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SPECIAL SECTION ON THE 2ND EUROPEAN FUEL CELL TECHNOLOGY AND APPLICATIONS CONFERENCE

Development of Micro- to Macropores in Conductive Polymer-Based Gas Diffusion Layers for Proton Exchange Membrane Fuel Cells

[+] Author and Article Information
Yves Deyrail

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

Frej Mighri1

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

Serge Kaliaguine

Department of Chemical Engineering, Laval University, Quebec, QC, G1K 7P4, Canada

1

Corresponding author.

J. Fuel Cell Sci. Technol 6(2), 021309 (Mar 05, 2009) (9 pages) doi:10.1115/1.3080558 History: Received February 01, 2008; Revised July 26, 2008; Published March 05, 2009

The aim of this work is to improve the porosity of gas diffusion layers (GDLs) for proton exchange membrane fuel cell electrodes. These GDLs are made by twin-screw extrusion process from conductive formulations composed of polyamide11 (PA11)/polystyrene (PS) as the polymer matrix phase and an appropriate mixture of carbon black (CB) and graphite (GR) as the conductive additives. Final GDL porosity, especially macroporosity, was generated by selective extraction of the PS phase using adequate solvents. Since the generation of pores was found to be directly related to blend morphology, several blend compositions were studied and small amounts (26wt%) of montmorillonite (MMT) clay were used as compatibilizer to improve the dispersion of the PS phase inside the PA11. It was observed that, although GDL volume porosity was not or slightly affected by the addition of MMT compatibilizer, its pore specific surface area was clearly increased. For GDLs made from a blend composed of 65wt% of PA11/PS (30/70) and 35wt% of GB/GR (57/43), an increase from 53m2/g (with no MMT) to around 75m2/g (with 2wt% MMT) was obtained. This improvement within the addition of MMT was attributed to the modification of the dispersion state of PS phase. Such modification led to a higher connectivity of pores and consequently more accessibility to the micro/mesopores of CB and GR. The major changes observed with the incorporation of MMT compatibilizer were obtained for the small pore sizes (in the range of 10–400 nm). Depending on MMT content, a considerable shift of pore size distribution in this range to smaller or higher values was obtained. Then the MMT compatibilization could be considered as an interesting route to tailor GDL porous properties.

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Copyright © 2009 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Recorded mixing torque for PA11/PS (30/70, 40/60, and 50/50) based blends with different MMT compatibizer contents

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Figure 2

GDL volume porosity (%) of PA11/PS (30/70) based blend as a function of PS extracting time at 25°C for three different solvents: THF, toluene, and acetone. Porosity values obtained with Soxhlet extractor (using THF at 65°C) are also represented for the sake of comparison.

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Figure 3

SEM micrographs of PA11/PS (30/70) based GDLs after PS extraction at 25°C for 72 h. The micrographs show the effect of MMT compatibilizer content on pore size. Magnification 10,000×: (a) no MMT, (b) 2 wt % MMT, (c) 4 wt % MMT, and (d) 6 wt % MMT.

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Figure 4

Effect of MMT clay on GDL porosity for PA11/PS (30/70), (40/60), and (50/50) based blends: (a) volume porosity (%) and (b) pore specific surface area (m2/g)

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Figure 5

Effect of MMT clay on GDL pore specific surface area in the micromesopore range for PA11/PS (30/70), (40/60), and (50/50) based blends

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Figure 6

Incremental pore volume as a function of pore diameter showing the effect of MMT clay on pore size distribution for PA11/PS based blends: (a) PA11/PS (30/70) and (b) PA11/PS (40/60)

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Figure 7

Cumulative pore volume as a function of pore diameter showing the effect of MMT clay on pore size distribution for PA11/PS based blends: (a) PA11/PS (30/70) and (b) PA11/PS (40/60)

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Figure 8

Example showing GDL pore size distribution for a PA11/PS (30/70) based blend after PS extraction in THF: (a) noncompatibilized blend (extraction at 25°C for 72 h, or with Soxhlet extractor at 65°C for 7 h) and (b) 2 wt % MMT compatibilized blend (extraction at 25°C for 72 h)

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Figure 9

TEM micrographs of PA11/PS (30/70) blend with different MMT clay contents. Localization of carbon additives and MMT clay: (a) PA11/PS (30/70), no MMT; (b) PA11/PS (30/70) +4 wt % MMT; (c) PA11/PS (30/70) +2 wt % MMT; and (d) PA11/PS (30/70) +4 wt % MMT. The scale bars correspond to 0.2 μm for (a)–(c) and 100 nm for (d).

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Figure 10

Effect of MMT clay on GDL through-plane resistivity for PA11/PS (30/70)

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