is carbon hydrophobic or hydrophilic

J Pharm Sci. There is a minor difference in that the voltages of the hydrophilic CB-MPL become lower at low current densities from around 0.4 A/cm2, while the limiting current density is slightly higher. 7a and 7c correspond to the MPL/CL interface.

1991 Apr 30;30(17):4237-44. doi: 10.1021/bi00231a019. BibTeX The voltage of the hydrophilic CF-MPL is higher than that of the hydrophobic CB-MPL under high current density conditions. Plots of (a) polarization curves and cell resistances, and (b) changes in the cell voltage and resistance at the constant current density of 0.7 A/cm2 with the hydrophilic CF-MPL and the hydrophobic CB-MPL. Cryo-SEM images of cross-sections of the hydrophilic CF-MPL with better performance for (a) the whole thickness, (b) the GDL side, and (c) the CL side after operating the cell at 0.7 A/cm2 for 1 hour. official website and that any information you provide is encrypted Figure 11. The oxygen gain of the hydrophilic CF-MPL is the lowest among the four types of MPLs, suggesting that the cell with the hydrophilic CF-MPL is less affected by the concentration overvoltage. 4a and 5b. If a molecule has polar covalent bonds, then it may be polar. The oxygen gains of the hydrophilic CB-MPL are higher than those of the hydrophobic CB-MPL and the hydrophobic CF-MPL even at the low current densities around 0.4 A/cm2, and becomes lower (than the two hydrophobic MPL cells) at current densities above 1.6 A/cm2. As expected, the voltages of the thinner MPL are lower than those of the thicker MPL. To validate this suggestion, the performance and ice distribution with a thinner hydrophilic CF-MPL were investigated. The hydrophilic CF-MPL is thicker and the inner structure is clearly different from the MPL with CB, and the pore sizes provided by the CF are much larger than those of the CB. 4a, even with sheets of ice present as in Figs. At the GDL side, there are parts where the pores were filled with large amounts of ice as shown in Fig. 4, 5 and 11). The difference in the cell voltages becomes larger as the current density increases, resulting in significant differences in the limiting current density when the voltage drops to around 0.2V. There are no significant differences in the resistance of these cells, and this suggests that the voltage difference is little affected by the ohmic resistance loss. Citation Yusuke Aoyama et al 2018 J. Electrochem. developed a novel exclusively hydrophilic MPL composed of carbon fibers and hydrophilic ionomer, and reported that cells using this hydrophilic MPL showed better performance than those using hydrophobic MPL under a wide range of humidity conditions.14,15 However, the mechanism of how the whole hydrophilic MPL contributes to the improvement of the cell performance is not fully understood. The fiber structure with the large pores may maintain the water as a film without the pores becoming completely filled, increase the surface area of the water film on the CF, and then the hydrophilic CF-MPL is able to promote evaporation of the water. 6b, ice also distributed uniformly from the CL to the GDL sides. Figure 5b shows the oxygen gains of the hydrophobic CB-MPL, the hydrophilic CB-MPL, the hydrophobic CF-MPL, and the hydrophilic CF-MPL.

2015 Feb;14(2):95-110. doi: 10.1038/nrd4486. We synthesized hydrophilic and hydrophobic carbon nanoparticles (CNPs) by femtosecond laser (0.8 m, 40 fs) irradiation of the water layer of an aerated benzene/water (B/W) bilayer solution. Contribution to the thermodynamics of protein folding from the reduction in water-accessible nonpolar surface area. Figure 4a shows the polarization curves and resistance of the cells using the hydrophilic CF-MPL and the conventional hydrophobic CB-MPL at the cathode side. The site is secure. Accessibility 10 that the hydrophilic CF-MPL promotes the draining of water from the CL to the MPL. The freezing method consisted of the following steps: first, after achieving constant current density operation at 0.7 A/cm2, the cell was shut down and immediately cooled at 40C in the thermostatic chamber to immobilize the water where it is at the instant of the shutdown. Introducing the CF increased the pore diameter of the MPL, and adding the ionomer made the wettability hydrophilic.14,15 To investigate the effects of the large pores with the CF and hydrophilic MPL with the ionomer separately, a hydrophilic MPL with the CB (hydrophilic CB) and a hydrophobic MPL with the CF (hydrophobic CF) were also compared.

This term arises because hydrophobic molecules do not dissolve in water. The time evolution of particle formation, products in water, and benzene dissolution behavior in water reveals that the surface properties are determined by the concentration of benzene in water. The https:// ensures that you are connecting to the Protein-Ligand Interactions: Thermodynamic Effects Associated with Increasing the Length of an Alkyl Chain. The bipolar plate has five straight flow channels and four lands, and is integrated with an electricity collector. 8b). 7b and 7c are the magnified images of the MPL at the GDL and the CL sides. This conclusion follows from an examination of the standard free energies of transfer of alkanes, alkenes, alkadienes, and arenes from water to hexadecane. Composition and structure of MPLs used in this study. applied another type of an additional layer, a hydrophilic MPL composed of carbon black, TiO2, and silicone, and reported that the cell performance can be improved under wet and dry conditions.13 These approaches investigate the incorporation of hydrophilic materials in hydrophobic MPL, and report the MPL wettability patterns in-plane911 and through-plane.12,13 Tanuma et al. Cramer DL, Cheng B, Tian J, Clements JH, Wypych RM, Martin SF. The water distribution inside the MPL is evaluated by a freezing method and cryo-SEM observations, and a comparison of the distribution and the cell performance of hydrophilic and hydrophobic MPL cells with various structures is made. This paper investigates the mechanism for improving the cell performance by the MPL with a hydrophilic CF based on observations of the water distribution in the vicinity of the cathode side MPL. This would be because the water vapor transport capacity driven by the saturation pressure gradient due to the temperature gradient, which was proposed by Owejan et al.,5 is sufficient to maintain unhindered passage under ordinary operating conditions.8 In Fig. Show Policy, Bulletin of the Chemical Society of Japan, PDF investigated the effect on the cell performance of a hydrophilic porous layer added between the hydrophobic MPL and the GDL, and suggested that the hydrophilic layer absorbs water and improves water removal from the CL to the GDL under wet conditions.12 Kitahara et al. This study investigates the effects of the wettability and structure of the MPL on cell performance and discusses the mechanism for improving cell performance by the hydrophilic CF-MPL at high humidity conditions. The ice distribution at the CL side (Fig. An examination of the standard free energies of transfer for the different classes of hydrocarbons from the gas phase to water and from the gas phase to hexadecane reinforces the conclusion that the number of hydrogen-carbon bonds in a molecule rather than its accessible surface area is the basis of the hydrophobic effect. The bipolar plates and the membrane electrode assembly (MEA) were enclosed by stainless-steel end-plates. Epub 2014 May 9. The cell temperature and the bubbler temperature were 70C (100% relative humidity (RH)) with the cell in a thermostatic chamber (HITACHI, EC-25MTP), and the cell temperature was controlled by the chamber temperature. 11). Figure 8. These MEAs were experimentally produced by Asahi Glass Co., Ltd.,14,15 and a detailed characterization of the GDL/MPL was reported in Ref. 1998 Aug;87(8):998-1014. doi: 10.1021/js9702980. and Lu et al. Recently, the authors have developed the limiting current analysis20,21 to apply to flooded conditions.22 In that analysis the total oxygen transport resistance in the cell, which is affected by the liquid water accumulated in the cell, is divided into two resistances: the resistance dependent on the total pressure of the cathode gas and that independent of the total pressure. MeSH 6a, there is no ice observed with the porous structure, similar to the situation before the start of operation. Before Then, the MEA was cut into three or four pieces and set in the sample holder in liquid nitrogen. sharing sensitive information, make sure youre on a federal Rather than the commonly and so far used 40 m thick CF-MPL, a thinner CF-MPL film of about 15 m was used, as shown in TableI. Figure 2. 2. Soc. In the polarization curve measurements, the current density was maintained for 2 minutes at each measurement point, to reach a steady state, and the cell was considered to have shut down if the cell voltage fluctuated widely and was not stabilized within the 2 minutes. The freezing method and the cryo-SEM observations show that ice distribution inside the hydrophilic CF-MPL is uneven in the through-plane direction of the MPL after the 70C operation at the current density of 0.7 A/cm. reported that the MPL reduces the amount of water passing through the cathode side of the gas diffusion layer by increasing the water flow from cathode to anode through the membrane.1,2 Gostick et al. Federal government websites often end in .gov or .mil. suggested that cracks in the MPL are pathways for the liquid water discharge, and that this results in limiting water access to the GDL inlet face and reduces water saturation in the GDL.3,4 Owejan et al. It has also been confirmed that the cell performance with the hydrophilic CF-MPL is improved in drier conditions (70C, 50%RH,19 and 80C, 30%RH).18 In this study, the investigations are focused on the phenomena under flooded conditions. Figure 7. This is consistent with the results reported by Tanuma et al. investigated water transport in the MPL by measuring the performance of cells with various types of MPL, and suggested that the primary role of the MPL is preventing condensed water from accumulating near the cathode CL surface.5. The stoichiometric ratios of anode hydrogen and cathode air are 11 and 19 at 0.7 A/cm2, respectively. The possible water transport in the hydrophilic CF-MPL, suggested by the experimental results of Figs. The hydrophilic CF-MPL shows the better performance with lower concentration overvoltages in Figs. The oxygen gains of the thinner MPL are also higher, supporting the above suggestion: the tolerance to flooding by the thinner hydrophilic CF-MPL is insufficient even with the larger pore size of the MPL provided by the fiber structure. Epub 2013 Jan 14. Bethesda, MD 20894, Web Policies The cell resistance was measured by an alternating impedance meter at 1kHz (TSURUGA, model 3566), and the cell voltage, resistance, and temperatures (cell, supply gases, and bubbler) were recorded. (a) Polarization curves and cell resistances of the hydrophilic CB-MPL and the hydrophobic CF-MPL, and (b) plot of the oxygen gains of the four types of MPLs. Relationship between the wettability and the pore diameter of the MPL in the investigations here. The thickness of the MPL depends on the amount of solid in the MPL slurry. This could be due to the larger diameter allowing liquid water to penetrate into the hydrophobic pores. The pressure independent resistance can be assumed to correspond approximately to the oxygen transport resistance in the CL, the Knudsen diffusion resistance in the pores of the CL, and the transport resistance from the gas in the pores to the Pt surface through the ionomer, and this allows the oxygen transport resistance in the CL to be evaluated quantitatively. Figure 6 shows cryo-SEM images inside (a) the hydrophobic CB-MPL and (b) the hydrophilic CB-MPL at the cathode side before and after operating the cell at 0.7 A/cm2 for 1 hour. If there are no local regions of high or low electron density in the molecule, it is called hydrophobic (Greek for "water-fearing"). 4, 5b, 8, and 9, is illustrated in schematic cross-sectional diagrams in Fig. Ion Mobility and Tandem Mass Spectrometry of Phosphatidylglycerol and Bis(monoacylglycerol)phosphate (BMP). These standard free energies of transfer are also directly proportional to the number of hydrogen-carbon bonds the hydrocarbons contain. The appearance of the hydrophobic CF-MPL (not shown here) was similar to the hydrophilic CF-MPL as well as to the two types of the MPLs with CB, and the effects of wettability on the MPL structure appear to be negligible in the experiments in this study. 10a. An interface between pores where ice was observed and empty pores (enclosed by a circle) is clearly shown in Fig. The present study investigates the effect of MPL wettability and structure on the cell performance under high humidity conditions to evaluate the mechanism for improving cell performance by the whole hydrophilic MPL in wet conditions. Polymer electrolyte membrane fuel cells using a hydrophilic micro-porous layer (MPL) consisting of carbon fiber (CF) and ionomer show better performance than those using conventional hydrophobic MPL with carbon black (CB) under a wide range of humidity conditions. To evaluate the water transport inside the MPL and its effect on the cell performance, the water distribution in the cells was observed by the freezing method and cryo-SEM. Figure 3. Figure 11 plots (a) the polarization curves and resistances and (b) the oxygen gains of the cells using the thinner and normally thick hydrophilic CF-MPLs (thinner MPL and MPL respectively in Fig. In the operation at 0.7 A/cm2, the rate of spreading of the produced water on the CF surface is balanced with the rate of evaporation of the water film, and a steady water distribution is maintained as suggested in Fig. Epub 2013 Jan 18. Number 7 Inside the hydrophobic CB-MPL after the operation of Fig. It should be noted that the cell voltage with the hydrophilic CF-MPL is also maintained higher than the cells with the other MPLs during this higher current density operation. The interface between the cathode side MPL and the CL was fabricated by the gas diffusion electrode (GDE) method. Please login to view your saved searches. This paper also discusses the water transport parameters improving the cell performance at high humidity conditions. 165 F484, 1 Division of Energy and Environmental Systems, Graduate School of Engineering, Hokkaido University, Sapporo, Hokkaido 060-8628, Japan, 2 Asahi Glass Co., Ltd. Research Center, Yokohama, Kanagawa 221-8875, Japan. Hankin JA, Murphy RC, Barkley RM, Gijn MA. 9c) is similar to that at the lower current density (Fig. Some thermodynamic effects of varying nonpolar surfaces in protein-ligand interactions. As the current density increases, the rate of water production becomes higher, and the water film spreads to the GDL side to increase the surface area with a concomitant higher evaporation rate of the total water present in the MPL, as shown in Fig. An official website of the United States government. 2013 Apr 17;587(8):1062-6. doi: 10.1016/j.febslet.2013.01.006. Bioorg Med Chem Lett. Figure 4b shows the changes in the cell voltage and the cell resistance for 1 hour of constant current density operation at 0.7 A/cm2 for both the cells with the hydrophilic CF-MPL and hydrophobic CB-MPL. Four types of MPLs with different wettabilities, hydrophilic or conventional hydrophobic properties, and different structures consisting of carbon fibers or conventional carbon blacks, are used. Publishing. 8a. The study used a small single cell with an active area of 1.8 cm2 (0.9cm 2.0cm) to allow the cell to be frozen and disassembled rapidly with the freezing method. government site. Applying thermodynamic profiling in lead finding and optimization. ACS Med Chem Lett. Relative importance of the hydrophobic effect on the solubility of hydrophobes and pharmaceuticals in H-bonded solvents. How can you tell if a molecule is polar or hydrophobic? Further, the water distribution inside the MPL is evaluated by the freezing method and cryo-SEM observations, and the relationship between the water distribution and the cell performance is identified. Protein-ligand interactions: probing the energetics of a putative cation- interaction. 7a and 7b correspond to the MPL/GDL interface, and the bottom of Figs. Published by ECS. The Author(s) 2018. This ice distribution was observed at all of the observation points, while the interface between the ice and the pores varied somewhat in location. developed a hydrophilic wicking MPL which contains hydrophilic alumosilicate fibers in the acetylene black and polytetrafluoroethylene (PTFE), and reported that the hydrophilic MPL contributes to enhance the cell performance regardless of the humidity conditions.10 Mukundan et al. Figure 5. 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6b, inside the hydrophilic CB-MPL after the operation there is ice filling some pores with some pores remaining vacant. 7c. Yusuke Aoyama https://orcid.org/0000-0001-9287-7050, Yutaka Tabe https://orcid.org/0000-0002-6160-1526, Received 19 March 2018 Export citation and abstract 8c), while there is no ice at the GDL side (Fig. 2014 Jul 15;24(14):3164-7. doi: 10.1016/j.bmcl.2014.04.114. Journal of The Electrochemical Society, The voltages of the hydrophilic CF-MPL are higher during the operation, as also suggested by the results in Fig. 2. 16. Clipboard, Search History, and several other advanced features are temporarily unavailable. The oxygen gain indicates the oxygen transport resistance in the cell, and a larger oxygen gain means a higher concentration overvoltage. 2015 Feb 15;378:255-263. doi: 10.1016/j.ijms.2014.08.026. Figure 12 shows a cryo-SEM image of the whole thickness of the thinner hydrophilic CF-MPL after operating the cell at 0.7 A/cm2 for 1 hour. 6. Eur J Med Chem. (a) Polarization curves and cell resistance, and (b) oxygen gains of the thinner hydrophilic CF-MPL, plotted with the hydrophobic CF-MPL in Figs. Polymer electrolyte membrane fuel cells (PEFCs) are expected to play a leading role as next generation power sources for automobiles, portable devices, and residential cogeneration systems (a so-called combined heat and power; CHP). To investigate factors that would be effective in improving the cell performance by the hydrophilic CF-MPL, cells using the hydrophilic CB-MPL and hydrophobic CF-MPL at the cathode side were also compared with a cell using the conventional hydrophobic CB-MPL. Figure 9 shows images of the hydrophilic CF-MPL after operation at 1.4 A/cm2 for 1 hour. Volume 165, Figure 1. By continuing to use this site you agree to our use of cookies. 4a and 5b. This site needs JavaScript to work properly. This difference in the effect of observed ice on the performance cannot be explained by the cryo-SEM analyses here, because of the difficulties of making a quantitative evaluation of the amounts and the structure of the ice in the MPL from the images. Additionally, large ice accumulations were formed at the port of the MPL/CL interface (not shown in Fig.

Similar images were also obtained with all of the observations of both the MPLs at various in-plane locations. 2020 Dec 15;208:112771. doi: 10.1016/j.ejmech.2020.112771. Even if a molecule has polar covalent bonds, if these bonds are arranged symmetrically, is quite polar, they are arranged symmetrically around the central carbon atom, 4a. We discuss the subsequent reaction mechanism leading to CNPs of different surface characters. When the same standard free energies of transfer are plotted as a function of the accessible surface areas of the hydrocarbons, the data do not fall upon the same line nor are the standard free energies of transfer directly proportional to the accessible surface areas. Int J Mass Spectrom. The region where ice was observed here has spread further toward the GDL side of the MPL in the image showing the whole thickness (Fig. Shortcomings of basing radical stabilization energies on bond dissociation energies of alkyl groups to hydrogen. 1. Figure 4. The Electrochemical Society was founded in 1902 to advance the theory and practice at the forefront of electrochemical and solid state science and technology, and allied subjects. The cell using the hydrophilic CF-MPL shows higher cell voltages than those using the MPL with the conventional hydrophobic CB-MPL at high current densities. Bookshelf This could suggest that the hydrophilic MPL with a conventional CB structure is more easily affected by water accumulation, but the effect is less likely to become a serious impediment than with the hydrophobic MPLs. The pores of the MPL at the CL side appear to be filled with large amounts of ice (Fig. The hydrophobic and hydrophilic CB-MPLs had similar structures and different wettabilities; the hydrophobic CF-MPL had similar wettability to the hydrophobic CB-MPL but a different structure with the larger pore diameters. Myslinski JM, Clements JH, Delorbe JE, Martin SF.

In the later discussion a thinner hydrophilic MPL with the ionomer, shown in brackets in TableI, will be introduced to consider the water transport phenomenon in the hydrophilic CF. From the comparison of the performance of the cells with the four types of MPLs, it may be concluded that the combination of increasing the pore diameter and applying a hydrophilic treatment contributes to the improvement in the cell performance of the hydrophilic CF-MPL, as shown in Fig. Because the experimental condition was wet, the concentration overvoltage is considered to be caused by water flooding, and the result indicates that the hydrophilic CF-MPL is the more effective to suppress an increase in the concentration overvoltage under severely flooded conditions. The CB is Vulcan XC-72R by Cabot Corporation. Copyright 2022 IOP The hydrophobic CNPs appeared to be nearly identical in size and morphology to hydrophilic CNPs. This indicates that only inadequate amounts of water evaporate, something that may be ascribed to the inadequate pore size of the MPL composed of the CB preventing the formation of a water film on the CB surface with the large surface area for the higher evaporation rate of water. The cryo-SEM observations were conducted at the Electron Microscope Laboratory, Research Faculty of Agriculture, Hokkaido University. Photos of the cell and the bipolar plate are shown in Fig.

A covalent bond is polar if one of the atoms in it has a significantly higher affinity for electrons (electronegativity) than the other. The hydrophilic CF-MPL draws up water from the CL due to the hydrophilic property with water spreading on the CF surface, as shown in Fig. 9a). From the measured cell performance and the observed ice distribution, a possible mechanism for the improvements in the cell performance by the hydrophilic CF-MPL is proposed to be that the hydrophilic CF-MPL enhances the transport of liquid water in the CL due to the hydrophilic properties with water able to spread across the CF surface, and promotes evaporation of the water with the large pores and sufficient thickness maintaining the water as a film and increasing the surface area of the water film on the CF. Cryo-SEM images of cross-sections of (a) the hydrophobic CB-MPL and (b) the hydrophilic CB-MPL before and after operating the cell at 0.7 A/cm2 for 1 hour. 4 and 5b suggest the possibility that there are sufficient open paths to ensure the passage of sufficient oxygen as long as a sufficient evaporation rate is achieved with the large surface area of the water film in the pores. There are two things to consider when trying to decide. Published 10 May 2018. A schematic view of the relationship between the wettability and the pore diameter of these MPLs is shown in Fig. Next, the cell was disassembled in the thermostatic chamber at 40C, and the MEA was cooled further in liquid nitrogen to prevent sublimation of the frozen water. Table I. Detailed analyses of the distribution and structure of the water in the hydrophilic CF-MPL are necessary to validate the hypothesis suggested here. These situations in Figs. 5b. The oxygen gains of the hydrophilic CF-MPL are also lower, and these results suggest that the hydrophilic CF-MPL prevents increases in the concentration overvoltage due to flooding under higher current density conditions. 8600 Rockville Pike 10. The .gov means its official. The properties of the particle surface were controlled simply by adjusting the laser focusing position, the duration between the preparation of B/W bilayer solution and the laser irradiation. FEBS Lett. To further confirm the reasons for the different cell performances, the oxygen gains of the cells with the four types of cathode MPLs in Figs. Unable to load your collection due to an error, Unable to load your delegates due to an error. 2013 Jan 29;110(5):1670-3. doi: 10.1073/pnas.1220825110. This site uses cookies. This research was supported by JSPS KAKENHI grant Number 261599. In the case of the hydrophilic CB-MPL after the operation in Fig. These results indicate that the hydrophilic CF-MPL enhances the liquid water transport from the CL due to the hydrophilic properties, and promotes water evaporation due to the large pores in the thick fiber structure. Epub 2015 Jan 23. Even though each of the C-Cl bonds Focusing intense femtosecond laser pulses onto water creates a high density of reactive species such as hydroxyl radicals in a well-confined volume; i.e., plasma filament. Cryo-SEM images of cross-sections of the hydrophobic CF-MPL for (a) the whole thickness, (b) for the GDL side, and (c) for the CL side after operating the cell at 0.7 A/cm2 for 1 hour. Recently, some studies have applied hydrophilic compounds to the MPL for further improvements in cell performance under wet and dry conditions.913 Schweiss et al.

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