Hydrophobic Nanoconfinement Enhances CO₂ Conversion to H₂CO₃

Understanding the formation of H₂CO₃ in water from CO₂ is important in environmental and industrial processes. Although numerous investigations have studied this reaction, the conversion of CO₂ to H₂CO₃ in nanopores, and how it differs from that in bulk water, has not been understood. We use ReaxFF metadynamics molecular simulations to demonstrate striking differences in the free energy of CO₂ conversion to H₂CO₃ in bulk and nanoconfined aqueous environments. We find that nanoconfinement not only reduces the energy barrier but also reverses the reaction from endothermic in bulk water to exothermic in nanoconfined water. Also, charged intermediates are observed more often under nanoconfinement than in bulk water. Stronger solvation and more favorable proton transfer with increasing nanoconfinement enhance the thermodynamics and kinetics of the reaction. Our results provide a detailed mechanistic understanding of an important step in the carbonation process, which depends intricately on confinement, surface chemistry, and CO₂ concentration.