Oxygen Diffusion Characteristics of Gas Diffusion Layers With Moisture

2008 ◽  
Author(s):  
Daigo Iwasaki ◽  
Yoshio Utaka ◽  
Yutaka Tasaki ◽  
Shixue Wang
Keyword(s):  
Porous Media ◽  
Liquid Water ◽  
Oxygen Diffusion ◽  
Gas Diffusion ◽  
Vacuum Impregnation ◽  
Impregnation Method ◽  
Moist Air ◽  
Oxygen Diffusivity ◽  
Diffusion Characteristics ◽  
Experimental Apparatus

The mass transfer characteristics of the gas diffusion layer (GDL) in a polymer electrolyte fuel cell (PEFC) are closely related to the performance. In this study, the oxygen diffusivity of paper and cloth type porous media, which are generally used as GDLs, were measured with respect to liquid water content, using experimental apparatus consisting of an oxygen sensor based on a galvanic battery. Paper type porous media, both non treated and hydrophilic treated, and the cloth type porous media with non treated surface were used as GDL specimens. The porosity of both specimens was almost the same, but the representative pore diameter of the cloth type GDL was approximately three times larger than that of paper type GDL. Two methods were utilized to impregnate liquid water into the porous GDL media to realize different water distributions in the specimens at the initial state; vacuum impregnation and moist air condensation impregnation. The oxygen diffusivities of the specimens were measured to clarify the influence of the two impregnation methods on the oxygen diffusion characteristics. Moreover, the relation between the measurement of oxygen diffusivity and the visualization of the liquid water distribution by using Neutron Radiography [Tasaki et al. (2007)] was investigated for the paper and cloth type GDLs. The oxygen diffusivity in the paper type porous media decreased precipitously with increasing water saturation by the vacuum impregnation method, whereas the diffusivity decrease was relatively small when impregnated by the moist air condensation method. For the cloth type porous media with weaving threads, oxygen diffusion characteristics were independent of the water impregnation method. Thus, the porous medium’s microstructure plays an important role in determining diffusion characteristics, especially in the presence of liquid water.

Microporous Layer Consisting of Alternating Porous Material With Different Wettability for Controlling Moisture in Gas Diffusion Layer of PEFC

2010 ◽  
Author(s):  
Yoshio Utaka ◽  
Ikunori Hirose
Keyword(s):  
Porous Media ◽  
Porous Material ◽  
Diffusion Layer ◽  
Oxygen Diffusion ◽  
Water Saturation ◽  
Gas Diffusion Layer ◽  
Gas Diffusion ◽  
Single Type ◽  
Oxygen Diffusivity ◽  
Diffusion Characteristics

The oxygen transfer characteristics of the gas diffusion layer are closely related to the cell performance of a polymer electrolyte fuel cell. In this study, a new hybrid gas diffusion layer is proposed in which two porous media with different wettabilities are arranged alternately for augmentation of the oxygen diffusivity in the gas diffusion layer. Since the movement of water from hydrophobic to hydrophilic media due to the difference in capillary pressure, the oxygen diffusion paths in the porous media can be maintained. The oxygen diffusion characteristics with respect to water saturation were measured using an experimental apparatus that uses a galvanic battery oxygen sensor as an oxygen absorber. The experimental results demonstrate that the hybrid structure has superior oxygen diffusion characteristics than a conventional gas diffusion layer with a single porous material with moisture. That is, the effective oxygen diffusivity of the hybrid configuration was almost five times larger than that of the single type at water saturation S = 0.2.

A FRACTAL MODEL FOR PREDICTING OXYGEN EFFECTIVE DIFFUSIVITY OF POROUS MEDIA WITH ROUGH SURFACES UNDER DRY AND WET CONDITIONS

Fractals ◽  
2021 ◽  
pp. 2150076
Author(s):  
BOQI XIAO ◽  
QIWEN HUANG ◽  
BOMING YU ◽  
GONGBO LONG ◽  
HANXIN CHEN
Keyword(s):  
Porous Media ◽  
Fractal Dimension ◽  
Oxygen Diffusion ◽  
Water Saturation ◽  
Rough Surfaces ◽  
Effective Diffusivity ◽  
Fractal Model ◽  
Relative Roughness ◽  
Oxygen Diffusivity ◽  
Dry And Wet Conditions

Oxygen diffusion in porous media (ODPM) with rough surfaces (RS) under dry and wet conditions is of great interest. In this work, a novel fractal model for the oxygen effective diffusivity of porous media with RS under dry and wet conditions is proposed. The proposed fractal model is expressed in terms of relative roughness, the water saturation, fractal dimension for tortuosity of tortuous capillaries, fractal dimension for pores, and porosity. It is observed that the normalized oxygen diffusivity decreases with increasing relative roughness and fractal dimension for capillary tortuosity. It is found that the normalized oxygen diffusivity increases with porosity and fractal dimension for pore area. Besides, it is seen that that the normalized oxygen diffusivity under wet condition decreases with increasing water saturation. The determined normalized oxygen diffusivity is in good agreement with experimental data and existing models reported in the literature. With the proposed analytical fractal model, the physical mechanisms of oxygen diffusion through porous media with RS under dry and wet conditions are better elucidated. Every parameter in the proposed fractal model has clear physical meaning, with no empirical constant.

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

2020 ◽  
pp. 095765092093431
Author(s):  
Mohammad Habiballahi ◽  
Hasan Hassanzadeh ◽  
Mohammad Rahnama ◽  
Seyed Ali Mirbozorgi ◽  
Ebrahim Jahanshahi Javaran
Keyword(s):  
Porous Media ◽  
Water Transport ◽  
Diffusion Layer ◽  
Liquid Water ◽  
Water Saturation ◽  
Polymer Electrolyte Membrane ◽  
Gas Diffusion Layer ◽  
Gas Diffusion ◽  
Electrolyte Membrane ◽  
Liquid Water Transport

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.

G133 Oxygen Diffusion Characteristics of Gas Diffusion Layer with Moisture

2007 ◽  
Vol 2007 (0) ◽  
pp. 239-240 ◽  
Author(s):  
Yutaka TASAKI ◽  
Shixue WANG ◽  
Yasushi ICHIKAWA ◽  
Denis. Kramer ◽  
Pierre. Boillat ◽  
...  
Keyword(s):  
Diffusion Layer ◽  
Oxygen Diffusion ◽  
Gas Diffusion Layer ◽  
Gas Diffusion ◽  
Diffusion Characteristics

E144 Oxygen Diffusion Characteristics for Wet Gas Diffusion Layer

2006 ◽  
Vol 2006 (0) ◽  
pp. 177-178
Author(s):  
Shixue WANG ◽  
Yoshio UTAKA ◽  
Yutaka TASAKI ◽  
Masanori MOCHIMARU
Keyword(s):  
Diffusion Layer ◽  
Oxygen Diffusion ◽  
Gas Diffusion Layer ◽  
Gas Diffusion ◽  
Wet Gas ◽  
Diffusion Characteristics

Effect of Liquid Water Saturation on Oxygen Transport in Gas Diffusion Layers of Polymer Electrolyte Fuel Cells

2010 ◽  
Author(s):  
Takeshi Shiomi ◽  
Richard S. Fu ◽  
Ugur Pasaogullari ◽  
Yuichiro Tabuchi ◽  
Shinichi Miyazaki ◽  
...  
Keyword(s):  
Fuel Cells ◽  
Water Content ◽  
Polymer Electrolyte ◽  
Liquid Water ◽  
Water Saturation ◽  
Liquid Water Content ◽  
Gas Diffusion ◽  
Polymer Electrolyte Fuel Cells ◽  
Oxygen Diffusivity ◽  
Liquid Saturation

Improved oxygen diffusivity is essential for reducing mass transport losses in polymer electrolyte fuel cells (PEFCs). In this work, effective oxygen diffusivity in the presence of liquid water inside a gas diffusion layer (GDL) was investigated by means of coupled experimental and numerical analyses. In order to control the liquid water content inside the GDL, a temperature gradient method was developed. In a separate experiment liquid water content inside the GDL was measured by neutron radiography (NR) and analyzed by using a two-phase, non-isothermal numerical model. The model accurately reproduced the total liquid water content and was in qualitative agreement with the liquid saturation trend as obtained from the NR experiments, which was utilized to estimate the liquid saturation in the limiting current experiment. Based on the predicted liquid water profile, the dependence of effective oxygen diffusivity on the liquid water saturation is deduced. It is found that the Bruggeman exponent factor is much larger than the predictions from network models and this suggests that the understanding of the relationship between liquid water transport and the GDL local structure is important.

Measurement of Oxygen Diffusion Characteristics of Porous Media Used for the Gas Diffusion Layer of Proton-Exchange Membrane Fuel Cells

2007 ◽  
Author(s):  
Shixue Wang ◽  
Yoshio Utaka ◽  
Yutaka Tasaki
Keyword(s):  
Porous Media ◽  
Diffusion Coefficient ◽  
Experimental Method ◽  
Diffusion Layer ◽  
Oxygen Diffusion ◽  
Proton Exchange Membrane ◽  
Gas Diffusion Layer ◽  
Gas Diffusion ◽  
Proton Exchange ◽  
Exchange Membrane

It is known that the mass transfer characteristics of the gas diffusion layer (GDL) are closely related to the performance of a proton-exchange membrane fuel cell. In this study, an experimental method was established for measuring the gas diffusion coefficient in porous media by using an oxygen concentration sensor based on a galvanic battery operating at normal temperature. The oxygen diffusion coefficient in air measured by this method corresponded with data in the literature within ±6% deviation. The oxygen diffusion coefficients of two kinds of porous media generally used for the GDL were measured by the experimental method for dry and wet samples. The results indicate that the gas diffusion coefficient in porous media not only depends on porosity but is also affected by other factors, for example, tortuosity. It was also found that the diffusion coefficient in different directions, for example, through-plane and in-plane, in porous media can be very different. The oxygen diffusion coefficient in the porous media containing liquid water varied nonlinearly with the saturation level and was strongly affected by other factors as well.

Pore Network Modeling of Oxygen Diffusion in Gas Diffusion Layer of Proton Exchange Membrane Fuel Cells

2009 ◽  
Author(s):  
R. Wu ◽  
X. Zhu ◽  
Q. Liao ◽  
H. Wang ◽  
Y. D. Ding
Keyword(s):  
Diffusion Layer ◽  
Liquid Water ◽  
Oxygen Diffusion ◽  
Water Saturation ◽  
Effective Diffusivity ◽  
Gas Diffusion Layer ◽  
Pore Network ◽  
Gas Diffusion ◽  
Shielding Effect ◽  
Water Permeation

In the present study, a three dimensional pore network, consisting of spherical pores and cylindrical throats, is developed to simulate the oxygen diffusion and liquid water permeation in gas diffusion layer (GDL) in low-temperature fuel cell. Oxygen transport in the throats is described by Fick’s law and liquid water permeation in the network is simulated using percolation invasion algorithm. The effects of heterogeneity of GDL, connectivity of pores, and liquid water saturation on oxygen effective diffusivity are investigated respectively. The simulation results show that the GDL structure has a significant influence on the oxygen and water transport in the GDL. The oxygen effective diffusivity increases with increasing pore connectivity and decreasing heterogeneity. The shielding effect of large throats by smaller ones enhances with increasing heterogeneity of the network. Furthermore, the oxygen transportation is blocked in the presence of liquid water permeation. Thus the oxygen effective diffusivity drops significantly with increasing water saturation.

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