On the Influence of Counter-Ion Nature on Properties of Perfluorosulfonic Acid Membranes with Long and Short Side Chain

Abstract

In this work, the study of water uptake, ionic conductivity, and Donnan potential in systems with perfluorosulfonic acid membranes in H+, Li+, Na+, and K+ forms and solutions of inorganic electrolytes is presented. The properties of the commercial Aquivion E87-05S and Nafion 212 membranes, as well as the membranes prepared from the dispersions of Nafion 212 in the solvents of different nature (N,N-dimethylformamide, 1‑methyl-2-pyrrolidone, isopropyl alcohol–water mixtures in volume ratio of 80–20) were investigated. The influence of the number of functional groups, the length of the side chains of the polymer macromolecules, and the polymer morphology in the membranes on their equilibrium and transport properties depending on the counter-ion nature was revealed. The effect of the relaxation and electrophoretic factors on the alkali metal ion transfer through the system of pores and channels of the perfluorosulfonic acid membranes was discussed. The slope of the concentration dependencies of the Donnan potential for all highly hydrated membranes in the H+ form was close to the Nernstian one, while the selectivity to the alkali metal ions increased for the membranes with the highest ion-exchange capacity or the lowest amount of sorbed water and diffusion permeability due to the exclusion of the co-ions from the membrane phase.