
378 Fuel Cells
9.3.1.7 Water Content in Naon—PEM
The water-absorbing capacity of a material is in general expressed in the
form of sorption isotherms as a function of humidity condition and tempera-
ture. The water content (λ) is dened as the ratio of number of water mole-
cules to number of charged sites
SO H
. Sorption isotherm for Naon-117
was measured experimentally based on humidity condition at 30°C and the
empirical correlation is given by Zawodzinski et al. (1991) (Springer et al.,
1991) in the form of water content (λ) as a function of water vapor activity (a).
The functional form of the sorption isotherm is given as follows