Gas Diffusion Layer Design Research Articles

Modeling the Effects of Using Gas Diffusion Layers With Patterned Wettability for Advanced Water Management in Proton Exchange Membrane Fuel Cells

We present a macrohomogeneous two-phase model of a proton exchange membrane fuel cell (PEMFC). The model takes into account the mechanical compression of the gas diffusion layer (GDL), the two-phase flow of water, the transport of the gas species, and the electrochemical reaction of the reactant gases. The model was used to simulate the behavior of a PEMFC with a patterned GDL. The results of the reduced model, which considers only the mechanical compression and the two-phase flow, are compared to the experimental ex-situ imbibition data obtained by neutron radiography imaging. The results are in good agreement. Additionally, by using all model features, a simulation of an operating fuel cell has been performed to study the intricate couplings in an operating fuel cell and to examine the patterned GDL effects. The model confirms that the patterned GDL design liberates the predefined domains from liquid water and thus locally increases the oxygen diffusivity.

Laser-perforated gas diffusion layer for promoting liquid water transport in a proton exchange membrane fuel cell

A laser was used to perforate gas diffusion layer (GDL) that enhances liquid water transport from the electrodes to the gas channels. The generated holes diameter is from 80 to 200 μm, and center-to-center spacing is from 1 to 3 mm. A three-dimensional numerical model, based on a level set method, was built to investigate the water transport characteristics through the perforations with different diameters and spacing. Experiments and simulation results show that there is a better correlation among the diameter, spacing of the perforation and the power density. When the perforation diameter is 100 μm and the perforation pitch is 2 mm, the water transfer effect is the best which enhances the water discharge effectively and avoids the liquid droplets obstructing the gas flow channel at the same time. These results may assist in the design of GDL for water management in the operation of proton exchange membrane fuel cells.

Experimental Investigation and Numerical Determination of Custom Gas Diffusion Layers on PEMFC Performance

The objective of this work is to investigate the design of gas diffusion layer (GDL) for fuel cells that possess specific transport properties. Various types of custom GDLs that have a microporous bilayer (MP) were studied. These GDLs have two different MP layers and a carbon substrate. GDLs with different bilayer MPs designs were tested and the fuel cells performance was investigated. The performance of the fuel cell was measured in-situ with different GDLs at several operating conditions. The pore morphology of the GDLs as well as pore size distribution of the GDLs including the MPs was determined. The data on the pore size distribution including the relationship between tortuosity and porosity was used as model parameters. The experimental data and model predictions confirm that introducing the bilayer MPs on the substrate could improve the transport resistant and increase the performance of PEMFC. The effect of carbon particle size and overall diffusivity also modified the value of MacMullin number and overall thickness of GDL causing the differences in performance and local distributions.

Improving the design of gas diffusion layers for intermediate temperature polymer electrolyte fuel cells using a sensitivity analysis: A multiphysics approach

Intermediate temperature (100–120 °C) polymer electrolyte fuel cells (IT-PEFCs) offer simplified water and thermal management compared to conventional PEFCs, since any water should exist in the vapour phase, allowing for easier removal. The higher operating temperature also facilitates greater temperature differentials between the fuel cell and the surrounding atmosphere, thus easing the thermal management of an IT-PEFC stack. However, the study of IT-PEFC is still a relatively poorly covered field within the literature and thus little information is available on performance characteristics.We therefore present a simple multiphysics model as a quantitative tool for describing the IT-PEFC. This tool is then used to optimise different materials and parameters within an IT-PEFC. Experimental data is presented as a test of the model, and excellent quantitative agreement is demonstrated.Having validated this model, we present a detailed study of the GDL materials in order to understand the influence of different parameters, namely: (i) porosity, (ii) permeability and (iii) electrical conductivity.We report that the optimal porosity for IT-PEFC operation is 40–50%, whereas that the GDL permeability was found to have little impact on the cell performance.Further, we used the model as a design tool: proposing a novel cell design, taking into account the considerable advantages when using a metallic GDL which yielded potential significant improvements in the system efficiency.

Experimental Investigation and Numerical Determination of Custom Gas Diffusion Layers to Understand Water Transports in PEMFC

Water management is an important impact to determine the polymer electrolyte membrane fuel cell (PEMFC) performance. In particular for fuel cell system operation at high humidity conditions and current densities, the proper water management requires good understanding of water transport in the different components of the cell. The gas diffusion layer (GDL) is one of the vital components of PEMFCs that has a variety of functions significant for their overall performance and durability. The GDL is usually a dual-layer carbon based porous substrate and tropically treated with polytetrafluoroethylene (PTFE) to make it hydrophobic in order to avoid liquid water blockage of its internal pores and keep them available for reactant gas transport to the adjacent catalyst layer [1]. When the gas phase is saturated with water vapor, water condensation takes place and resulting liquid water starts to fill the open pores of the GDL and covers the catalyst particles, rendering them electrochemically inactive [2]. The maximum current density is limited by oxygen concentration at the cathode catalyst surface [3]. This value represents the oxygen transport limitation through the GDL. The mass transfer through the GDL may indeed be rate limiting at high current densities when the GDL is saturated with water [4].In this study, the different designs of GDL with the introduction of two micro porous layers were investigated on PEMFC performance through characterization of their materials and structures as shown in Fig. 1. This new design of GDLs has been modified from standard AvCarb GDLs by adding two micro porous layers. Each set has been treated with two different methods in order to provide two different value of diffusivity. Polarization curves were collected at different designs of GDL as shown in Fig. 2. Further, the internal fuel cell resistance was measured by high frequency resistance (HFR) technique at 1000 Hz. Pore size distribution (PSD) data of the different GDLs were reported and analyzed. It is well known that tortuosity (τ) and porosity (ε) are two important parameters to relate free-stream properties with the actual mass transport in GDL [5]. The relationship of tortuosity (τ) and porosity (ε) was measured as the MacMullin number.In addition to these experiments, we present a computational fluid dynamic (CFD) analysis of the PEMFC operation with provided GDL characterization information, specifically the MacMullin number and PSD to compare with experiment data. The CFD prediction of current density distribution and gas/water transports in PEMFC will be used to understand the effect of these new designs of GDL. Acknowledgement This project is supported by the Department of Energy Contract Grant# DE-EE0000471 References M.V. Williams, et al., J Electrochem Soc, 151 (2004) A1173-A1180.U. Pasaogullar,i et al., J Electrochem Soc, 151 (2004) A399-A406.A.A. Kulikovsky, Electrochem Commun, 4 (2002) 845-852.J.T. Gostick, et al., J Power Sources, 173 (2007) 277-290.M.J. Martinez et al., J Electrochem Soc, 156 (2009) B80-B85.

A numerical investigation of the effects of membrane swelling in polymer electrolyte fuel cells

A two-dimensional computational fluid dynamics model of PEM fuel cell is developed by taking into account the electrochemical, mass and heat transfer process occurring in the cathode compartment. Additionally, this model includes the effect of water content in the membrane swelling phenomenon. Several parameters such as gases temperature, inlet velocity and membrane characteristics are too investigated to establish their effect on the PEM fuel cell performance. The membrane water content and the air fraction variation in the gas channel are examined for diverse values of Reynolds number. In particular, the desirable inlet flow for enhancing the performance of the PEM fuel cell is determined by examining membrane water content patterns. The methodology in this study is useful to the control of water management and gas diffusion layer design.

Water dynamics inside a cathode channel of a polymer electrolyte membrane fuel cell

The present study focuses on the investigation of water dynamics inside a polymer electrolyte membrane fuel cell using two different modelling approaches: Eulerian two-phase mixture and volume of fluid interface tracking models. The Eulerian two-phase mixture model has provided overall information of species distribution inside a fuel cell and identified that the liquid water usually accumulates under the land area. The volume of fluid interface tracking model has then been implemented to investigate the emergence of water droplets from the gas diffusion layer into the cathode channel and the subsequent removal of water from the channel. Further, the effects of the location of water emergence in the cathode channel on the dynamic behavior of liquid water have been investigated. The present study shows that the water emerging into the channel near the side walls greatly reduces the surface water coverage of the channel. In order to control the water path into the channel near side walls, a further discussion has been provided that a gas diffusion layer design based on hydrophilic fibres distributed inside a hydrophobic fibre matrix could provide a precisely controlled water path through the gas diffusion layer.

Effect of Gas Diffusion Layer Design on PEM Fuel Cell MEA Water Removal in an Under Humidified Environment

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Effects of cathode gas diffusion layer design on polymer electrolyte membrane fuel cell water management and performance

The effects of a microporous layer (MPL) on performance and water management of polymer electrolyte fuel cells are investigated. The presence of an MPL on the cathode side is found to slightly improve performance, although the voltage gain is less significant than that obtained by wetter reactants. The effect of the MPL on water management depends on the cathode inlet-gas humidity. Differences in water crossover rate are insignificant for wet cathode feed (RH = 75%), while they are significant for dry feed (RH = 25%). A model based on transport resistance of the MPL is proposed to explain the experimental trends observed. Modeling results suggest that the presence of the MPL on the cathode side causes a reduction of the water flux from the cathode catalyst layer to the flow channels, effectively promoting water back diffusion through the membrane. Higher cathode humidity reduces the driving force for water transport from the electrode to the gas channels, also reducing the importance of the water transport resistance due to the presence of the MPL.

Mitigation of Water Management in PEM Fuel Cell Cathodes by Hydrophilic Wicking Microporous Layers

AbstractThis study introduces a novel strategy for enhancing the performance of polymer electrolyte fuel cells at high current densities by means of an advanced gas diffusion layer design. The incorporation of hydrophilic wicking agents into microporous layers of the cathode gas diffusion layer improves water management, thus increasing the maximum power density of polymer electrolyte fuel cells. Ex situ measurements with respect to water and vapour transport, and electrochemical polarisation data provide evidence suggesting that the beneficial effect has to be attributed to enhanced liquid water removal through the microporous layer.

Gas diffusion layer design focusing on the structure of the contact face with catalyst layer against water flooding in polymer electrolyte fuel cell

High humidity must be maintained inside polymer electrolyte fuel cells to achieve high ion conductivity. However, water condensation blocks the diffusion of the reaction gas in the gas diffusion layer under water saturation conditions which are produced by the product water. This effect is known as flooding and causes a sudden drop in the cell voltage. Therefore, advanced water management is required in such fuel cells. Internal water management is generally carried out by making adjustments to the gas diffusion layer. This study reports that the extremely highly flood-resistant gas diffusion layer has been developed, based on simple carbon paper. It was experimentally revealed that flooding is controlled by a gas diffusion layer with a smaller pore-structure facing the catalyst layer and it is one of the governing factors for flooding in the gas diffusion layer.

An X-Ray Tomography Based Lattice Boltzmann Simulation Study on Gas Diffusion Layers of Polymer Electrolyte Fuel Cells

This work reports a feasibility study into the combined full morphological reconstruction of fuel cell structures using X-ray computed micro- and nanotomography and lattice Boltzmann modeling to simulate fluid flow at pore scale in porous materials. This work provides a description of how the two techniques have been adapted to simulate gas movement through a carbon paper gas diffusion layer (GDL). The validation work demonstrates that the difference between the simulated and measured absolute permeability of air is 3%. The current study elucidates the potential to enable improvements in GDL design, material composition, and cell design to be realized through a greater understanding of the nano- and microscale transport processes occurring within the polymer electrolyte fuel cell.

Graphical Estimation of Interfacial Capacitance of PEM Fuel Cells from Impedance Measurements

Graphical methods were used to extract values of constant-phase element (CPE) parameters and interfacial capacitance from the high-frequency part of impedance data collected on a polymer electrolyte membrane (PEM) fuel cell. The impedance data were recorded as a function of current density, time, temperature, backpressure, and flow channel and gas diffusion layer design. The effective capacitance was estimated under the assumption that the CPE behavior could be attributed to two-dimensional (2D) potential and current distributions. The value of the interfacial capacitance was reduced when the cell was operated under dry or flooded conditions. The interfacial capacitance decreased with time over a time scale consistent with the approach to a steady state. In addition to providing insight into physical processes, the parameters obtained from graphical methods can be used for model reduction when regressing impedance data. The methodology presented can be applied to electrochemical systems for which the high-frequency data reveal CPE behavior caused by 2D potential and current distributions.

Current trends in the design of gas-diffusion layers for fuel cells

The fundamental trends in the design of porous materials (composites) used as gas-diffusion layers (GDL) for fuel cells (FC) were examined. It was shown that the evolution of the FC market has made it necessary to develop manufacturing processes for production of GDL with optimum specifications that provide for mass production of GDL at low cost. It was shown that the current design of GDL emerged from the technical region of basic functionality into the space defined by the vectors of modern technologies and economic characteristics.