Determination of the Relationship Between Capillary Pressure and Saturation in PEMFC Gas Diffusion Media

2008 ◽  
Author(s):  
Joshua D. Sole ◽  
Michael W. Ellis
Keyword(s):  
Capillary Pressure ◽  
Liquid Water ◽  
Polymer Electrolyte Membrane ◽  
Catalyst Layer ◽  
Gas Diffusion ◽  
Carbon Cloth ◽  
Electrolyte Membrane ◽  
Diffusion Media ◽  
Capillary Pressures ◽  
The Relationship

This paper describes a method of measuring the relationship between capillary pressure and porous media saturation in the gas diffusion layer (GDL) of a polymer electrolyte membrane fuel cell (PEMFC). Such a relationship is commonly used to model the liquid water flow in the GDL. The method utilized to characterize the GDL behavior mimics the actual transport of liquid water within the GDL by utilizing the actual fluids of interest in a PEMFC cathode (water and air), and by introducing all water from a single face to simulate the water production at the catalyst layer. Other porosimetry methods rely on totally non-wetting or totally wetting fluids to achieve saturation and consequently the resulting capillary pressure measurements must be scaled to the emulate the situation in the PEMFC GDL. Capillary pressure versus saturation curves for two different GDL materials (one paper, one cloth), each with four different bulk loadings of PTFE (0, 10, 20 and 30 wt%), were measured. Results show that the PTFE loading has a relatively small effect on the capillary pressure within the pressure range normally associated with PEMFC water transport. The results also show that carbon cloth based GDL materials require greater capillary pressures than paper materials to achieve significant saturation and that compression has a homogenizing effect on the pore structure and the slope of the capillary pressure – saturation Pc(S) behavior of both materials. Representative curves for the derivative of the Pc(S) function are developed for each type of diffusion media within the appropriate saturation range.

Predicted Liquid Water Saturation in Unstructured Pore Networks Based on PEMFC GDL Porosity Profiles

2010 ◽  
Author(s):  
J. Hinebaugh ◽  
Z. Fishman ◽  
A. Bazylak
Keyword(s):  
Liquid Water ◽  
Water Saturation ◽  
Pore Space ◽  
Polymer Electrolyte Membrane ◽  
Gas Diffusion ◽  
Pore Network Model ◽  
High Porosity ◽  
Pore Networks ◽  
Electrolyte Membrane ◽  
Capillary Pressures

An unstructured, two-dimensional pore network model is employed to describe the effect of through-plane porosity profiles on liquid water saturation within the gas diffusion layer (GDL) of the polymer electrolyte membrane fuel cell. Random fibre placements are based on the porosity profiles of six commercially available GDL materials recently obtained through x-ray computed tomography experiments. The pore space is characterized with a Voronoi diagram, and invasion percolation-based simulations are performed. It is shown that water tends to accumulate in regions of relatively high porosity due to the lower associated capillary pressures. It is predicted that GDLs tailored to have smooth porosity profiles will have fewer pockets of high saturation levels within the bulk of the material.

Graduated Flow Resistance Through a GDL in a Novel PEM Stack

2009 ◽  
Author(s):  
Terry B. Caston ◽  
Kanthi L. Bhamidipati ◽  
Haley Carney ◽  
Tequila A. L. Harris
Keyword(s):  
Fuel Cell ◽  
Polymer Electrolyte Membrane ◽  
Catalyst Layer ◽  
Current Density Distribution ◽  
Pem Fuel Cell ◽  
Bipolar Plate ◽  
Gas Diffusion ◽  
Carbon Paper ◽  
Carbon Cloth ◽  
Electrolyte Membrane

The goal of this study is to design a gas diffusion layer (GDL) for a polymer electrolyte membrane (PEM) fuel cell with a graduated permeability, and therefore a graduated resistance to flow throughout the GDL. It has been shown that using conventional materials the GDL exhibits a higher resistance in the through-plane direction due to the orientation of the small carbon fibers that make up the carbon paper or carbon cloth. In this study, a GDL is designed for an unconventional PEM fuel cell stack, where the reactant gases are supplied through the side of the GDL rather than through flow field channels, which are machined into a bipolar plate. The effects of changing in-plane permeability, through-plane permeability, and thickness of the GDL on the expected current density distribution at the catalyst layer are studied. Three different thicknesses are investigated, and it is found that as GDL thickness increases, more uniform reactant distribution over the face of the GDL is obtained. Results also show that it is necessary to design a GDL with a much higher in-plane resistance than through-plane resistance for the unconventional PEM stack studied.

Predicting Liquid Water Saturation Through Differently Structured Cathode Gas Diffusion Media of a Proton Exchange Membrane Fuel Cell

2012 ◽  
Vol 9 (2) ◽  
Author(s):  
N. Akhtar ◽  
P. J. A. M. Kerkhof
Keyword(s):  
Fuel Cell ◽  
Liquid Water ◽  
Proton Exchange Membrane ◽  
Water Saturation ◽  
Catalyst Layer ◽  
Gas Diffusion ◽  
Proton Exchange ◽  
Diffusion Media ◽  
Exchange Membrane

The role of gas diffusion media with differently structured properties have been examined with emphasis on the liquid water saturation within the cathode of a proton exchange membrane fuel cell (PEMFC). The cathode electrode consists of a gas diffusion layer (GDL), a micro-porous layer and a catalyst layer (CL). The liquid water saturation profiles have been calculated for varying structural and physical properties, i.e., porosity, permeability, thickness and contact angle for each of these layers. It has been observed that each layer has its own role in determining the liquid water saturation within the CL. Among all the layers, the GDL is the most influential layer that governs the transport phenomena within the PEMFC cathode. Besides, the thickness of the CL also affects the liquid water saturation and it should be carefully controlled.

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