The water uptake of several perfluorosulfonic acid membranes from liquid water over the temperature range 25 to 130~ and from water vapor at 80~ was determined. For water uptake from liquid water, the water uptake depended on the immersion temperature, the ion exchange capacity of the membrane, and the pretreatment of the membrane. The effects of pretreatment were not significant at immersion temperatures higher than 100 to 110~ For water uptake from water vapor at 80~ the sorption isotherms were similar in shape to those reported by previous investigators for 18.5 to 30~ although the water uptake at 80~ was less than that reported for the lower temperatures. The water uptake from water vapor of some membranes that have been found to give relatively good performance when used in polymer electrolyte fuel cells was higher then that observed with, e.g., Nafion|

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Gas permeation properties for Nafion membranes and their composites were investigated under various conditions. The permeability coefficients of Nafion depended greatly on the water content, the cation form, and the ion‐exchange capacity. The gas permeation rate through a same sample varied with temperature, pressure, and membrane thickness. The permeabilty of hydrogen was about twice as great as that of oxygen. The electrocatalyst plated on the membrane did not serve as a barrier for gas permeation, but the structure of the catalyst layer played an important role in gas permeation during water electrolysis.

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