Lewis acidic water as a new carrier for facilitating CO2 transport

Abstract

We report the formation of a reversible complex between CO₂ 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 CO₂ permeation by offering an additional carrier-mediated pathway, which is distinct from the commonly recognized bicarbonate or carbonate ion-mediated CO₂ transport. These findings were exploited to develop an advanced polymeric membrane for separating CO₂ directly from wet flue gases. A simply prepared poly(ethylene oxide)-based membrane containing potassium salts exhibits selective super-permeable characteristics for CO₂ in humid environments; an exceptionally high CO₂ permeance of 4650 gas-permeation units (GPU) with an ideal separation factor of 1500 was achieved for CO₂/N₂, which lies far above the upper bound of the selectivity–permeability trade-off curve, without any significant performance degradation over 6 months.