Engineering oxygen functional groups in reduced graphene oxide for use in high‐performance flexible supercapacitors

Abstract

Graphene-based flexible supercapacitors (FSCs) are promising energy-storage devices that can potentially power the next generation of wearable and portable electronics owing to their high-power densities, quick charging/discharging rates, and excellent cycle lives. The manufacture of FSC devices with extended potential windows can help increase their energy density. However, the poor reaction kinetics of graphene (which has electric double-layer capacitive properties) can lead to low energy densities. In this study, graphene nanosheets with different oxygen contents are fabricated on a flexible carbon cloth substrate through thermal treatments in an argon atmosphere. The effects of the degree of disorder, surface area, and oxygen moieties on the supercapacitive properties of the nanosheets are explored systematically. Graphene oxide electrodes reduced at 300°C are used as the cathode and anode, and they exhibit large areal capacitances of 82.7 and 324.4 mF cm−2, respectively, at 4 mA cm−2. When the proposed device is used as a symmetric FSC cell, the electrode exhibits an excellent areal capacitance (70.3 mF cm−2 at 1 mA cm−2) and long cycle life in the 0 to 1.4 V voltage window. Furthermore, the FSC cell has a maximum energy density of 19.1 μW h cm−2 at a power density of 0.69 mW cm−2.