Effects of Surface\nComplexity and Moisture on Graphene\nOxide–Ionic Liquid Interfaces

Supercapacitors based on the interface between graphene\noxide (GO)\nand ionic liquids (ILs) are an appealing and potentially safe energy\nstorage solution due to both the low volatility of IL electrolytes\ncompared to many traditional electrolytes and the cost effectiveness\nof using GO as electrodes. Molecular dynamics (MD) simulations can\nprovide key insights into the atomic-scale structuring of these electrolyte–electrode\ninterfaces. However, prior simulation studies of GO–IL interfaces\nhave typically modeled GO as an idealized single layer of intact graphene\nwith a near-homogeneous distribution of hydroxyl and epoxy groups.\nSuch models neglect known GO structural complexities such as turbostratic\nsheet stacking, the presence of lateral sheet gaps and porosity, nonhomogeneous\noxygen group distributions, and topological defects that induce roughness.\nHere, MD simulations of a typical IL electrolyte, ethyl-methylimidazolium\nbis(trifluoromethylsulfonyl)imide [EMIM][TFSI], interfaced with three\nstructurally complex multilayered GO stacks are reported: one with\nheterogeneous oxygen distribution and defects, one as an “aged”\nvariant with reduced oxygen content, and a traditional model with\nuniform oxygen distribution, flat surface, and no defects. The influence\nof the presence of water on interfacial structuring is also explored.\nThe outcomes indicate that heterogeneous oxygen distribution and subnanoscale\nsurface roughness do not greatly alter the IL structuring at the interface\ncompared to a smoother GO surface with homogeneous oxygen distribution,\nprovided that the total average surface oxygen content is similar.\nHowever, the presence of a small amount of water greatly increases\nion mobility in both the interface and the bulk liquid and was found\nto enhance ion mobility at lateral GO sheet edges. These findings\ncontribute to our understanding of how to design GO–IL-based\nenergy storage materials.