Polytetrafluoroethylene Distribution Research Articles

Improvement of surface insulating performance for polytetrafluoroethylene film by atmospheric pressure plasma deposition

The surface flashover phenomenon across a vacuum-dielectric interface severely limits the service life and operational reliability of high voltage electrical equipment. Surface modification by atmospheric pressure plasma treatment is a promising method to improve the surface insulating performance of polymers. In order to explore the mechanism of plasma processing on the vacuum flashover characteristics of polymer materials, atmospheric pressure plasma deposition was used to treat polytetrafluoroethylene (PTFE) film. The surface parameters under different processing conditions, such as surface chemical composition, surface resistivity, surface charge decay and trap distribution, were tested and analyzed. The space charge distribution of PTFE and the flashover voltage in vacuum were measured. The results show that Si–O–Si and Si–OH groups are introduced on the surface of PTFE, and the characteristic peaks of PTFE are gradually weakened with the increase of processing time. The surface trap density increases and more traps with lower energy level arise with longer processing time. The plasma deposition changes the space charge distribution in PTFE body, and leads to positive charge accumulation inside the sample. The flashover field strength respectively increases by 15% and 70% in direct current (DC) voltage and microsecond pulse voltage after plasma deposition. The rapid dissipation of surface charge is the main reason for pulse flashover voltage enhancement, while the increase of surface leakage current due to lower surface resistivity and space charge accumulation in PTFE body make the DC flashover voltage reach the saturation point. Therefore the surface insulating and body performance of polymer materials after plasma modification processing should be considered comprehensively based on different applications.

Investigation of flow characteristics on porous gas diffusion layer microstructure that generated with binder and polytetrafluoroethylene distribution

The drainage properties of a gas diffusion layer (GDL) are essential factors in the performance of proton exchange membrane fuel cells. The GDL consisting of a three-dimensional (3D) carbon paper microstructure was developed and meshed with pore-scale reconstruction models in this paper. Localized binder and polytetrafluoroethylene (PTFE) structures were added to the carbon paper microstructure through 3D morphological imaging processing. The monitoring data of 1000 planes were multi-peaky fitted as a function of gas permeability and height to amend the macroscopic porous medium model. We analyzed drainage properties under different contact angles (θ) for the carbon paper with binder and PTFE. We described the mutual intrusion of moisture and air in GDL under different pressure differences. The results show that the pore-scale reconstruction model has the advantages of describing the flow in GDL accurately and with details, detecting low-flow resistance channels that spontaneously formed in GDL, and describing the variation of permeability as a function of location. In a hydrophobic environment, the liquid film connected to a GDL is challenging to split spontaneously. At the same time, the splitting motion of discrete droplets is more prominent than that of the liquid film. The pressure that enables complete water intrusion into the GDL is between 1 and 10 MPa.

Lattice Boltzmann simulation of a gas diffusion layer with a gradient polytetrafluoroethylene distribution for a proton exchange membrane fuel cell

The content and distribution of polytetrafluoroethylene are key factors that determine liquid transport behaviors in gas diffusion layers and, thus, the performance of proton exchange membrane fuel cells. In this study, by employing a stochastic algorithm, the two-dimensional microstructure of a representative gas diffusion layer with the real distributed property of polytetrafluoroethylene was reconstructed. Subsequently, the influence of polytetrafluoroethylene content and gradient distributions on liquid water transport behaviors was examined by implementing a multiphase lattice Boltzmann method. The results supported the findings that an increased content of polytetrafluoroethylene in the conventional gas diffusion layer favors liquid removal, but an extremely high content could cause a marked decrease in the corresponding effective porosity of the gas diffusion layer, hence weakening cell performance. The simulation found that the optimal polytetrafluoroethylene content for the conventional gas diffusion layer was 10 wt%. More importantly, the study reveals that a reasonably higher polytetrafluoroethylene content in the inlet region of the gas diffusion layer benefits the enhancement of water drainage. Compared with the conventional gas diffusion layer with a polytetrafluoroethylene content of 10 wt%, the optimal bigradient and trigradient polytetrafluoroethylene gas diffusion layer exhibits a lower liquid water saturation, a shorter steady-state time of liquid water and gas, and an effective porosity increased by 4.2% and 5.8%, indicating higher water drainage performance. The study here can provide guidelines for the design of high-performance fuel cells with a gradient gas diffusion layer.

Measurement of Contact Angles at Carbon Fiber-Water-Air Triple Phase Boundaries inside Gas Diffusion Media of Polymer Electrolyte Membrane Fuel Cells from Xray Computed Tomography

Gas diffusion layers (GDLs) are porous fiber layers that are used for various electrochemical applications, including fuel cells, electrolyzers, CO2 reduction reaction electrolyzers, and redox flow batteries. Depending on its application, a GDL’s wettability is controlled by the addition of polytetrafluoroethylene (PTFE). The PTFE addition is highly stochastic, resulting in inhomogeneous distribution. Furthermore, the fibers, carbonaceous binder, and PTFE all have different surface roughness and surface properties that dictate GDL wettability. To determine the contact angle of the GDL, goniometer measurements of external contact angle are used, where a droplet of water is placed on the top of the GDL and a contact angle is projected onto a detector. However, this form of measurement has limitations that need to be accounted for as the GDL is highly porous and its surface and internal contact angles might be different due to inhomogeneous binder and PTFE distribution. For the first time, we have applied a method to calculate the internal contact angle distribution of water inside various commercial GDLs. Lattice Boltzmann water transport simulations using these contact angle distributions yielded results much closer to experimental values than simulations that used goniometer-measured constant contact angles. XPS was used to correlate surface oxide groups to measured internal contact angles.AlRatrout et al. developed an open-source C++ code to compute local contact angles at triple phase boundary points (comprised of a solid and two fluids) from micro Xray computed tomography (XCT) images of porous media [1]. We applied it to segmented micro XCT images of water filled commercial GDL samples and computed local contact angles at air-GDL-water triple phase contacts points (Figure 1A). We obtained a state of mixed wettability inside all GDL samples, with contact angles ranging from 0° to 180° inside the pores (Figure 1B). Several works have calculated average contact angles similar to our results using other methods [2, 3]. Hydrophilicity is due to the presence of surface oxide groups on GDL fibers while hydrophobicity is due to the chemical nature of carbon and the roughness of the GDL fibers. Lattice Boltzmann water transport simulations were performed with the spatially distributed, mapped contact angles and constant contact angles measured with a goniometer (Figure 1C-F) [4]. When our mapped, mixed-wettability contact angle distributions were used, the simulation revealed several regions of high liquid saturation that the constant contact angle simulations did not capture. These results agreed with experimental observations. Thus, for robust water transport simulations, we suggest that distributed contact angles should be used instead of goniometer-measured constant contact angles.

Mechanism and Model for Optimizing Polytetrafluoroethylene Distribution to Improve the Electrical and Thermal Conductivity of Treated Carbon Fiber Paper in Fuel Cells.

Employing polytetrafluoroethylene (PTFE)-treated carbon fiber paper (CFP) as the substrate of the gas diffusion layer (GDL) is a common practice to improve water management in proton exchange membrane fuel cells (PEMFCs), but the resulting increase in electrical and thermal resistance is a critical problem that restricts the performance output of PEMFCs. Hence, studying the mechanism and prediction model for both the electrical and thermal conductivity in CFP is essential. This work established a mathematical graph theory model for CFP electrical and thermal conductivity prediction based on the observation and abstraction of the CFP characteristic structures. For the PTFE-treated CFP, the electrical and thermal conductivity of CFP can be effectively increased by optimizing the PTFE distribution in CFP. A "filter net effect" mechanism was proposed to reasonably explain PTFE distribution's influence on the CFP performance. Finally, the equivalent effect of multiple factors on conductivity was revealed using contour maps, which provides inspiration for further reducing the electrical and thermal resistance in CFP.

Flexible graphite bipolar plates for vanadium redox flow batteries

The effects of polytetrafluoroethylene (PTFE) additives on expanded graphite bipolar plates (BPs) for vanadium redox flow batteries (VRFB) are investigated. Pure expanded graphite plates have immense potential for use in low-cost, rapid, and continuous fabrication of high performance VRFBs. However, pure expanded graphite BPs suffer from severe swelling in vanadium electrolytes over short periods of time, exhibiting decreased efficiency of 2.3% within 35 charge/discharge cycles. In contrast, expanded graphite BPs containing 6 and 10 wt% PTFE do not experience swelling or efficiency loss during cycle tests. The prevention of swelling is a key factor contributing to the use of expanded graphite plates for VRFB stacks. Microstructural analysis reveals that our fabrication method provides uniform PTFE distribution. PTFE polymers suppress swelling by providing coverage of surface cracks, repelling aqueous solutions due to their hydrophobicity, and more importantly, providing binding forces between expanded graphite layers. PTFE additives increase electrical resistivity, but improve flexibility, allowing for the fabrication of very thin plates. Thin flexible BPs exhibit low areal electrical resistance and thus the ohmic voltage loss of the BPs with 6 wt% PTFE is less than 1.2 mV (<0.1% of the VRFB nominal voltage of 1.25 V) even at a high current density of 0.2 A cm−2, which is negligible compared with other factors.

Small-angle neutron scattering studies on the distribution of polytetrafluoroethylene within microporous layers for polymer electrolyte fuel cells

The performance of polymer electrolyte fuel cells depends on the nanostructure of the polymer composites in their components. The microporous layer within the cells, which generally comprises a composite of carbon black and polytetrafluoroethylene (PTFE), is a key component that prevents mass-transport losses in electrochemical reactions of the cells; therefore, we studied the distribution of PTFE within microporous layers using contrast-variation small-angle neutron scattering. By performing annealing above the PTFE melting point, its self-aggregations were reduced, and this effect was explained via the surface energies of PTFE and carbon black. Moreover, fuel cell performance testing demonstrated that better mass-transport properties were achieved when there were fewer PTFE self-aggregations within the microporous layers. Our findings suggest that an optimal PTFE distribution within fuel cell microporous layers can be achieved by engineering the surface energies of carbon black.

Titanium nitride (TiN)–polytetrafluoroethylene (PTFE)-modified carbon paper used in PEM fuel cells: characterization and corrosion-resistant mechanism

Titanium nitride (TiN) nanoparticles (NPs) were added into polytetrafluoroethylene (PTFE) emulsion for the hydrophobic treatment of carbon papers (CPs). The addition of the nano-sized conducting nanoparticles in impregnation solution could improve the corrosion resistance, electrical conductivity, hydrophobicity and durability of the treated CPs. It is found that the corrosion resistance and electrical conductivity of the as-treated CPs increased gradually as the increment of TiN content. CPs impregnated with PTFE emulsion containing 8 wt% TiN NPs displayed the optimal improved corrosion resistance with corrosion potential and corrosion current density at 0.16 V and 0.056 μA/cm2, respectively. Characterizations by SEM, Raman and XPS demonstrate that this improvement is associated with the formation of TiN coating and the improved distribution of PTFE on CPs.

Enhancement in corrosion resistance and electrical conductivity of hydrophobic‐treated CP by PTFE emulsion containing TiN NPs

Titanium nitride (TiN)-modified hydrophobic-treated carbon paper (CP) was prepared by impregnating CP with polytetrafluoroethylene (PTFE) emulsion containing TiN nanoparticles (NPs). Electrochemical measurements showed that CP witnessed an increase in corrosion resistance and electrical resistivity after treated with 5 wt% PTFE emulsion. Since the sacrifice in electrical conductivity is not beneficial to the application in proton exchange membrane fuel cells (PEMFCs), conductive ceramic NPs – TiN NPs were introduced into the CP to further improve its electrical conductivity. It was found that after adding TiN NPs, the electrical resistivity of CP (immersed in 5 wt% PTFE emulsion containing 8 wt% TiN NPs) decreased to a level (3.8 mΩ cm) similar to that of untreated CP (3.5 mΩ cm), and meanwhile there is a further improvement in corrosion resistance, where the corrosion current density (at 1.4 V) of TiN-modified CP stabilises at the lowest value of 5.50 μA/cm2, as compared with 32.8 and 12.7 μA/cm2 for raw CP and PTFE-treated CP. According to microstructure characterisation, these improvements could be attributable to the formation of conductive networks and improved PTFE distribution due to the addition of TiN NPs.

Lattice Boltzmann simulation of liquid water transport inside and at interface of gas diffusion and micro-porous layers of PEM fuel cells

In this study, an optimized stochastic model is developed to reconstruct the realistic 3D microstructure of gas diffusion layer (GDL) and micro porous layer (MPL). With considering GDL and MPL microstructure simultaneously, a 3D lattice Boltzmann (LB) model is developed to study the role of MPL macro crack in liquid water transport and redistribution at GDL/MPL interface. The proposed model is validated with visualization experiment in literature, and then the effects of different Poly Tetra Fluoroethylene (PTFE) distributions and pressure differences are investigated. The results show that PTFE distribution under vacuum-drying is almost uniform inside GDL, and the continuous switching of wettability between carbon fiber and PTFE can accelerate the liquid water permeation. PTFE under air-drying will accumulate at one side of GDL and reduce the porosity in this region, and thus the larger pressure difference or longer time is needed for liquid water break-through. As the pressure difference increases, the retaining amount of liquid water inside the narrow pore is increased. Inserting of MPL only latches the liquid water in GDL region close to macro crack, which helps reduce the water flooding and improve the gas transport to active sites.

Two-phase flow in the mixed-wettability gas diffusion layer of proton exchange membrane fuel cells

Polytetrafluoroethylene (PTFE) is widely employed to improve the hydrophobicity of gas diffusion layer (GDL) in proton exchange membrane (PEM) fuel cells. In this study, the effects of different PTFE loadings on the relationship of the capillary pressure Pc and water saturation s in the mixed-wettability GDL, i.e. Pc-s, are investigated using a three-dimensional (3D) volume of fluid (VOF) model. The simulated Pc-s curves are presented and compared with results obtained from the lattice Boltzmann model (LBM) and experiments. The good agreement between the VOF predictions and experiment data is achieved, indicating that the mixed wettability in the PTFE treated GDL is an important feature to understand two-phase behaviors in fuel cells. The homogeneous and heterogeneous PTFE distributions resulted from two PTFE drying methods (i.e. the vacuum and air dryings, respectively) are studied. It was found that the air drying GDL yields a high PTFE concentration near the water inlet and reduces water imbibition near the inlet. The simulated Pc-s correlation from VOF model was compared with standard Leverett correlation.

Impact of PTFE distribution across the GDL on the water droplet removal from a PEM fuel cell electrode containing binder

By progress of the new generation of electrical powertrains and reducing of the fossil fuel resources, vehicle industry becomes more interested in utilizing proton exchange membrane (PEM) fuel cells. However, practical utilization of them is faced with some challenges including liquid water accumulation in the porous electrodes. The common belief for mitigating this issue is the treatment of electrodes' gas diffusion layers (such as carbon papers consisting of carbon fibers and binder for binding fibers) with a highly hydrophobic material such as poly-tetra-fluoro-ethylene (PTFE). In the current investigation, 3D stochastic reconstructions and 3D lattice Boltzmann simulations are employed to discover the impact of PTFE distribution as well as the role of binder content on the removal process of a water droplet from a PEM fuel cell electrode for the first time. Nine different simulations with three dissimilar PTFE distributions and three dissimilar binder contents are implemented. The results demonstrate that the PTFE distribution and the existence of binder can greatly affect the removal efficiency of water droplet from gas diffusion layer. Unexpectedly, for higher binder contents, the uniform distribution of PTFE is less effective. Besides, for a specific PTFE distribution adding binder can effectively hinder the removal process of droplet.

Impact of PTFE content and distribution on liquid–gas flow in PEMFC carbon paper gas distribution layer: 3D lattice Boltzmann simulations

A 3D multiphase lattice Boltzmann model (LBM) was established and employed to study the impact of polytetrafluoroethylene (PTFE) content and distribution on the liquid–gas transport in proton exchange membrane fuel cell (PEMFC) carbon-paper gas distribution layer (GDL). In the computer-generated carbon paper GDL, part of the fibers’ surface was randomly specified as PTFE to achieve a desired PTFE content and distribution. For non-uniform PTFE distribution cases, a GDL sub-region neighboring to gas channel (GC) was set to have higher PTFE content. PTFE content and distribution show important influence on the liquid–gas flow and on the relationship of relative permeability versus phase saturation. The GDL sub-region of more PTFE acts like a capillary barrier and raises the liquid saturation level in the rest part of GDL. The simulated liquid saturation level in GDL diminishes with the increase of PTFE content in GDL. The liquid phase relative permeability is larger in the GDL of lower PTFE content if the (overall) liquid saturation is lower than a threshold value, whereas it becomes smaller if the liquid saturation is higher than this threshold value. The liquid phase relative permeability in the GDL with non-uniform PTFE distribution is reduced when the liquid saturation in GDL is lower than a certain value, but when the liquid saturation is higher than this value, it is larger compared with that in the GDL with uniform PTFE distribution. The gas phase relative permeability in the GDL of lower PTFE content is larger than tat in the GDL of higher PTFE content and the non-uniform distribution of PTFE in GDL slightly reduces the gas phase relative permeability value.

Composition analysis of a polymer electrolyte membrane fuel cell microporous layer using scanning transmission X-ray microscopy and near edge X-ray absorption fine structure analysis

The novel application of scanning transmission X-ray microscopy (STXM) to the microporous layer (MPL) of a polymer electrolyte membrane fuel cell is investigated. A spatially resolved chemical component distribution map is obtained for the MPL of a commercially available SGL 25 BC sample. This is achieved with near edge X-ray absorption fine structure spectroscopic analysis. Prior to analysis the sample is embedded in non-reactive epoxy and ultra-microtomed to a thickness of 100 nm. Polytetrafluoroethylene (PTFE), carbon particle agglomerates, and supporting epoxy resin distributions are identified and reconstructed for a scanning area of 6 μm × 6 μm. It is observed that the spatial distribution of PTFE is strongly correlated to the carbon particle agglomerations. Additionally, agglomerate structures of PTFE are identified, possibly indicating the presence of a unique mesostructure in the MPL. STXM analysis is presented as a useful technique for the investigation of chemical species distributions in the MPL.

Effect of through-plane polytetrafluoroethylene distribution in gas diffusion layers on performance of proton exchange membrane fuel cells

This experimental study identifies the effect of through-plane polytetrafluoroethylene (PTFE) distribution in gas diffusion backing (GDB) on the performance of proton exchange membrane fuel cells (PEMFC). PTFE-drying under vacuum pressure created a relatively uniform PTFE distribution in GDB compared to drying under atmospheric pressure. Carbon paper samples with different PTFE distributions due to the difference in drying conditions were prepared and used for the cathode gas diffusion layer (GDL) of PEMFCs. Also investigated is the effect of MPL application on the performance for those samples. The current density (i) – voltage (V) characteristics of these PEMFCs measured under high relative humidity conditions clearly showed that, with or without MPL, the cell using the GDL with PTFE dried under vacuum condition showed better performance than that dried under atmospheric condition. It is suggested that this improved performance is caused by the efficient transport of liquid water through the GDB due to the uniform distribution of PTFE.

Effect of through-plane polytetrafluoroethylene distribution in a gas diffusion layer on a polymer electrolyte unitized reversible fuel cell

The relationship between through-plan polytetrafluoroethylene (PTFE) distribution on a gas diffusion layer (GDL) and unitized reversible fuel cell (URFC) performance was investigated. Titanium (Ti) - felt was used for the oxygen-side GDL and treated with 10wt.% PTFE dispersion to enhance hydrophobicity. The dependence of PTFE distribution on the PTFE drying conditions was examined using scanning electron microscopy (SEM)-based energy dispersive X-ray spectroscopy (EDS) imaging. The EDS image maps revealed that the PTFE distribution strongly depended on the drying condition of the PTFE; drying under atmospheric pressure yielded a highly non-uniform PTFE distribution in the through-plane direction, whereas drying under vacuum pressure yielded a relatively uniform PTFE distribution. The cell performance of URFCs was then evaluated based on measured current–voltage characteristics during both electrolysis and fuel cell operation modes. Results verified that compared with non-uniform PTFE distribution, a uniform distribution in the Ti-felt GDL improved the fuel cell performance under the fully wet condition (relative humidity = 100%). By applying the Ti-felt GDL with uniform PTFE distribution in the through-plane direction, the current density at the cell voltage of 0.6 V was increased by a factor of about 1.9 compared with the Ti-felt with non-uniform PTFE distribution.

PTFE Distributions in Diffusion Media of PEFCs and Related Effects on Water Transport

The objective of this work is to examine the impact of polytetrafluoroethylene (PTFE) distribution on water transport in the diffusion media of polymer electrolyte fuel cells (PEFCs). The structure of a commercial gas diffusion layer (GDL) sample was captured previously using X-ray computed tomography. In this study, several PTFE distribution cases are generated on the internal surface of the measured GDL structure. The full/pore morphology model is applied to capture the impact of the PTFE distributions on water transport in the GDL.

Effect of through-Plane Polytetrafluoroethylene Distribution in a Gas Diffusion Layer

In this study, in order to investigate the effect of polytetrafluoroethylene (PTFE) though-plane distribution on the water discharge characteristic, limiting current measurements were performed under various humidity conditions using a small-scale proton exchange membrane fuel cell (PEMFC). Based on the limiting current measurement, we could evaluate the correlation between the PTFE distribution and the gas transport resistance through the carbon paper GDL.

Effect of through-Plane Polytetrafluoroethylene Distribution in a Gas Diffusion Layer

During operation of a proton exchange membrane fuel cell (PEMFC), the oxygen reduction reaction rate at the cathode is the limiting kinetic step and determines the maximum operating current density. This rate strongly depends on the transport rate of oxygen from the flow channel to the catalyst sites. Although the electrolyte membrane needs liquid water to retain proton conductivity, the oxygen gas transport can be greatly hindered when liquid water accumulates either in the catalyst layer (CL) or the gas diffusion layer (GDL) of the cathode. Consequently, for optimal water management and performance in PEMFCs, water retention/expulsion properties must be carefully balanced.We previously investigated the relationship between the treatment process of polytetrafluoroethylene (PTFE) and the resulting PTFE distribution in through-plane direction of carbon papers [1]. The dependence of PTFE distribution on the PTFE drying conditions was examined using SEM-EDS analysis. The EDS image maps revealed that the PTFE distribution strongly depended on the drying condition; PTFE-drying under atmospheric pressure created highly heterogeneous PTFE distributions in the through-plane direction, with high concentrations near both the upper and lower surfaces, whereas PTFE-drying under vacuum pressure created a relatively uniform PTFE distribution.In this study, in order to investigate the effect of PTFE though-plane distribution on the water discharge characteristic, limiting current measurements were performed under various humidity conditions using a small-scale PEMFC, which has the electrode area of 1 cm2. Based on the limiting current measurement, we could evaluate the gas transport resistance through the carbon paper GDL [2,3]. Because the small-scale cell was applied, we could minimize the effect of the distribution of current density and humidification, that is, the effect of local flooding across the flow channel depending on the change of humidification.ReferencesH. Ito et al., J. Power Sources , 248, 822 (2014).D. R. Baker et al., J. Electrochem. Soc., 156, B991 (2009).N. Nonoyama et al., J. Electrochem. Soc., 158, B416 (2011).

PTFE Distributions in Diffusion Media of PEFCs and Related Effects on Water Transport

The diffusion media (DM) of polymer electrolyte fuel cells (PEFCs) typically consists of a macro-substrate (or gas diffusion layer, GDL) coated with a micro-porous layer (MPL). The GDL portion is manufactured from carbon fibers/binder and is often treated with polytetrafluoroethylene (PTFE) to increase the hydrophobicity. Similarly, the MPL is manufactured from a slurry containing carbon nanoparticles and PTFE. While the distribution of PTFE undoubtedly influences water transport within the DM, the actual 3-D distribution of PTFE is extremely difficult to capture using a single, standalone device. Therefore, the objective of this work is to examine the impact of PTFE distribution on water transport by generating various PTFE distributions within the measured 3-D structures of DM materials.A commercial DM sample was previously analyzed using X-ray computed tomography (XCT) and focused ion beam-scanning electron microscopy (FIB-SEM) to capture the 3-D structures of the GDL and MPL regions, respectively [1]. In this study, three different PTFE distribution cases are generated on the internal surface of the measured GDL structure: i) random PTFE surface pixels; ii) random PTFE surface clusters; and iii) wetting of PTFE into GDL crevices to mimic the PTFE treatment process used during manufacturing. Similarly, cases (i) and (ii) are generated in the measured MPL structure. In each case, PTFE is assigned to existing solid pixels so that the structure of the measured sample is preserved.The well-established pore morphology or full morphology (FM) model [1,2], used for determining capillary pressure-saturation behavior in uniformly wetting pore structures, was recently extended to account for locally different wetting surfaces in a structure [3,4]. The extended-FM approach is applied here in 3-D to capture the impact of the PTFE distributions on water transport in the DM, by assuming one contact angle for the carbon fiber/binder surface and a different contact angle for the hydrophobic PTFE surface. Two uniform surface conditions (i.e., traditional FM approach) are also considered for comparison: one in which an average contact angle for carbon fiber/binder and PTFE is assumed, and another in which PTFE is neglected (i.e., untreated GDL sample). The capillary pressure-saturation results are compared with experimental and modeling studies available in literature.