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Cation-exchange membranes with sulfonylimide groups showing a high ionic conductivity in water/organic amide mixed systems
Cation-exchange membranes based on polystyrene block-copolymer with phenylsulfonylimide ionogenic groups in the Na+-form show conductivities up to 0.2 mS cm−1 in organic amides such as N-methylpyrrolidone and N,N-dimemylacetamide. These values are 2-2.5 orders of magnitude higher compared to those of conventional sulfonated cation-exchange membranes. A strong dependence of solvation degree and ionic conductivity on dielectric permittivity, chemical structure, and composition of the solvent, as well as on the nature of the membrane functional group, was noted and discussed. Further, based on the dependence of membrane’s solvation on the dimethylacetamide or acetonitrile content in the water/organic solvent mixtures and thermodynamic properties of these solvent mixtures the reasons for the difference in ionic conductivity with a variation in the composition of the solvent and the functional groups of membranes are described. It was shown that conductivity of the cation-exchange membranes can increase dramatically even at low water concentration in the acetonitrile solution. It was demonstrated that the membranes with phenylsulfonylimide groups have high ionic conductivity in water/dimethylacetamide mixtures of any concentrations, which opens new prospects for their applications in electrochemical desalination and metal-ion batteries.