(83b) Capacitance and Ion Dynamics of Ionic Liquids Near Oxidized Graphene

Supercapacitors are being adopted for a wide range of electrical energy applications due to their relatively high energy and power densities. With the supercapacitor research community, graphene and room-temperature ionic liquids (RTILs) are commonly studied electrode and electrolyte materials respectively. However, surface chemistry, such as oxygen groups and defects, can be easily introduced to the graphene surface during synthesis. Nevertheless, there is limited knowledge concerning the influence of surface functional groups on energy density and power density of graphene-based supercapacitor.

In this work, we first investigate the capacitance of RTILs near oxidized graphene surface using molecular dynamics (MD) simulation. The structure of electrical double layers (EDL) is discussed and related to the capacitive performance. Cyclic voltammetry experiments further validate the influence of surface oxidization on capacitance. The diffusivities of ions in the EDL are examined by calculating their self-diffusion coefficients, which are presented as a function of the distance to the electrode surface. Ion diffusivities are compared between charged surface and neutral surface, as well as between pristine graphene and oxidized graphene. This integrated study provides a comprehensive understanding of both energy and power density of oxidized graphene.