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Research Papers

Development of Porous Electrode Gas Diffusion Layers for Proton Exchange Membrane Fuel Cells

[+] Author and Article Information
Dinçer Yakisir

Center for Applied Research on Polymers and Composites (CREPEC), Department of Chemical Engineering, Laval University, QC, G1K 7P4, Canada

Frej Mighri1

Center for Applied Research on Polymers and Composites (CREPEC), Department of Chemical Engineering, Laval University, QC, G1K 7P4, Canadafrej.mighri@gch.ulaval.ca

Mosto Bousmina

Center for Applied Research on Polymers and Composites (CREPEC), Department of Chemical Engineering, Laval University, QC, G1K 7P4, Canada; Canada Research Chair on Polymer Physics and Nanomaterials, Department of Chemical Engineering, Laval University, QC, G1K 7P4, Canada; Hassan II Academy of Science and Technology, 225 Mohamed Belhassen El ouazzani avenue, Rabat, Morocco

1

Corresponding author.

J. Fuel Cell Sci. Technol 5(3), 031008 (May 23, 2008) (9 pages) doi:10.1115/1.2889053 History: Received June 19, 2006; Revised October 05, 2007; Published May 23, 2008

The aim of this work was to develop a porous film structure for an electrode gas diffusion layer (GDL) used for proton exchange membrane fuel cells (PEMFCs). This film was made from a matrix composed of two immiscible polymers filled with a mixture of electrically conductive materials fabricated via a twin-screw extrusion process followed by selective extraction of one of the two polymers. The matrix consisted of low-viscosity polypropylene and polystyrene (PS) and the conductive additives were composed of high specific surface area carbon black and synthetic flake graphite. The conductive blends were first compounded in a corotating twin-screw extruder and subsequently extruded through a flexible film die to obtain a GDL film of around 500μm having high electronic conductivity. The PS phase was then extracted with tetrahydrofuran (THF) solvent and a film of controlled porosity was generated. The morphology of the GDL porous structure was then analyzed by scanning electron microscopy. GDL porosity characterization was done by both Brunauer–Emmett–Teller (BET) and mercury-intrusion porosimeter. The effects of PS concentration and extraction time with THF on GDL porosity were also studied. Pore-size distribution obtained by BET and mercury-intrusion porosimetry revealed that the GDL structure is composed by both mesopores and macropores. Mesopores represent more than 60% of the total pore volume inside the GDL film.

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Copyright © 2008 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Sketch of a PEMFC unit showing the electrochemical reactions (not drawn to scale)

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Figure 2

Apparent viscosity as a function of shear rate at 230°C: (a) pure PS-1 and PS-2 and their corresponding PP/PS/CB/GR blends of the same components concentrations. (b) Pure PP and PS-1 together with three PP/PS-1/CB/GR blends. The three blends are, respectively, composed of 60wt%, 70wt% and 80wt% of 50∕50 PP/PS-1 mixtures, and 40wt%, 30wt%, and 20wt% of 60∕40 CB/GR mixtures. (c) Pure PP and PS-1, together with four different PP/PS-1/CB/GR blends having identical PP/PS-1 phase and CB/GR phase concentrations. Only PS-1 concentration is varied from 25wt%to35wt%.

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Figure 3

In-plane and through-plane film resistivities and their corresponding blend viscosities (at a shear rate of 500s−1 and T=230°C) as a function of CB/GR phase concentration

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Figure 4

In-plane and through-plane blend resistivities of different porous extruded films after the extraction of PS-1 phase with THF solvent, as a function of PS-1 weight fraction, which was varied from 25wt%to42wt%

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Figure 5

SEM micrographs of porous films (uncompressed) after PS-1 extraction for different PS-1 phase concentrations. The films were microtomed along the extrusion direction. (a) S-1: ([35wt%PP+25wt%PS-1]+[24wt%CB+16wt%GR]); (b) S-4: ([25wt%PP+35wt%PS-1]+[24wt%CB+16wt%GR]); (c) S-5: ([22wt%PP+38wt%PS-1]+[24wt%CB+16wt%GR]); (d) S-6: ([20wt%PP+40wt%PS-1]+[24wt%CB+16wt%GR]); (e) S-7: ([18wt%PP+42wt%PS-1]+[24wt%CB+16wt%GR]).

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Figure 6

SEM micrographs of porous films (uncompressed) after PS-1 extraction for different PS-1 phase concentrations. The films were microtomed perpendicular to the extrusion direction: (a) S-4: ([25wt%PP+35wt%PS-1]+[24wt%CB+16wt%GR]); (b) S-5: ([22wt%PP+38wt%PS-1]+[24wt%CB+16wt%GR]); (c) S-6: ([20wt%PP+40wt%PS-1]+[24wt%CB+16wt%GR]); (d) S-7: ([18wt%PP+42wt%PS-1]+[24wt%CB+16wt%GR]).

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Figure 7

Relationship between P∕V(Po−P) and P∕Po obtained from Eq. 3 for films made from blends S-1 to S-7 after PS-1 extraction by THF

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Figure 8

BET specific surface area for film made from blend S-4 as a function of PS-1 extraction time

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Figure 9

BET specific surface area as a function of PS-1 weight concentration for both one-step and two-step mixing techniques

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Figure 10

BET specific surface area of porous uncompressed and compressed films as a function of initial PS-1 concentration

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Figure 11

Resistivity and BET surface area of porous uncompressed films as a function of initial PS-1 concentration

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Figure 12

Pore-size distribution obtained by BET and mercury-intrusion techniques: (a) specific pore volume and (b) cumulative pore volume

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