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Academic literature on the topic 'Hydrophobic graded gas diffusion layer'

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Published: 10 December 2022
Last updated: 28 January 2023

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Journal articles on the topic "Hydrophobic graded gas diffusion layer"

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Das, Prodip. "(Invited, Digital Presentation) Tuning Gas-Diffusion-Layer Surface Wettability for Polymer Electrolyte Fuel Cells." ECS Meeting Abstracts MA2022-01, no. 38 (July 7, 2022): 1709. http://dx.doi.org/10.1149/ma2022-01381709mtgabs.

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In the present scenario of a global initiative toward securing global net-zero by mid-century and keeping 1.5 degrees within reach, polymer-electrolyte fuel cells (PEFCs) are considered to play an important role in the energy transition, particularly for the decarbonization of transit buses, trucks, rail transport, ships and ferries, and the residential heating sector. However, PEFCs are not economically competitive with the internal combustion engine powertrains [1]. Moreover, their durability standards in widely varying conditions have yet to be established and water management remains a critical issue for performance degradation and durability [1-3]. Thus, the mission of my research team is to conduct original research to make PEFCs economically viable and optimize their performance and durability [4,5]. In this talk, I will highlight our research on PEFC’s gas diffusion layer (GDL), as its interfaces with the flow channel and microporous layer play a significant role in water management. This research was aimed at selectively modifying GDL surfaces with a hydrophobic pattern to improve water transport and water removal from flow channels; thus, improving the durability and performance of PEFCs. Sigracet® GDLs were used as a base substrate and two different monomers, polydimethylsiloxane (PDMS) added with fumed silica (Si) and fluorinated ethylene propylene (FEP) were used to print a selective pattern on the GDL surfaces [6]. Both the additive manufacturing and spray coating techniques were utilized for creating the hydrophobic pattern on the GDL surfaces. The results of this study demonstrated a novel but simple approach to tune GDL surfaces with selective wetting properties and superhydrophobic interfaces that would enhance water transport. I will discuss some of these results and highlight how these results will benefit the water management of next-generation high-power PEFCs. This work was funded by the Engineering and Physical Sciences Research Council (EP/P03098X/1) and the STFC Batteries Network (ST/R006873/1) and was supported by SGL Carbon SE (www.sglcarbon.com). References [1] A.Z. Weber et al., "A critical review of modeling transport phenomena in polymer electrolyte fuel cells," J. Electrochem. Soc., vol. 161, pp. F1254-F1299, 2014. [2] A.D. Santamaria et al., "Liquid-water interactions with gas-diffusion layers surfaces," J. Electrochem. Soc., vol. 161, pp. F1184-F1193, 2014. [3] P.K. Das and A.Z. Weber, "Water management in PEMFC with ultra-thin catalyst-layers," ASME 11th Fuel Cell Science, Engineering and Technology Conference, Paper No. FuelCell2013-18010, pp. V001T01A002, 2013. [4] L. Xing et al., "Membrane electrode assemblies for PEM fuel cells: A review of functional graded design and optimization," Energy, vol. 177, pp. 445-464, 2019. [5] L. Xing et al., "Inhomogeneous distribution of platinum and ionomer in the porous cathode to maximize the performance of a PEM fuel cell," AIChE J., vol. 63, pp. 4895-4910, 2017. [6] D. Thumbarathy et al., "Fabrication and characterization of tuneable flow-channel/gas-diffusion-layer interface for polymer electrolyte fuel cells," J. Electrochem. Energy Convers. Storage, vol. 17, pp. 011010, 2020.
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Trocino, Stefano, Carmelo Lo Vecchio, Sabrina Campagna Zignani, Alessandra Carbone, Ada Saccà, Vincenzo Baglio, Roberto Gómez, and Antonino Salvatore Aricò. "Dry Hydrogen Production in a Tandem Critical Raw Material-Free Water Photoelectrolysis Cell Using a Hydrophobic Gas-Diffusion Backing Layer." Catalysts 10, no. 11 (November 13, 2020): 1319. http://dx.doi.org/10.3390/catal10111319.

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A photoelectrochemical tandem cell (PEC) based on a cathodic hydrophobic gas-diffusion backing layer was developed to produce dry hydrogen from solar driven water splitting. The cell consisted of low cost and non-critical raw materials (CRMs). A relatively high-energy gap (2.1 eV) hematite-based photoanode and a low energy gap (1.2 eV) cupric oxide photocathode were deposited on a fluorine-doped tin oxide glass (FTO) and a hydrophobic carbonaceous substrate, respectively. The cell was illuminated from the anode. The electrolyte separator consisted of a transparent hydrophilic anionic solid polymer membrane allowing higher wavelengths not absorbed by the photoanode to be transmitted to the photocathode. To enhance the oxygen evolution rate, a NiFeOX surface promoter was deposited on the anodic semiconductor surface. To investigate the role of the cathodic backing layer, waterproofing and electrical conductivity properties were studied. Two different porous carbonaceous gas diffusion layers were tested (Spectracarb® and Sigracet®). These were also subjected to additional hydrophobisation procedures. The Sigracet 35BC® showed appropriate ex-situ properties for various wettability grades and it was selected as a cathodic substrate for the PEC. The enthalpic and throughput efficiency characteristics were determined, and the results compared to a conventional FTO glass-based cathode substrate. A throughput efficiency of 2% was achieved for the cell based on the hydrophobic backing layer, under a voltage bias of about 0.6 V, compared to 1% for the conventional cell. For the best configuration, an endurance test was carried out under operative conditions. The cells were electrochemically characterised by linear polarisation tests and impedance spectroscopy measurements. X-Ray Diffraction (XRD) patterns and Scanning Electron Microscopy (SEM) micrographs were analysed to assess the structure and morphology of the investigated materials.
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Yoon, Gug-Ho, Sung Bum Park, Eun Hyung Kim, Myung-Hoon Oh, Kyeong-Sik Cho, Soon Wook Jeong, Sungjin Kim, and Yong-il Park. "Novel hydrophobic coating process for gas diffusion layer in PEMFCs." Journal of Electroceramics 23, no. 2-4 (October 3, 2007): 110–15. http://dx.doi.org/10.1007/s10832-007-9321-1.

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Imazato, Minehisa, Hayato Hommura, Go Sudo, Kenji Katori, and Koichi Tanaka. "The Amount of Hydrophobic Resin Binder in the Micro Diffusion Layer for DMFC." Journal of Fuel Cell Science and Technology 1, no. 1 (July 5, 2004): 66–68. http://dx.doi.org/10.1115/1.1794710.

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The micro-diffusion layer for DMFC consists of carbon and hydrophobic resin used as a binder. The function of the micro diffusion layer on carbon paper is not only to support the catalyst layer to conduct electricity, but also to maintain a stable mixture of gas and liquid. The amount of hydrophobic resin binder in the micro diffusion layer is therefore a critical parameter. The amount of hydrophobic resin binder is normally less than 50wt%, but we investigated this parameter and found that there is another high performance area around 80wt%.
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Wang, Peng, Hironori Nakajima, and Tatsumi Kitahara. "Hydrophilic and Hydrophobic Microporous Layer Coated Gas Diffusion Layer for Enhancing PEFC Performance." ECS Transactions 104, no. 8 (October 1, 2021): 117–27. http://dx.doi.org/10.1149/10408.0117ecst.

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Wang, Peng, Hironori Nakajima, and Tatsumi Kitahara. "Hydrophilic and Hydrophobic Microporous Layer Coated Gas Diffusion Layer for Enhancing PEFC Performance." ECS Meeting Abstracts MA2021-02, no. 36 (October 19, 2021): 1034. http://dx.doi.org/10.1149/ma2021-02361034mtgabs.

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Wang, Peng, Hironori Nakajima, and Tatsumi Kitahara. "(Digital Presentation) Effect of the Hydrophilic Layer in Double Microporous Layer Coated Gas Diffusion Layer on PEFC Performance." ECS Meeting Abstracts MA2022-02, no. 39 (October 9, 2022): 1383. http://dx.doi.org/10.1149/ma2022-02391383mtgabs.

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The polymer electrolyte fuel cells (PEFCs) are commonly used in the vehicle industry, but the relatively higher costs of power generation limit the potential for further application. The PEFCs output power can be mainly undermined by the water management of the membrane electrode assembly (MEA). If the water content balance in the MEA is broken by fast water expelling, the dehydrated membrane significantly raises the proton transport resistance, which results in severe ohmic resistance loss. Oppositely, the slow water removal pace makes the production water stay at the catalyst layer (CL) surface, and the reactants are prohibited from accessing the reaction area and causing high reactants concentration overpotential during the high current density range. To elongate the limiting current density and raise the output power, beneficial water management should keep the MEA from dehydration by using the water generated from electrochemical reactions and can expel additional water from the CL and gas diffusion layer (GDL) interface. To implement the favorable water balance in the cell, the GDL with the microporous layer (MPL) is necessary. Traditional MPL mainly contains carbon black and hydrophobic binder Polytetrafluoroethylene (PTFE), which can guarantee water-unoccupied pathways for gas transport. The produced water can be expelled by the relatively large pores, and the water transportability is mainly controlled by the pore size and hydrophobicity. When the pore size is excessively narrow, the easily gathered water creates flooding between the CL and GDL. Large pores can solve this issue but bring the water stored in the MPL. Thus, a double MPL is developed to achieve better water management when it cannot forwardly enlarge the pore sizes under low and high humidity conditions. A commercially available hydrophobic MPL coated GDL (SGL 22BB) is the standard sample in this study. As for double MPL coated GDL, the hydrophilic layer is coated on the hydrophobic MPL coated GDL. One candidate composition uses Nafion as the hydrophilic binder, TiO2 as the hydrophilicity improvement particles, and the rest of the part is carbon black; the other way applies only Polyvinyl alcohol (PVA) as the hydrophilic binder and mixes with carbon black. Both types of hydrophilic slurry are directly coated on the 22BB, and the maximum pore diameter slightly changed from 45um (SGL 22BB) to a smaller size. These very thin hydrophilic layers modify the surface properties, which can help reduce the surface contact angle and make water easier to be introduced into the hydrophobic MPL. According to the tests, the performance of the double MPL containing PVA binder becomes worse than the Nafion-TiO2 double MPL, even than standard hydrophobic MPL. Due to the strong hydrophilicity of the PVA binder, even though a tiny amount of it is added to the top layer, water accumulation still occurs in the MPL, so the PVA binder is not suitable for the MPL property modification. The double MPL, which applied a Nafion-TiO2 hydrophilic layer, achieves lower oxygen transport resistance under high humidity conditions than the standard hydrophobic MPL. Besides, the appropriate composition of the hydrophilic contents is determined. With the increase of the TiO2 and Nafion content, the significantly enhanced hydrophilicity leads to more water absorption. However, it blocks the gas pathways, showing terrible reactants transport and high concentration over-potential. When the hydrophilic content becomes overly low, it is not enough to afford the water expelling, and water still occupies the MPL and CL interface. The thickness of the top hydrophilic MPL is another critical design parameter. A too thick hydrophilic layer can hold more water and cause a high risk of hampering reactants supply. The moderate thickness of the hydrophilic layer should be less than 5μm, which guarantees the function of the water transport and keeps away from severe water absorption.
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Munekata, Toshihisa, Takaji Inamuro, and Shi-aki Hyodo. "Gas Transport Properties in Gas Diffusion Layers: A Lattice Boltzmann Study." Communications in Computational Physics 9, no. 5 (May 2011): 1335–46. http://dx.doi.org/10.4208/cicp.301009.161210s.

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AbstractThe lattice Boltzmann method is applied to the investigations of the diffusivity and the permeability in the gas diffusion layer (GDL) of the polymer electrolyte fuel cell (PEFC). The effects of the configuration of water droplets, the porosity of the GDL, the viscosity ratio of water to air, and the surface wettability of the GDL are investigated. From the simulations under the PEFC operating conditions, it is found that the heterogeneous water network and the high porosity improve the diffusivity and the permeability, and the hydrophobic surface decreases the permeability.
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Kudo, Kazuhiko, Akiyoshi Kuroda, Shougo Takeoka, and Yosuke Shimazu. "B112 Modeling of water transmission in hydrophobic gas diffusion layer of PEFC." Proceedings of the Thermal Engineering Conference 2006 (2006): 39–40. http://dx.doi.org/10.1299/jsmeted.2006.39.

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Kudo, Kazuhiko, Akiyoshi Kuroda, Takashi Yamaguchi, Shougo Takeoka, and Hitoshi Watanabe. "G132 Modeling of Water Transmission through Hydrophobic Gas Diffusion Layer of PEFC." Proceedings of the Thermal Engineering Conference 2007 (2007): 237–38. http://dx.doi.org/10.1299/jsmeted.2007.237.

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Dissertations / Theses on the topic "Hydrophobic graded gas diffusion layer"

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Ke, Yu-Wei, and 柯煜偉. "Gas Diffusion Layer with Various Hydrophobic Properties Effect on Alkaline Anion Exchange Membrane Fuel Cells." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/45c9fh.

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碩士
國立中興大學
精密工程學系所
106
In this study, the water management in alkaline anion exchange membrane fuel cells (AEMFC) by testing six kinds of carbon materials was studied, which are GDL 120, GDL120+30% PTFE, GDS310, GDS310+30% PTFE, GDL340, and GDL340+30% PTFE, respectively. The Pt/C of 0.8 mg/cm2 and with different ratios component were prepared for two catalysts as the cathode and anode electrode. In addition, the prepared Pt/C catalysts were coated on the carbon materials surface for Scanning electron microscope (SEM) testing to measure the surface and proved the Pt/C attached to the black carbon status. Then, the surface tension measuring instrument was used to measure the contact angle of each carbon material and determined the hydrophilicity/hydrophobicity of the material for further discussion of the AEMFC water management. For double verification, anion exchange membranes at different thicknesses were used to test the fuel cell discharge experiment. The results showed that one of the anode or cathode without adding hydrophobic material PTFE will cause water clogged so that the inlet gas could not smoothly pass through the electrodes and then the AEMFC performance was declined. Using hydrophobic carbon material GDL340+30% PTFE at the anode and cathode showed a better ion conductivity without flooding phenomenon. Moreover, The AEMFC with the GDL340+30% PTFE used for both anode and cathode and the FAA-3-PK-75 membrane can achieve an optimal power density of 82mW/cm2 at 0.4V whereas the AEMFC discharge test with the same types of the anode and cathode, but the other thinner FAS-30 membrane obtained a significantly high power density of 279 mW/cm2 at 0.4 V.
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Peng, J. C., and 彭兆強. "Effect of Hydrophobic Treatment of Gas Diffusion Layer of PEMFC on Mass Transport and Electric Conductivity." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/54790419475331714764.

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碩士
大葉大學
機械工程研究所碩士班
94
ABSTRACT The objectives of this research are to look into the fundamental properties of the gas diffusion layer of a PEMFC and to investigate the influence of hydrophobic treatments of gas diffusion layer on its electric conductivity. Furthermore, with an aim to thoroughly understand its functional variations, this thesis also carries out experiments to measure the changes in porosity, thickness, and electric conductivity of gas diffusion layer under various pressure levels. The gas diffusion layer, made of carbon fibers, is a kind of porous media whose structural properties depend substantially on its hydrophobic treatments. In this research, apparatus are fabricated to measure the variation of porosity due to its hydrophobic treatments. Then, measurements of the electric conductivity on the gas diffusion layer are performed under pressure load; finally SEM is adopted to investigate the structure change of fibers before and after pressure loading. The results show that the porosity of a gas diffusion layer decreases as the extent of hydrophobic treatments increases. However, under pressure load, the decrease in porosity is mitigated with the help of hydrophobic treatments because the robustness of the gas diffusion layer is enhanced by the hydrophobic treatments. Fragmentation of fibers has also been observed after pressure loading, while the electric conductivity of gas diffusion layer increases, which may attribute to the compactness of the gas diffusion layer under pressure loading. Key Words：PEMFC, Gas diffusion layer, Hydrophobic, Porosity
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Huang, Jian-Jun, and 黃建鈞. "Influence of hydrophobic gas diffusion media and micro-porous layer on the performance of polymer electrolyte membrane fuel cell." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/15501394134132132668.

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碩士
逢甲大學
材料科學所
96
The time changes with each new day which in the modern science and technology, the petroleum and so on the energy material short question in the life which we comfortably facilitates, is extremely needs the urgent improvement the question. Among them, the fuel cell studies is each kind of substitution energy in at present in the choice, promotes to the present most environmental protection electricity generation way, thus the present stage receives the focal point which from all walks of life warmly focuses attention. In the fuel cell, uses all kinds of includes the hydrogen atom the fuel to carry on the response to emit the electric current, polymer electrolyte membrane fuel cell (PEMFC) the research is at present often is most studied in the present paper experiment and the discussion, because it besides has the high electric discharge potency, the zero pollution is one of reasons which it receives focuses attention on, its principle is using the hydrogen works as the fuel gas, the penetration proton exchange membrane dissociates the hydrogen ions and the electron thus discharge it, hydrogen ions with another end oxygen union, but produces the only by-product - liquid water. In the fuel cell components, the gas diffusion layer use is the gas even diffusion to the catalyst layer, causes to gas can reaction fully, but the liquid water production, can cause the gas circulation to encounter the limit to receive blocks, so studies of hydrophobic gas diffusion media and micro-porous layer in this paper changes the nature to the gas diffusion layer, can cause the gas diffusion layer the question thorough improvement which is blocked by the water, simultaneously discusses to influence overall cell performance factor of proton exchange membrane fuel cell which it to contain impregnations and sprays and so on the quantity, thickness, resistance, gas permeability, density.
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Conference papers on the topic "Hydrophobic graded gas diffusion layer"

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Kudo, Kazuhiko, Akiyoshi Kuroda, Shougo Takeoka, and Yosuke Shimazu. "Modeling of Flooding Phenomena in Hydrophobic Gas Diffusion Layer of PEFC." In ASME/JSME 2007 Thermal Engineering Heat Transfer Summer Conference collocated with the ASME 2007 InterPACK Conference. ASMEDC, 2007. http://dx.doi.org/10.1115/ht2007-32110.

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The mechanism of liquid water removal, water vapor diffusion and oxygen diffusion in cathode side gas diffusion layer (GDL) of PEFC is studied by modeling the GDL as a hydrophobic flat plate with many straight holes with different diameters. As the results of the consideration using the model, following results are obtained. The spots where liquid water condensation is taken place between GDL-MEA gap are limited to the inlets of holes with larger diameters, and the condensed water is drained to air flow channel only through the larger holes. Other holes with smaller diameters are free of liquid water, and oxygen diffuses from the air flow channel to the catalyst surface through such holes. The reduction of output voltage of fuel cell due to the increase in the current density may be caused by the reduction of the oxygen concentration in GDL-MEA gap. The condensate tends to penetrate into larger holes instead of filling the gap of GDL and MEA.
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Tahseen, Siddiq Hussain, Kehan Chen, Mehdi Shahraeeni, Samuel C. M. Yew, and Mina Hoorfar. "Measurement of Liquid Water Content Inside the Gas Diffusion Layer." In ASME 2012 10th International Conference on Fuel Cell Science, Engineering and Technology collocated with the ASME 2012 6th International Conference on Energy Sustainability. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/fuelcell2012-91084.

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The amount of the liquid water present at the gas diffusion layer (GDL) has an impact on the diffusivity, capillary pressure and the permeability which in turn influences convective and diffusive transport. A prodigious amount of research has been conducted to study and measure the different properties (time of breakthrough and capillary pressure versus saturation) associated with the breakthrough condition. However, most of the reported data ignored the impact of expansion of different components in the set-up (such as tubing) and the condition after the time of breakthrough. The focus of this study is to measure the breakthrough pressure and time of breakthrough and hence determine the liquid water content inside the GDL before the time of breakthrough. The measurements are performed for different samples to study the effect of the thickness and hydrophobic contents. The results show that expansion has significant difference in the determination of water volume inside the GDL.
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Utaka, Yoshio, and Ikunori Hirose. "Microporous Layer Consisting of Alternating Porous Material With Different Wettability for Controlling Moisture in Gas Diffusion Layer of PEFC." In 2010 14th International Heat Transfer Conference. ASMEDC, 2010. http://dx.doi.org/10.1115/ihtc14-22197.

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The oxygen transfer characteristics of the gas diffusion layer are closely related to the cell performance of a polymer electrolyte fuel cell. In this study, a new hybrid gas diffusion layer is proposed in which two porous media with different wettabilities are arranged alternately for augmentation of the oxygen diffusivity in the gas diffusion layer. Since the movement of water from hydrophobic to hydrophilic media due to the difference in capillary pressure, the oxygen diffusion paths in the porous media can be maintained. The oxygen diffusion characteristics with respect to water saturation were measured using an experimental apparatus that uses a galvanic battery oxygen sensor as an oxygen absorber. The experimental results demonstrate that the hybrid structure has superior oxygen diffusion characteristics than a conventional gas diffusion layer with a single porous material with moisture. That is, the effective oxygen diffusivity of the hybrid configuration was almost five times larger than that of the single type at water saturation S = 0.2.
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Mukherjee, Partha P., Rangachary Mukundan, and Rodney L. Borup. "Modeling of Durability Effect on the Flooding Behavior in the PEFC Gas Diffusion Layer." In ASME 2010 8th International Conference on Fuel Cell Science, Engineering and Technology. ASMEDC, 2010. http://dx.doi.org/10.1115/fuelcell2010-33241.

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The gas diffusion layer (GDL) plays a critical role in the overall performance of a polymer electrolyte fuel cell (PEFC), especially in the mass transport control regime due to suboptimal liquid water transport. Liquid water blocks the porous pathways in the catalyst layer and gas diffusion layer thereby causing hindered oxygen transport from the channel to the active reaction sites. This phenomenon is known as “flooding” and is perceived as the primary mechanism leading to the limiting current behavior in the cell performance. The pore morphology and wetting characteristics of the cathode GDL are of paramount importance in the effective PEFC water management. Typical beginning-of-life GDLs exhibit hydrophobic characteristics, which facilities liquid water transport and hence reduces flooding. Experimental data, however, suggest that the GDL loses hydrophobicity over prolonged PEFC operation and becomes prone to enhanced flooding. In this work, we present a pore-scale modeling framework to study the structure-wettability-durability interplay in the context of flooding behavior in the PEFC GDL.
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Al Shakhshir, Saher, Yonxin Wang, Yongtaek Lee, and Xianguo Li. "Impact of One Side Hydrophobic Gas Diffusion Layer on Water Removal Rate and Proton Exchange Membrane Fuel Cell Performance." In SAE 2012 World Congress & Exhibition. 400 Commonwealth Drive, Warrendale, PA, United States: SAE International, 2012. http://dx.doi.org/10.4271/2012-01-1221.

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Osman, Sameer, Shinichi Ookawara, and Mahmoud Ahmed. "Effect of Anode Flow Channel Design on the Carbon Dioxide Bubble Removal in Direct Methanol Fuel Cells." In ASME 2020 14th International Conference on Energy Sustainability. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/es2020-1659.

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Abstract On the anode side of a direct methanol fuel cell, carbon dioxide bubbles are generated as a result of the methanol oxidation reaction. The accumulation of such bubbles prevents methanol from reaching the gas diffusion layer. Hence, a significant reduction in the reaction rate occurs, which limits the maximum current density of the cell. To keep carbon dioxide bubbles away from the gas diffusion layer interface, a new design of the anode flow channel besides wall surface treatment is developed. Such a design can introduce the Concus-Finn phenomena, which forces the carbon dioxide bubbles to move away from the gas diffusion layer due to capillary forces. This can be achieved by using a trapezoidal shape of the flow channel, as well as the combined effect of hydrophobic and hydrophilic surface treatments on the gas-diffusion layer and channel walls. To identify the optimal design of the anode flow channel, a three-dimensional, two-phase flow model is developed. The model is numerically simulated and results are validated with available measurements. Results indicated that treating the gas-diffusion layer with a hydrophilic layer increases the area in direct contact with liquid methanol. Besides, the hydrophobic top channel surfaces make it easier for the carbon dioxide bubbles to attach and spread out on the channel top surface. The current findings create a promising opportunity to improve the performance of direct methanol fuel cells.
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Rensink, Dirk, Jo¨rg Roth, and Stephan Fell. "Liquid Water Transport and Distribution in Fibrous Porous Media and Gas Channels." In ASME 2008 6th International Conference on Nanochannels, Microchannels, and Minichannels. ASMEDC, 2008. http://dx.doi.org/10.1115/icnmm2008-62087.

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In a polymer electrolyte membrane (PEM) fuel cell water is produced by electrochemical reactions in the catalyst layer on the cathode side. The water diffuses through the catalyst layer and a fibrous substrate into gas channels where it is transported away by convection. The fibrous substrate represents the gas diffusion media (GDM). Sometimes the GDM has a thin microporous layer on the side facing the catalyst layer. The same layer structure can be found on the anode side. All layers together are the porous layers of a PEM fuel cell. Under certain operating conditions condensation can occur in the porous layers which might lead to flooding conditions and — if the liquid water forms droplets which grow together in the gas channels — the complete blockage of the channels. Both situations can lead to a local starvation of reactant gases with negative impact on fuel cell performance and durability. The void space of the hydrophobic fibrous substrate in a PEM fuel cell can be interpreted as micro channels in a broader sense, especially if liquid phase transport from the catalyst layer towards the gas channels is in focus. Due to the small dimensions with effective channel diameter in the range of micrometer the flow of liquid water is governed by capillary forces. The same applies for the gas channels at low gas velocities since the Bond and Capillary numbers are well below one. Thus the investigation of liquid water flow and distribution under low gas velocities in the hydrophobic fibrous substrate and the spreading of liquid water along the hydrophilic gas channel walls under capillary action is of special interest for PEM fuel cells and investigated here.
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Owejan, J. P., T. A. Trabold, D. L. Jacobson, M. Arif, and S. G. Kandlikar. "Effects of Flow Field and Diffusion Layer Properties on Water Accumulation in a PEM Fuel Cell." In ASME 2007 5th International Conference on Nanochannels, Microchannels, and Minichannels. ASMEDC, 2007. http://dx.doi.org/10.1115/icnmm2007-30142.

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Water is the main product of the electrochemical reaction in a proton exchange membrane (PEM) fuel cell. Where the water is produced over the active area of the cell, and how it accumulates within the flow fields and gas diffusion layers, strongly affects the performance of the device and influences operational considerations such as freeze and durability. In this work, the neutron radiography method was used to obtain two-dimensional distributions of liquid water in operating 50 cm2 fuel cells. Variations were made of flow field channel and diffusion media properties, to assess the effects on the overall volume and spatial distribution of accumulated water. Flow field channels with hydrophobic coating retain more water, but the distribution of a greater number of smaller slugs in the channel area improves fuel cell performance at high current density. Channels with triangular geometry retain less water than rectangular channels of the same cross-sectional area, and the water is mostly trapped in the two corners adjacent to the diffusion media. Also, it was found that cells constructed using diffusion media with lower in-plane gas permeability tended to retain less water. In some cases, large differences in fuel cell performance were observed with very small changes in accumulated water volume, suggesting that flooding within the electrode layer or at the electrode-diffusion media interface is the primary cause of the significant mass transport voltage loss.
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Shahraeeni, Mehdi, and Mina Hoorfar. "Numerical Investigation of Fluid Flow Inside the Porous Medium of GDL." In ASME 2010 8th International Conference on Nanochannels, Microchannels, and Minichannels collocated with 3rd Joint US-European Fluids Engineering Summer Meeting. ASMEDC, 2010. http://dx.doi.org/10.1115/fedsm-icnmm2010-30594.

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A pore-network model is developed to study numerically the transient flow of fluid through the gas diffusion layer (GDL) of the PEM fuel cell. It is shown that the agglomeration of water droplet on the interface of the GDL and catalyst layer occurs faster for the samples with smaller pore diameters and lower contents of the hydrophobic agent. The study suggests that analysis of the temporal response of the GDL is a useful tool to evaluate its performance against transporting liquids.
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Friess, Brooks, and Mina Hoorfar. "Fluorescence Microscopy for the Measurement of the Surface Properties of the Gas Diffusion Layers of Fuel." In ASME 2010 International Mechanical Engineering Congress and Exposition. ASMEDC, 2010. http://dx.doi.org/10.1115/imece2010-39523.

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One of the major problems of current proton exchange membrane (PEM) fuel cells is water management. The gas diffusion layer (GDL) of the fuel cell plays an important role in water management since humidification and water removal are both achieved through the GDL. Various numerical models developed to illustrate the multiphase flow and transport in the fuel cell require the accurate measurement of the GDL properties (wettability and surface energy). In a recent study, the capillary penetration technique has been used to measure indirectly the wettability of the GDL based on the experimental height penetration of the sample liquid into the porous sample. In essence, a high resolution microscope/camera was used to detect the rate of penetrated height into the sample GDL. The shortcoming of this type of visualization is that it can only be used for thin hydrophilic GDL samples with zero Teflon loadings. For the thick and high Teflon loading GDLs, there is not enough contrast to detect the height of the penetrated liquid. In the real fuel cells, the GDLs are made of the micro-porous and macro-porous layers with an optimum Teflon loading. Therefore, it is required to develop a new experimental methodology capable of detecting the rate of penetration and as a result the wettability of GDLs samples used in fuel cells. In this paper, the fluorescence microscopy technique is integrated into the experimental setup of the capillary penetration method to improve the contrast between the wetted and non-wetted area. The fluorescence setup uses a powder die, dissolved in the test fluid, which is excited by a concentrated ultraviolet light illuminated in the vertical manner. To acquire the profile images of the penetrated liquid, an optical mirror was used. This new setup has the added advantage of providing a visual representation of the different regimes of penetration (e.g., the fingering effect reported for the pathways of the liquid penetrated into the GDLs) that are defined by the capillary number and mobility ratio of each fluid. Since the GDL samples used in this study are relatively hydrophobic (e.g., with 40% Teflon loadings), the pattern of liquid penetration is not uniform. Thus, an image analysis program was developed to determine the average height of penetration based on the area under the entire wetted area. The general Washburn equation was then used to fit the extracted height data and provide the average internal contact angle for each test liquid.
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