Tailoring reduction extent of flash-reduced graphene oxides for high performance supercapacitors

Abstract

The reduction extent of reduced graphene oxide plays a critical role in determining the energy storage performance when it is used as supercapacitor electrodes. Despite the increasing interest in graphene oxide (GO) reduction using flash, the relationship between reduction extent of flash-reduced GO (FRGO) electrodes and the supercapacitor performance remains elusive, which hinders the realization of supercapacitors with optimum performance. In this work, we present a comprehensive study on how reduction extent of FRGO electrodes can influence their properties and hence electrochemical performance. By controlling flash power, the reduction extent of FRGO materials can be finely tuned. The key electrode properties, namely the carbon-to-oxygen (C/O) atomic ratio or oxygen content, the porosity, and the electrical conductivity are characterized and analyzed in a coherent way. Surprisingly, we found that optimal electrode specific capacitance (166.7 F g−1) and supercapacitor energy density (78 W h kg−1) have been achieved when the C/O atomic ratio is relatively low at the flash light reduction threshold. In this case, despite not having the largest specific surface area and conductivity, the high oxygen content in such FRGO substantially contributes to capacitance through redox reactions with electrolyte. The present work has significant implication for developing supercapacitors with optimum performance.