Investigations confirmed the feasibility and potential advantage of using mixed perfluorosulfonate/carboxylate membranes for nitric acid dehydration. Experimentation consisted of in situ generation of pure sulfonate and mixed sulfonate/carboxylate (as high as 71 mol % carboxylate) polymer films from a perfluorosulfonyl fluoride precursor membrane, the characterization of the material, and a study of the transport characteristics of these membranes. The carboxylate concentration was determined using direct Fourier transform infrared and X-ray fluorescence spectroscopy. Nitric acid dehydration transport tests confirmed that bulk fluxes decreased and the water separation factor dramatically increased as the carboxylate side-chain content increased to 53 mol %.