Stability of a Monoethanolamine-CO₂ Zwitterion at the Vapor/Liquid Water Interface: Implications for Low Partial...

The need to chemically convert CO₂ at the interface of aqueous amine solutions has become particularly relevant for the development and the broad distribution of cost-effective and near-future devices for direct air capture working at low (e.g., ambient) partial pressure. Here, we have determined the stability of a CO₂-monoethanolamine zwitterion and its chemical conversion into carbamate at the vapor/liquid water interface by first-principles molecular dynamics simulations coupled with a recently introduced enhanced sampling technique. Contrary to the bulk water case, our results show that both the zwitterion and carbamate ions are poorly stable at the vapor/amine aqueous interface, further stating the differences between the homogeneous and heterogeneous CO₂ chemical conversion. The design of novel and cost-effective capture systems, such as those offered by amine-based scrubbing solutions, working at low (e.g., ambient) CO₂ partial pressure should explore the use of novel solvents, different from aqueous mixtures, to overcome the limits of the current absorbents.