TABLE OF CONTENTS Gas permeation data for the precursor polymers were not available; data for FEP perfluorinated ethylene-propylene co-poplymer at 25 C are given as an approximation: hydrogen = 14; helium = 40; nitrogen = 2.15; oxygen = 5.9; and carbon dioxide = 1.7 Barrers (1 Barrer = 10 ?11 cm 3 cm/cm 2 s mmHg). For the ionic forms, an enhancement of the transport of water soluble gases, such as carbon dioxide, is observed. For the hydrogen form of Nafion, the following values are reported: hydrogen = 15, nitrogen = 0.5, oxygen = 1.5, carbon dioxide = 300, and carbon monoxide = 30. This is a case of facilitated transport where an additive in the polymer film (in this case water) selectively enhances the transport of some gases [64].
In the case of carbon dioxide, ethylene diamine (EDA) is the additive that has received the most attention [65,66]. When a perfluorinated sulfonic acid ionomer, such as Nafion is equilibrated with an excess of EDA in aqueous solution, the monoprotonated EDAH + cation will be the counter-ion in the polymer. Depending on the EDA concentration in the solution, the ionomer will imbibe an additional amount of free EDA base as a highly polar solvent. One may expected that in such a medium carbon dioxide would be absorbed in the form of a carbonate or bicarbonate ion. However, Yamaguchi et al. suggested the reaction of carbon dioxide with the free amino group of...
