Enhancing CO₂ Transport Across a PEEK-Ionene Membrane and Water-Lean Solvent Interface

Efficient direct air capture (DAC) of CO₂ will require strategies to deal with the relatively low concentration in the atmosphere. One such strategy is to employ the combination of a CO₂-selective membrane coupled with a CO₂ capture solvent acting as a draw solution. Here, the interactions between a leading water-lean carbon-capture solvent, a polyether ether ketone (PEEK)-ionene membrane, CO₂, and combinations were probed using advanced NMR techniques coupled with advanced simulations. We identify the speciation and dynamics of the solvent, membrane, and CO₂, presenting spectroscopic evidence of CO₂ diffusion through benzylic regions within the PEEK-ionene membrane, not spaces in the ionic lattice as expected. Our results demonstrate that water-lean capture solvents provide a thermodynamic and kinetic funnel to draw CO₂ from the air through the membrane and into the bulk solvent, thus enhancing the performance of the membrane. The reaction between the carbon-capture solvent and CO₂ produces carbamic acid, disrupting interactions between the imidazolium (Im⁺) cations and the bistriflimide anions within the PEEK-ionene membrane, thereby creating structural changes through which CO₂ can diffuse more readily. Consequently, this restructuring results in CO₂ diffusion at the interface that is faster than CO₂ diffusion in the bulk carbon-capture solvent.