The concentration of positive moieties determines the ion exchange capacity (IEC) of the membrane: for Tokuyama A201, IEC = 1.1 mM g -1 and a fully hydrated membrane (corresponding to water activity a H 2 O = 1) was characterized to have λ = 11 . We note that Tokuyama A201 is a hydrophilic membrane (there are no hydrophobic channels as in Nafion, for example) and the CO 2 , as well as all the other aqueous species, is transported solely as solute in water through the membrane.