (ZnO) NPs were covalently attached on the surface of the ethoxysilane-functionalized cross-linked PVDF inner layer. The results of related testes show that the incorporation of the ZnO NPs could render the textile antibacterial property as well as enhance the water wettability of the inner, thus the moisture transport property of the textile is also strongly improved. Also, the ZnO NPs show very good anti-wash property due to the covalent bonding with the inner layer. Thus the potential health risk caused by the detachment of the NPs could be avoided. In summary, the research results presented in this thesis provide effective strategies to enhance the capillary motion and moisture transport property of the textile, as well as achieve dual functionalities. The design concepts demonstrated in this PhD research can be used as model systems for development of novel multifunctional textiles in industries.

The anisotropic mass transport issues inside a fuel cell membrane have been studied in this thesis using computer modelling. The polymer electrolyte membrane (PEM) conductivity of a PEM fuel cell (PEMFC) depends on the hydration state of the hydrophilic charged sites distributed in the pores of the membrane. Water humidification of these charged sites is crucial for sustaining the membrane conductivity and reducing concerning voltage losses of the cell. During the operation of a PEMFC, the transport of humidified inlet gases (fuel/oxidant) is influenced by external design factors such as flow field plate geometry of the gas circulating channels. As a result, there arises a distribution in the mass transport of water inside the membrane electrode assembly. A two-dimensional, cross-the-channel, fuel cell membrane layer mass transport model, developed in this work, helps the study of the impact of factors causing the distribution in the membrane ionic conductivity on ohmic losses.<p>The governing equations of the membrane mathematical model stem from the multicomponent framework of concentrated solution theory. All mass transport driving forces within the vapour and/or liquid equilibrated phases have been accounted in this research. A computational model, based on the finite control volume method, has been implemented using a line-by-line approach for solving the dependent variables of the mass transport equations in the two-dimensional membrane domain. The required boundary conditions for performing the anisotropic mass transport analysis have been obtained from a detailed agglomerate model of the cathode catalyst layer available in the literature.<p>The results obtained using boundary conditions with various flow field plate channel-land configurations revealed that the anisotropic water transport in the cathode half-cell severely affects the ohmic losses within the membrane. A partially humidified vapour equilibrated membrane simulation results show that a smaller channel-land ratio (1:1) sustains a better membrane performance compared to that with a larger one (2:1 or 4:1). Resistance calculations using the computer model revealed that ohmic losses across the membrane also depend on its physical parameters such as thickness. It was observed that the resistance offered by a thinner membrane towards vapour phase mass transport is comparatively lower than that offered by a thicker membrane. A further analysis accounting the practical aspects such as membrane swelling constraints, imposed by design limitations of a fuel cell, revealed that the membrane water content and ionic conductivity are altered with an increase in the compression constraint effects acting upon a free swelling membrane.

The anisotropic mass transport issues inside a fuel cell membrane have been studied in this thesis using computer modelling. The polymer electrolyte membrane (PEM) conductivity of a PEM fuel cell (PEMFC) depends on the hydration state of the hydrophilic charged sites distributed in the pores of the membrane. Water humidification of these charged sites is crucial for sustaining the membrane conductivity and reducing concerning voltage losses of the cell. During the operation of a PEMFC, the transport of humidified inlet gases (fuel/oxidant) is influenced by external design factors such as flow field plate geometry of the gas circulating channels. As a result, there arises a distribution in the mass transport of water inside the membrane electrode assembly. A two-dimensional, cross-the-channel, fuel cell membrane layer mass transport model, developed in this work, helps the study of the impact of factors causing the distribution in the membrane ionic conductivity on ohmic losses.<p>The governing equations of the membrane mathematical model stem from the multicomponent framework of concentrated solution theory. All mass transport driving forces within the vapour and/or liquid equilibrated phases have been accounted in this research. A computational model, based on the finite control volume method, has been implemented using a line-by-line approach for solving the dependent variables of the mass transport equations in the two-dimensional membrane domain. The required boundary conditions for performing the anisotropic mass transport analysis have been obtained from a detailed agglomerate model of the cathode catalyst layer available in the literature.<p>The results obtained using boundary conditions with various flow field plate channel-land configurations revealed that the anisotropic water transport in the cathode half-cell severely affects the ohmic losses within the membrane. A partially humidified vapour equilibrated membrane simulation results show that a smaller channel-land ratio (1:1) sustains a better membrane performance compared to that with a larger one (2:1 or 4:1). Resistance calculations using the computer model revealed that ohmic losses across the membrane also depend on its physical parameters such as thickness. It was observed that the resistance offered by a thinner membrane towards vapour phase mass transport is comparatively lower than that offered by a thicker membrane. A further analysis accounting the practical aspects such as membrane swelling constraints, imposed by design limitations of a fuel cell, revealed that the membrane water content and ionic conductivity are altered with an increase in the compression constraint effects acting upon a free swelling membrane.

The global movement of aquatic non-indigenous species can have severe ecological, environmental and economic impacts emphasizing the need to identify potential invaders and transport pathways. Initial transport is arguably the most important stage of the invasion process owing to its role in selectively determining potential invasion candidates. This study characterizes a well defined human-mediated dispersal mechanism, ballast water transport, as a vector for the introduction of non-indigenous zooplankton. Ballast water exchange in the open ocean is the most widely adopted practice for reducing the threat of aquatic invasions and is mandatory for most foreign vessels intending to release ballast in Canadian waters. Ships entering Canadian ports are categorized into the following three shipping classes based on current regulations: overseas vessels carrying exchanged ballast water, intra-coastal vessels carrying exchanged ballast water or intra-coastal vessels carrying un-exchanged ballast water. This study characterizes zooplankton communities associated with each of these shipping classes sampled from ports on Canada’s Pacific coast, Atlantic coast and the Great Lakes Basin. Ballast water samples were collected and analyzed from 77 vessels between 2006 - 2007. The ballast water environment was found to be diverse, with over 193 zooplankton taxa, 71 of which were non-indigenous to their receiving environments. Intracoastal vessels containing un-exchanged coastal water transported the greatest density of non-indigenous zooplankton into Canadian ports. Total zooplankton density was found to be negatively correlated with ballast water age The absence of mandatory ballast water exchange and the younger ballast water age of coastal un-exchanged vessels is likely responsible for the higher density of non-indigenous zooplankton in intracoastal un-exchanged vessels. Propagule pressure, invasion history and environmental suitability are all useful in evaluating invasion potential and all suggest that intracoastal un-exchanged vessels pose the greatest invasion threat to Canadian aquatic ecosystems. In conclusion, although the risk of primary introductions from overseas ports may have been reduced through open-ocean exchange of ballast water, secondary introductions from previously invaded ports in North America may be the primary threat to Canadian aquatic ecosystems via this transport vector.

The global movement of aquatic non-indigenous species can have severe ecological, environmental and economic impacts emphasizing the need to identify potential invaders and transport pathways. Initial transport is arguably the most important stage of the invasion process owing to its role in selectively determining potential invasion candidates. This study characterizes a well defined human-mediated dispersal mechanism, ballast water transport, as a vector for the introduction of non-indigenous zooplankton. Ballast water exchange in the open ocean is the most widely adopted practice for reducing the threat of aquatic invasions and is mandatory for most foreign vessels intending to release ballast in Canadian waters. Ships entering Canadian ports are categorized into the following three shipping classes based on current regulations: overseas vessels carrying exchanged ballast water, intra-coastal vessels carrying exchanged ballast water or intra-coastal vessels carrying un-exchanged ballast water. This study characterizes zooplankton communities associated with each of these shipping classes sampled from ports on Canada’s Pacific coast, Atlantic coast and the Great Lakes Basin. Ballast water samples were collected and analyzed from 77 vessels between 2006 - 2007. The ballast water environment was found to be diverse, with over 193 zooplankton taxa, 71 of which were non-indigenous to their receiving environments. Intracoastal vessels containing un-exchanged coastal water transported the greatest density of non-indigenous zooplankton into Canadian ports. Total zooplankton density was found to be negatively correlated with ballast water age The absence of mandatory ballast water exchange and the younger ballast water age of coastal un-exchanged vessels is likely responsible for the higher density of non-indigenous zooplankton in intracoastal un-exchanged vessels. Propagule pressure, invasion history and environmental suitability are all useful in evaluating invasion potential and all suggest that intracoastal un-exchanged vessels pose the greatest invasion threat to Canadian aquatic ecosystems. In conclusion, although the risk of primary introductions from overseas ports may have been reduced through open-ocean exchange of ballast water, secondary introductions from previously invaded ports in North America may be the primary threat to Canadian aquatic ecosystems via this transport vector.

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No description available.