Transport In Gas Diffusion Layer Research Articles

Improving mass transfer in anion exchange membrane water electrolysis by ordered gas diffusion layer

For tight assembly electrochemical gas evolution devices, such as anion exchange membrane water electrolysis (AEMWE), bubbles blocking gas diffusion layer (GDL) channels is one of the key reasons for cell performance degradation under high current densities. To enhance mass transport in GDLs at high current densities, herein we report a 3D printed Ni GDL (GDL3D print) with straight-through pores and three-dimensional periodic structures. Due to its periodic structures and high hydrophilicity, GDL3D print is more conducive to the rapid escape of bubbles and timely replenishment of water, showing higher mass transfer efficiency and lower ohmic resistance. Therefore, compared with the commercial nickel foam (NF), GDL3D print exhibits better cell performance not only in 1 mol/L KOH solutions but also in pure-water-fed AEMWE, and the cell voltage of AEMWE using GDL3D print as the anode GDL is only 1.8 V at 1 A cm−2. This work provides a useful guidance for GDL design for tight assembly electrochemical gas evolution devices.

Simulation on water transportation in gas diffusion layer of a PEM fuel cell: Influence of non-uniform PTFE distribution

Proton exchange membrane fuel cells (PEMFCs) are promising clean power sources with high energy conversion efficiency, fast startup, and no pollutant emission. The generated water in the cathode can cause water flooding of the catalyst layer (CL), which in turn can significantly decrease the fuel cell performance. To address this significant issue of PEMFC, a new gas diffusion layer (GDL) with non-uniform distribution of PTFE is proposed for water removal from the CL. The feasibility of this new GDL design is numerically evaluated by a Lattice-Boltzmann Method (LBM)-based two-phase flow model. The porous structure of the new GDL design is numerically reconstructed, followed by LBM simulations of the water transport in GDL. Three types of different wetting conditions are considered. It is found that liquid water transported 7.87% more with a single row of wetted solids and 13.36% more with two rows of wetted solids. The results clearly demonstrate that the liquid water can be effectively removed from the GDL by proper arrangement of hydrophilic solids in the GDL.

Pore-scale simulation of two-phase flow and oxygen reactive transport in gas diffusion layer of proton exchange membrane fuel cells: Effects of nonuniform wettability and porosity

Enhancing oxygen transport and reducing water flooding in the gas diffusion layer (GDL) of proton exchange membrane fuel cells are important for improving cell performance. In this study, a pore-scale model based on the lattice Boltzmann method is proposed, which considers two-phase flow, oxygen diffusion and electrochemical reaction in the GDL. The invasion speed of the water into the GDL is determined by the water generation rate and correspondingly the oxygen consumption rate. The model is then adopted to study effects of wettability and porosity distribution on the liquid water saturation, oxygen concentration and current density. The results demonstrate that while reducing the total saturation in the GDL is important, decreasing the local saturation near the microporous layer (MPL)/GDL interface is also crucial for enhancing cell performance. It is found that GDL with locally enhanced hydrophobicity at the MPL/GDL interface or gradually increased porosity from the GDL bottom to the GDL top can improve cell performance. Particularly, by delicately designing the GDL porosity, the current density can be considerably increased by 201%. The developed pore-scale model provides a useful tool for understanding the underlying multiphase reactive transport processes in GDL and designing the microscopic structures of GDL.

Effects of the Structure, Wettability, and Rib-Channel Width Ratio on Liquid Water Transport in Gas Diffusion Layer Using the Lattice Boltzmann Method

Effects of the Structure, Wettability, and Rib-Channel Width Ratio on Liquid Water Transport in Gas Diffusion Layer Using the Lattice Boltzmann Method

Pore network simulations of liquid water and oxygen transport in gas diffusion layers with spatially variable wettability

The wettability modification of the gas diffusion layer has a significant effect on water management in proton exchange membrane fuel cells. Therefore, a three-dimensional regular pore network model is developed to numerically investigate the liquid water and oxygen transport in gas diffusion layer with spatially variable wettability. Four types of hydrophilicity configuration are taken into account: uniform configuration, symmetric graded configuration, positive graded configuration and negative graded configuration. Pore-scale analysis shows that adding hydrophilic elements first enhances liquid-gas transport and then decreases. There is an optimum hydrophilic pore fraction (fc) leading to minimum liquid water saturation and maximum limiting current density in each wettability configuration, and the value of fc is related to wettability configuration and gradient but independent of inlet injection points. In addition, the results reveal that oxygen transport not only depends on total liquid water saturation, but also depends on water distribution. Uniform water distribution in the through-plane direction is helpful for oxygen transport, so the gas diffusion layer with positive graded hydrophilicity configuration obtains the highest limiting current density.

Pore-Scale Modeling of Air–Water Two Phase Flow and Oxygen Transport in Gas Diffusion Layer of Proton Exchange Membrane Fuel Cell

Understanding multiphase flow and gas transport occurring in electrodes is crucial for improving the performance of proton exchange membrane fuel cells. In the present study, a pore-scale model using the lattice Boltzmann method (LBM) was proposed to study the coupled processes of air–water two-phase flow and oxygen reactive transport processes in porous structures of the gas diffusion layer (GDL) and in fractures of the microscopic porous layer (MPL). Three-dimensional pore-scale numerical results show that the liquid water generation rate is gradually reduced as the oxygen consumption reaction proceeds, and the liquid water saturation in the GDL increases, thus the constant velocity inlet or pressure inlet condition cannot be maintained while the results showed that at t = 1,200,000 iterations after 2900 h running time, the local saturation at the GDL/MPL was about 0.7, and the maximum value was about 0.83, while the total saturation was 0.35. The current density reduced from 2.39 to 0.46 A cm−2. Effects of fracture number were also investigated, and the results showed that for the fracture numbers of 8, 12, 16, and 24, the breakthrough point number was 4, 3, 3, and 2, respectively. As the fracture number increased, the number of the water breakthrough points at the GDL/GC interface decreased, the liquid water saturation inside the GDL increased, the GDL/MPL interface was more seriously covered, and the current density decreased. The pore-scale model for the coupled multiphase reactive transport processes is helpful for understanding the mechanisms inside the porous electrodes of PEMFC.

Effect of wettability heterogeneity and compression on liquid water transport in gas diffusion layer coated with microporous layer of PEMFC

This study applied the pseudo-potential Lattice Boltzmann method (LBM) for investigating liquid water transport in the microporous layer (MPL) and gas diffusion layer (GDL) of polymer electrolyte fuel cell. The MPL and GDL reconstruction is performed by using a stochastic method. Unlike previous studies that examined the GDL as two distinct layers of hydrophilic and hydrophobic, this study considered the wettability heterogeneity. In the present study, some of the carbon fibers in the GDL are randomly considered hydrophilic. Moreover, liquid water transport in the compressed and uncompressed GDL with different hydrophilic fibers percentage are compared. The effect of hydrophilic fibers percentage and the compression ratio of the GDL on the liquid water saturation level, the steady-state time, and the formation and growth of droplets in the gas channel (GC) are investigated. The results indicated that more than 10% of hydrophilicity of the fibers lead to the formation of discontinuous water clusters. This phenomenon increased the steady-state time and water saturation level significantly. The simulation showed that compression increased the number of discontinuous water clusters in the GDL. The obtained results demonstrated that the hydrophilic fibers may have positive or negative effects on water transport in the GDL due to their location. In addition, this study indicated that for 10% of hydrophilic fibers with 10% compression, water saturation level and time required to reach steady-state decreased by 5.2% and 22% respectively compared to purely hydrophobic GDL.

Effect of porosity gradient in cathode gas diffusion layer of polymer electrolyte membrane fuel cells on the liquid water transport using lattice Boltzmann method

In this paper, a two-dimensional model has been developed to simulate the liquid water transport in a cathode gas diffusion layer with different porosity gradients in polymer electrolyte membrane fuel cells (PEMFCs). Due to the complexity of porous media, the simulation was carried out by lattice Boltzmann method. According to dimensionless numbers that characterize liquid water transport in porous media, simulation conditions were similar to the liquid water transfer into the gas diffusion layer of PEMFC. Different gas diffusion layers were created randomly by solid circular particles with an average diameter of [Formula: see text] and the numerical code was validated by conducting several tests. The results indicated that capillary force is the main factor in liquid water transport in the gas diffusion layer, while viscous and gravitational forces do not have a significant effect. In addition to improve the water management, the gas diffusion layer should have a positive porosity gradient, i.e. the porosity increases along the thickness. Also, under the same boundary conditions and at the average porosity (0.659), the saturation distribution curves in three porous media were compared including the gas diffusion layer with porosity gradient, the gas diffusion layer with the micro-porous layer, and the gas diffusion layer with uniform porosity. The average liquid water saturation in the gas diffusion layer with the 10% porosity gradient was 20.2% lower than in the gas diffusion layer with uniform porosity and 10.5% lower than the gas diffusion layer + micro-porous layer. Furthermore, upon elevation of the porosity gradient in the gas diffusion layer, the average liquid water saturation in the gas diffusion layer decreased. Specifically, as the porosity gradient rose from 10% to 14% and 18.5%, the average liquid water saturation values decreased to 29.8% and 38.8%, respectively compared with the gas diffusion layer with uniform porosity.

Bibliometric Analysis of the Mass Transport in a Gas Diffusion Layer in PEM Fuel Cells

The growth trend of publications in the field of Proton Exchange Membrane Fuel Cell (PEMFC) was analyzed using bibliometric techniques to the identification of the areas with significant development and the orientations that have guided the research on energy cells. This study extracted the data from Scopus and Web of Science (WoS) databases to compare the bibliometric indicators of the published productions. In spite of bibliometric analysis advantages to knowing about the trends in a study area, this research requires methods to support the investigation process through the selection of a relevant bibliographic portfolio. This study applied the Methodi Ordinatio that provides a new approach to achieve it. A proposed list of the articles ranked by InOrdinatio is presented to compose the final portfolio. The obtained results in the research sub-theme of the Mass Transport in Gas Diffusion Layer (GDL) confirm the complexity in the study area by presenting erratic patterns of exponential growth. United States, China, and Japan are the leading countries on PEMFC publications. These countries have in common a strong spending by the business sector for R&D, and their gross domestic product is greater than 2%.

A two-dimensional numerical study of liquid water breakthrough in gas diffusion layer based on phase field method

Liquid water transport in gas diffusion layer is essential to water management in proton exchange membrane fuel cells. Based on the Phase-field method, the Cahn-Hilliard equation and Navier-Stokes equation are used to capture two-phase interfaces in the cathode of a fuel cell. Two kinds of porous media structures, i.e. regularized porous media and randomly generated porous media based on the quartet structure generation set, are constructed to make the representative two-dimensional geometry of a gas diffusion layer. The effects of contact angle, porosity and temperature on the liquid water breakthrough process are studied, whilst the shape and breakthrough path of the liquid water are successfully captured in the simulation. By regulating the distribution of contact angles, the accumulation of liquid water in a porous medium can be alleviated and the liquid water can be quickly broken out from the gas diffusion layer. The work is helpful for material design and water management of fuel cells.

Water Transport in Gas Diffusion Layer of PEFC with Wettability Distribution in Thickness Direction

Polymer electrolyte fuel cell (PEFC) is promising as a next generation power source for vehicles due to the high efficiency. To make the PEFC commercially competitive, the reduction of the cost is necessary. For the reduction of the cost of PEFC, it is required to increase the maximum current density. Under the high current density operation, the water produced in a catalyst layer (CL) accumulates in a gas diffusion layer (GDL) and the supply of oxygen is suppressed. Therefore, the water transport in the GDL is important to increase the maximum current density of PEFC. To improve the water transport in the GDL, the wettability distribution is important factor. Utaka el al. showed that better cell performance is obtained by forming the hydrophilic region in the hydrophobic GDL because the water transport in the GDL is controlled by the hydrophilic region (1). Similarly, Forner-Cuenca et al. showed that the cell performance is improved by the GDL with the hydrophilic region (2). There are some reports which showed the water transport is improved by the control of the wettability of the GDL. However, these reports are focused on the planer distribution in the GDL and the effect of the wettability distribution in the thickness direction is not clear. For the optimization of GDL structure, it is necessary to clarify the effect of the wettability distribution in the thickness direction. Therefore, in this study, the effect of the wettability distribution in the thickness direction was investigated. To evaluate the water transport in the GDL with the wettability distribution in the thickness direction, a lattice Boltzmann method (LBM) was used (3). Figure 1 shows the simulation domain and boundaries. The size of GDL is 80μm × 80μm × 80μm and the porosity of GDL is 70%. The bottom of the simulation domain is assumed the micro-porous layer (MPL) and it is treated as a solid wall. MPL crack as inlet boundary is set in the MPL. The top of the simulation domain is outlet boundary. The four sides of the simulation domain are solid walls. The contact angle of GDL, MPL and side walls is set 130º. The density of the two-phase in the simulation is set identical to water, ρ = 978kg/m3. The interfacial tension between the two-phase is σ = 6.40×10-2N/m, and liquid and gas viscosities are μL = 4.04×10-4Pa∙s and μG = 2.30×10-5Pa∙s respectively. Figure 2 shows simulation results of water transport in GDL. Figure 2 (a) shows the result for the GDL without the wettability distribution. The contact angle of the GDL is uniform (130 º). Figure 2 (b) shows the result for the GDL with the wettability distribution in the thickness direction. The contact angle from the GDL surface to the depth of 16 μm is 50º and the other regions of the GDL is 130º. In these figures, the water is shown in red. With the water transport in the GDL without the wettability distribution (Fig. 2 (a)), the water was inflowed to the large pore in the center of the GDL (0.32ms). The water was spread in the large pore (0.96ms). After the much water was accumulated in the GDL, the water was reached at the GDL surface (1.9ms). With the water transport in the GDL with the wettability distribution in the thickness direction (Fig. 2 (b)), the water was inflowed to the large pore in the center of the GDL and the water accumulated in the GDL as well as the GDL without the wettability distribution (0.32ms, 0.96ms). When the water was reached at the hydrophilic region in the top of GDL, the water in the GDL was pulled up to the GDL surface and the amount of the water in the center of the GDL was reduced (1.2ms). Compared with the GDL without wettability distribution, the time when the water reached the GDL surface was earlier in the GDL with wettability distribution. Therefore, the water transport in the thickness direction is improved by the wettability distribution in the thickness direction. In the final full paper, the large-scale simulation including the rib and channel will be carried out and the effect of the wettability in the thickness direction will be discussed. Reference (1) Y. Utaka, R. Koresawa, J. Power Sources, 363, 227-233 (2017). (2) A. Forner-Cuenca, J. Biesdorf, V. Manzi-Orezzoli, L. Gubler, T. J. Schmidt, P. Boillat, J. Electrochem. Soc., 163 (13), F1389 (2016). (3) S. Sakaida, Y. Tabe, and T. Chikahisa, J. Power Sources, 361, 133-143 (2017). Figure 1

Water Transport in Gas Diffusion Layer of PEFC with Wettability Distribution in Thickness Direction

To improve the water transport of a gas diffusion layers (GDL) in a polymer electrolyte fuel cell (PEFC), the effect on the wettability distribution in the thickness direction of the GDL was investigated by a lattice Boltzmann method (LBM). Because much water is generally accumulated in the GDL under rib, the water behavior in the GDL under rib was the focus. The result showed the water in the GDL was significantly reduced by the wettability distribution in the thickness direction made by weak and strong hydrophobicity because the water in the lower of GDL was pulled up to the upper of GDL and the water in the upper of GDL was transported into the channel along the weak hydrophobic region. The depth of the weak hydrophobic region from the GDL surface equivalent to about four pores advantageous to reduce the water in the GDL.

An integrated model of the water transport in nonuniform compressed gas diffusion layers for PEMFC

Abstract Water transport in gas diffusion layer (GDL) is a very important issue for high power density Proton Exchange Membrane Fuel Cell (PEMFC). During the GDL and bipolar plate (BPP) assembly process, the water transport behavior is greatly influenced by the nonuniform compression on the GDL, which leads to uneven distribution of the internal mass transport pores. In this study, an integrated model is developed to predict the water transport in nonuniform compressed GDL. Firstly, a GDL compression deformation model is built to obtain the relationship between the GDL deformation and assembly clamping force based on energy method. Then, a water transport model is established by considering the probability density function (PDF) of the pore size for the compressed GDL. The accuracy of the integrated model has been verified by comparing with the finite element method (FEM) and the computational fluid dynamics (CFD) simulation results. The influence of assembly clamping force, GDL thickness and channel geometry are analyzed based on the integrated model. Drainage pressure increases monotonically with the assembly clamping force and is divided into three stages. For the baseline case, 0.2 mm of GDL thickness and small rib-channel ratio is conducive to improving drainage capacity. It provides the guidance for matching of GDL/BPP assembly condition and performance prediction of PEMFC.

Hysteresis of output voltage and liquid water transport in gas diffusion layer of polymer electrolyte fuel cells

The hysteresis of PEM fuel cell output voltage of the single cell and multi-cell stack is presented by experiments, during which the in-situ liquid water visualization at certain point of gas channel, quantitative measurement of the RH (relative humidity) and HFR (high frequency resistance) by EIS (electrochemical impedance spectroscopy) were carried out. It is found that HFR makes little contribution to the hysteresis of voltage. Instead, the hysteresis of liquid water saturation s in GDL is believed to dominant this process. Although the hysteresis of capillary pressure of liquid water in GDL has already been the presented in previous works, it is for the first time that a simplified one-dimensional model on liquid water saturation is updated considering this effect to understand the possible relation between them. Two different liquid water saturation s distributions during imbibition and drainage are obtained by simulation and related hypothesis of different water morphology in GDL is proposed. Furthermore, according to the simulation results, the GDL consisting of material with high resistance to water penetrating is found to have the better performance in the flooding condition, but weak capability to maintain residual water during drainage of PEM fuel cell.

Durability Failure Analysis of Proton Exchange Membrane Fuel Cell and Its Effect on Oxygen Transport in Gas Diffusion Layer

The poor durability of proton exchange membrane fuel cells still is their greatest barrier preventing commercialization. In this paper, we perform a 1465 h in situ durability test with a single fuel cell operating at a constant-current of 800mA cm−2. Polarization curves, cyclic voltammetry, and electrochemical impedance spectroscopy are used for diagnostics and to understand changes in performance during the test. Limiting current method is used to analyze the oxygen transport resistance of the gas diffusion layer (GDL) before and after durability test. The results indicate that the oxygen transport resistance in single cell increases greatly, and GDL is the first component leading to fuel cell failure after1465h test. At 150 kPa and 20% dry oxygen mole fraction, the limiting current decreases to about 700mA cm−2 and total oxygen transport resistance increases by 0.1623s cm−1, implying more serious flooding occurs in GDL after the 1465 h durability test. The increase of oxygen transport resistances of the substrate and micro porous layer of GDL confirm the loss of water management capability of GDL. SEM images show that these may be caused by oxidation of carbon and loss of polytetrafluoroethylene in GDL.

Study on PEFC Gas Diffusion Layer with Designed Wettability Pattern Tolerant to Flooding

For reduction of the cost of a polymer electrolyte fuel cell (PEFC), it is desired to increase the maximum current density. Under high current density operation, it is important to control water drainage for smooth supply of oxygen. A gas diffusion layer (GDL) which is placed between separator and CL plays an important role for the water transport. Therefore, the improvement of GDL design is important to increase the maximum current density. Recently, there is a report which shows that better cell performance was obtained using the GDL with designed hydrophobic and hydrophilic lines (1). However, the water transport in the GDL is still unclear because the detail observation of liquid water behavior in GDL is difficult due to the quite complex structure and the very small pores (pore diameter: approximately 10 mm). Therefore, there is some room for improving the GDL structure. The objective of this study is to investigate the water transport in GDL with designed wettability pattern and to develop the ideal GDL. To evaluate the water transport in the GDL, a lattice Boltzmann method (LBM) is applied. The LBM is a simulation method to analyze the fluid behavior by tracking movements of large number of particle ensembles. The particle density is expressed by distribution functions, and the distribution functions are calculated by a simple law of collision and transition ensuring the continuity equation and the Navier-Stokes equations for incompressible fluids. Due to the simplicity of the algorithm, it has an advantage of adaptability for complex boundary geometries. Therefore, the LBM is suitable model to simulate the water behavior in the GDL. For high speed calculation, the LBM treating two-phases as having the same density is applied in this study although the densities of air and water are very different. The applicability of this LBM model for the simulation in GDL has been confirmed in the previous study (2). The density of the two-phase in the simulation is set identical to water, ρ = 978kg/m3. The interfacial tension between the two-phase is σ = 6.40×10-2N/m, and liquid and gas viscosities are μL = 4.04×10-4Pa∙s and μG = 2.30×10-5Pa∙s respectively. Figure 1 shows the simulation domain and boundaries. The lower half of simulation domain is GDL layer, on which rib and channel space are placed. Size of GDL is 240μm × 240μm × 100μm and the porosity of GDL is 75%. Sizes of rib and channel are both 120μm × 240μm × 160μm. The bottom of the simulation domain is assumed the micro-porous layer (MPL) and it is treated as a solid wall. Commonly, much water stays in the GDL region under rib. Therefore, to focus on the water behavior in GDL under rib, MPL crack as inlet boundary is set at MPL under rib. Top of the channel is outlet boundary. Four side boundaries are solid walls. The contact angle of GDL, MPL and side walls is set 130º. The contact angle of rib is set 50º. Figure 2 shows simulation results of water transport in GDL without designed wettability pattern. In the simulation, the water is transported randomly and water spreads in the x-y plane of GDL. Finally, the water is drained to channel from pores which is slightly away from the rib. Figure 3 shows simulation results of water transport in GDL with designed wettability pattern. The pattern is set in the center of GDL structure and the size is 50μm × 240μm × 100μm. The contact angle of designed wettability pattern is 50º. Here, the GDL structure is same as Fig. 2. In the simulation, the water is accumulated in the designed wettability pattern of GDL and the smooth water transport from the GDL region under rib to the GDL region under channel is achieved. It is known that water tends to retain in the GDL under ribs and smooth removal of the water is important to avoid flooding. In Ref. (1), it seems that the cell performance using the GDL with designed wettability pattern was improved by the smooth water transport from GDL under rib to GDL under channel. In the final full paper, the effect of the structural characteristics of the GDL such as the contact angle of the pattern and the pore distributions will be discussed. Figure 1

Study on wettability effect in water transport in gas diffusion layer of PEFC by scale model experiment and LBM simulation

Study on wettability effect in water transport in gas diffusion layer of PEFC by scale model experiment and LBM simulation

Large Scale LBM Simulation of Condensed Water Transport in Gas Diffusion Layer and Separator of Polymer Electrolyte Fuel Cell

Large Scale LBM Simulation of Condensed Water Transport in Gas Diffusion Layer and Separator of Polymer Electrolyte Fuel Cell

Using Orthorhombic Lattice Boltzmann Model to Research the Liquid Transport in Gas Diffusion Layer with Different Micro Porous Layer Coated

Using Orthorhombic Lattice Boltzmann Model to Research the Liquid Transport in Gas Diffusion Layer with Different Micro Porous Layer Coated

Study on wettability effect in water transport in gas diffusion layer of PEFC by scale model experiment and LBM simulation

Study on wettability effect in water transport in gas diffusion layer of PEFC by scale model experiment and LBM simulation