Rational functionalization of reduced graphene oxide with imidazolium-based ionic liquid for supercapacitor application

Abstract

Graphene-based materials are very promising for the development of energy storage devices like supercapacitor. Herein, we describe the rational covalent functionalization of reduced graphene oxide (rGO) with hydrophilic imidazolium-based ionic liquid (Im-IL) and the development of aqueous and all-solid supercapacitor devices. The rational functionalization of rGO significantly alters the wettability and increases the interlayer distance of the honeycomb carbon network. It effectively prevents the restacking of individual honeycomb carbon sheets. Im-IL functionalization on rGO surface significantly decreases the water contact angle (94°–37°). Aqueous symmetric electrical double layer supercapacitor based on functionalized rGO sheet (rGO-Im-IL) has been developed and it shows excellent performance with a wide potential window of 0–2 V. The device could provide an energy density of 36.67 Wh kg−1 at a power density of 2 kW kg−1. It has very good cycling stability and it retains 97% of its initial specific capacitance even after 5000 continuous charge–discharge cycles. The enhanced wettability, increased interlayer distance, large surface area and high electronic conductivity contributes to the excellent performance of the supercapacitor. The potential application of rGO-Im-IL is demonstrated by fabricating an all-solid-state supercapacitor device with gel electrolyte.