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

Abstract

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.