Influence of wettability on the electrolyte electrosorption within graphene-like nonconfined and confined space

Electrosorption near the interface is of fundamental importance in various energy storage applications, e.g., electric double-layer capacitors (EDLCs) that store energy via electrosorption/desorption of electrolyte near the charged electrode. Especially, wettability, a fundamental surface property, has significant effects on the electrosorption, while it has not been elaborated quantitatively nor resolved clearly. In this work, we explore the effects of wettability on the electrosorption dynamics of electrolytes within non confined and confined space via numerical simulations. We demonstrate that wetting property could drastically change the microscopic electrosorption of electrolytes (i.e., ions and solvent molecules), thereby influencing the formation of interfacial EDL microstructure and energy storage capability. For nonconfined space, a monotonic decrease of capacitance is recognized with the increasing wettability. This unusual trend of capacitance is principally attributed to the strong electrosorption of solvents at the interface rather than ions. Specifically, with the increment of wetting property, higher ion population stimulated by the reduced energy barriers facilitates the decay of interfacial electric fields, while the strong electrosorption of highly restricted, ordered solvents significantly suppresses the dielectric screening ability for shielding the electrode charges. More importantly, a nonmonotonic wettability dependence of capacitance (i.e., an asymmetric bell-shaped curve) is demonstrated for initially empty confined space, challenging the long-held axioms that capacitance is expected to increase monotonically with the improved wetting state. Noteworthy, the as-obtained findings on the wettability effects can also be extended to the solvent-free ionic liquids and interpret their diverse temperature dependences of capacitance. (C) 2018 Elsevier Ltd. All rights reserved.