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 differ-ences 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.

Automated summary

Understanding the formation of H2CO3 in water from CO2 is crucial in environmental and industrial processes. This study reveals significant differences in the free energy and reaction characteristics between bulk and nanoconfined water. Nanoconfinement not only lowers the energy barrier, but also alters the reaction from endothermic to exothermic. The stronger solvation and improved proton transfer under nanoconfinement enhance the reaction's thermodynamics and kinetics.