The Structure of Carbon Dioxide at the Air-Water Interface and its Chemical Implications

The efficient reduction of CO₂ into valuable products is a challenging task in an international context marked by the climate change crisis and the need to move away from fossil fuels. Recently, the use of water microdroplets has emerged as an interesting reaction media where many redox processes which do not occur in conventional solutions take place spontaneously. Indeed, several experimental studies in microdroplets have already been devoted to study the reduction of CO₂ with promising results. The increased reactivity in microdroplets is thought to be linked to unique electrostatic solvation effects at the air-water interface. In the present work, we report a theoretical investigation on this issue for CO₂ using first-principles molecular dynamics simulations. We show that CO₂ is stabilized at the interface, where it can accumulate, and that compared to bulk water solution, its electron capture ability is larger. Our results suggest that reduction of CO₂ might be easier in interface-rich systems such as water microdroplets, which is in line with early experimental data and indicate directions for future laboratory studies. The effect of other relevant factors which could play a role in CO₂ reduction potential is discussed.