Effects of basic gas diffusion layer components on PEMFC performance with capillary pressure gradient

The amount of the liquid water present at the gas diffusion layer (GDL) has an impact on the diffusivity, capillary pressure and the permeability which in turn influences convective and diffusive transport. A prodigious amount of research has been conducted to study and measure the different properties (time of breakthrough and capillary pressure versus saturation) associated with the breakthrough condition. However, most of the reported data ignored the impact of expansion of different components in the set-up (such as tubing) and the condition after the time of breakthrough. The focus of this study is to measure the breakthrough pressure and time of breakthrough and hence determine the liquid water content inside the GDL before the time of breakthrough. The measurements are performed for different samples to study the effect of the thickness and hydrophobic contents. The results show that expansion has significant difference in the determination of water volume inside the GDL.

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A Study on the Bypass Flow in a Gas Diffusion Layer of a PEMFC With Serpentine Flow Channels

ASME 2008 6th International Conference on Fuel Cell Science, Engineering and Technology ◽

10.1115/fuelcell2008-65204 ◽

2008 ◽

Author(s):

Kyoungyoun Kim ◽

Young-Jun Sohn ◽

Minjin Kim ◽

Choong-Won Cho ◽

Won-Yong Lee

Keyword(s):

Pressure Gradient ◽

Diffusion Layer ◽

Current Density ◽

Stokes Equations ◽

Three Dimensional ◽

Gas Diffusion Layer ◽

Gas Diffusion ◽

Bypass Flow ◽

Local Current Density ◽

Local Current

The serpentine channel widely employed in fuel cells has a strong pressure gradient between adjacent channels in specific regions. Due to the pressure gradient, some amount of reactant gas can be delivered to a catalyst layer by convection as well as diffusion processes in a gas diffusion layer (GDL). The enhancement of the convective flow, so-called bypass flow affects performance of a PEMFC since the bypass flow can lead to significant concentration loss at the downstream of the gas channel. The purpose of the present paper is to examine the effect of the bypass flow in the GDL on performance of a PEMFC with serpentine channels. By performing three-dimensional numerical simulation, we have investigated the bypass flow in the GDL and its effects on the distribution of reactant concentration and local current density. Three-dimensional Navier-Stokes equations are solved with the source and sink terms associated with the electrochemical reactions in the fuel cell. Several values of GDL permeability have been tested to see the effects of GDL permeability on the bypass flow for different cathode stoichiometry rate. The present numerical results show that, with increasing GDL permeability, local current density distribution changes significantly and becomes more inhomogeneous.

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A Study on Liquid Water Removal From Gas Diffusion Layer by Pressure Gradient

ASME 2009 7th International Conference on Fuel Cell Science, Engineering and Technology ◽

10.1115/fuelcell2009-85228 ◽

2009 ◽

Author(s):

Jae Wan Park ◽

Kui Jiao ◽

Xianguo Li

Keyword(s):

Pressure Gradient ◽

Diffusion Layer ◽

Liquid Water ◽

Cross Flow ◽

Gas Diffusion Layer ◽

Surface Hydrophobicity ◽

Pem Fuel Cells ◽

Gas Diffusion ◽

Water Removal ◽

Flow Channels

Water removal from the gas diffusion layer (GDL) is crucial for the stable and efficient operation of proton exchange membrane (PEM) fuel cells. The static pressure gradient induced by reactant flow in the flow channel is one of the main driving potential for the liquid water to be drawn from the GDL. In the PEM fuel cells with interdigitated and serpentine flow channels, considerable amount of reactant flows through the GDL due to the pressure gradient between adjacent flow channels. Such pressure gradient and resultant cross flow may also play an important role for the water removal from GDL during operation. In this work, liquid water transport in the GDL is studied numerically to investigate the effect of pressure gradient and the surface hydrophobicity on the water removal from the GDL. The fibrous porous structure of carbon paper is modeled by distributing impermeable cylinders in random directions. Unsteady two phase simulation has been performed utilizing a commercial software FLUENT based on the volume of fluid (VOF) scheme to determine the phase boundary. The permeability of the numerical medium is compared with the experimental measurements in literature resulting in a good agreement. It is shown that the surface hydrophobicity of the fiber is a dominant parameter to initiate the water transport in the GDL for the pressure gradient in typical operating conditions. Cross flow occurring in the serpentine flow channels may be effective to get rid of the liquid water in the gas diffusion layer. Present work may provide useful data to design and optimize the important properties of gas diffusion layer such as permeability and surface hydrophobicity.

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