Exploiting the chemistry of redox active compounds to enhance the capacitance of reduced graphene oxide

Abstract

The restacking of graphene sheets leading to poor electrical conductivity and reduced surface area strongly affects the capacitance properties of reduced graphene oxide (RGO). Many strategies employed to mitigate the restacking issue include the introduction of spacer materials between the graphene layers, hetero atom doping, compositing with metal oxides, etc. Herein, we report the enhancement of the capacitance properties of RGO by the addition of a small amount of redox active compounds, such as benzoquinone, KI, and NaI in the electrolyte. RGO is prepared by chemical exfoliation of graphite followed by a hydrothermal reduction in the presence of a small amount of hydrazine hydrate. The quality of prepared RGO is examined by microscopic and Raman spectroscopic studies. X-ray photoelectron spectroscopic studies reveal doping of 1.97 atomic weight % of nitrogen in RGO. The specific capacitance values of 105, 244, 322 and 414 F g(-1) at a current density of 2 A g(-1) are obtained for RGO in 0.25M H2SO4 and 0.25M H2SO4 containing 0.05M of NaI, KI and benzoquinone, respectively. The enhancement in the specific capacitance of RGO is attributed to the reversible redox reaction of the additives. Interestingly, the mechanism of charge storage of RGO in NaI and KI containing electrolytes is different. Owing to rather slow kinetics of redox reaction of electrolyte additives, the rate performance of RGO has slightly compromised in redox active electrolytes.