Polymer electrolyte membrane containing potassium bis(trifluoromethanesulfonyl) imide (KTFSI) dissolved in a polymeric solvent of Pebax 2533 demonstrated facilitated transport for effective CO2 separation. Reversible interactions of CO2 with both K+ and TFSI-dissolved in Pebax 2533 were directly observed by both solid state K-39 and C-13 NMR and FT-IR spectroscopy for the first time, inducing the CO2 carrier activity for the facilitated transport. Additionally, through comparing the CO2 separation performance of LiTF2N, NaTF2N and KTF2N, it was concluded that alkali cation has play an important role in helping to interact with CO2 for the CO2 carrier activity and that K+ was the best as a CO2 carrier among alkali metals used. Consequently, the KTFSI/Pebax 2533 polymer electrolyte membrane showed significant improvement of the CO2 separation performance due to the carrier action of both K+ and TFSI-in the solid state with long-term stability.