Gas Diffusion Layer Intrusion Research Articles

Ex-Situ Investigation of Membrane Swelling in an Electrolyzer Using X-Ray Tomography

In this contribution, we focus on the membrane swelling of a catalyst coated Nafion© 212 in the compound of a polymer electrolyte membrane electrolyzer. So far, the swelling of the catalyst coated membrane (CCM) is mostly investigated isolated from the surrounding components as porous transport layers (PTL) and the flow field plates[1-4]. To explore the swelling, ex-situ tests were carried out, using a special device [5] to control contact pressure and compression and computer tomography. This allowed the swelling of the CCM to be studied at different positions in the structure and at different compression pressures as well as the interaction of the different components. Figure 1 shows a comparison of the dry (a) and (c) and flooded (b) and (d) state of the CCM. The black lines indicate the surface of the CCM. In the flooded state, the thickness of the CCM increases by 20 % from about 50 µm to 60 µm, while the distance of the expanded metal sheets stays constant. This means, that the thickness increase of the CCM results in a decrease of at least one PTL thickness. One main goal of the experiment was to show, whether the swelling of the membrane is dependent or independent of the compression pressure and therefore may cause a different water uptake, which might give an explanation of the decreasing high frequency resistance with increasing pressure [4, 6].[1] Ito, H., Maeda, T., Nakano, A., & Takenaka, H. (2011). Properties of Nafion membranes under PEM water electrolysis conditions. International journal of hydrogen energy, 36(17), 10527-10540[2] Budinski, M. K., & Cook, A. (2010). Osmotic pressure of water in Nafion®. Tsinghua Science & Technology, 15(4), 385-390[3] Kusoglu, A., Kienitz, B. L., & Weber, A. Z. (2011). Understanding the effects of compression and constraints on water uptake of fuel-cell membranes. Journal of the Electrochemical Society, 158(12), B1504[4] Borgardt, E., Giesenberg, L., Reska, M., Müller, M., Wippermann, K., Langemann, M., Lehnert, W., & Stolten, D. (2019). Impact of clamping pressure and stress relaxation on the performance of different polymer electrolyte membrane water electrolysis cell designs. International journal of hydrogen energy, 44(42), 23556-23567[5] Hoppe, E., Janßen, H., Müller, M., & Lehnert, W. (2021). The impact of flow field plate misalignment on the gas diffusion layer intrusion and performance of a high-temperature polymer electrolyte fuel cell. Journal of Power Sources, 501, 230036[6] Stähler, M., Stähler, A., Scheepers, F., Carmo, M., Lehnert, W., & Stolten, D. (2020). Impact of porous transport layer compression on hydrogen permeation in PEM water electrolysis. International journal of hydrogen energy, 45(7), 4008-4014 Figure 1

Porous media flow field for polymer electrolyte membrane fuel cell: Depression of gas diffusion layer intrusion, deformation, and delamination

Porous media flow fields have received a growing attention for polymer electrolyte membrane (PEM) fuel cell application due to their multiple benefits, including enhancements in thermal removal, electron conduction, and two-phase flow control. This study numerically investigates the intrusion of the gas diffusion layer (GDL) into the gas flow channel (GFC) and potential delamination at the GDL and microporous layer (MPL) interface upon land compression and evaluates their depressions by adoption of the porous media flow field. Finite element simulation is conducted to predict the GDL deformation and stresses for both porous media and traditional hollow GFCs. The model predictions are compared with other literature data of GDL intrusion/deformation for traditional hollow GFCs. The results show that GDL intrusion may significantly reduce the GFC space and GDL deformation causes a large spatial variation of porosity and permeability of traditional GFCs. Adoption of the porous media GFCs significantly depresses the GDL intrusion and deformation and hence the porosity/permeability spatial variation. In addition, the shear and tensile stresses at the GDL-MPL interface are evaluated, which are major causes for delamination. It is found that both compressive and tensile stresses may be induced by assembly pressure for traditional GFCs. The shear stress can be significantly depressed and tensile stress can be avoided by porous media GFCs, thereby mitigating the risk of GDL/MPL delamination.

The impact of flow field plate misalignment on the gas diffusion layer intrusion and performance of a high-temperature polymer electrolyte fuel cell

Tolerances in the production process of flow field plates for polymer electrolyte fuel cells (PEFCs) and the assembly of single cells and stacks can lead to a misalignment among the flow field plates. Due to clamping and misalignment, shear stresses can be forced on the membrane electrode assembly (MEA). Furthermore, the gas diffusion layer (GDL) intrudes into the channel. In this study, five different degrees of misalignment (0 to 1000μm) are applied to a fuel cell model consisting of two flow field plates with five adjacent channels each (1 mm width) and an MEA in between them. For each degree, the MEA is compressed by about 30% and 3D images (tomograms) are recorded using an X-ray computer tomograph (CT). Analyzing the cross-section of the channels, the maximum intrusion depth varies for each channel. Furthermore, the shape of the membrane becomes ever more wavelike, with increasing misalignment and the position of the maximum intrusion depth shifts sideways from the center of the channel. Additionally, high-temperature polymer electrolyte fuel cell (HT-PEFC) single cell experiments are carried out. Two degrees of misalignment are set (normal assembly and 1000μm). The performances of both degrees of misalignment are within 5% at a power density of 0.24 W.cm−2.

Effect of anisotropic structure of gas diffusion layer on the cathode dead-end mode of polymer electrolyte membrane fuel cells for the submarine

Experimental and numerical studies of the effects of an anisotropic gas diffusion layer (GDL) on the performance of a dead-end fuel cell system were carried out. The performance of a dead-end mode fuel cell system with aligning the machine direction of an anisotropic GDL in parallel (0o GDL) and perpendicular (90o GDL) direction to the main flow direction of the channel was examined. First, the deformation and intrusion of 0o and 90o GDLs were compared. Then, the permeability of each GDL under the rib part was measured. Using measured values, a model to analyze the current density distribution within the cell was developed. Lastly, the performance of the dead-end mode fuel cell was analyzed using both GDLs. The performance of the fuel cell improved by 3.6 % when the 90o GDL was introduced to the dead-end mode fuel cell compared with that of the 0o GDL. Moreover, the purge interval of the 90o GDL was 1.7 times longer than that of the 0o GDL. Therefore, the cell performance and utilization of fuel improve when the 90o GDL was introduced to the dead-end fuel cell system.

Effects of assembly pressure on PEM fuel cell performance by taking into accounts electrical and thermal contact resistances

In this paper, a three-dimensional multiphase model of the polymer exchange membrane (PEM) fuel cell is simulated to study the effect of assembly pressure on the contact resistance between the gas diffusion layer (GDL) and bipolar plate (BP) interface. The results reveal that the increase of assembly pressure is associated with a decrease in the contact resistance between the GDL and BP interface, which results in reaching an ideal fuel cell performance. The performance improves until the assembly pressure of 4.5 MPa and it slightly drops with a clamping pressure of 5.5 MPa in the ohmic loss region of the polarization curve. Additionally, the variation of the electrical field in a cross-section of the channel length shows that the intrusion of GDL into the flow channel increases with increasing assembly pressure; consequently, the maximum electrical current will increase. The cell temperature rises at higher assembly pressure when considering the thermal contact resistance. This increase is higher on the cathode side because of the existence of the reaction heat source. Additionally, it is found that the distribution of electrical potential and oxygen concentration is more uniform at higher clamping pressure. This results in the development of the PEM fuel cell life cycle.

Thermal and electrochemical performance analysis of a proton exchange membrane fuel cell under assembly pressure on gas diffusion layer

In this study, the effect of clamping pressure on the performance of a proton exchange membrane fuel cell (PEMFC) is investigated for three different widths of channel. The deformation of gas diffusion layer (GDL) due to clamping pressure is modeled using a finite element method, and the results are applied as inputs to a CFD model. The CFD analysis is based on finite volume method in non-isothermal condition. Also, a comparison is made between three cases to identify the geometry that has the best performance. The distribution of temperature, current density and mole fraction of oxygen are investigated for the geometry with best performance. The results reveal that by decreasing the width of channel, the performance of PEMFC improves due to increase of flow velocity. Also, it is found that intrusion of GDL into the gas flow channel due to assembly pressure deteriorates the PEMFC performance, while decrease of GDL thickness and GDL porosity have smaller effects. It is shown that assembly pressure has a minor effect on temperature profile in the membrane-catalyst interface at cathode side. Also, assembly pressure has a significant effect on ohmic and concentration losses of PEMFC at high current densities.

Effect of Gdl(+MPL) Compression on the PEM Fuel Cell Performance

Two components of the PEM fuel cells play a critical role in obtaining a good performance, namely the gas diffusion layer (GDL) and the micro porous layer (MPL). The target of the reported investigation was the influence of the required gas diffusion layer compression, during stack assembly, onto PEM fuel cell performance. For developing a fuel cell it is necessary to assembly all the components together in order to ensure a good connection and to reduce the leakage problem, and this is done under a compression load. The compression applied can deform the GDL and modify its thickness, porosity, hydrophobicity and electrical resistance, and these can result in damaging or decreasing the performance of the PEM fuel cell. Also, the GDL may intrude in the flow field channels and can lead in significant disturbance of the reactants flow in the channels and consequently to a drop in the performance. Numerical simulations based on ANSYS software were carried out in order to investigate the effect of the clamping force on the fuel cell performance. Therefore, 4 geometries were considered in our study, by taking into account the uncompressed and compressed GDL and the presence or absence of MPL. Different levels of GDL compression and intrusion were considered and simulated. The 3D multiphase model revealed that the GDL compression and intrusion influence the in-plane gradient in liquid saturation, oxygen concentration, membrane water content, and especially current density profiles. Also, our study showed that inserting a micro porous layer between catalyst layer and GDL can lead to an improvement of the cell performance because it helps ensuring a good water management, reducing liquid saturation.

Effect of Gdl(+MPL) Compression on the PEM Fuel Cell Performance

Numerical simulations based on ANSYS Fluent software were carried out in order to investigate the effect of the clamping force and MPL addition on the fuel cell performance. The influence of the required gas diffusion layer (GDL) compression, during assembly process, onto fuel cell performance is investigated by considering four cases (0%, 15.7 %, 31.5%, 47.4%) and the optimum compression ratio was obtained (31.5%). The study revealed that the GDL compression and intrusion into the channels affect the fuel cell performance and some aspects related to its influence on liquid saturation are presented. Then, our study analyzed the role of the micro porous layer (MPL) inserted between catalyst layer (CL) and GDL and it found that an improvement in the cell performance can be achieved since it can help to reduce the ohmic and the concentration polarization losses.

An engineering approach to optimal metallic bipolar plate designs reflecting gas diffusion layer compression effects

GDL (Gas diffusion layer) intrusion into gas feeding channels narrows the effective channel cross-sectional area and eventually results in performance degradation of PEFCs (polymer electrolyte fuel cells). Therefore, cross-sectional channel design of metallic bipolar plates should be optimized to resolve this problem. In this study, effects of the cross-sectional configuration of metallic gas channels on pressure drops are numerically investigated for the comprehensive fluid dynamic analysis of channel flow. Multi-physics numerical systems combining solid mechanics and fluid dynamics are applied to figure out the GDL behavior. First, static structural analysis is performed to determine elastic deformation of GDLs under clamping forces. Subsequently, computational flow analysis in the deformed regions is conducted to visualize flow patterns and estimate corresponding pressure drops. Four cross-sectional parameters are selected: channel to rib width ratio, draft angle, inner fillet radius and clamping pressure. Results are validated against experimental data. The GDL intrusion is found to be greatly affected by draft angle and channel to rib ratio. Cross-sectional area is reduced down to 45% in the most shrunk channel, leading additional pressure drop of 0.12 bar. It is suggested that fluid dynamics should be combined with solid mechanics for better accuracy in computational fuel cell modeling.

A numerical investigation of the effects of GDL compression and intrusion in polymer electrolyte fuel cells (PEFCs)

The purpose of this work is to numerically investigate the effects of non-uniform compression of the gas diffusion layer (GDL) and GDL intrusion into a channel due to the channel/rib structure of the flow-field plate. The focus is placed on accurately predicting two-phase transport between the compressed GDL near the ribs and uncompressed GDL near the channels, and its associated effects on cell performance. In this paper, a GDL compression model is newly developed and incorporated into a comprehensive three-dimensional, two-phase PEFC model developed earlier. To assess solely the effects of GDL compression and intrusion, the new fuel cell model is applied to a simple single-straight channel fuel cell geometry. Numerical simulations with different levels of GDL compression and intrusion are carried out and simulation results reveal that the effects of GDL compression and intrusion considerably increase the non-uniformity, particularly, the in-plane gradient in liquid saturation, oxygen concentration, membrane water content, and current density profiles that in turn results in significant ohmic and concentration polarizations. The present three-dimensional GDL compression model yields realistic species profiles and cell performance that help to identify the optimal MEA, gasket, and flow channel designs in PEFCs.

Optimum design of the slotted-interdigitated channels flow field for proton exchange membrane fuel cells with consideration of the gas diffusion layer intrusion

The design of the flow field greatly affects the flow distribution and the final performance of the proton exchange membrane fuel cell (PEMFC) system. The clamping force between the gas diffusion layer (GDL) and the flow field plate (FFP) will cause the inhomogeneous compression of the GDL. Then the GDL will be intruded into the reactant gas channels and eventually change the flow distribution. This paper presents a study on the effect of the intrusion of the GDL on the flow field in a PEMFC, and tries to explain the reason for poor performance of the previous design of the flow field other than those have been studied in other papers such as GDL roughness, porosity, etc. First of all, a linear analytical model is used to analyze the sensitivities of the flow field to the GDL intrusion, and then used to estimate the effect of the GDL intrusion on the flow field distribution. Secondly, a multi-objective optimization model is proposed to eliminate the nonuniform distribution in the flow field with the GDL intrusion taken into consideration. Subsequently, three different designs are analyzed and compared with each other as a demonstration to show the effect of the GDL intrusion. From the analysis results, it is recommended that the effect of the GDL intrusion on the multi-depth flow field should be taken into consideration and the flow field should be insensitive to the GDL intrusion to obtain high robust performance. The results obtained in the study provide the designer some useful guidelines in the concept design of flow field configurations.

Analytical model of flow maldistribution in polymer electrolyte fuel cell channels

Gas–liquid, two-phase flow through channels of a polymer electrolyte fuel cell (PEFC) is of great interest as reactant oxygen is supplied and liquid product water is removed via these PEFC channels. Gas diffusion layer (GDL) intrusion in the channels, which is inherent to the process of PEFC cell and stack assembling, increases the local flow resistance in the intruded channels and consequently lowers their flowrates. This flow maldistribution renders the intruded channels more susceptible to liquid water accumulation or flooding. A one-dimensional analytical model is developed in this work to elucidate the two-phase flow maldistribution in PEFC channels resulting from GDL intrusion. Relative humidity (RH) and the stoichiometric flow ratio of inlet gases are found to be the two key parameters controlling the flow maldistribution in PEFC channels. Interestingly, our analysis shows that decreasing the inlet RH worsens flow maldistribution. As GDL intrusion in channels is inevitable, a good flow-field design must be inherently tolerable to flow maldistribution. Using the analytical model presented herein, the number of flow channels and their U-turns are optimized to minimize the detrimental effect of GDL intrusion.

Uneven gas diffusion layer intrusion in gas channel arrays of proton exchange membrane fuel cell and its effects on flow distribution

Intrusion of the gas diffusion layer (GDL) into gas channels due to fuel cell compression has a major impact on the gas flow distribution, fuel cell performance and durability. In this work, the effect of compression resulting in GDL intrusion in individual parallel PEMFC channels is investigated. The intrusion is determined using two methods: an optical measurement in both the in-plane and through-plane directions of GDL, as well as an analytical fluid flow model based on individual channel flow rate measurements. The intrusion measurements and estimates obtained from these methods agree well with each other. An uneven distribution of GDL intrusion into individual parallel channels is observed. A non-uniform compression force distribution derived from the clamping bolts causes a higher intrusion in the end channels. The heterogeneous GDL structure and physical properties may also contribute to the uneven GDL intrusion. As a result of uneven intrusion distribution, severe flow maldistribution and increased pressure drop have been observed. The intrusion data can be further used to determine the mechanical properties of GDL materials. Using the finite element analysis software program ANSYS, the Young's modulus of the GDL from these measurements is estimated to be 30.9 MPa.

Two-Phase Flow Maldistribution and Mitigation in Polymer Electrolyte Fuel Cells

Flow maldistribution among polymer electrolyte fuel-cell (PEFC) channels is of concern because this leads to nonuniform distributions of fuel and oxidizer, which in turn result in nonuniform reaction rates in the catalyst layers and thus detrimentally affect PEFC performance and durability. Channels with low flow rates risk flooding by liquid water. This can cause catalyst support corrosion and hence the undesirably accelerated aging of PEFCs. Multiphase flow computations are performed to examine the effects of gas diffusion layer (GDL) intrusion and manifold design on reducing flow maldistribution. Velocity field, hydrodynamic pressure, and liquid saturations are computed in the parallel gas channels using the multiphase-mixture formulation in order to quantify the flow nonuniformity or maldistribution among PEFC channels. It is shown that, when channel flow is in single phase, employing two splitter plates in the header manifold can bring down the flow maldistribution to less than half of that for the case with 20% area maldistribution due to the GDL intrusion. When channel flow occurs in the two-phase regime, the liquid-water front can be pushed downstream and the effect of GDL intrusion on the maximum liquid saturation can be decreased by more than one-third by using flow splitters.

A numerical study of flow crossover between adjacent flow channels in a proton exchange membrane fuel cell with serpentine flow field

The focus of this paper is to study the flow crossover between two adjacent flow channels in a proton exchange membrane (PEM) fuel cell with serpentine flow field design in bipolar plates. The effect of gas diffusion layer (GDL) deformation on the flow crossover due to the compression in a fuel cell assembly process is particularly investigated. A three-dimensional structural mechanics model is created to study the GDL deformation under the assembly compression. A three-dimensional PEM fuel cell numerical model is developed in the aforementioned deformed domain to study the flow crossover between the adjacent channels in the presence of the GDL intrusion. The models are solved in COMSOL Multiphysics—a finite element-based commercial software package. The pressure, velocity, oxygen mass fraction and local current density distribution are presented. A parametric study is conducted to quantitatively investigate the effect of the GDL’s transport related parameters such as porosity and permeability on the flow crossover between the adjacent flow channels. The polarization curves are also examined with and without the assembly compression considered. It is found that the compression effect is evident in the high current density region. Without considering the assembly compression, the fuel cell model tends to over-predict the fuel cell’s performance. The proposed method to simulate the crossover with the deformed computational domain is more accurate in predicting the overall performance.

Inhomogeneous compression of PEMFC gas diffusion layer: Part I. Experimental

This paper presents a study on the effect of inhomogeneous compression of gas diffusion layer (GDL) caused by the channel/rib structure of flow-field plate. The experimentally evaluated properties are GDL intrusion into the channel, gas permeability, in-plane and through-plane bulk electric conductivities, and contact resistances at interfaces as a function of compressed thickness of GDL. It was found that the GDL is compressed very little under the channel whereas GDL under the rib is compressed to gasket thickness. The compression of GDL reduces gas permeability and contact resistance, and improves bulk conductivity. Hence, the inhomogeneous compression of GDL may lead into significant local variation of mass and charge transport properties in the GDL. These effects have been ignored in most of the published modeling studies. This contribution, part I, covers the experimental setup and measurement results, and a model which takes the inhomogeneous compression of GDL into account is presented in part II.