Through-plane Permeability Research Articles

Development of a 4-in-1 device for measuring properties of gas diffusion layers and porous transport layers in proton exchange membrane fuel cells and water electrolyzers

The carbon-based gas diffusion layer (GDL) and the Ti-based porous transport layer (PTL) are essential components in proton exchange membrane (PEM) fuel cells and water electrolyzers, respectively. The performance of these cells is significantly influenced by the properties of the GDL/PTL, especially under operational compression. This study utilizes a previously developed 4-in-1 device designed to simultaneously measure parameters under compression (UC), including thickness (TUC), resistivity (RUC, through-plane), and in-plane permeability (IPP-UC), and to separately measure through-plane permeability (TPP). The simultaneous measurement of TUC, RUC, and IPP-UC is achieved using an annular sample. Through the use of a two-piece adapter, TPP can also be measured using a disk sample. The device successfully measured TUC, RUC, IPP-UC, and TPP for diverse GDLs and PTLs, including commercially available and in-house prepared materials. The results were compared, showing variability in compressibility (by up to 45 % at 4 MPa), resistivity (with differences up to 25-fold at 1 MPa), and permeability (comparable at 1 MPa) among samples investigated. The 4-in-1 device has proven effective for GDL/PTL characterization, supporting component development and quality control in both the PEM fuel cell and water electrolyzer technologies.

Characterisation of hydraulic properties of commercial gas diffusion layers: Toray, SGL, MGL, woven carbon cloth

This study utilises computational fluid dynamics simulations with the OpenFOAM computational framework to investigate and compare the in-plane and through-plane permeability properties of four different gas diffusion layers (GDLs). Also the through-plane water and air relative permeability values and water saturations at different rates were simulated. Permeability analysis enhances our understanding of fluid flow, ways to decrease pressure loss in the GDL, and methods to enhance oxygen concentration at the catalyst layer interface through convection. The analysis reveals that the investigated GDL materials have spatial heterogeneity of porosity and permeability, especially in the Sigracet SGL 25 BA GDL. However, the porosity and permeability of the Toray TGP-H 060 and AvCarb 370 MGL GDLs exhibit less variations. The two-phase flow studies on GDL saturation show that at the same water injection flowrate, the AvCarb 370 MGL GDL has the largest remaining water saturation, with Sigracet SGL 25 BA GDL being the less saturated GDL among the four investigated GDLs. The compression from the ribs significantly affected the in-plane permeabilities of both Toray TGP-H 060 and especially impacted Sigracet SGL 25 BA GDL. This impact was expected as the pore size distribution varied significantly in the areas under the ribs versus the channel.

Development of a 4-in-1 Device to Measure Component Properties of Gas Diffusion Layer/Porous Transport Layer for Both Proton Exchange Membrane Fuel Cell and Water Electrolyzer

This work aims at developing a 4-in-1 device to simultaneously measure parameters under compression (UC), including thickness (TUC), resistivity (RUC, through-plane), and in-plane permeability (IPP-UC), and to separately measure through-plane permeability (TPP). The simultaneous measurement of TUC/RUC/IPP-UC is accomplished through an annulus sample by measuring the flow rate–pressure relationship in a radial flow [1]. By adding a two-piece adaptor, TPP can also be measured using a disk sample. Typical TUC/RUC/IPP-UC/TPP curves of a gas diffusion layer (GDL) are shown in Figure 1. Upon the design requirements, the TUC/RUC/IPP-UC/TPP tester is calibrated and validated.The 4-in-1 device was originally designed for the characterization of the GDL, a key component of the membrane electrode assembly (MEA) for a proton exchange membrane (PEM) fuel cell. The GDL properties are greatly associated with the cell performance, especially under compression. To ensure the quality of GDLs, it is of great importance to characterize GDL properties with respect to the component standardization and specification. The application of the 4-in-1 device was later extended for the characterization of the porous transport layer (PTL), a crucial component for the anode of PEM water electrolyzer in responding to the increased research and efforts made in the development of, mostly, Ti-based PTLs for PEM water electrolysis [2]-[4] , as commercially available PTLs are basically materials borrowed from other applications, e.g., filtration.The developed TUC/RUC/IPP-UC/TPP device has been proven to be a useful tool for the quality control (QC) of GDLs and PTLs, facilitating the component development, complementing the component supply chain, contributing to cell reliability, and thus reduction of cost, for both the PEM fuel cell and PEM water electrolysis technologies. Acknowledgements This work is financially supported by the Office of Energy Research and Development (OERD) and the Advanced Clean Energy (ACE) Program of the National Research Council Canada (project #NRC-23-140).

Utilization of 3-D Volume of Fluid Simulations to Understand Oxygen Evolution through Multilayer Porous Transport Layers for PEMWE Improvement

In this work, direct numerical modeling techniques were applied to 3-D generated porous transport layers (PTL), with the addition of a microporous layer (MPL), to understand the effect pore structure has on oxygen evolution. Proton Exchange Membrane Water Electrolyzers rely on PTLs to remove oxygen from the catalyst layer. Traditionally, an MPL is added to the PTL surface in contact with the catalyst layer. This creates a bilayer PTL, which is believed to improve oxygen removal, while maintaining liquid saturation. Two questions arise when creating a PTL sample for PEMWE application. First, how thick should the MPL be to achieve adequate oxygen removal? Second, is a bilayer PTL sufficient, or does a multilayer PTL result in improved oxygen removal?The objectives of this work are to observe the influence that the MPL has on oxygen transport, the effect of the MPL on oxygen removal when compared to a single layer PTL, determine an ideal MPL to PTL ratio, and identify if multilayer PTLs aid in oxygen removal. Each sample is created through an improved image processing technique that eliminates the need for interface communication when meshing. This process allows for multilayer PTL structures to be created as one geometry. Due to the improved imaging technique, meshing of these complex structures is possible. The Finite Volume Method combined with a volume of fluid model was used to simulate two phase flow, liquid water and gaseous oxygen, through all PTL samples. Each PTL/MPL combination has three different MPL thickness, which corresponds to a PTL/MPL ratio of 90:10, 80:20, and 70:30. Bilayer, trilayer, and quadlayer PTL samples were also studied. Oxygen bubble evolution, growth, and surface interaction through all sample microstructures was observed. In-plane and through-plane permeability, liquid saturation, and liquid/gas interfacial area were calculated from simulation results. Findings from this work will provide insight into ideal MPL thickness and number of MPL layers for improved oxygen removal inside PEMWEs.

Sintered Electrospun Fibrous Electrodes via Compression and Laser Perforation for Redox Flow Battery

The principal sources of new renewable energy, such as solar and wind power, depend strongly on the weather conditions, leading to the unstable electric power supply. Energy storage systems (ESS) has been developed to address this problem. One of the most promising technologies for energy storage device is redox flow batteries due to its high capacity and design flexibility. In particular, the vanadium redox flow battery is considered as a next-generation battery because of its safety and high efficiency, but not yet widely deployed owing to its low power density. The carbonized electrospun fibrous materials have been utilized as electrodes to overcome the flaw, because of their high specific surface area for reaction, high porosity to support flow and diffusion, and good electrical conductivity through the interconnected fibers. Typically, smaller fiber is preferential due to the exponential increase of surface area, but the small pores among the fibers reduce the permeability, limiting the electrolyte transportation or increasing parasitic pumping costs. In this study, flow battery electrodes made of electrospun carbon fibers were synthesized by applying compression during the stabilization stage. The objective was to create flow battery electrodes with higher volumetric surface area to support the electrochemical reaction while retaining the permeability. A porosity reduction of 12% was attained by this method, yielding a 50% increase of volumetric surface area, while the in-plane permeability and tortuosity were found to remain consistent. In addition, the holes perforated by a carbon dioxide laser addressed the issue of low through-plane permeability caused by the compacted fibers. All electrospun samples outperformed commercial carbon mats in flow cell tests. The compressed samples showed markedly better performance in the activation region but showed serious mass transport polarization at higher current density. The laser perforations significantly eliminated this flaw, yielding the best performance over the entire range of current density. Figure 1

Improvement of vanadium redox flow battery performance obtained by compression and laser perforation of electrospun electrodes

Flow battery electrodes made of electrospun carbon fibers were synthesized with substantially lower porosity than typical electrospun mats by applying compression during the stabilization stage. The objective was to create flow battery electrodes with higher volumetric surface area to support the electrochemical reaction. The physical, structural, and transport properties of these novel mats were characterized extensively. A porosity reduction of 12% was attained by this method, yielding a 50% increase volumetric surface area, while the in-plane permeability and tortuosity were found to remain relatively consistent. On the other hand, the fibers near the surfaces were somewhat compacted, which hurt the through-plane permeability, so holes were created using a CO2 laser to perforate the structure. The loss of specific surface area caused by laser perforation was quite negligible and still showed improvement compared to the uncompressed control sample. Flow battery performance tests were conducted on all samples. All electrospun samples outperformed commercial carbon mats, with the compressed samples without and without laser perforations showing markedly better performance in the activation region. The non-perforated compressed sample showed mass transfer limitations at higher current density, while the laser perforations largely eliminated this effect, yield the best performance over the entire range of current density.

Effect of fabric structure on in-plane and through-plane hydraulic properties of nonwoven geotextiles

The intrinsic in-plane (IP) permeability (K∥) and through-plane (TP) permeability (K⊥) of nonwoven geotextiles were measured experimentally. Also, the realistic 3D images of the samples were acquired by the nondestructive μCT technique and their microstructural characteristics were measured. This information was used to simulate virtual fibrous structures resembling the microstructure of geotextiles. The flow of fluid was then simulated through realistic and virtual structures and K∥ and K⊥ were calculated. The experimental and predicted results were compared with each other and those of some empirical, analytical and numerical studies. A non-linear relation between both the K∥ and K⊥ and geotextile porosity was observed. It was found that for the same porosity, coarser fibers provide higher K∥ and K⊥ and this is more pronounced at higher porosity values. It was observed that by increasing the IP fiber orientation in the flow direction, K∥ increases exponentially, while K⊥ is independent of IP fiber orientation. The anisotropic permeability ratios λ=K∥/K⊥ of samples were calculated and it was established that nonwoven geotextiles show highly anisotropic behavior with λ tending to unity with the increase of geotextile porosity. It was shown that K⊥ increases with the increase of fiber orientation through the thickness direction.

A Study on the Through-Plane Permeability of Anisotropic Fibrous Porous Material by Fractal Stochastic Method.

The through-plane permeability is of great importance for understanding the transport phenomenon in anisotropic fibrous porous material. In this paper, a novel pore-scale model based on the equilateral triangle representative unit cell (RUC) and capillary bundle model is developed for the fluid flow through the anisotropic fibrous porous material according to fractal theory, and the effective through-plane permeability is presented accordingly. The digital structures of the fibrous porous material are generated by a fractal stochastic method (FSM), and the single-phase fluid flow through the 3D-reconstructed model is simulated by using the finite element method (FEM). It was found that the effective through-plane permeability depends on the fiber column size, porosity, and fractal dimensions for pore and tortuosity. The results show that the predicted through-plane permeability by the present fractal model indicates good agreement with numerical results and available experimental data as well as empirical formulas. The dimensionless through-plane permeability is positively correlated with the porosity and negatively correlated with the fractal dimensions for pore and tortuosity at certain porosity.

Evaluation of gas permeability in porous separators for polymer electrolyte fuel cells: Computational fluid dynamics simulation based on micro-x-ray computed tomography images.

Pore structures and gas transport properties in porous separators for polymer electrolyte fuel cells are evaluated both experimentally and through simulations. In the experiments, the gas permeabilities of two porous samples, a conventional sample and one with low electrical resistivity, are measured by a capillary flow porometer, and the pore size distributions are evaluated with mercury porosimetry. Local pore structures are directly observed with micro-x-ray computed tomography (CT). In the simulations, the effective diffusion coefficients of oxygen and the air permeability in porous samples are calculated using random walk Monte Carlo simulations and computational fluid dynamics (CFD) simulations, respectively, based on the x-ray CT images. The calculated porosities and air permeabilities of the porous samples are in good agreement with the experimental values. The simulation results also show that the in-plane permeability is twice the through-plane permeability in the conventional sample, whereas it is slightly higher in the low-resistivity sample. The results of this study show that CFD simulation based on micro-x-ray CT images makes it possible to evaluate anisotropic gas permeabilities in anisotropic porous media.

Effect of composition and structure of gas diffusion layer and microporous layer on the through‐plane gas permeability of PEFC porous media

The through-plane permeability of the gas diffusion media (GDM) is investigated experimentally with regard to the microporous layer (MPL) composition and the gas diffusion layer (GDL) composition and structure. The MPL composition is held constant at 80% carbon powder and 20% polytetrafluorethylene (PTFE) (by weight) for various carbon loadings. The decrease or increase in GDM permeability was found to be dependent on the structure of the GDL used in conjunction with the type of carbon powder. It was found that low-surface-area carbon powder (Vulcan XC-72R) forms thin, dense MPLs with small cracks when compared to high-surface-area powder (Ketjenblack EC-300J), which creates thick, rough MPLs with large cracks with increased carbon loadings. For most cases, the permeability decreases with increasing carbon loading; however, the non-woven, straight fibre carbon papers using Ketjenblack EC-300J show the lowest permeability at the lowest carbon loading. Furthermore, the percentage reduction from the GDL substrate permeability appears to be predictable for similar structures with increasing carbon loading. The increase in PTFE loading from 10% to 30% in the GDL was shown to have a significant impact on the percentage reduction from the original GDL permeability of ~9% to 15% for the GDM composed of Vulcan XC-72R as carbon powder; however, such effects are insignificant when using Ketjenblack EC-300J carbon powder.

Study of the anisotropic permeability of proton exchange membrane fuel cell gas diffusion layer by lattice Boltzmann method

In proton exchange membrane fuel cells (PEMFCs), the gas diffusion layers (GDLs) are located between the flow channel and the catalytic layer, which not only provides a transport channel for the reaction gas and the output water, but also its fibrous skeleton is the key structure for the electron load transfer, and its transport performance is an important factor that affects the performance of the cell. In this paper, GDLs are stochastically reconstructed and the Lattice Boltzmann method (LBM) is adopted to study permeability. The changes of through-plane permeability and in-plane permeability are studied by varying the porosity, fiber diameter, and pressure drop. It is found that the porosity plays a dominant role in the variation of permeability, and the through-plane permeability at a porosity of 0.85 is 24.78 times greater than that at 0.5. The influence of fiber diameter can not be ignored. When the diameter is larger than 8 μm, the influence on permeability is more obvious, and the permeability is no longer sensitive to changes in diameter after a certain degree of porosity has been reached. The pressure drop only changes the magnitude of the average cross-sectional velocity of the gas diffusion layer, and the effect on the permeability is negligible. The in-plane permeability is larger than the through-plane permeability. In the scope of the paper research, the ratio of the two values ranges from 1.3 to 1.7.

A Compressible Fluid Flow Model Coupling Channel and Porous Media Flows and Its Application to Fuel Cell Materials

A multi-dimensional, compressible fluid flow solver, valid in both channel and porous media, is derived by volume-averaging the Navier–Stokes equations. By selecting an appropriate average density/velocity pair, a continuous, stable solution is obtained for both pressure and velocity. The proposed model is validated by studying the pressure drop of two commonly used experimental setups to measure in-plane and through-plane permeability of fuel cell porous media. Numerical results show that the developed model is able to reproduce the experimentally measured pressure drop at varying flow rates. Further, it highlights that previously used methods of extracting permeability, which rely on the use of simplified one-dimensional models, are not appropriate when high flow rates are used to study the porous media. At high flow rates, channel–porous media interactions cannot be neglected and can result in incorrect permeability estimations. For example, at flow rates of 1 SLPM a discrepancy of 12% in pressure drop was observed when using previous permeability values instead of the values obtained in the article using the proposed 3D model. Given that at high flow rate one-dimensional models might not be appropriate, previous estimations of Forchheimer permeability might not be accurate. To illustrate the suitability of the numerical model to fuel cell applications, fluid flow bypass in serpentine and interdigitated fuel cell flow channels is also investigated.

A Mass Transport Model for Flows in Channels and Porous Media of Fuel Cells

Low-temperature fuel cells are a promising alternative technology to conventional energy systems such as internal combustion engines. However, their large-scale commercialization is still limited due to several challenges, such as mass transport losses at high power densities [1]. Estimation of gas transport properties in porous materials of fuel cells, such as gas diffusion layers (GDLs), is therefore critical. Several experimental studies in literature estimated the permeability of different GDL samples using a one-dimensional model, which does not account for channel effects [1-6]. Some authors in literature have assumed that the flow is incompressible in their numerical studies [7-10]. This hypothesis is not justified because the error in permeability estimation with an incompressible fluid flow model compared to the estimation with a compressible fluid flow model can be as high as 20% [2]. Numerical models for channels and porous media require volume-averaged formulations, and an in-depth discussion on the physical meaning of density and velocity in these models is seldom found in literature. Also, most of the existing numerical studies neglect the anisotropic nature of GDLs.In this work, a volume-averaged form of the steady-state, compressible, and isothermal Navier-Stokes equations for flows in channels and porous materials is developed and implemented in the open-source framework OpenFCST [11]. Particular attention is given to flows in channels and GDLs of polymer electrolyte fuel cells. The fluid flow model in porous materials is derived by means of the method of volume averaging [12]. A continuous Galerkin finite element method is used to discretize and numerically solve the resulting system of governing equations in the framework of a single domain approach. The coupling boundary conditions at the internal interface between channels and porous media are discussed and a stable non-oscillatory pair of solution variables in the porous domain is obtained. The study reveals that for volume-averaged formulations, the permeability obtained in experiments has to be corrected with the sample porosity. The model is used to estimate in-plane and through-plane permeabilities of fuel cell diffusion media, which is compared to experimental data. Three-dimensional simulations show that channel effects cannot be neglected and therefore one-dimensional models for permeability estimation are limited. Assuming that the fluid is incompressible is only valid for through-plane permeability, and a compressible formulation should be used for in-plane simulations, even at moderate gas flow rates. The suitability of the mathematical model for fuel cell applications is illustrated by estimating the change in pressure drop in a serpentine channel in contact with either a solid wall or a gas diffusion media. An interdigitated channel design is also considered in order to compare the pressure drop and the velocity in the GDL with the results observed with a serpentine channel.

Microstructure-property relationships in a gas diffusion layer (GDL) for Polymer Electrolyte Fuel Cells, Part I: effect of compression and anisotropy of dry GDL

New quantitative relationships are established between effective properties (gas diffusivity, permeability and electrical conductivity) for a dry GDL (25 BA) from SGL Carbon with the corresponding microstructure characteristics from 3D analysis. These microstructure characteristics include phase volume fractions, geodesic tortuosity, constrictivity and hydraulic radius. The latter two parameters include information from two different size distribution curves for bulges (continuous PSD) and for bottlenecks (MIP-PSD). X-ray tomographic microscopy is performed for GDL at different compression levels and the micro-macro-relationships are then established for the in-plane and through-plane directions. The predicted properties based on these relationships are compared with numerical transport simulations, which give very similar results and which can be summarized as follows:Gas diffusivity is higher in the in-plane than in the through-plane direction. Its variation with compression is mainly related to changes of porosity and geodesic tortuosity. Permeability is dominated by variations in hydraulic radius. Through-plane permeability is slightly higher than in-plane. Anisotropy of electrical conductivity is controlled by tortuosity, which is higher for the through-plane direction. A table with new quantitative relationships is provided, which are considered to be more accurate and precise than older descriptions (e.g. Carman-Kozeny, Bruggeman), because they are based on detailed topological information from 3D analysis. Furthermore, when using these relationships as input for macro-homogenous modeling, this enables to simulate microstructure effects of real GDL (SGL 25 BA) more accurately. In future, the same methodology can be used to study micro-macro relationships in wet GDL and to predict relative liquid permeability and relative gas diffusivity.

The effects of the composition of microporous layers on the permeability of gas diffusion layers used in polymer electrolyte fuel cells

The effects of the composition of the microporous layer (MPL) on the through-plane permeability of the gas diffusion layers (GDLs) used in polymer electrolyte fuel cells (PEFCs) have been thoroughly experimentally investigated in this paper. For a given PTFE loading in the MPL, the GDL permeability was found to decrease with increasing carbon loading and this is due to the increase in the thickness of the MPL. For all the investigated carbon loadings of the MPL, the permeability values of the GDLs were found to have common trends for the PTFE loadings ranging from 10 to 50% (by weight): the GDL permeability increases when the PTFE loading in the MPL is increased from 20 to 50%; the GDL permeability decreases when the PTFE loading in the MPL is increased from 10 to 20%; and the GDL permeability is a minimum at 20% PTFE loading present in the MPL. On the other hand, the permeability of the GDL was found to depend on the carbon loading of the MPL in the PTFE range 0–10%. The effects of the MPL composition on the MPL permeability were found to be similar to those on the GDL permeability. However, the permeability values of the MPLs of the same composition, which were supposed to be ideally the same, were found to significantly vary. This was attributed to the MPL penetration into the body of the carbon substrates.

Predicting transport parameters in PEFC gas diffusion layers considering micro-architectural variations using the Lattice Boltzmann method

A deep understanding of the behavior of microstructural parameters in proton exchange fuel cells (PEFCs) will help to reduce the material cost and to predict the performance of the device at cell scale. Changes in morphological configuration, that is, fiber diameter and fiber orientation, of the gas diffusion layers (GDLs) result in variations of fluid behavior throughout the layer, and therefore, the microstructural parameters are affected. The aim of this study is to analyze, for three selected fiber diameters and different percentage presence of inclined fibers, the behavior of the different microstructural parameters of the GDLs. This study is carried out over digitally created two-dimensional GDL models, in which the fluid behavior is obtained by means of the lattice Boltzmann method. Once the fluid behavior is determined, the microstructural parameters, that is, the porosity, gas-phase tortuosity, obstruction factor, through-plane permeability, and inertial coefficient, are computed. Several relationships are found to predict the behavior of such parameters as function of the fiber diameter, presence of inclined rods, or porosity. The results presented in this work are compared and validated by previous theoretical and experimental studies found in the literature. Copyright © 2016 John Wiley & Sons, Ltd.

Impact on Diffusion Parameters Computation in Gas Diffusion Layers, Considering the Land/Channel Region, Using the Lattice Boltzmann Method

A deep understanding of the behavior of microstructural parameters in proton exchange fuel cells (PEFCs) will help to reduce the material cost and to predict the performance of the device at cell scale. Changes in morphological configuration, i.e., fiber diameter and fiber orientation, of the gas diffusion layers (GDLs) result in variations of fluid behavior throughout the layer, and therefore; the microstructural parameters are affected. The aim of this study is to analyze, for three selected fiber diameters and different percentages presence of inclined fibers, the behavior of the different microstructural parameters of the GDLs. This study is carried out over digitally created two-dimensional GDL models in which the fluid behavior is obtained by means of the Lattice Boltzmann method (LBM). Once the fluid behavior is determined, the microstructural parameters, i.e., the porosity, gas-phase tortuosity, obstruction factor, through-plane permeability, and inertial coefficient, are computed. Several relationships are found to predict the behavior of such parameters as function of the fiber diameter, presence of inclined rods or porosity. The results presented in this work are compared and validated by previous theoretical and experimental studies found in the literature.

Active multi-scale modeling and gas permeability study of porous metal fiber sintered felt for proton exchange membrane fuel cells

Porous metal fiber sintered felt (PMFSF) is a promising critical component in proton exchange membrane fuel cells, having the ability of simultaneously acting as the flow field plate, gas diffusion layers and also the catalyst layers support, and owing the property of multi-scale surface morphology. A simple multi-scale mathematical method was proposed to actively construct three dimensional models of PMFSF’s microstructure by synthesizing the implicit periodic surface (PS) model and the Weierstrass-Mandelbrot (W-M) fractal geometry. In this method, the PS model described the macro overall fiber shape, and the W-M fractal geometry modeled the micro fractal roughness topography attached. Based on the method, multi-scale fractal PMFSF models were reconstructed according to morphology parameters of physical PMFSFs, and were discretized in ANSYS/ICEM to generate refined mesh for computational fluid dynamics analysis. To verify the validity of the proposed modeling approach, PMFSFs with different porosity and fiber orientation are generated, and then the effects of the fractal surface topography and the fractal parameters such as fractal dimension and height scaling parameter on the gas permeability of PMFSF were investigated. The numeric simulation results show that the influence of the fractal topography on the in-plane and through-plane permeability of PMFSF cannot be ignored, and the permeability of fractal PMFSF models agrees with experimental measurements better. Especially, the results imply that the fractal morphology may have the potential to adjust the anisotropic properties of PMFSFs’ permeability. It is further found that the larger the fractal dimension is and the lower the height scaling parameter is, the better the permeability of PMFSF will be. The synthesis approach and numerical simulation method may facilitate the development of active functional design mode to predict and optimize key characteristics of PMFSF ahead of manufacture.

Compress effects on porosity, gas-phase tortuosity, and gas permeability in a simulated PEM gas diffusion layer

Among the parameters to take into account in the design of a proton exchange membrane fuel cell (PEMFC), the energy conversion efficiency and material cost are very important. Understanding in deep the behavior and properties of functional layers at the microscale is helpful for improving the performance of the system and find alternative materials. The functional layers of the PEMFC, i.e., the gas diffusion layer (GDL) and catalyst layer, are typically porous materials. This characteristic allows the transport of fluids and charges, which is needed for the energy conversion process. Specifically, in the GDL, structural parameters such as porosity, tortuosity, and permeability should be optimized and predicted under certain conditions. These parameters have effects on the performance of PEMFCs, and they can be modified when the assembly compression is effected. In this paper, the porosity, gas-phase tortuosity, and through-plane permeability are calculated. These variables change when the digitally created GDL is under compression conditions. The compression effects on the variables are studied until the thickness is 66% of the initial value. Because of the feasibility to handle problems in the porous media, the fluid flow behavior is evaluated using the lattice Boltzmann method. Our results show that when the GDL is compressed, the porosity and through-plane permeability decrease, while the gas-phase tortuosity increases, i.e., increase the gas-phase transport resistance. Copyright © 2015 John Wiley & Sons, Ltd.

Experimental study of mass transport in PEMFCs: Through plane permeability and molecular diffusivity in GDLs

An experimental study of convective-diffusive transport in polymer electrolyte fuel cell (PEFCs) porous materials is presented. The study is used to estimate through-plane viscous permeability and effective molecular diffusivity of different gas diffusion layers (GDLs). A diffusion bridge based experimental setup is used for molecular diffusivity measurements, with oxygen and nitrogen flowing across the bridge. The pressure difference across the bridge is adjusted to control convective transport. The oxygen transport across porous media is measured using an oxygen sensor, and experimental data is fitted to a combined Fick's and Darcy's model to estimate effective diffusivity. To measure permeability, a variation of the diffusion bridge is used, where a single gas is forced to go through the GDL. The pressure drop across the GDL is measured, and fitted to Darcy's law to estimate viscous permeability. Through-plane permeability and effective molecular diffusivity are measured for several Toray samples with different polytetrafluoroethylene (PTFE) loading. Results show that permeability varies with PTFE loading between 1.13×10−11 - 0.35×10−11m2 and diffusibility between 0.209 - 0.071. Increase in the PTFE content in GDLs was found to have an adverse effect on permeability and diffusibility.