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 F-19 NMR spectroscopy and thermogravimetric analysis (TGA). The XPS data revealed the increased binding energy of K2p(3/2) up to 294.6 eV 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/N-2 and CO2/CH4 of 25.62 and 25.87, respectively, with a CO2 permeance of 52.01 GPU. 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. (C) 2014 Elsevier B.V. All rights reserved.