Molecular Dynamics Simulations of Supercritical Carbon Dioxide and Water using TraPPE and SWM4-NDP Force Fields.

The increased levels of carbon dioxide (CO2) emissions due to the combustion of fossil fuels and the consequential impact on global climate change have made CO2 capture, storage, and utilization a significant area of focus for current research. In most electrochemical CO2 applications, water is used as a proton donor due to its high availability and mobility and use as a polar solvent. Additionally, supercritical CO2 is a promising avenue for electrochemical applications due to its unique chemical and physical properties. Consequently, understanding the interactions between water and supercritical CO2 is of great importance for future electrochemical applications. Molecular dynamics (MD) simulation is a powerful tool that enables atomistic-resolution dynamics of molecular systems, which can complement and guide future experimental investigations. This study employed atomistic MD to study the cosolubilities, codiffusivities, and structure of supercritical CO2 and water systems, with a polarizable water model (SWM4-NDP) and a nonpolarizable CO2 model (TraPPE). Additionally, ab initio MD simulations were used to better understand how atomistic polarizable/nonpolarizable models compare to explicit modeling of electron densities. The polarizable water model exhibited substantial improvement in water-associated properties. We anticipate the development of a compatible polarizable CO2 model to yield similar improvement, providing a pathway for realizing novel high-pressure electrochemical systems.