(406e) A Multiscale Approach Toward Direct Air Capture of CO2 By Biocompatible Ionic Liquids

Global warming is known to be severely caused by the elevation of carbon dioxide (CO₂) emissions to the environment, a major threat to humanity. A vast majority of these emissions originate from the consumption of fossil fuels, especially for electricity generation, making it crucial to reduce the release of CO₂ into the atmosphere. Currently, the most widely used technology for post-combustion CO₂ capture is amine scrubbing, a chemical absorption CO₂ reaction process with aqueous amine solvents. However, it has several major drawbacks, such as thermal and oxidative degradation of the solvents, corrosion leading to costly equipment replacement, and high energy utilization for reclaiming the solvents. Additionally, the makeup of lost solvents can be costly, and the degradation products can be hazardous if exposed to the environment. Ionic liquids are seen as a promising alternative for CO₂ capture through direct air capture due to their low vapor pressure and high thermal stability. Specifically, amino acid ionic liquids (AAIL) have additional advantages due largely to their biocompatibility, cost-effective synthesizability, and large chemical tunability. Understanding structural flexibility in AAIL can be especially important for the chemisorption process involving chemical reactions. A few studies have attempted to reveal the reaction mechanisms for CO₂ chemisorption by AAIL using density functional theory (DFT) calculations, but the molecular mechanisms remain unclear and cannot be fully explained by static DFT calculations with only a few explicit molecules in the gas phase. A detailed understanding of dynamic features during chemisorption is urgently needed. In this work, we investigate important dynamic and kinetic aspects of the chemisorption process involving proton transport, which can be a major factor governing the overall CO₂ direct air capture process in condensed phases such as AAIL, based on ab initio molecular dynamics with enhanced sampling methods. Our analysis based on free-energy sampling reveals both thermodynamic and kinetic favorability for all possible reaction pathways from the zwitterion intermediate to carbamate products during the chemisorption. We further examine the intermolecular interaction and kinetic features that may play a vital role in the CO₂ reaction process. This work highlights the critical kinetic features of the direct air capture of CO₂ by ionic liquids from explicit ab initio free-energy sampling.