Lewis acidic water as a new carrier for facilitating CO2 transportElectronic supplementary information (ESI) available. See DOI: 10.1039/c8ta10871d

We report the formation of a reversible complex between CO 2 and a bound water coordinating alkaline metal cation (Lewis-acidic water) by nuclear magnetic resonance (NMR) analysis for the first time. Such a unique property of water can facilitate CO 2 permeation by offering an additional carrier-mediated pathway, which is distinct from the commonly recognized bicarbonate or carbonate ion-mediated CO 2 transport. These findings were exploited to develop an advanced polymeric membrane for separating CO 2 directly from wet flue gases. A simply prepared poly(ethylene oxide)-based membrane containing potassium salts exhibits selective super-permeable characteristics for CO 2 in humid environments; an exceptionally high CO 2 permeance of 4650 gas-permeation units (GPU) with an ideal separation factor of 1500 was achieved for CO 2 /N 2 , which lies far above the upper bound of the selectivity-permeability trade-off curve, without any significant performance degradation over 6 months. We report the formation of a reversible complex between CO 2 and a bound water coordinating alkaline metal cation (Lewis-acidic water) by nuclear magnetic resonance (NMR) analysis for the first time.