Microwave-exfoliated Graphene Oxide for High Voltage “Water-in-Salt” Electrolyte-based Supercapacitor

Exfoliated and reduced graphene oxide (MEGO) was fabricated by rapid microwave irradiation. When MEGO was used as the electrode of 17 m NaClO4 “water-in-salt” (WIS) electrolyte-based supercapacitors, the cell exhibited stable double layer capacitant behavior up to 2.5 V, much higher than the electrochemical stable window of water. The MEGO exhibited high energy density of 22 Wh/kg at a power density of 12.5 kW/kg, attributable to fast motion of ion clusters in the large space of exfoliated nanosheets in MEGO. Exfoliated graphene oxide prepared by rapid microwave irradiation exhibited high specific capacitance even at high current density. The specific capacitance of the exfoliated graphenes in 17 m NaClO4 electrolyte increased with higher operating voltage. The environmentally friendly supercapacitor composed of MEGO/graphite and aqueous 17 m NaClO4 electrolyte had operating voltage of 2.5 V with high energy density and power density.