Relationships of acid and water content to proton transport in statistically sulfonated proton exchange membranes: Variation of water content via control of relative humidity

被引:71
作者
Peckham, Timothy J. [1 ]
Schmeissert, Jennifer [1 ]
Holdcroft, Steven [1 ,2 ]
机构
[1] Simon Fraser Univ, Dept Chem, Burnaby, BC V5A 1S6, Canada
[2] Natl Res Council Canada, Inst Fuel Cell Innovat, Vancouver, BC V6T 1W5, Canada
关键词
D O I
10.1021/jp077218t
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
An in-depth analysis for proton exchange membranes to examine the effects of acid concentration and effective proton mobility upon proton conductivity as well as their relationship to water content was carried out on two main-chain, statistically sulfonated polymers at 25 degrees C. These polymer systems consisted of poly(ethylenetetrafluoroethylene-graft-polystyrenesulfonic acid) (1) and sulfonated trifluorostyrene (BAM) membrane (2). Nafion (3) was used for comparison. Water content (as represented by X-v, the water volume fraction, where X-v = volume of water in hydrated PEM divided by volume of hydrated PEM), for each sample was varied by adjusting the relative humidity (RH) of the membrane environment from 50% to 98%. It was found that, at low RH (RH < 70%), the major factor determining proton conductivity is proton mobility. In order to remove the differences in acid strength for the membranes, proton mobility values at infinite dilution (X-v = 1.0) and 25 degrees C were calculated and found to be 2.6 +/- 0.2 x 10(-3) (average of la-c), 1.6 +/- 0.3 x 10(-3) (average of 2a-e), and 2.32 +/- 0.01 x 10(-3) cm(2) s(-1) V-1 (3). These were then compared to the theoretical value for the mobility of a free proton at infinite dilution and to previously reported data. Possible differences in tortuosity and the juxtaposition of acid groups are proposed in order to account for the significant deviations of all samples from the theoretical value.
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页码:2848 / 2858
页数:11
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