Synthesis of reduced graphene oxide by an ionothermal method and electrochemical performance

Abstract

An easy ionothermal method is proposed to deoxygenate graphene oxide (GO) for preparation of graphene by using a choline chloride (ChCl)/urea mixture-based ionic liquid. In the synthesis process, the urea portion in the ionic liquid breaks up to release NH₃ at around 100 °C. This reacts with the oxygen functional groups of the GO sheets, leading to the formation of graphene. The ionothermal method is an environmentally-friendly and attractive strategy for reducing GO because both ChCl and urea are naturally biocompatible compounds. X-Ray photoelectron spectroscopy indicates that nitrogen atoms can be doped into the graphene skeleton accompanied by the reduction of GO. As an electrode for an electrochemical double layer capacitor in aqueous KOH, the ionothermally reduced GO exhibits a gravimetric capacitance of 155 F g⁻¹ at a current density of 0.2 A g⁻¹ and good cycling performance, which is comparable to the hydrazine reduced GO. We expect that the ionothermal method will have implications for the use of ionic liquids in the large-scale synthesis of graphene-based materials.