Hydrophilic Gas Diffusion Layers Research Articles

Experimental study and modeling of water transport through short-side-chain perfluorosulfonic acid membranes

Perfluorosulfonic acid polymer membranes are state-of-the-art electrolytes in PEMFCs and PEMWEs, and their degradation represents still one of the limiting factor to increase lifetime of electrochemical devices. Due to significant role of water in stressing degradation mechanisms, this work, through an experimental and theoretical analysis, deepens comprehension of materials and constructive properties of short-side-chain (SSC) membranes on dynamic water transport. A systematic analysis is carried out by analysing samples with different membrane thickness and EW, coupled with different gas diffusion layers. A model was adopted to analyse both steady-state and transient water transport tests, evaluating individual contributions to the total water mass transfer. Particular attention was given to swelling/shrinking mechanism, highlighting its strong impact on water sorption and membrane hydration. Membrane diffusion and interfacial mass transfer were independently investigated, identifying their interconnections with material-bulk and superficial properties. Results highlight that membrane with low EW (790 g mol−1), coupled with hydrophilic gas diffusion layers that oppose negligible interfacial resistances to water transport, allows to reduce total resistance by approximately 39% compared to reference configuration (980 g mol−1, hydrophobic).

Lattice Boltzmann simulation of the structural degradation of a gas diffusion layer for a proton exchange membrane fuel cell

The aging of a gas diffusion layer (GDL) significantly impacts water drainage and mass diffusion within a proton exchange membrane fuel cell (PEMFC). This study employs a stochastic algorithm to reconstruct a 2D microstructure of carbon fiber-type GDL with various different aged degrees. Subsequently, a multiphase lattice Boltzmann method (LBM) is employed to examine water transport within the reconstructed GDLs. Results support the finding that as the GDL ages, its water elimination performance remarkably decreases and much water is retained inside the GDLs. Compared with the degradation of carbon fibers, the degradation of polytetrafluoroethylene (PTFE) leads to a more hydrophilic GDL, thereby reducing the local capillary pressure and forming multipaths for water transport, resulting in a more severe water flooding problem. A proper increase in PTFE content favors GDL antiaging performance, but an excessively high content can occupy pores and reduce the effective porosity, thus reducing the fuel cell performance. These results demonstrate that GDL with a PTFE content of 10 wt% shows better antiaging performance and the highest effective porosity. The study here provides an accurate assessment of liquid water drainage performance of GDL with various different aged degrees and guideline for designing GDLs with high antiaging performance.

Hydrophobicity Graded Gas Diffusion Layer for Stable Electrochemical Reduction of CO2

AbstractTo mitigate flooding associated with the gas diffusion layer (GDL) during electroreduction of CO2, we report a hydrophobicity‐graded hydrophobic GDL (HGGDL). Coating uniformly dispersed polytetrafluoroethylene (PTFE) binders on the carbon fiber skeleton of a hydrophilic GDL uniformizes the hydrophobicity of the GDL and also alleviates the gas blockage of pore channels. Further adherence of the PTFE macroporous layer (PMPL) to one side of the hydrophobic carbon fiber skeleton was aided by sintering. The introduced PMPL shows an appropriate pore size and enhanced hydrophobicity. As a result, the HGGDL offers spatial control of the hydrophobicity and hence water and gas transport over the GDL. Using a nickel‐single‐atom catalyst, the resulting HGGDL electrode provided a CO faradaic efficiency of over 83 % at a constant current density of 75 mA cm−2 for 103 h operation in a membrane electrode assembly, which is more than 16 times that achieved with a commercial GDL.

Hydrophobicity Graded Gas Diffusion Layer for Stable Electrochemical Reduction of CO2.

To mitigate flooding associated with the gas diffusion layer (GDL) during electroreduction of CO2 , we report a hydrophobicity-graded hydrophobic GDL (HGGDL). Coating uniformly dispersed polytetrafluoroethylene (PTFE) binders on the carbon fiber skeleton of a hydrophilic GDL uniformizes the hydrophobicity of the GDL and also alleviates the gas blockage of pore channels. Further adherence of the PTFE macroporous layer (PMPL) to one side of the hydrophobic carbon fiber skeleton was aided by sintering. The introduced PMPL shows an appropriate pore size and enhanced hydrophobicity. As a result, the HGGDL offers spatial control of the hydrophobicity and hence water and gas transport over the GDL. Using a nickel-single-atom catalyst, the resulting HGGDL electrode provided a CO faradaic efficiency of over 83 % at a constant current density of 75 mA cm-2 for 103 h operation in a membrane electrode assembly, which is more than 16 times that achieved with a commercial GDL.

Study on droplet motion behavior on a rough gas diffusion layer surface of a PEM fuel cell

Understanding the dynamic characteristics of the droplets on the gas diffusion layer (GDL) of the proton exchange membrane fuel cell (PEMFC) is important to improve fuel cell performance. This paper studies the dynamic characteristics of water droplet detachment from a simplified rough GDL surface by volume of fluid (VOF) method. The rough GDL surface was restructured by designing grooves with cubic pillars on the GDL surface. Results indicate that the gas velocity, space distance, and wettability of the cubic pillars remarkably affect the water droplet detachment. On a high hydrophilic, water droplet exhibits a shorter detachment time regardless of spatial distance and gas velocity. Whereas on a moderate hydrophilic GDL, a large space distance benefits the droplet detachment. However, in both situations referred to above, droplets tend to deviate and adhere to the corner between the channel wall and the GDL surface. On a high hydrophobic GDL, a large space distance and a high gas velocity favor droplet detachment, moreover, droplet shows Cassie mode and can be easily drained out. These findings can guide the optimal design of GDL for water management of high-performance fuel cells.

A Development of Pore Network Model Coupled Thermal Transport for Hydrophilic Porous Media of PEM Electrolyser

Hydrogen is a highly promising energy carrier vector. Water electrolysis process that provides splits of water to hydrogen and oxygen through the electricity has gained great recognition for hydrogen production because it provides high conversion efficiency, clean and purified hydrogen in recent years. A Polymer Electrolyte Membrane electrolyser that brings important advantages such as compactness, and the ability to work at low operating temperature, is an electrochemical device. From the gas channels in the cathode, the water enters the hydrophilic porous transport layer (PTL), also known as the gas diffusion layer (GDL), to the catalyst layer (CL) in which the electrolysis reactions occur.At high current densities (higher than 1 A/cm2), the PEM electrolyser is also favorable to produce a high amount of hydrogen; however, management of heat and mass transfer in the GDL becomes crucial as the two-phase flow occurs, and can be lead to hot spots. Moreover, the mass transport overpotentials become important issues at high current densities and lead to be 25% losses in the overall electrolyzer overpotential. A development of model is crucial to understand and enhance the heat and mass transport mechanisms in CL-GDL interface. Here, pore network model (PNM) has gained a significant interest as it offers strong tool to simulated multiphase flow in three-dimensional (3D) porous media for electrochemical energy conversion. The principle behind of this modelling approach is that a porous medium behaves as a network of pores that connected by throats. Through this framework, the discretization approach to transport modelling becomes dramatically simple, and the computational cost and time are reduced among the continuum modelling approaches (e.g., Lattice-Boltzmann, CFD).In this work, to the best knowledge of authors, the first pore network model coupled heat transfer model is developed to characterize available GDL. Here, the pore network is extracted from the micro CT image of a hydrophilic GDL through the Snow algorithm employed in OpenPNM software (An open-source Pore Network Modeling Package) and reconstructed in this environment, while the geometry of catalyst layer is created randomly. The effective two-phase 2D model is developed to predict water transport in the GDL and CL through the percolation algorithm. For this purpose, the sink and source terms are employed for some pores in the network (especially near GDL-CL interface) according to electrolyser operating conditions. Similarly, heat transport equations are applied for each pore in the network with adding source and sink terms due to the evaporation and condensation, respectively according to operating conditions. Therefore, under electrolyser operating conditions, the heat and mass transfer performance of GDL and especially in GDL-CL interface are investigated. Moreover, the effect of GDL-CL morphology (e.g., pore and throat sizes, and porosity) on heat and mass transport mechanism is investigated in detail.

Droplet dynamic behaviors on gas diffusion layer surface of various wettabilities in a PEMFC gas flow channel

ABSTRACT Droplet dynamic behaviors in a gas flow channel (GFC) of proton exchange membrane fuel cell (PEMFC) with gas diffusion layer (GDL) of various wettabilities are observed by using the volume of fluid (VOF) method in this work. Droplet deformation, detachment, breakup, and multiple droplets coalescence are investigated via an analysis of forces over the droplet. Results show that droplets tend to detach from a hydrophobic GDL surface at a high airflow velocity; while exhibiting significant deformation even breakup on a hydrophilic GDL surface. Besides, the interaction among the pressure force, shear force, wall adhesion force (arising from surface tension), and lift force over the droplet is examined to qualitatively elucidate the droplet dynamic behaviors. It is found that a hydrophobic GDL with a moderate airflow velocity can facilitate water removal from the GFC and maintain a relatively small spreading area; however, too high or too low an airflow velocity can cause a breakup or a slow drainage of the droplet, especially on a hydrophilic GDL surface. Thus, the design and operation of the PEMFC should consider both the wettability of GDL surface and the airflow velocity to achieve effective water management.

Effect of the porosity distribution on the liquid water transport in the gas diffusion layer of PEMFC

Water management significantly influences the life and power output of the proton exchange membrane fuel cell (PEMFC). The gas diffusion layer (GDL) provides key transport paths of reactant gas and liquid water in the PEMFC. This study uses the volume of fluid (VOF) method to numerically investigate the liquid water transport in the GDL with different porosity distributions. The GDL geometry is reconstructed based on the stochastic parameter method. Five GDL structures with different porosity distributions are investigated on the liquid water transport. And different contact angles are defined on the carbon fiber surface and their effect is discussed. The results show that the porosity distribution and contact angle have dramatic influence on the water distribution and saturation in the GDL. The liquid water accumulation tends to occur in the high porosity GDL region. The water saturation is higher and flow rate is lower in the GDL with inverted “V” shaped porosity distribution than “V” shaped porosity distribution. The water saturation and flow rate is smaller when the porosity gradient is greater for both the “V” and inverted “V” shaped porosity, due to fewer water penetration paths. The water saturation in the hydrophilic GDL is higher than in the hydrophobic GDL for all the five porosity distributions.

Study on water transport in hydrophilic gas diffusion layers for improving the flooding performance of polymer electrolyte fuel cells

For hydrogen-based polymer electrolyte fuel cells (PEFCs), water transport control in gas diffusion layers (GDLs) by wettability distribution is useful to suppress the flooding problem. In this study, the water transport of a novel GDL with hydrophilic-hydrophobic patterns was investigated. First, we clarified that the water motion in the hydrophilic GDL with microstructures could be reproduced by the enlarged scale model. The scale model experiment also showed that the same water behavior in hydrophilic GDL can be obtained from Capillary numbers (Ca) in a range of Ca ~ 10−5 to 10−3. As the computational load is inversely proportional to Ca, the computational load could be reduced by 1/100th by using Ca ~ 10−3, which is 100 times higher than PEFC operation (Ca ~ 10−5). Finally, the simulation with Ca ~ 10−3 was performed, and we showed that the GDL with straight region of contact angle 50° minimized the water accumulation.

Enhanced low-humidity performance in a proton exchange membrane fuel cell by developing a novel hydrophilic gas diffusion layer

An ultrathin layer of hydrophilic titanium dioxide (TiO2) is coated on the gas diffusion layer (GDL) to enhance the performance of a proton exchange membrane fuel cell (PEMFC) at low relative humidity (RH) and high cell temperature. Both of the modified and unmodified GDLs are characterized using contact angles, and the cell performance is evaluated at various RHs and cell temperatures. It is found that the modified GDL, which contains a hydrophilic TiO2 layer between the microporous layer (MPL) and the gas diffusion-backing layer (GDBL), exhibits better self-humidification performance than a conventional GDL without the TiO2 layer. At 12% RH and 65 °C cell temperature, the current density is 1190 mA cm−2 at 0.6 V, and it maintains 95.8% of its initial performance after 50 h of continuous testing. The conventional GDL, however, exhibits 55.7% (580 mA cm−2) of its initial performance (1040 mA cm−2) within 12 h of testing. The coated hydrophilic TiO2 layer acts as a mini humidifier retaining sufficient moisture for a PEMFC to function at low humidity conditions.

Transient, spatially resolved desaturation of gas diffusion layers measured via synchrotron visualization

The transient 3-D visualization of the desaturation process of flooded gas diffusion layers (GDLs) is presented for the first time. Desaturation rates and pathways are reported for two commercial GDL samples, one with a PTFE treatment and the other without. On-the-fly Synchrotron X-ray CT is performed while the GDL sample is subjected to a humidified or dry air flow stream to visualize the transient desaturation. The two humidification conditions assist in separating the convective and evaporative components of the desaturation process, showing a slight contribution from the convective effect, while the majority of the desaturation is due to evaporative removal. The convective removal is found to be insufficient to fully desaturate either GDL, with water remaining trapped underneath the channel rib with the more hydrophobic GDL and within the pore space in the more hydrophilic GDL. Stop-and-shoot Synchrotron X-ray computed tomography (CT) is then used in conjunction with program-assisted segmentation to determine initial saturation water volumes. These are then combined with the desaturation times found from the on-the-fly experiments to determine desaturation rates for both GDLs. The desaturation rate using dry air flow for the more hydrophobic GDL is found to be nearly four times faster than that of the more hydrophilic GDL. Results demonstrate that an evaporative contribution is necessary for either GDL sample to reach full desaturation.

Approaching 2 W∙cm-2 AEMFCs through Electrode Engineering and Controlling the Cell Water Content and Balance

In recent years, advances in alkaline exchange membrane fuel cells (AEMFCs) with anion exchange membrane (AEM) solid polymer electrolytes have gained traction due to their distinct – and potentially game-changing – advantages over proton exchange membrane fuel cells. However, AEMs and AEMFCs are at a significantly less mature stage in their developmental than proton exchange membrane fuel cells (PEMFCs), and have experienced limitations specifically in the area of stability, carbonation, and achievable current and power densities, exhibiting a sizable performance gap vs PEMFCs.1 This talk will focus on several fundamental and engineering advances that have enabled the creation of AEMFCs that are able to achieve up to 1.9 W∙cm-2 peak power (> 2 W∙cm-2 iR-corrected) and 100’s of hours of stable operation, bringing AEMFCs much closer to the incumbent PEMFC technology, and opening the way to overcome the cost barrier that has slowed the growth and large scale market implementation of fuel cells in the transportation sector.2 One of the largest contributors to the challenges faced in AEMFCs is the cell water content and balance, where the role of water has an impact on the anode (generation through the hydrogen oxidation reaction), cathode (consumption through the oxygen reduction reaction), and movement from the cathode to anode through electro-osmotic drag. This results in a significantly larger current-driven movement of water than PEMFCs, where less water required for the transport of the protons and there is no electrochemical consumption, and a need to provide adequate water to maintaining proper ionomer and membrane hydration while avoiding catalyst layer flooding or dry-out. Back diffusion of water from anode to cathode in the AEMFC, which is coupled to the membrane conductivity, is a promising way to decrease the extreme water gradient, and simplify the water balance problem in AEMFCs.3 In this study, we will discuss the influence of the membrane, ionomer and gas diffusion layer as well as the flow rate and dew points of the anode and cathode gases on AEMFC performance. Using a hydrophilic gas diffusion layer without a microporous layer increases membrane hydration, but also increases the possibility for flooding. Catalyst layer engineering – through adjusting the carbon/ionomer/catalyst loadings, adjusting hydrophilicity/hydrophobicity, manipulating electrode thickness and porosity, etc. – is investigated. We will also discuss controlling the total amount of water fed to the AEMFC through the gas feeds, as well as the water balance between the anode and cathode. Manipulating the dew points led to the counter-intuitive discovery that the cell performs better with the humidity higher at the anode than the cathode, despite water generation and electro-osmotic drag towards that electrode. In fact, removing too much water from the anode caused instability in the cell, while increasing the water at the anode decreased the membrane resistivity. Water back diffusion from the anode to the cathode likely plays an important role in membrane hydration and hydroxide transport through the membrane. Finally, we will also discuss the behavior of the AEM and powder anionomer in the presence of air both with and without CO2.

Importance of balancing membrane and electrode water in anion exchange membrane fuel cells

Anion exchange membrane fuel cells (AEMFCs) offer several potential advantages over proton exchange membrane fuel cells (PEMFCs), most notably to overcome the cost barrier that has slowed the growth and large scale implementation of fuel cells for transportation. However, limitations in performance have held back AEMFCs, specifically in the areas of stability, carbonation, and maximum achievable current and power densities. In order for AEMFCs to contend with PEMFCs for market viability, it is necessary to realize a competitive cell performance. This work demonstrates a new benchmark for a H2/O2 AEMFC with a peak power density of 1.4 W cm−2 at 60 °C. This was accomplished by taking a more precise look at balancing necessary membrane hydration while preventing electrode flooding, which somewhat surprisingly can occur both at the anode and the cathode. Specifically, radiation-grafted ETFE-based anion exchange membranes and anion exchange ionomer powder, functionalized with benchmark benzyltrimethylammonium groups, were utilized to examine the effects of the following parameters on AEMFC performance: feed gas flow rate, the use of hydrophobic vs. hydrophilic gas diffusion layers, and gas feed dew points.

Improving Performance in Alkaline Membrane Fuel Cells through Enhanced Water Management

Water management in anion exchange membrane fuel cells (AEMFCs) is more complex than proton exchange membrane fuel cells (PEMFCs). In the PEM system, water is generated at the cathode and otherwise only serves as the membrane proton transport medium. In the hydroxide AEMFC, water is generated at the anode, consumed at the cathode, and is greatly needed for transport of the larger hydroxide ion. The challenge this introduces is the need to provide adequate water to maintain the membrane humidity without flooding the catalyst or gas diffusion layers.1 One method being used to achieve the necessary high membrane water content is utilizing hydrophilic gas diffusion layers without microporous layers.2 Others have used gas diffusion layers with a hydrophobic coated microporous layer while raising the temperature of the humidifiers well above the cell temperature.3 Gas stream dew points above 100% relative humidity and back pressure are common approaches in increasing the membrane water content. However there is instability in the cell performance and conditions that generate high performance levels are not easily repeatable. The problem is the line between proper membrane hydration and flooded catalysts layers is very thin, and non-existent in some cases. In this study, the influence of the membrane, ionomer and gas diffusion layer as well as the flow rate and dew points of the anode and cathode gases on AEMFC performance were explored. Tokuyama A201 membranes and AS-4 ionomer were investigated alongside quaternary-ammonium-functionalized radiation-grafted ETFE alkaline anion-exchange membranes and ionomers.4 Using a hydrophilic gas diffusion layer without a microporous layer increased membrane hydration, but as expected increased the potential for flooding. Manipulating the dew points led to the counter-intuitive discovery that the cell performs better with the humidity higher at the anode than the cathode, despite water generation and electro-osmotic drag towards that electrode. In fact, removing too much water from the anode caused instability in the cell, while increasing the water at the anode decreased the membrane resistivity. Back diffusion likely plays an important role in membrane hydration and hydroxide transport through the membrane. A very high flow rate (1.0 L/min) also increased cell performance, despite being several orders of magnitude above the stoichiometric need. Combining all areas of improvement resulted in a very high performing AEMFC with a maximum current density of 2.2 A/cm2 (at 0.1 V) and max power density of 670 mW/cm2 (880 mW/cm2 iR-corrected) with a membrane resistivity of 75 mOhms*cm2 (Figure 1a). Only a minor drop in the current was observed using air at the cathode with the same 1.0 L/min flow rate as oxygen, giving max current density of 1.7 A/cm2 and a max power density of 580 mW/cm2 with a resistivity of 74 mOhms*cm2 (Figure 1b). This near identical behavior confirms that the amount of reactant present supplied by the higher flow rate is not necessary, but the volumetric flow rate is needed for water management. It is likely that the pressure drop along the single pass cell hardware allows the gas to “jump the bar” only at very high flowrates, which results in better water removal and limits cell flooding in the cell.

Improving Performance in Alkaline Membrane Fuel Cells through Enhanced Water Management

Water management is one of the most critical parameters in the production of high performance membrane electrode assemblies for anion exchange membrane fuel cells. In this work, we have systematically studied the influence of the feed gas flow rate, hydrophobic vs hydrophilic gas diffusion layers, the presence of a microporous layer, and humidifier temperature on cell performance. Work was performed using both on standardized Tokuyama products as well as quaternary-ammonium radiation-grafted alkaline anion-exchange membranes and ionomers synthesized by our team.

Advanced Water Management in PEFCs: Diffusion Layers with Patterned Wettability I. Synthetic Routes, Wettability Tuning and Thermal Stability

A novel type of fuel cell gas diffusion layer with patterned wettability is herein reported. The production of hydrophilic patterns by radiation grafting depends on two main steps: electron beam activation and polymerization reaction. In this first part of the series, we are giving extensive details about the synthetic routes for modifying porous media's wettability. Two monomers (acrylic acid and N-vinylformamide) were used for the hydrophilization of the fluoropolymer and a parametric study was performed. Finally, a preliminary thermal degradation study was carried out.We found conditions to produce hydrophilic gas diffusion layers with short reaction times (about 10 minutes) and proved that the synthetic method is suitable for creating local modifications. For hydrophilic surfaces, the coating load significantly impacts wetting dynamics.

A Direct Methanol Alkaline Fuel Cell Based on Poly(phenylene) Anion Exchange Membranes

The Investigation of the performance of poly(phenylene) based anion exchange membranes (AEMs) in a direct methanol fuel cell is reported. The fuel cell performances were tested with different anode gas diffusion layers as a function of concentrations of fuel and electrolyte using two commercially available platinum catalysts supported on carbon. Normalized current density values demonstrated good performance for a poly(phenylene) AEM, with a cation consisting of six methylene spacers attached to a trimethyl ammonium group, with a maximum current density of 11.8 mA cm−2 mg−1 in a KOH free fuel. The platinum catalyst (46%) from Tanaka showed a better performance (10.4 mA cm−2 mg−1) compared to the platinum catalyst from E-TEK (5.1 mA cm−2 mg−1) in 1M methanol fuel feed under identical conditions. We observed that the MEA with a Zoltek gas diffusion layer on the anode showed the best performance (226 mA cm−2 and 53.8 mW cm−2) in the presence of KOH, suggesting that a hydrophilic gas diffusion layer plays a significant role in improving the fuel cell performance. A durability test for a MEA in 1M methanol and 1M KOH for 67 h showed an overall degradation rate of 400 μV h−1.

On the hydrophobicity and hydrophilicity of the cathode gas diffusion layer in a polymer electrolyte fuel cell

An anomaly in the modelling of two-phase flow in the porous cathode gas diffusion layer (GDL) of a polymer electrolyte fuel cell is investigated asymptotically and numerically. Although not commented on previously in literature, the generalized Darcy model used most commonly leads to the surprising prediction that a hydrophilic GDL can lead to better cell performance, in terms of current density, than a hydrophobic one. By analysing a reduced one-dimensional steady-state model and identifying the capillary number as a small dimensionless parameter, we find a potential flaw in the original model, associated with the constitutive relation linking the capillary pressure and the pressures of the wetting and non-wetting phases. Correcting this, we find that, whereas a hydrophilic GDL can sustain a two-phase (gas/liquid) region near the water-producing catalytic layer and gas phase only region further away, a hydrophobic GDL cannot; furthermore, hydrophobic GDLs are found to lead to better cell performance than hydrophilic GDLs, as is indeed experimentally the case.

The performance improvement of membrane and electrode assembly in open-cathode proton exchange membrane fuel cell

An investigation was made to explore the effect of the structural combination of the membrane and electrode assembly (MEA) on the performance improvement of the open-cathode proton exchange membrane (PEM) fuel cell. Two typical MEAs of GDE (gas diffusion electrode) and CCM (catalyst coated membrane) were used, and the results show that the CCM-based MEA could maximize the catalyst utilization under room temperature, and the power density was 818mWcm−2. The employment of hydrophilic gas diffusion layers (GDLs) can further improve the performance of the CCM-based MEA at elevated cell temperature in spite of its high contact resistance and low gas permeation. The variation of cell voltage under different air stoichiometry and cell temperatures was also explored, and the results show that CCM-based MEA with hydrophilic GDLs gives good performance and stability even at 60°C.

Numerical investigation of liquid water transport and distribution in porous gas diffusion layer of a proton exchange membrane fuel cell using lattice Boltzmann method

Lattice Boltzmann method (LBM) is used to investigate liquid water transport and distribution in a porous gas diffusion layer (GDL). The GDL with microscopic porous structures is obtained from three-dimensional reconstruction using the stochastic method, and its macroscopic transport properties including permeability and effective diffusivity are numerically predicted which agree well with the existing experimental results. Simulation results show that liquid water transport mechanism in the GDL is capillary fingering and liquid water pathway is interconnected, which confirms the previous experimental results in literature. Further, effects of GC wettability are explored and it is found out that a hydrophilic GC leads to less liquid water accumulated in the GDL compared with a hydrophobic GC. In addition, effects of GDL wettability on liquid water distribution are explored. Simulation results show that PTFE content itself cannot determine liquid water distribution inside the GDL and detailed distributions of hydrophobic and hydrophilic regions within the GDL also play an import role. Moreover, a hydrophilic GDL is more beneficial for reactant transport than a hydrophobic GDL if liquid water presents as separated droplets or films in the GDL.