Porous Flow Field Research Articles

Effect of tapered porous ribs on the performance of Proton exchange membrane fuel cells

The conventional trench ridge structure suffers from the difficulty of removing liquid water and poor gas transport performance. The water removal and gas transport performance inside the flow field are enhanced by introducing a tapered porous rib flow field (TPRFF). In order to investigate the performance of TPRFF, a complex three-dimensional, multiphase, non-isothermal agglomeration model was developed using numerical techniques. The numerical results show that the TPRFF exhibits significant improvements in oxygen concentration distribution, oxygen distribution uniformity and water removal compared to a conventional parallel flow field (CPFF). In addition, the dissolved water content remained almost constant while the liquid water saturation was lower. The study also investigated the effect of different cathode exit heights on the performance of the fuel cell using TPRFF. The results showed that the net power density increased by 14.0 %, 11.9 %, 8.7 %, and 1.5 % for outlet heights of 1.3 mm, 1.0 mm, 0.7 mm, and 0.4 mm, respectively, while it decreased by 27 % for an outlet height of 0.1 mm. Finally, the effect of different stoichiometric ratios on cell performance was also investigated in the novel flow field.

Predicting carbonate rock dissolution using multi-scale residual neural networks with prior knowledge

The factors that affect carbonate dissolution are complex, and it is crucial to acquire efficient and accurate knowledge of carbonate dissolution characteristics for CO2 capture and storage (CCS) projects. In current research, the most precise outcomes can be achieved through experimental or simulation techniques, but they are frequently computationally demanding and time-consuming. Data-driven machine learning methods can efficiently perform regression prediction tasks. In this paper, we propose a multi-scale hierarchical regression model for the dissolution problem based on residual neural networks, incorporating prior knowledge. We have developed new equations for carbonate rock dissolution and have incorporated the factors that influence this process into 3D image data by introducing Dissolution Degree (Dd) parameters. This allows the image data to include both the pore space structure and dissolution information with physical meaning. We utilize the pore phase and matrix phase grayscale thresholds (Pt, Mt) to eliminate voxel noise in the characteristic maps obtained from the model. This ensures that the predicted characteristics of carbonate rock dissolution are consistent with practical physics knowledge. We selected a total of 5 core samples to test the model. Among them, three samples are from the test set, and the additional two core samples selected have strong and weak correlations with the training set samples, respectively. The predictions were evaluated using semantic segmentation evaluation parameters, porosity, geometrical and topological structure parameters, Péclet and Damköhler numbers, porous media flow field simulations, and absolute permeability. The results of both visual comparisons and quantitative analyses demonstrated a high degree of consistency between predicted and experimental results, and the trained multi-scale hierarchical regression residual neural network with prior knowledge (MSR-Net) demonstrates good accuracy and generalization ability. The results of this study demonstrate that model based on MSR-Net can be utilized to predict the dissolution properties of the pore space in the formation where the core was extracted, along with the related formation.

Entropy generation in a partially heated hybrid nanofluid saturated wavy porous cavity

PurposeA porous cavity flow field generates entropy owing to energy and momentum exchange within the fluid and at solid barriers. The heat transport and viscosity effects on fluid and solid walls irreversibly generate entropy. This numerical study aims to investigate convective heat transfer together with entropy generation in a partially heated wavy porous cavity filled with a hybrid nanofluid.Design/methodology/approachThe governing equations are nondimensionalized and the domain is transformed into a unit square. A second-order finite difference method is used to have numerical solutions to nondimensional unknowns such as stream function and temperature. This numerical computation is conducted to explore a wide range of regulating parameters, e.g. hybrid nano-particle volume fraction (σ = 0.1%, 0.33%, 0.75%, 1%, 2%), Rayleigh–Darcy number (Ra = 10, 102, 103), dimensionless length of the heat source (ϵ = 0.25, 0.50,1.0) and amplitude of the wave (a = 0.05, 0.10, 0.15) for a number of undulations (N = 1, 3) per unit length.FindingsA thorough analysis is conducted to analyze the effect of multiple factors such as thermal convective forces, heat source, surface corrugation factors, nanofluid volume fraction and other parameters on entropy generation. The flow and temperature fields are studied through streamlines and isotherms. The average Bejan number suggested that entropy generation is entirely dominated by irreversibility due to heat transport at Ra = 10, and the irreversibility due to the viscosity effect is severe at Ra = 103, but the increment in s augments irreversibility due to the viscosity effect over the heat transport at Ra = 102.Originality/valueTo the best of the authors’ knowledge, this numerical study, for the first time, analyzes the influence of surface corrugation on the entropy generation related to the cooling of a partial heat source by the convection of a hybrid nanofluid.

Investigation on performance of full-scale proton exchange membrane fuel cell: Porous foam flow field with integrated bipolar plate/gas diffusion layer

Aiming at the problems of inconsistent local distribution of reactant gas and easy blockage of water in the traditional “bipolar plate (BP) + gas diffusion layer (GDL)” structure flow field (FF). A new type of porous foam flow field (PFFF) with integrated BP/GDL (taking the pore of decahedral structure as matrix) is proposed. Firstly, three-dimensional (3D) proton exchange membrane fuel cell (PEMFC) saturation model is applied to analyze the influence of the availability of GDL components and different channel (CH) widths. GDL is essential for channel-rib (CR) FF because its elimination leads to the non-uniform mass distribution in fuel cell (FC). Secondly, by comparing CRFF and PFF with “BP + GDL” structure and PFFF with integrated BP/GDL, it is found that the limiting current density of PFF increases by 49.9 % compared with CRFF, and the mass transmission loss is reduced. Compared with PFF, the performance of PFFF is greatly enhanced, the pressure drop is moderate, and the amount of liquid water in CH is reduced by 39.1 %. Therefore, GDL component that eliminate PFF is extremely beneficial to improve FC efficiency and reduce stack volume. Finally, the output performance of FC under various porosities and pore number is explored.

Porous metal foam flow field and heat evaluation in PEMFC: A review

Abstract A proton-exchange membrane fuel cell (PEMFC) generates electricity, heat, and water from oxygen and fuel. Hydrogen is recommended as a fuel because it is a renewable fuel when manufactured, for example, by water electrolysis using renewable energy power. Porous metal has excellent characteristics such as controlled permeability, low density, and high porosity. Corrosion is now the most major hurdle to the use of porous metal in PEMFCs, and owing to the porous metal’s complicated internal structure, additional challenges must be addressed in the coating preparation process. As a result, this article figures out how to successfully handle the porous metal corrosion problem in a PEMFC setting, which increases the porous metal utilization in the fuel cell industry. This article also examined the flow field in PEMFC and important characteristics. The influence of flow field in the fuel cell was also investigated.

Measuring porous media velocity fields and grain bed architecture with a quantitative PLIF-based technique

Porous media flows are common in both natural and anthropogenic systems. Mapping these flows in a laboratory setting is challenging and often requires non-intrusive measurement techniques, such as particle image velocimetry (PIV) coupled with refractive index matching (RIM). RIM-coupled PIV allows the mapping of velocity fields around transparent solids by analyzing the movement of neutrally buoyant micron-sized seeding particles. The use of this technique in a porous medium can be problematic because seeding particles adhere to grains, which causes the grain bed to lose transparency and can obstruct pore flows. Another non-intrusive optical technique, planar laser-induced fluorescence (PLIF), can be paired with RIM and does not have this limitation because fluorescent dye is used instead of particles, but it has been chiefly used for qualitative flow visualization. Here, we propose a quantitative PLIF-based methodology to map both porous media flow fields and porous media architecture. Velocity fields are obtained by tracking the advection-dominated movement of the fluorescent dye plume front within a porous medium. We also propose an automatic tracking algorithm that quantifies 2D velocity components as the plume moves through space in both an Eulerian and a Lagrangian framework. We apply this algorithm to three data sets: a synthetic data set and two laboratory experiments. Performance of this algorithm is reported by the mean (bias error, B) and standard deviation (random error, SD) of the residuals between its results and the reference data. For the synthetic data, the algorithm produces maximum errors of B & SD = 32% & 23% in the Eulerian framework, respectively, and B & SD = −0.04% & 3.9% in the Lagrangian framework. The small-scale laboratory experimental data requires the Eulerian framework and produce errors of B & SD = −0.5% & 33%. The Lagrangian framework is used on the large-scale laboratory experimental data and produces errors of B & SD = 5% & 44%. Mapping the porous media architecture shows negligible error for reconstructing calibration grains of known dimensions.

Two-phase flow in porous metal foam flow fields of PEM fuel cells

Porous metal foam (PMF) flow field is a potential option for proton exchange membrane fuel cells (PEMFCs) due to its excellent capabilities in gas distribution and water drainage. However, the gas-liquid two-phase flow in the PMF flow field on the pore scale is still unclear. In this study, we investigate the gas-liquid two-phase flow in the PMF flow field. Film, plug, and ligament flows are found in the hydrophilic PMF flow field, while slug and droplet flows are found in the hydrophobic PMF flow field. The results suggest that optimizing the pore size, increasing the metal foam surface hydrophobicity, and optimizing the operating condition are helpful for the water management of the PMF flow field. The frequency analysis of the pressure drop also shows that the dominant frequency can be used as an indicator to analyze the transition between different flow patterns.

Porous Carbon Fiber Flow Fields for Heavy-Duty Polymer Electrolyte Fuel Cell (PEFC) Applications

The US Department of Energy (DOE) interim (2030) targets for polymer electrolyte fuel cells (PEFCs) in heavy duty vehicle applications accentuate reduced system cost (US $80/kW), increased peak efficiency (68%), and longer system lifetime (25,000 hrs) [1]. The bipolar plate in a PEFC has to serve several functions such as uniform reactant distribution with minimum pressure loss, efficient product water removal, and maintain high electronic and thermal conductivity. Multiple studies [e.g., 2-4] describe novel materials and engineered designs potentially meet these performance and durability requirements; however, cost is the limiting factor in most cases. For example, the cost of a state-of-the art stainless steel (SS 316L) plate, already approaching minimum feasible plate thickness, is estimated to be (US $3.5/kWnet), which is 17% higher than current DOE target [1]. Thus, low-cost substrate alternatives are required to reduce the cost and facilitate commercialization in heavy-duty applications. One such alternative is a novel PEFC architecture [5] utilizing a laminated structure consisting of flat thin metal foils that separate flow fields with channels formed into the porous gas diffusion layer (GDL). This architecture enables the use of much thinner metal plates compared to stamped ones, reducing the overall system mass and cost. The current study explores the performance of a wide aspect ratio (200 mm x 30 mm) PEFC test fixture with porous carbon fiber flow field compared to conventional solid flow field over a wide range of operating conditions. The wide aspect ratio and channel/rib dimensions for both the porous and the conventional solid flow field are chosen to provide a reasonable pressure loss relevant to heavy-duty PEFC stack application. This new architecture is expected to enable comparable system performance while reducing plate weight and cost.

Numerical simulation of rice drying process in a deep bed under an angular air duct

AbstractThe deep‐bed drying process of rice grains was investigated through numerical simulation, employing the porous medium flow field theory and the local thermal nonequilibrium method. Moisture field of rice grains described using thin‐layer equations. On this basis, the deep‐bed drying of rice grains modeled with COMSOL, and verified its plausibility. The results showed that the drying rate of rice grains was significantly accelerated when the hot air temperature was increased from 40°C to 70°C, but the inhomogeneity of rice grains temperature increased by 29.79%, 22.31%, and 17.41% for every 10°C increase. Drying grains faster with vertically arranged an angular air duct, with a 4.88% increase in drying speed in 300 min. The temperature difference between the top and the bottom of an angular air duct with a small width is smaller, about 11°C, and the heating efficiency is better at the top, by 31.28%.Practical ApplicationsGrain dryers are often used in high‐volume grain drying operations and it has been a great challenge to save the energy consumption of the drying process. It is necessary to use numerical simulation to design a reasonable structure of the heating section to improve the energy utilization efficiency of the heating section of the grain dryer. The numerical model proposed in this article can effectively simulate the spatial distribution of moisture content of rice under different structures of grain drying units, which can be used not only for the prediction of drying time but also for analyzing the optimal heating structure from it. A technical basis is provided for the design of grain dryers.

Transition to unstable oscillatory flames in porous media combustion

The flames inside porous burners with low filtration velocity are prone to oscillatory behavior similar to unstable combustion in narrow channels but accompanied by complicated dynamics due to the irregularity of porous structure, flow field, and thermal gradient formed as a result of heat recuperation. This work is a numerical study within the framework of the pore-scale simulation approach devoted to investigating the flame oscillation mechanisms and characteristics in a two-dimensional pseudo-irregular packed bed of particles generated using the Voronoi tessellation algorithm with constant pore size. The results demonstrate that unstable flame oscillations like flames with repetitive extinction and ignition (FREI) lead to the velocity pulsation in adjacent pore channels, where the stable flame fragments are exposed to the hydrodynamically-driven fluctuations. In the case of the flow rate close to the stability threshold, the flow pulses can reach a magnitude enough to shift the stable flame in the upstream quenching zone, promoting its oscillations with repetitive extinction and ignition. Results of parametric simulation with a variation of the particle diameter and flow velocity were summarized in the regime diagram revealing the transition between stable normal flame, FREI, and stable weak flame with the velocity reduction. The pulsating transitional regime was detected between the stable normal flame and the FREI. The amplitude and intensity of such pulsations increase monotonically with the flow rate reduction in a narrow range. Oscillations of the unstable flame and hydrodynamically-driven flame pulsations are similar in dynamics but different in their physical mechanisms. However, in irregularly packed beds of particles, both these phenomena unavoidably coexist and interfere significantly with each other due to the connectivity of the pore channels.

Structural optimization of fiber porous self-humidifying flow field plates applied to proton exchange membrane fuel cells

In existing fuel cell flow field design, porous flow fields have shown to have excellent self-humidifying capability due to its highly controllable pore space, capillary pumping ability, and certain structural flexibility. However, the uniformly distributed structure is difficult to adapt to the complex water-gas distribution inside the fuel cell. Therefore, this paper designs an optimized structure based on the pre-developed fiber porous flow field. Experimental results show that, compared with the original fuel cell, the peak power density of the optimized fiber porous self-humidifying flow field is increased by 15.21%, and the average output current of long-term constant voltage (0.4 V) is increased by 3.5%. It is also found that the temperature rises under long-time operation (45 °C–56 °C) will further enhance the output power.

Structure Design for Ultrahigh Power Density Proton Exchange Membrane Fuel Cell.

Next-generation ultrahigh power density proton exchange membrane fuel cells rely not only on high-performance membrane electrode assembly (MEA) but also on an optimal cell structure. To this end, this work comprehensively investigates the cell performance under various structures, and it is revealed that there is unexploited performance improvement in structure design because its positive effect enhancing gas supply is often inhibited by worse proton/electron conduction. Utilizing fine channel/rib or the porous flow field is feasible to eliminate the gas diffusion layer (GDL) and hence increase the power density significantly due to the decrease of cell thickness and gas/electron transfer resistances. The cell structure combining fine channel/rib, GDL elimination and double-cell structure is believed to increase the power density from 4.4 to 6.52kW L-1 with the existing MEA, showing nearly equal importance with the new MEA development in achieving the target of 9.0kW L-1 .

Flow field plate of polymer electrolyte membrane fuel cells: A review

Recently, pursuing a strategic alternative to traditional fossil fuels has become an important method to meet the increasing energy demands and environmental improvement needs. Polymer electrolyte membrane fuel cells (PEMFCs) can directly convert the chemical energy of fuels into electricity without contamination and the restriction of the Carnot cycle effect. The flow field plate (FFP) is a critical part of a PEMFC that provides mechanical support, conductive medium, the channel of reaction gases, and water and thermal management. However, the complicated mechanisms of the FFP are not very clearly understood since the materials and structures are associated closely with cost, performance, and lifetime. In this paper, different materials and structures are analyzed and their characteristics are summarized. Meanwhile, an opinion was proposed that the porous metal foam flow field will be the most promising development direction in the future, mainly focusing on surface treatment, pattern, and manifold design.

Porous Flow Field for Next-Generation Proton Exchange Membrane Fuel Cells: Materials, Characterization, Design, and Challenges.

Porous flow fields distribute fuel and oxygen for the electrochemical reactions of proton exchange membrane (PEM) fuel cells through their pore network instead of conventional flow channels. This type of flow fields has showed great promises in enhancing reactant supply, heat removal, and electrical conduction, reducing the concentration performance loss and improving operational stability for fuel cells. This review presents the research and development progress of porous flow fields with insights for next-generation PEM fuel cells of high power density (e.g., ∼9.0 kW L-1). Materials, fabrication methods, fundamentals, and fuel cell performance associated with porous flow fields are discussed in depth. Major challenges are described and explained, along with several future directions, including separated gas/liquid flow configurations, integrated porous structure, full morphology modeling, data-driven methods, and artificial intelligence-assisted design/optimization.

Comparison of various structure designs of SO2-depolarized electrolysis cell

SO2-depolarized electrolysis (SDE) is the key step of the hybrid sulfur (HyS) process, which is one of the simplest thermochemical cycles for producing hydrogen by water splitting. Exploration and optimization of flow field/structure design is essential for improving the efficiency of SDE. In this work, graphite plates with different flow channels, together with porous graphite felts or carbon papers as diffusion layers are adopted to fabricate SDE cells with different structures. Evaluation of the cell structures is carried out, by comparing the SDE performance and taking into account the fluid resistance (pressure drop) of anode side. The effects of graphite felt compression ratio, hydrophilicity or hydrophobicity of carbon papers, anodic fluid flow rate, and operating temperature on the SDE performance are investigated. Square porous flow fields provided by graphite felts show excellent performance. Serpentine channel covered by hydrophobic carbon paper reveals advantages when adopted on the cathode side. Combination of above two flow fields and using them on anode and cathode sides respectively, could achieve excellent SDE performance. Under the condition of 40 °C and 360 mL/min anolyte flow rate, the current density could reach 760 mA/cm2 at the cell voltage of 1.19 V.

Visualization Method for Porous Groundwater Seepage Flow Field Based on Particle Flow: Case of Yancheng City in the East Coast of China

Porous groundwater seepage flow field reflects the spatiotemporal dynamic characteristics of porous groundwater movement. The geometric point and vector line methods are the traditionally used visualization methods for groundwater seepage flow field; however, they exhibit difficulty in describing the characteristics and attributes of a seepage flow field. Therefore, a new particle flow method in the field of computer graphics is introduced in this study to visualize seepage flow field, including the storage conditions, transport mechanism, and seepage field properties of porous groundwater. This visualization method is discussed from four aspects: the generation of seed points, the life cycle of particles, the movement velocity of particles, and the formation of particle trajectory and smooth processing. The seepage field of confined aquifer III groundwater expressed via particle flow and the contour of critical groundwater level are superimposed and analyzed in Yancheng City in the east coast of China. Results show that particle flow can be effectively applied to the visualization of groundwater seepage flow field and provide spatial auxiliary decision-making support for the sustainable exploitation of groundwater and the formulation of geological environment protection measures.

Constructing region-specific porous flow field to enhance heat, mass and charge transports in proton exchange membrane fuel cells

The pursuit of ever-improving performance in proton exchange membrane fuel cells (PEMFCs) requires more appropriate flow field design to reduce the electrode polarizations. Herein, a region-specific porous flow field (rs-PFF) that simultaneously enhances the heat, mass and charge transports is proposed, of which gas permeability and heat conductivity are respectively higher in marginal region and central region than those of the conventional uniform porous flow field (u-PFF). A three-dimensional non-isothermal PEMFC model that considers the multi-phase multi-species transfer is adopted to elucidate the impacts of the rs-PFF. It is demonstrated that the oxygen concentration in weak flow regions is increased by 26.3 % while the temperature in main flow region is decreased by 2.14 K, thus yielding a 5.5 % increase in peak power density. The rs-PFF is effective to reduce reactant supply, thereby saving the system energy consumption. Additionally, even the lower humidified rs-PFF-based PEMFC shows the better performance than the fully humidified u-PFF-based PEMFC. This region-specific design strategy has the potential to be applied to other types of flow field design for improving cell performance.

Wet Gas Water Feed of Polymer Electrolyte Membrane Electrolyzer for Simultaneous Hydrogenation of Organic Chemical Hydride Energy Carrier and Water Decomposition

To utilize renewable electricity with fluctuation and localization, large-scale energy storage and transportation technologies using hydrogen energy carrier have been expected. In order to improve hydrogen energy carrier synthesis, we have studied one-step electrolysis for toluene electrohydrogenation and water decomposition using proton exchange membrane (PEM) electrolysis. This process has 1.09 V of theoretical decomposition voltage for simultaneous water electrolysis and toluene hydrogenation.As shown in Figure 1, anode reaction produces oxygen and proton, and proton transports cathode electrocatalyst layer through the PEM with water molecular. Water inhibits toluene transportation to reaction side and hydrogen evolution occurs as side reaction. We have reported electrolyzers that has cathode side of PEFC’s MEA like structure using PtRu/C and anode side of industrial electrolyzer like structure using mesh shape of DSE® electrode for oxygen evolution reaction, and sulfuric acid solution feeds as anolyte that is not only reactant but also for water management. Water back diffusion from cathode to anode enhances with sulfuric acid concentration. In addition, current efficiency with mesh type anode was higher than that with sintered fiber sheet type anode. The mesh shape of electrode makes current distribution that affects mass transfer pass distribution to improve current efficiency, although sheet type anode is lower overpotential because of large surface area [1 – 3]. As practical system, water transportation from anode to cathode should be supressed without sulfuric acid utilization, and electrochemical surface- area of anode should extend to reduce overpotential.In this study, we have investigated wet gas water feed for PEM electrolysis to reduce water transfer to cathode, because water transfer would control by relative humidity of wet gas that feed to anode for oxygen evolution reaction. Here, PEM water electrolysis type anode catalyst layer with ionomer was employed to reduce anode overpotential and to maintain ionic conduction in catalyst layer.Figure 1 shows the schematic drawing of toluene direct hydrogenation electrolyzers with water splitting. Figure 1 (a) is our conventional electrolyzer of H2SO4 solution feed, and Figure 1 (b) is wet air feed in this study. The anode side for wet air feed had polymer electrolyte fuel cell type serpentine gas flow channel. Anode catalyst layer was 1.0 mg cm-2 of IrOx (TKK) with Nafion ionomer. The porous transport layer was platinum plated sintered titanium sheet. PEM was Nafion 117 (Du Point), cathode catalyst layer was 0.5 mg cm-2 of PtRu/C with Nafion ionomer supported on a porous flow field of a carbon paper that was loaded 0.02 mg cm-2 platinum for chemical reaction of toluene and hydrogen.5 mL min-1 of toluene or 10% toluene – methylcyclohexane and 1.0 L min-1 of wet air fed to cathode and anode, respectively. Operation temperature was 80oC. After the 100 % RH feed electrolysis, there is no product except methylcyclohexane in the liquid phase and water transportation from anode to cathode reduced one twentieth from the conventional electrolyzer fed 1 M H2SO4 operation at 60oC. In this condition, IR free cell voltage of the wet gas fed electrolyzer was significantly smaller than that of the conventional one because of high surface area anode. Internal resistance of the wet gas feed determined by AC impedance method was about two times higher than that of the conventional, and current efficiency maintained in the low current density region. The internal resistance increased in the high current density region where the membrane and ionomer dry up with electro osmosis water. In this region, current efficiency also decreases.In summary, wet gas feed water electrolysis for electrohydrogenation of toluene using a PEM electrolyzer is an interesting technology that combines water electrolyzer with water purification system and manages water feed to reduce water transportation to cathode to maintain current efficiency of with accurate control of relative humidity and gas feed amount.AcknowledgementThis study was based on results obtained from the Development of Fundamental Technology for Advancement of Water Electrolysis Hydrogen Production in Advancement of Hydrogen Technologies and Utilization Project (P14021) commissioned by the New Energy and Industrial Technology Development Organization (NEDO).References Nagasawa, K. Tanimoto, J. Koike, K. Ikegami, S. Mitsushima, J Power Sources, 439, 227070 (2019).Oi, K. Nagasawa, T. Takamura, Y. Misu, K. Matsuoka, S. Mitsushima, ECS Meeting s, MA2021-02, 1737 (2021).Mitsushima, Y. Sugita, J. Koike, Y. Kuroda, K. Matsuoka, Y. Sato, K. Nagasawa, ECS Meeting s, MA2020-02, 2494 (2020). Figure 1

Effect of Thickness and Outlet Area Fraction of Macroporous Gas Diffusion Layers on Oxygen Transport Resistance in Water Injection Simulations

Enhanced water removal through the gas diffusion layer (GDL) is important for the design of high-performance proton exchange fuel cells. In this work, the effects of GDL thickness and open area fraction at the GDL/flow field interface are examined under water invasion for a carbon-paper GDL (similar to Toray TGP-H series). Both uncompressed and inhomogeneously compressed samples are considered. Transport in heterogeneous, macroporous GDLs is modeled by means of a hybrid 3D discrete/continuum formulation based on a subdivision of the porous medium into control volumes due to the lack of a well-defined separation between pore and layer scales. Capillary-dominated transport of liquid water is simulated with an invasion percolation algorithm, while oxygen diffusion is simulated with a continuum formulation. Model predictions are validated with previous numerical and experimental data. It is shown that the combination of thin GDLs (mathrm {thickness} sim 100; mu mathrm {m}) and high GDL/flow field open area fractions can facilitate water removal/oxygen supply from/to the catalyst layer and can provide a more uniform oxygen distribution over large cell active areas. In agreement with previous work, porous flow fields with pore sizes comparable to the GDL thickness are good candidates to meet the above requirements, while improving water removal from the flow field (higher gas-phase velocity than conventional millimeter-sized channels) and ensuring a more uniform assembly compression.

A metallic gas diffusion layer and porous media flow field for proton exchange membrane fuel cells

Recently, metal foams have been intensively studied to be used as alternative flow fields to the conventional channel-rib flow field in proton exchange membrane fuel cells (PEMFC) to enhance the uniformity of gas distribution and reduce the weight of fuel cells. This work demonstrates a simple and compact design at the cathode side for achieving effective electrons and gas transport in PEMFCs, which includes a porous metal foam flow media coated with a microporous layer (MPL) on its top to form one single hierarchical porous component functioning as both the gas distributor and diffusion media. With this low-cost and light-weight design, the conventional gas diffusion layer (GDL) can be eliminated. A comparative analysis of PEM fuel cell performances for the conventional carbon paper-based GDL and three metallic GDL designs containing different MPLs is conducted under varied stoichiometric ratios and relative humidity (RH). At 100% RH, the optimum performance is achieved on the CB/CNT MPL-coated metal foam, with the maximum power density increased by 21% than that of the conventional design when the stoichiometric ratio of air is 1.5. Under dry conditions (40% RH), all the metallic GDL structured cells outperform the conventional one at a low airflow rate (stoichiometric ratio = 1.5).