Wetting Behavior and Interfacial Structure of Aqueous Ionic Liquids on Graphene Surface

Ionic liquids (ILs) are considered to be promising electrolytes due to their excellent physicochemical properties. The wettability of the electrolyte in the electrode plays a crucial role in determining the energy storage performance of supercapacitors. Here, molecular dynamics simulations were performed to explore the wetting characteristics of aqueous IL droplets on graphene surfaces. The results show that as the water content increased to 7.41 mol/L, the contact angles of the aqueous IL droplets wetting on the graphene surface decreased by 55.3° and 47.6° for the hydrophilic and hydrophobic IL systems, respectively. To elucidate the mechanism through which water enhances the wetting behavior, the hydrogen bonds formed among molecules were analyzed. It was observed that hydrophilic groups have a higher propensity for establishing hydrogen bonds with water molecules, whereas hydrogen bonds predominantly form among water molecules in hydrophobic IL systems. Additionally, the diffusion coefficients of the ions increased as the water content rose, resulting in the formation of a denser ionic layer near the wall, ultimately enhancing the wettability of the IL droplets on the graphene surface. The findings of this study offer important insights into the design of electrode materials and the control of the electrolyte wetting performance for supercapacitors.