Cation Effects on Pre-Reactive CO2 Accessibility and Interfacial Transfer in Aqueous Glycinate Solutions via Molecular Dynamics.

Abstract

Alkali-metal amino acid solutions are attractive liquid sorbents for carbon capture. Potassium glycinate shows more favorable CO2 capture behavior than sodium and lithium analogues despite sharing the same reactive amine motif. However, the molecular origin of this countercation effect remains unresolved. Here, we use molecular dynamics simulations to examine how K+, Na+, and Li+ regulate CO2 accessibility and transport in aqueous glycinate solutions. We treat CO2 uptake as a multistep process in which interfacial accessibility and transport precede chemical conversion, and we isolate this pre-reactive stage. Li+ forms a compact coordination environment with glycinate and water, restricting molecular mobility and reducing CO2 access to glycinate-centered regions. In contrast, K+ maintains a more diffuse solvation environment, supporting higher diffusivities, larger interfacial CO2 populations, and more frequent vapor-to-liquid transfer events. Collectively, these results identify interfacial gating, defined as cation-dependent control of CO2 population and exchange frequency at the vapor-liquid boundary, as the interfacial manifestation of a cation-controlled CO2 accessibility mechanism around glycinate.