Liquid Water Formation Research Articles

Influence of the Clamping Force and the Formation of Liquid Water Along the Channel on the Local Diffusion Processes in PEMFCs

A novel measurement setup, technique, and segmented model are introduced to spatially resolve mass transport losses along the channel in a PEMFC. The newly designed segmented cell enables not only the measurement of local current and voltage data but also the capture of local temperature and compression levels. By extending the commonly used limiting current method, the local mass transport resistance is determined as a function of local operating parameters. The local current and temperature are directly measured, while the operating conditions along the channel such as pressure, oxygen fraction, and relative humidity are obtained empirically from a 1-D differential model. Leveraging both measured and empirically-based simulation results, this comprehensive approach facilitates the characterization of mass transport resistance distribution along the gas channel. The learnings from this study provide valuable insight into the optimization of channel and materials design for enhancing large active area fuel cell performance and durability.

Influence of the Clamping Force and the Formation of Liquid Water Along the Channel on the Local Diffusion Processes in PEMFCs

A novel measurement setup, technique, and segmented model are introduced to spatially resolve mass transport losses along the channel in a PEMFC. The newly designed segmented cell enables not only the measurement of local current and voltage data but also the capture of local temperature and compression levels. By extending the commonly used limiting current method, the local mass transport resistance is determined as a function of local operating parameters. The local current and temperature are directly measured, while the operating conditions along the channel such as pressure, oxygen fraction, and relative humidity are obtained empirically from a 1-D differential model. Leveraging both measured and empirically-based simulation results, this comprehensive approach facilitates the characterization of mass transport resistance distribution along the gas channel. The learnings from this study provide valuable insight into the optimization of channel and materials design for enhancing large active area fuel cell performance and durability.

Spatio‐temporal wet snow dynamics from model simulations and remote sensing: A case study from the Rofental, Austria

AbstractThe formation and concentration of liquid water (LW) in the snowpack constitute key processes linking snow and runoff. Hence, the LW content of the snowpack represents a crucial target variable to investigate for snowmelt‐induced runoff predictions. In this study, we capture the wet snow dynamics at higher than hectometre resolution in the alpine headwater catchment Rofental, Tyrol, Austria (98.1 km2) by means of distributed model simulations and remote sensing data for the 5 year period 10/2017–09/2022. The model simulations are conducted using the intermediate complexity open‐source snow‐hydrological model openAMUNDSEN. Simulation results are compared to wet snow maps (WSM) derived from Sentinel‐1 data. Our investigations indicate that distributed snow models of intermediate complexity, such as openAMUNDSEN and satellite‐based wet snow data are well capable of capturing the wet snow dynamics in high spatial and temporal resolutions. The areal extents of wet snow as well as the upward movement of the wet snow line to higher elevation with progressing snowmelt are captured well by both approaches. In order to evaluate the snow simulations, we use fractional snow cover (FSC) data based on Sentinel‐2, which proved to provide valuable small‐scale snow and snow redistribution patterns in alpine catchments. The comparison of model simulations with FSC maps with more than 50% of the non‐glaciated area being cloud‐free (i.e. 364 images) results in an accuracy of 0.91. This study represents a further step towards a serviceable operational snow‐hydrological monitoring and modelling framework for mountain regions including wet snow dynamics in high spatial and temporal resolutions.

Numerical Study of Liquid Water Formation and Transport in Porous Media

Fundamental understanding of liquid water formation and transport in fuel cells is of great importance for achieving high durability, reliability, and maximizing cell performance. For low temperature fuel cells, water may exist as vapor or liquid phase and is involved in various electrochemical reactions and transport mechanisms. The condensation process occurs when local water vapor pressure exceeds the saturation pressure. In this work, we first investigate the permeation of liquid water in the gas diffusion layer (GDL). To this aim, a two-dimensional isothermal model considering reconstructed GDL microstructure in conjunction with VOF model is implemented. The effects of mixed wettability of materials, operating temperature, and Polytetrafluoroethylene (PTFE) loadings on liquid water transport in the porous media are investigated numerically. The liquid water breakthrough and the capillary fingering regime are captured and compared. The results show that liquid water saturation in the GDL increases with decreasing PTFE loadings. Moreover, the results demonstrated that the local microstructure in the GDL has a strong effect and can dominate the overall water distribution. To further study water condensation, the isothermal model is expanded to non-isothermal for including physics of phase change heat transfer and species transport. In addition, anisotropic thermal conductivity is incorporated to study its effect on temperature distribution and liquid water distribution. The results show that initially the liquid water is formed as micro droplets and then these micro droplets are combined to form large droplets. Moreover, the impacts of water generation rate, temperature gradient, operating pressure, and contact angle on condensation have been investigated. The findings of this work are expected to provide insights into designing more reliable GDL in fuel cells. Figure 1

Role of Ammonia in Aerosol Liquid Water, pH, and Secondary Inorganic Aerosols Formation at an Ammonia-rich City in Changzhou

Ammonia （NH3） is an important alkaline reactive nitrogen, which, as a precursor of fine particulate matter, raises public health issues. In this study, online NH3, SO2, NO2, PM2.5, and its water-soluble inorganic ions were detected to deduce the influence of NH3 on aerosol liquid water content （AWC） and aerosol pH, including the formation of water-soluble secondary ions in PM2.5 in winter in Changzhou, an ammonia-rich city in the Yangtze River Delta area in winter. The results showed that NH4+ mainly existed in the form of NH4NO3 and （NH4）2SO4, and the remaining NH4+ existed as NH4Cl. Owing to the NH3-NH4+ buffer system, the aerosol pH values were found at 4.2 ± 0.4, which was positively correlated with the NH3 content. The aerosol pH value variation narrowed with the increase in PM2.5 concentration and tended to be between 4 to 5. AWC increased exponentially with the increase in humidity and SNA content, among which NH4NO3, （NH4）2SO4, and NH4Cl contributed 58.5%, 18.4%, and 8.3%, respectively, due to their hygroscopicity. Aerosol pH, AWC, and NH3-NH4+ conversion promoted the gas-to-particle conversion of SO2 and NO2. In Changzhou, rich NH3-NH4+ were found to maintain relatively high pH values, push up AWC, and promote the heterogeneous reaction of SO2, whereas NO3- generation was dominated by a homogeneous reaction, which was accelerated by NH3. According to the simulation results, relatively noticeable changes in aerosol pH and AWC could be found by the reduction of up to 30% of NH3.

From Agriculture to Clinics: Unlocking the Potential of Magnetized Water for Planetary and Human Health.

Magnetized water (MW) is a form of liquid water that has been exposed to a magnetic field to alter its hydrogen bonding structure, resulting in the formation of water molecule clusters of various sizes and configurations connected by hydrogen bonds. This magnetization process induces several changes in the physicochemical properties of water, such as increased pH, electrical conductivity, and dissolved oxygen content, as well as decreased surface tension, density, and evaporation temperature compared to untreated water. In this narrative review, we explore the effective utilization of MW in agriculture, where it has a well-established history of applications, and its potential for direct applications in the medical field, which are currently at the forefront of research. MW is one of the most promising innovations for facilitating the transition from unsustainable to sustainable agriculture, which is expected to yield positive human health outcomes by promoting the consumption of less processed foods and reducing resource consumption. In addition to these indirect effects on human health, preclinical research utilizing animal models has demonstrated that water magnetization exerts beneficial effects on diabetes, renal function, bone health, and fertility. These health benefits appear to stem from the ability of MW to increase the activity of antioxidant enzymes while decreasing lipid peroxidation and inflammatory markers. In terms of direct human applications, MW has been primarily studied in the fields of dentistry and dermatology. MW mouthrinse has consistently shown efficacy against Streptococcus mutans, with studies reporting comparable effects to chlorhexidine. In dermatology, the topical application of MW has demonstrated improvements in skin biophysical parameters, increased hair count and hair mass index, and promoted the healing of challenging wounds. Intriguingly, these effects on human skin seem to be mediated by local activation of autophagy, potentially through mild alkaline stress. In conclusion, this review underscores the promising role of MW in promoting a holistic approach to planetary and human health. Future studies should focus on standardizing the magnetization process, exploring the molecular mechanisms underlying MW-induced autophagy, and investigating the potential of MW as a complementary strategy for treating human diseases characterized by impaired autophagy.

Determination Of Two-Phase Flow Regimes Of A Condensing Water-Air Mixture In An Array Of Micro Channels

Proton exchange membrane (PEM) full cells (FCs) are a promising alternative to combustion engines for mobile applications. Their signature low operating temperature leads to the possible existence of product water in its liquid form. Liquid water formation and transport are important phenomena to understand and model in order to facilitate the development of new, more efficient PEMFCs. This contribution investigates the two-phase flow phenomena separately by introducing a gaseous air-vapor mixture into an optically accessible fuel cell flow plate with 14 parallel micro channels (confinement number Co = 7.3) and a carbon paper inlay representing the FC's gas diffusion layer and bringing it to the point of onset of condensation. Special care is taken to provide a controlled and reproducible air-vapor mixture with low pressure pulsation. One key feature of the experiment is that the flow plate used is designed to be as similar to a regular research fuel cell flow plate as possible, retaining its channel surface properties and electrical parameters. It can also be heated to a given temperature to mimic the fuel cell operating conditions. Therefore, the same plate can also be used in in-situ experiments in an operated fuel cell. An air mass flow rate of 500 - 1000 mLn / min with relative humidities of 75% - 95% at 65°C and 75°C was investigated. The emerging flow patterns were captured using a high-speed camera at 250 Hz and categorized using canonical two-phase flow regime nomenclature. It is shown that the present setup can produce the relevant two-phase flow patterns that can be found in operated fuel cells as reported by previous studies and is furthermore equipped to investigate flow states not easily reached with an operated fuel cell (e.g. flooded channels).

T–x diagrams for the CO2–H2O system: The importance of water content in CO2 transportation for carbon capture and storage

AbstractWhen water is present in a CO2 pipeline, corrosion or plugging can occur due to the formation of liquid water or gas hydrate, respectively. Understanding how corrosion and hydrate plugging can be avoided is important for enhanced oil recovery and carbon dioxide capture and storage processes. If the CO2 is sufficiently dried prior to transportation, the formation of these problematic free‐water phases can be avoided. In this work, isobaric T–x diagrams were developed from the P–T diagram for the CO2–H2O binary system. Pressures ranging from just below the lower quadruple point to above the lower critical end point were studied. These diagrams are meant to give the reader a better conceptual understanding of how the water composition in CO2–H2O mixtures will influence phases that form at different temperatures and pressures. The diagrams are analyzed from the perspective of flow assurance in CO2 transportation.

Distribution and transformation characteristics of water vapor field in the fissured rock mass and its ecological significance

Opencast mining has produced a large number of high and steep rock slopes, leading to serious safety and environmental challenges. Extreme water scarcity conditions severely impede the survival and development of natural and artificial vegetation when carrying out ecological restoration work. The water vapor field within rocks is a significant but often neglected component of the terrestrial hydrologic cycle and can provide a hidden but critical source of water for plants. However, there is a lack of understanding of the distribution characteristics of the water vapor field within rocks and the pattern of liquid water formation as well as whether it is quantitatively significant and ecologically relevant. This study conducted monitoring experiments on the water vapor field of fissured rock mass and studied the distribution and transformation characteristics of water vapor field in the fissured rock mass and its ecological significance. The results showed temperature and absolute humidity gradually decreased with horizontal depth in spring and summer, and the opposite in autumn and winter. Relative humidity increased rapidly and stabilized with horizontal depth in the spring and summer, and increased rapidly in the autumn and winter, before decreasing slightly. The driving force of water vapor migration is the water vapor partial pressure gradient. In spring and summer, water vapor migrated from air along the fissures to the deep part of the rock mass, while the opposite was true in autumn and winter. While the water vapor migrated through the fissured rock mass, water vapor saturation zones would be produced locally, where potential condensate is generated. The fissure network functioned as a sustained system of water supply pipelines, and the plant roots that grew into the fissures could absorb the condensate, continuously supplying the growth and development of the rock slope plants. This study provides a comprehensive understanding of the rock water vapor field and its effects on ecosystems in arid and semi-arid areas, which can guide the restoration of ecosystems on rock slopes.

Two-phase flow dynamics study in the trapezoidal gas channel of PEM fuel cell based on lattice Boltzmann model

ABSTRACT Water management is a critical challenge in ensuring the performance and durability of low-temperature proton exchange membrane fuel cells (PEMFCs). This study utilizes the phase-field lattice Boltzmann method to conduct three-dimensional numerical simulations, investigating the dynamics of two-phase flow in the cathode gas channel (GC) of PEMFC with a trapezoidal cross-section. The effects of the water inlet location, the surface wettability of GC, the open angle of GC, and the air velocity on liquid water distribution and discharge are analyzed. The results indicate that positioning the water inlet in the middle of the GC significantly enhances PEMFC performance while having minimal impact on average pressure drop. A wall contact angle of 70° or 110°Can optimize fuel cell performance from different directions. Setting a wall contact angle at 70° optimizes gas flow stability and maintains a low-pressure drop value for the GC. A wall contact angle of 110° focuses on optimizing gas reactant diffusion ability into porous electrodes and GC drainage rate. An opening angle of 55° for the trapezoidal gas channel improves overall fuel cell performance. Increasing air velocity facilitates the film flow formation of liquid water on top wall surfaces within the GC.

Melting of a single ice microparticle on exposure to focused near-IR laser beam to yield a supercooled water droplet.

We observed for the first time that a single ice microparticle supported on a substrate melted photothermally to form a supercooled water droplet on exposure to tightly focused illumination with a 1064-nm laser beam that generated a point heat source. In situ Raman micro-spectroscopy clearly showed the formation of liquid water at the expense of ice. The observation of this melting is only possible when the experiment is performed with micrometer-sized ice particles. A previous attempt to melt millimeter-sized ice through photothermal heating of gold nanoaggregates fell short of expectations because only vapor formation, rather than liquid water formation, has been postulated. Our observation is significant because thermal confinement in a microscale compartment using a water-air interface as a heat-insulated wall can achieve particle temperatures above the melting point of water, whereas, in an unlimited space of ice, heat transfer from the heating center to the surroundings causes steep temperature decays, resulting in limited temperature increase.

Laser-induced fabrication of a supercooled liquid droplet embedded in an ice microcrystal.

Optical heating of an ice microparticle supported on a hydrophobic substrate enabled local melting, yielding a liquid microdroplet. To demonstrate this effect, a liquid droplet entrapped in an ice microcrystal was fabricated by illuminating a focused continuous-wave laser beam in the near-IR at temperatures below -10 °C. Droplets formed in this way are either persistent as a supercooled liquid or short-lived, resulting in recrystallization, depending on the presence of salt additives. Salts were added to reduce the vapor pressure of water because vaporization from ice due to laser heating competed with melting. Without salts, melting occurred only during illumination and there was marked vaporization. In situ Raman micro-spectroscopy assisted by optical microscopy imaging provided clear evidence of liquid water formation at the expense of ice. During illumination, the initial Raman signal of ice was gradually replaced by that of liquid water suggesting that melting proceeded with ice and liquid coexisting. Supercooled droplets embedded in ice microparticles eventually transformed into isolated liquid droplets because the surrounding ice either vaporized or merged into the original droplets. Fundamental features of fabrication based on optical-heating-induced melting were elucidated in the experiments described here.

Importance of Directed Water Removal: Intruding Microporous Layer Material into the Gas Diffusion Layer Substrate

Proton exchange membrane fuel cells (PEMFC) are an essential component of net zero emission scenarios by the International Energy Agency (IEA), most prominent in the heavy-duty transportation sector.[1-2] During operation, the PEMFC is subject to different operating conditions, particularly wet conditions where liquid water removal is crucial. It was observed that a microporous layer (MPL), commonly consisting of a carbon component (e.g. carbon black, carbon fibers) and a hydrophobic binder (e.g. PTFE), placed at the interface of the catalyst layer (CL) and the gas diffusion layer substrate (GDL-S), has a large impact on the water removal properties. Among other advantages, the addition of an MPL can guide the localization of water clusters in the GDL.[3] However, if interfaces exhibit large interfacial gaps, as was demonstrated for the CL/MPL interface,[4] liquid water can accumulate in the large openings, thereby creating a mass transport barrier. Seeking to understand the importance of interfaces, which can either guide water formation or create obstacles, this study further investigates the MPL/GDL-S interface.We created an intruding MPL by pressing the MPL slurry into the GDL-S using mechanical force (further on referred to as “intruded-GDL”) and compared it to a GDL, where the MPL sits quasi on top (further on referred to as “sheet-GDL”). Figure 1a shows a cross-sectional scanning electron microscopy (SEM image) of the sheet-GDL, while Figure 1b shows an intruded-GDL. The boundaries between the MPL material and the GDL-S are marked in red. The MPL/GDL-S interface of the sheet-GDL is relatively flat, following only the surface contour of the GDL-S, while the MPL/GDL-S interface of the intruded-GDL is pressed into the GDL-S and locally penetrates deeper into the GDL-S. It is also visible that the penetration into the GDL-S is inhomogeneous. We characterized the altered morphology using SEM (see Figure 1), mercury intrusion porosimetry (MIP), and x-ray tomographic microscopy (XTM). We found that the MPL of the intruded-MPL intrudes significantly into the GDL-S and preferably fills the larger pores of the GDL-S.Both types of GDLs were subject to single-cell fuel cell testing under various operating conditions. We found that the intruding MPL poses an additional oxygen transport resistance at dry conditions compared to the sheet-GDL. Under conditions where liquid water formation can be expected, the intruded-GDL starts to have an advantage compared to the sheet-GDL. From the data obtained in this study, a delicate interplay between the additional dry transport resistance, the missing macropores that were filled with MPL material, and the guided water removal properties can be deduced. We can derive an improved water removal mechanism for the intruded-GDL as a cause of the structural changes, which can serve as a guideline to improve GDL design parameters.

Influence of Ionomer Chemistry on Oxygen Permeability in Hydrocarbon-Based Proton-Exchange Membrane Fuel Cells

The pursuit of alternatives to perfluorinated sulfonic acid (PFSA) materials is of particular interest in light of the global and European mid-term goals to avoid fluorinated materials, and the technical target to operate proton-exchange membrane (PEM) fuel cells at temperatures of 120°C. Non-fluorinated hydrocarbon ionomers offer improved chemical stability at temperatures above 100°C, are less environmentally hazardous, exhibit lower gas crossover, and have the potential to reduce production costs.1 Recent years have seen significant progress in the development of hydrocarbon-based membranes and electrodes, with performance on par with that of state-of-the-art PFSA-based fuel cells under optimized conditions.2 However, a performance gap between hydrocarbon- and PFSA-based PEM fuel cells persists under application-relevant conditions, necessitating an understanding of the limitations that arise. Mass transport-related phenomena, particularly at the ionomer/catalyst interfaces, play a crucial role in controlling PEM fuel cell performance.3 While extensive studies have been conducted for PFSA-based fuel cells to deconvolute the local from the total transport resistance of the cathode catalyst layer, no such studies have been conducted for hydrocarbon ionomers. In this study, we investigated gas transport resistance and its components in hydrocarbon-based PEM fuel cells using H2- and O2 limiting current methods and ex-situ investigations in ionomer thin film behavior, while varying the ionomer's ion-exchange capacity. Our results show that local transport resistances are similar to those measured with PFSA-based cells with respect to different ionomer to carbon mass ratios (I/C). However, higher transport-induced resistances are observed under the potential formation of liquid water in the range of high current densities. We attribute these effects to the more pronounced water uptake of the ionomer thin film compared to the PFSA based reference. Thus, reducing ionomer swelling while maintaining the necessary proton conductivity of the ionomer thin film is crucial for next-generation hydrocarbon PEM fuel cells.References(1) H. Nguyen, C. Klose, L. Metzler, S. Vierrath and M. Breitwieser, Adv. Energy Mater., 2022, 12, 2103559.(2) H. Nguyen, F. Lombeck, C. Schwarz, P. Heizmann, M. Adamski, H. F. Lee, B. Britton, S. Holdcroft, S. Vierrath and M. Breitwieser, Sustainable Energy Fuels, 2021, 5, 3687–3699.(3) T. Schuler, A. Chowdhury, A. T. Freiberg, B. Sneed, F. B. Spingler, M. C. Tucker, K. L. More, C. J. Radke and A. Z. Weber, J. Electrochem. Soc ., 2019, 166(9), F3020.

(Invited) Pulsed Neutron and Synchrotron X-Ray Imaging of Liquid Water Formation and Transport in Polymer Electrolyte Fuel Cells

Fuel-cell electric vehicles (FCEVs) powered by hydrogen are expected to be the ultimate eco-friendly cars, and so developing low-cost, high-performance, and highly reliable FCEVs is strongly demanded. Polymer electrolyte fuel cells (PEFCs) consist of an electrolyte membrane sandwiched between an anode and a cathode, where both the anode and cathode have laminated structures composed of a catalyst-coated membrane (CCM) and gas channels in contact with a gas diffusion layer (GDL). The GDL consists of a microporous layer (MPL) and a substrate. One problem with PEFCs is that liquid water generated as a by-product of the electrochemical reaction at the catalyst accumulates in the GDL, and prevents oxygen from being transported through the gas channels to the catalyst. Therefore, to achieve a high power density, it is necessary to develop new materials and optimize the design of the gas channel to discharge water from the cathode to the exterior of the cell. We are currently constructing a multiscale analysis methodology that combines quantum beam analysis using X-rays and neutrons to clarify water behavior in a PEFC [1-9].In this presentation, we introduce three topics related to water behavior on scales ranging from several micrometers (pores in GDLs) to hundreds of millimeters (automotive fuel cells). The first topic concerns imaging the liquid water distribution in an MPL [2, 6]. The imaging analysis was performed using time-resolved synchrotron X-ray computed tomography while water vapor was supplied to the MPL side of the GDL. With increasing exposure to water vapor, the average volume of wet domains in the MPL initially increased, whereas the overall number of such domains decreased. This implies that wet domains expand by absorbing water vapor and combining with each other. As the exposure to water vapor was further increased, the volume fraction of wet domains in the MPL reached a steady state, indicating that liquid water was discharged to the outer surface of the MPL and to the substrate side. The second topic is obtaining mechanistic insights into water behavior in a subscale PEFC [8]. Time-resolved operando synchrotron X-ray radiography to determine the effects of temperature and relative humidity on the condensation and transport of water in PEFCs. The results show that condensation and transport to the channel can be classified into four categories: 1) concurrent liquid and vapor transport, 2) mainly liquid transport, 3) vapor transport, and 4) accumulation near the ribs. X-ray imaging experiments were conducted at the TOYOTA Beamline (BL33XU) at the SPring-8 facility. The third topic is operando neutron imaging of the water distribution and identifying water/ice phases in large automotive PEFCs during a cold start. We developed an experimental system using a pulsed spallation neutron beam at the RADEN instrument at BL22 of the Materials and Life Science Experimental Facility (MLF) in the Japan Proton Accelerator Research Complex (J-PARC). The results showed direct evidence of stepwise freezing inside the PEFC. The water initially accumulated in the center of the PEFC and began to freeze, and this was followed by PEFC shutdown as freezing progressed. We defined the time interval between the beginning of freezing and shutdown as the “extended time”. This is expected to be useful as an indicator for optimizing the cold-start protocol, cell design, and choice of material.Reference1) Y. Nagai, J. Eller, T. Hatanaka, S. Yamaguchi, S. Kato, A. Kato, F. Marone, H. Xu and F. N. Büchi, J. Power Sources, 435 (2019) 226809.2) S. Kato, S. Yamaguchi, W. Yoshimune, Y. Matsuoka, A. Kato, Y. Nagai and T. Suzuki, Electrochem. Commun., 111 (2020) 106644.3) S. Yamaguchi, S. Kato, A. Kato, Y. Matsuoka, Y. Nagai and T. Suzuki, Electrochem. Commun., 128 (2021) 107059.4) Y. Higuchi, D. Setoyama, K. Isegawa, Y. Tsuchikawa, Y. Matsumoto, J. D. Parker, T. Shinohara and Y. Nagai, Phys. Chem. Chem. Phys., 23 (2021) 1062-10715) S. Yamaguchi, S. Kato, W. Yoshimune, D. Setoyama, A. Kato, Y. Nagai, T. Suzuki, A. Takeuchi and K. Uesugi, J. Synchrotron Radiat., 29 (2022) 1258-1264.6) S. Kato, S. Yamaguchi, Y. Matsuoka, A. Kato, T. Suzuki and Y. Nagai, InterPore2022, Book of s, p139.7) K. Isegawa, D. Setoyama, Y. Higuchi, Y. Matsumoto, Y. Nagai and T. Shinohara, Nucl. Instrum. Methods Phys. Res. A 1040, 167260 (2022).8) A. Kato, S. Kato, S. Yamaguchi, T. Suzuki and Y. Nagai, J. Power Sources, 521 (2022), 230951.9) Y. Higuchi, W. Yoshimune, S. Kato, S. Hibi, D. Setoyama, K. Isegawa, Y. Matsumoto, H. Hayashida, H. Nozaki, M. Harada, N. Fukaya, T. Suzuki, T. Shinohara and Y. Nagai, to be submitted.

Slope Instability Analysis in Permafrost Regions by Shear Strength Parameters and Numerical Simulation

With the onset of global warming, the environment has profoundly changed. The melting of ice and slope instability were widely observed in the permafrost regions of the Qinghai–Tibet Plateau, which has destroyed infrastructure and threatened people’s safety. For this study, we conducted a direct shear test, monitored field temperature, and performed a numerical simulation to explore the mechanism of slope instability in the permafrost regions of the Qinghai. The results show that the shear strength of the permafrost soil decreased with the increases in water content and thawing condition. Moreover, the thawing depth of the slopes increased with the rising temperature. From the temperature monitoring data and field observations, cracks and slope instability phenomena were observed in the Qinghai and occurred with the thawing of the permafrost soil. The safety of slopes in the permafrost regions decreased with increases in the temperature, slope gradient, and pore water pressure and with decreases in the shear strength parameters. In addition, the sliding interface had a direct correlation with the freeze–thaw interface, which is a migrated interface of water in liquid form. Therefore, the thawing of the permafrost soil causes the shear strength to decrease and pore water pressure to increase, which leads to slope instability in the permafrost regions of the Qinghai.

Computational Modeling of Tubular Flow Fields for PEM Fuel Cells

The bipolar plates of polymer electrolyte membrane fuel cells (PEMFCs) are of focus for improvement since they are responsible for most of the fuel cell stack weight and volume. Traditionally these flow fields are machined or stamped out of a graphitic or metallic material. Recent research has shown that additively manufactured metal plates show comparable performance to those made with conventional method. Due to the layer-by-layer nature, there is a great deal of design flexibility for additively manufactured parts. This allows for far more freedom in flow field designs, such as a tubular flow field with internal channels.In recent years there have been developments of tubular PEMFCs. Numerical simulation reported in literature have shown that tubular PEMFCs provide higher power density [1], more uniform reactant gas velocity distribution [2], and a smaller pressure gradient [3].The goal of the tubular model in our study was to replicate in size a standard AAA battery , so the total dimensions of the fuel cell were limited at a height of 40.5 mm and a diameter of 10.5 mm, with a cell active area of 987 mm2. The tubular channel length was approximately 400 mm. For reference, a conventional (planar) single serpentine fuel cell with a comparable 982 mm2 active area was used, replicating a scaled down commercially available design from Fuel Cell store. This planar design had square channels with a depth of 1.016 mm and a channel width of 0.7874 mm. The length of the channel was approximately 550 mm. For both designs, the land widths were 0.7874 mm to maintain a 1:1 channel-land width ratio. The gas diffusion layer (GDL), microporous layer (MPL), catalyst layer, and membrane had respective thicknesses of 360 μm, 50 μm, 10 μm, and 50 μm. The channel geometry for the tubular fuel cell was changed from rectangular to a semicircle, as the additive manufacturing process is not adept at building overhangs with supports. To maintain an accurate comparison, the cross-sectional area of the planar and tubular channels was kept constant at 0.79 mm2. This flow field would be incorporated into the outer anode flow field of the final tubular design, so hydrogen at 80°C was used as the fluid. A volumetric flow of 0.24 L/min was used as the inlet boundary condition.Initially, basic fluid flow simulations were performed on several tubular serpentine flow field designs (Figure 1). The double corkscrew Tubular v4 design had the greatest pressure drop, which was due to the fact the cross-sectional area was divided into two smaller sections. Tubular v2 and v3 had similar results being the most alike geometrically. Tubular v1, which split off into two symmetrical flow channels, exhibited the lowest pressure drop as the half channels cut down on the distance the hydrogen would have to travel inlet to outlet.With the chosen design Tubular v1, this geometry was used for the PEMFC module. Various changes were made to the tubular model to simulate the new design. Our proprietary membrane electrode assembly (MEA) design had no GDL present in the cathode layer, with oxygen being pumped directly through the cathode catalyst layer. This design assured that the supplied O2 concentration is much higher since its transport is by convection instead of diffusion. The ANSYS PEMFC model will not run if there is no defined GDL between the gas channel and MPL, so this was circumvented by directly changing the properties of the catalyst layer. To model this, the mass fraction of the oxygen in the cathode catalyst layer was increased from 0.2 to 0.3. It is also expected for the flowing of oxygen to flush away any water formation, so the water formation was limited. Due to the water mass balance taking place in the model, limiting liquid water formation increased the dissolved water inside of the membrane. The electrochemical surface area was increased to account for the higher surface area of the Pt catalyst in our proprietary MEA design.These modifications showed an increase in performance for the tubular cell when compared with the standard planar design as seen in Figure 2. Limiting the liquid water formation and selecting a geometry with a more uniform pressure distribution resulted in a cell with higher power density. The removal of the GDL and increase of air flow allowed for a higher oxygen concentration at the cathode catalyst interface. With oxygen no longer being a limiting reactant, the cell was able to perform at a higher power output. Figure 1

Experimental study on liquid water formation characteristics in a novel transparent proton exchange membrane fuel cell

Water management is critical to the operation of a proton exchange membrane fuel cell (PEMFC). The accumulation of water in the cathode channel of a newly designed transparent PEMFC is investigated in this work. The electric quantity per square metre (qe) produced by electrochemical reaction is used to estimate the liquid water formation characteristics. Results show that the water produced by the electrochemical reaction first exists in a gaseous state in the flow channel and then transforms to liquid water.Liquid water begins to appear in the flow channel when qe reaches approximately 1.8 × 105 C·m−2 in different current density and loading rate. However, a higher current density and loading rate would decrease liquid water forming time of the fuel cell channel. In addition, cell temperature affects the qe value, and when the cell temperature rises from 45 to 75 °C, qe decreases from 2.25 × 105 to 1.5 × 105 C·m−2; the amount of charge is approximately inversely proportional to the cell temperature. Liquid water first appears at the inlet of the flow channel, specifically at the contact point between the inlet flow channel and carbon paper. Liquid water is concentrated at the edge channel of the flow field area and rarely distributed in the middle of the single cell.

Proton Exchange Membrane Fuel Cell Flow Field Configuration: Modelling and Experimental Verification

Improper design of flow field channels may lead to water stagnation and flooding and may therefore lead to a poor fuel cell performance. The main purpose of this work is to investigate liquid water formation inside the flow field of the proton exchange membrane (PEM) fuel cell and to find optimal flow field configuration such as: number of channels, channel width to rib ratio and channel depth. To achieve this goal advanced numerical model of PEM fuel cell was developed. Model was simulated in Fluent, using computational fluid dynamics (CFD). Based on the obtained simulation results, graphite bipolar plate with optimal channel design was machined, integrated into the single PEM fuel cell unit, and experimentally tested.

A physics-based 1-D PEMFC model for simulating two-phase water transport in the electrode and gas diffusion media

While significant progress in PEMFC research has been achieved in recent years, simulation of liquid water formation and transport accurately still remains a significant challenge. Under wet operating conditions, liquid water may condense in the channel, gas diffusion layer, or electrode, which introduces complicated transport phenomena. In this work, we present a physics-based, steady-state, 1-D, non-isothermal, and two-phase PEMFC model that captures the interactive nature of gas and liquid transports to simulate fuel cell performance. Limiting current experiments are employed to study both dry and wet oxygen transport resistances of Toray-H-060 carbon fiber paper with PTFE impregnation and a microporous layer. A two-phase model based on limiting current diagnostics is proposed to simulate water transport in the gas diffusion layer using tendril length to represent liquid water penetration. This newly constructed model is capable of predicting the total transport resistance under dry, transition, and wet regions. In addition, an empirical catalyst utilization model is proposed to correlate the electrode water activity with catalyst utilization. The two-phase electrode model provides key insights into the relationship between catalyst utilization and electrode flooding. The newly developed 1-D two-phase model is highly efficient in predicting PEMFC performance under a wide range of operating conditions and the empirical approach can be applied and adopted to studies with novel materials and designs.