Influence of Wettability on Liquid Water Transport in Gas Diffusion Layer of Proton Exchange Membrane Fuel Cells (Pemfc) (original) (raw)
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Water permeation through gas diffusion layers of proton exchange membrane fuel cells
Journal of Power Sources, 2011
Water transport through gas diffusion layer of proton exchange membrane fuels cells is investigated experimentally. A filtration cell is designed and the permeation threshold and the apparent water permeability of several carbon papers are investigated. Similar carbon paper with different thicknesses and different Teflon loadings are tested to study the effects of geometrical and surface properties on the water transport. Permeation threshold increases with both GDL thickness and Teflon loading. In addition, a hysteresis effect exists in GDLs and the permeation threshold reduces as the samples are retested. Moreover, several compressed GDLs are tested and the results show that compression does not affect the breakthrough pressure significantly. The measured values of apparent permeability indicate that the majority of pores in GDLs are not filled with water and the reactant access to the catalyst layer is not hindered.
Effect of Gas Diffusion Layer Deformation on Liquid Water Transport in Proton Exchange Membrane Fuel Cell, 2014
In this study, a three-dimensional numerical model, based on the volume-of-fluid (VOF) method, was developed to investigate the water transport characteristics in the cathode of a proton exchange membrane fuel cell (PEMFC) taking into account the deformation of the gas diffusion layer (GDL). Simulations are carried out with different inlet flow rates, amount of liquid water in the GDL, positions of water droplet in the flow channel, and contact angles of the GDL and flow channel surfaces. Two mechanisms of liquid water droplet leaving the GDL are observed. One is driven by the surface tension when the gas flow rate is low, whereas the other is driven by the gas flow at high gas flow rates. Meanwhile, the deformation of the GDL and other factors highly influence the water droplet dynamics. Keywords: proton exchange membrane fuel cell, volume of fluid, gas diffusion layer, water transport, deformation
International Journal of Hydrogen Energy, 2012
Loss of hydrophobicity in the gas diffusion layers (GDL) is sometimes suggested as a potential mechanism to explain in part the performance loss of PEMFC. The present study proposes a numerical methodology to analyse this effect by combining pore network modelling (PNM) and performance modelling (PM): the PNM/PM approach. PNM allows simulating the decrease of through-plane gas diffusion coefficient in the GDL as a function of the hydrophobicity loss, which is taken into account through the increase in the fraction of hydrophilic pores in GDL. Then PM based on Darcy equations allows simulating performance loss of PEMFC as a function of gas diffusion decay. This coupling shows that the loss of hydrophobic treatment increases flooding, decreases performance, and increases current density heterogeneities between inlet and outlet of the cell. Interestingly, this degradation is found to be highly non-linear, mainly because of the non-linear influence of the fraction of hydrophilic pores on gas diffusion (this is due to the existence of a percolation threshold associated with the hydrophilic pore sub-network) as well as the non-linear behaviour of electrochemistry with gas diffusion. This study also shows that the loss of hydrophobicity in a GDL is a very suitable candidate to explain performance loss rates that are classically observed during long-term tests. The proposed methodology may also help linking other local properties of components to fuel cell global performance.
Review on microstructure modelling of a gas diffusion layer for proton exchange membrane fuel cells
Renewable and Sustainable Energy Reviews, 2017
A gas diffusion layer (GDL) is the key component in a proton exchange membrane fuel cell (PEMFC), where transportation of reactants and oxidants to electrodes and removal of water from the cell occur. Accurate prediction of the effective transport properties of GDL is important in understanding its effects on PEMFC performance. However, prediction of GDL behavior is challenging because of the complex geometries involved. Hence, microstructure modelling of GDL is highly beneficial in this condition. This article reviews numerous research endeavors that focused on GDL modelling and the parameters that affect the GDL microstructure. This review aims to understand how each parameter affected the GDL performance. The highlighted parameters in this article are fiber diameter, GDL thickness, porosity, and the effect of polytetrafluoroethylene (PTFE).
Two-phase flow processes in cathode catalyst layer are modelled at the pore scale. The effects of hydrophilic and hydrophobic conditions are explored. Diffusivity, available surface area, and oxygen consumption rate are calculated. Final saturation of 0.28 was obtained for contact angle of 150 due to water removal. a b s t r a c t The production of liquid water in cathode catalyst layer, CCL, is a significant barrier to increase the efficiency of proton exchange membrane fuel cell. Here we present, for the first time, a direct three-dimensional pore-scale modelling to look at the complex immiscible two-phase flow in CCL. After production of the liquid water at the surface of CCL agglomerates due to the electrochemical reactions, water spatial distribution affects transport of oxygen through the CCL as well as the rate of reaction at the agglomerate surfaces. To explore the wettability effects, we apply hydrophilic and hydrophobic properties using different surface contact angles. Effective diffusivity is calculated under several water saturation levels. Results indicate larger diffusive transport values for hydrophilic domain compared to the hydrophobic media where the liquid water preferentially floods the larger pores. However, hydro-phobic domain showed more available surface area and higher oxygen consumption rate at the reaction sites under various saturation levels, which is explained by the effect of wettability on pore-scale distribution of water. Hydrophobic domain, with a contact angle of 150, reveals efficient water removal where only 28% of the pore space stays saturated. This condition contributes to the enhanced available reaction surface area and oxygen diffusivity.
Electrochimica Acta, 2009
A pore-network model was developed to study the water transport in hydrophobic gas diffusion layers (GDLs) of polymer electrolyte membrane fuel cells (PEMFCs). The pore structure of GDL materials was modeled as a regular cubic network of pores connected by throats. The governing equations for the twophase flow in the pore-network were obtained by considering the capillary pressure in the pores, and the entry pressure and viscous pressure drop through the throats. Numerical results showed that the saturation distribution in GDLs maintained a concave shape, indicating the water transport in GDLs was strongly influenced by capillary processes. Parametric studies were also conducted to examine the effects of several geometrical and capillary properties of GDLs on the water transport behavior and the saturation distribution. The proper inlet boundary condition for the liquid water entering GDLs was discussed along with its effects on the saturation distribution.
Water transport through porous media and in flow channels of proton exchange membrane fuel cell
2014
Proton exchange membrane (PEM) fuel cell has been known as a promising power source for different applications such as automotive, residential and stationary. During the operation of a PEM fuel cell, hydrogen is oxidized in anode and oxygen is reduced in the cathode to produce the intended power. Water and heat are inevitable byproducts of these reactions. The water produced in the cathode should be properly removed from inside the cell. Otherwise, it may block the path of reactants passing through the gas channels and/or gas diffusion layer (GDL). This deteriorates the performance of the cell and eventually can cease the operation of the cell. Water transport in PEM fuel cell has been the subject of this PhD study. Water transport on the surface of the GDL, through the gas flow channels, and through GDL has been studied in details. For water transport on the surface of the GDL, droplet detachment has been measured for different GDL conditions and for anode and cathode gas flow chan...
Hydrogen, Fuel Cell & Energy Storage, 2016
The produced liquid water in cathode catalyst layer (CCL) has significant effect on the operation of proton exchange membrane fuel cell (PEMFC). To investigate this effect, the transport of oxygen in CCL in the presence of immiscible liquid water is studied applying a two-dimensional pore scale model. The CCL was reconstructed as an agglomerated system. To explore the wettability effects, different contact angles were considered at the surface of agglomerates. The effective diffusivity of oxygen was calculated under different contact angles at various saturation levels. The same effective diffusivity was obtained for hydrophilic and hydrophobic domains at lower saturations, however, at saturation above 0.4, hydrophobic domain provided higher effective diffusivity values. The effect of water coverage at reaction surface areas was investigated. The results showed that, at the saturation of 0.4, the hydrophobic domain with the contact angle of 150 has about 2 times more available surface area, due to different distribution of water phase compared to the hydrophilic domain with the contact angle of 20.
Energy, 2016
In this study, synchrotron X-ray imaging is used to investigate the water transport inside newly developed GDM (gas diffusion medium) in polymer electrolyte membrane fuel cells. Two different measurement techniques, namely in-situ radiography and quasi-in-situ tomography were combined to reveal the relationship between the structure of the MPL (microporous layer), the operation temperature and the water flow. The newly developed MPL is equipped with randomly arranged holes. It was found that these holes strongly influence the overall water transport in the whole adjacent GDM. The holes act as nuclei for water transport paths through the GDM. In the future, such tailored GDMs could be used to optimize the efficiency and operating conditions of polymer electrolyte membrane fuel cells.