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Research Papers

Effect of Bridging Groups on Sulfonated Poly(imide-Siloxane) for Application in Proton Exchange Membrane

[+] Author and Article Information
Chi-Hung Lee, Jia-Ru Chen, Hung-Wei Shiu, Yen-Zen Wang

Department of Chemical and Materials Engineering, National Yunlin University of Science and Technology, 123 University Road, Section 3, Douliou, Yunlin 64002, Taiwan

Ko-Shan Ho

Department of Chemical and Materials Engineering, National Kaohsiung University of Applied Sciences, 415 Chien-Kuo Road, Sanmin District, Kaohsiung City 80778, Taiwan

Shinn-Dar Wu

Department of Mechanical Engineering, National Chiao Tung University, 1001 Ta Hsueh Road, Hsinchu 30010, Taiwan

Kuo-Huang Hsieh

Institute of Polymer Science and Engineering, National Taiwan University, 1 Roosevelt Road, Section 4, Taipei 10617, Taiwan

J. Fuel Cell Sci. Technol 7(2), 021023 (Jan 25, 2010) (6 pages) doi:10.1115/1.3200906 History: Received April 13, 2008; Revised January 09, 2009; Published January 25, 2010; Online January 25, 2010

A series of six-membered sulfonated poly(imide-siloxane)s (SPIs) was synthesized using 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA), aminopropyl-terminated polydimethylsiloxane (PDMS) 2,2-benzidinedisulfonic acid (BDSA), as the sulfonation target diamine groups, and various nonsulfonated diamine monomers behaving as bridging groups. The structure-property relationship of SPI-SXx membranes is discussed in detail according to the chemical structure of the various nonsulfonated diamines of the SPI-SXx membranes from the viewpoints of proton conductivity, ion exchange capacity (IEC), and membrane properties (water uptake and membrane swelling) at equal PDMS content SPI-SXx. The PDMS was introduced to enhance the proton conductivity and water uptake attributed from the high flexibility of the siloxane segments. The conductivity and water uptake of angled SPI-SXm and oxydianiline-based SPI-SX membranes (SPI-SXO) are greater than those prepared from diaminodiphenylmethane-based SPI-SX membranes (SPI-SXD) at a given IEC. These differences resulted from the increased number of entanglements of the SPI-SXx membrane. The SPI-SXD showed almost isotropically dimensional changes with the increase in water uptake, and the volume were slightly smaller than those estimated from the additivity rule. Free volume in the SPI-SXx increased with the increase in bulky irregular packing in nonsulfonated segments, which augmented the water uptake and, in turn, the conductivity of the polymer. With the increase in temperature, conductivity increased more rapidly in SPI-SXx than in Nafion 117. Microscopic analyses revealed that these smaller (<10nm) and well-dispersed hydrophilic domains contribute to better proton conducting properties. The new sulfonated poly(imide-siloxane)s have proved to be a possible candidate as the polymer electrolyte membrane for polymer electrolyte fuel cells (PEFCs) and direct methanol fuel cells (DMFCs).

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

Grahic Jump Location
Figure 2

The FTIR spectra of SPI-SXx

Grahic Jump Location
Figure 4

Proton conductivity of SPI-SXx and Nafion 117 membranes as a function of temperature, at 100% relative humidity

Grahic Jump Location
Figure 5

TEM image of SPIX-EP40 membrane (in Ag+ salt form, cross section): (a) SPI, (b) SPI-SXD, and (c) SPI-SXm (200,000×)

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