Atomistic insights into confinement and electric potential effects on the electric double layer of CO₂/IL at slits

The structure and evolution of electric double layers (EDLs) under nanoscale confinement critically govern interfacial electrochemical processes, particularly in CO₂-related electrochemical systems. While extensive studies have explored EDLs formed by ionic liquids (ILs) on planar electrodes, the coupled effects of geometric curvature, slit confinement, and electric potential on EDL formation remain insufficiently understood. Herein, molecular dynamics simulations are employed to investigate the adsorption behavior and EDL characteristics of CO₂/IL mixtures confined within curved slit pores formed by concentric carbon nanotubes (CNTs). The slit width and electrode potential are systematically varied to elucidate their roles in regulating molecular arrangement, charge distribution, and interfacial thermodynamics. The results reveal a critical slit width governing EDL formation: under severe confinement (width of silt equals 0.8 nm), spatial restriction suppresses ionic layering, preventing the establishment of a stable EDL. When the slit width increases to 1.2 nm or above, alternating ionic layers emerge, indicating EDL formation accompanied by pronounced CO₂ enrichment. Curvature-induced asymmetry leads to stronger adsorption on the outer CNT surface, while electric potential polarity results in distinct screening mechanisms at the cathode and the anode. Notably, CO₂ participates directly in anode potential shielding and adopts a preferentially parallel orientation to the electrode surface. Free energy and interfacial entropy analyses further demonstrate that EDL regions coincide with high free energy barriers and reduced molecular freedom, whereas wider slits enable effective potential screening and facilitate ion transport. These findings provide molecular-level insight into the interplay between confinement, curvature, and electrostatics, offering guidance for the rational design of electrochemical interfaces for CO₂ capture and conversion.