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Abstract: In this study, we report the enhanced carrier activity of potassium cation (K+) not only with fluoride but also fluorosilicate anions, prepared by the simple heat-treatment of polymer electrolyte solution in glass vial. The formation of water-soluble fluorosilicate anions such as SiF5(H2O)– was investigated by 19F NMR spectroscopy and thermogravimetric analysis (TGA). The XPS data revealed the increased binding energy of K2p3/2 up to 294.6eV with broad spectrum for F1s binding energy. The interaction between K+ and the amide groups of PVP was confirmed by FT-IR spectroscopy. As a result, membranes containing K+ demonstrated a selectivity ratio CO2/N2 and CO2/CH4 of 25.62 and 25.87, respectively, with a CO2 permeance of 52.01GPU. This enhanced separation performance was mostly attributable to the counter-anion effect on K+ carrier activity, resulting in the increased CO2 transport compared to the previous system. [Copyright &y& Elsevier]