Ionic liquid modified graphene for supercapacitors with high rate capability

Ionic liquids (ILs) with large electrochemical windows up to 4 V have been employed as the electrolyte to boost the energy density of graphene-based supercapacitors. However, due to the larger molecular size, lower conductivity, and higher viscosity of the IL electrolyte, graphene-based supercapacitors in IL electrolyte usually exhibit low rate capability. To make graphene-based electrodes more compatible with the IL electrolyte, we functionalized chemically reduced graphene oxide with the same IL which is also used as the electrolyte. Electrochemical test results show that the relaxation time and charge transfer resistance at electrode-electrolyte interface for IL modified electrode is one third and one fourth of that for the pristine graphene electrode, respectively, indicating the improved compatibility between the IL modified electrode and the electrolyte. Furthermore, the capacitance retention of the IL modified electrode from current density of 0.5 to 20 A g(-1) is 85%, which is much higher than that of the pristine electrode (53%). (C) 2015 Elsevier Ltd. All rights reserved.