Interfacial properties of aqueous ionic liquids on graphene surface in supercapacitors

Abstract

It is expected to improve the energy density of supercapacitors by applying ionic liquids (ILs) with wide voltage window as electrolyte and graphene high specific surface area as the electrode. Due to the hygroscopic nature of ILs, some water presenting in ILs electrolyte is found to be easy stacked near the positive electrode and effect the supercapacitors’ performance. In this work, acetonitrile (ACN) was taken to add into the ILs electrolyte to solve this problem, and the interfacial properties of aqueous ACN-ILs on charged graphene surface in supercapacitors was investigated from microscopic perspective. The effect of ACN content and charge density was also discussed. The results show that the addition of ACN not only increases the wettability of aqueous ILs on graphene surfaces, but also significantly inhibits the aggregation of water molecules on the positive electrode surface and reduces the aggregation degree of anions and cations in the electrolyte solution, particularly within hydrophilic ILs systems. In addition, cyclic voltammetry experiments confirmed that the electrochemical window of aqueous ILs was improved with addition of ACN. This study provides a significant foundation for further promoting the application of ILs as electrolyte in supercapatiors.