The Role of Nonequilibrium\nSolvent Effects in Enhancing\nDirect CO<sub>2</sub> Capture at the Air–Aqueous Amino Acid\nInterface

Direct air capture (DAC) technologies are limited by\nthe poor understanding\nof the dynamic role of interfaces in modulating the chemisorption\nof CO<sub>2</sub> from air into solutions. While the reactivity of\naqueous amine-based solvents in the bulk environment is strongly inhibited\nby nonequilibrium solvent effects, promoting DAC at interfaces posits\na possibility to reduce the coupling with the solvent and significantly\naccelerate DAC. Building on an experimentally proven concept to bring\nan anionic glycine absorbent to the interface through ion-pairing\ninteractions with a positively charged surfactant, we establish the\nfundamental time scales for key elementary steps involved in DAC with\nrate theory and enhanced-sampling <i>ab initio</i> molecular\ndynamics simulations. We elucidate the mechanism by which water influences\nthe free energy barriers and dynamical crossing-recrossing of those\nbarriers, affecting the reaction rates. We find that water reorganizes\nto partially dehydrate [-NH<sub>2</sub>], facilitating S<sub>N</sub>2-based CO<sub>2</sub> conversion to a zwitterion, which then releases\na proton via overhydration of [-NH<sub>2</sub>]. The low-density interfacial\nwater favors dehydration over overhydration, leading to a comparatively\nhigher barrier (slower kinetics) for proton release. The barrier-recrossing\nevents neutralize this effect, letting both steps occur at the same\ntime scale (sub-microseconds) and making the overall DAC process faster\nat the interface than in the bulk water. Such an understanding of\nenvironment-sensitive solvent effects on the reaction kinetics will\nhelp design tailored interfaces for enhanced CO<sub>2</sub> capture\nkinetics via control of solvation and ion paring.