High voltage binder free hybrid supercapacitor based on reduced graphene oxide/graphene oxide electrodes and “water in salt” electrolyte

Abstract

In the present work, a new low-cost and high-voltage aqueous symmetric supercapacitor cell using a blend of graphene oxide and reduced graphene oxide as binder free active material and “water-in-salt” electrolyte was developed. A reliable operating cell voltage of 2.3 V was achieved for this aqueous hybrid device. The symmetrical two electrode cell is able to exhibit a maximum specific energy of 43.8 W h/kg (325.7 µW h cm−2) at power density of 115.6 W kg−1 (858.6 µW cm−2) at a current density of 0.1 A/g with high cycle stability. It retains 84% of its initial specific energy even after 10,000 charge/discharge cycles. In addition, it exhibits outstanding charge storage capacity, reaching a specific capacity of 59.7 F g−1 (283 mF cm−2) in 17 m NaClO4 “water in salt” electrolyte at 0.1 A g−1. The superior energy storage capability is mainly attributed to the use of very high specific surface area of reduced graphene oxide and the participation of the electrochemical activity of graphene oxide surface functional groups in the charge storage process. The presence of graphene oxide eliminates the need to use non-conductive electro inactive adhesives and due to enhanced hydrophilicity of the electrode synergistically improves diffusion of the hydrated cations and anions to the surface of hydrophobic RGO.