Electrochemical investigation of free-standing reduced graphene oxide hydrogel

Abstract

Free-standing reduced graphene oxide (RGO) hydrogel was synthesized through two-stepped hydrothermal reduction treatment of aqueous graphene oxide (GO) suspension. GO with high interface affinity for overlapping of cross-linking graphene sheets contributes to forming steady-state RGO hydrogel. RGO hydrogel shows higher B band/G band intensity ratio than GO suspension in Raman spectrum analysis, indicating well-restored hexagonal carbon rings with the enhanced crystal structure. Free-standing RGO hydrogel could be directly acted as supercapacitor electrode without using any substrate material. The specific capacitance decreases from 253.9 to 92.3 F g−1 in 1.0 M Na2SO4 electrolyte and from 275.3 to 125.9 F g−1 in 1.0 M KOH electrolyte when the current density increased from 0.3 to 4.0 A g−1, presenting the capacity retention of 36.4% and 45.7% respectively. Free-standing RGO hydrogel presents specific capacitance in alkaline KOH electrolyte rather than neutral Na2SO4 electrolyte. KOH electrolyte with superior ionic diffusion coefficient of hydroxyl ion leads to higher current response and electrical double-layer capacitance performance. The capacitance retention ratio of 97.8% at 4.0 A g−1 in 1.0 M KOH electrolyte after 1000 charge-discharge cycles presents superior cycling stability. Accordingly, free-standing RGO hydrogel applied well as superior supercapacitor electrode presents the promising energy storage application.