Reduced graphene oxide film modified by tannic acid for high areal performance supercapacitors

When graphene oxide (GO) was reduced, the stacking of reduced graphene oxide (rGO) sheets would lead to far lower of its specific capacitance than the theoretical value of graphene. In order to solve this problem, we use tannic acid (TA) to modify the rGO layered film by vacuum filtration of the mixture of GO and TA in solution, and then mild thermal reduction at 180℃. Due to the rich redox active functional groups of TA, the introduction of TA can not only alleviate the stacking of rGO sheets and promote the reduction process of GO at relatively low temperature, but also provide additional pseudocapacitance. When used for two-electrode symmetrical supercapacitor in 6 M KOH electrolyte, the TrGO-0.5 gives areal capacitance of 525 mF cm⁻², and energy density of 72.2 uWh cm⁻² at power density of 250.9 uW cm⁻². It also has capacitance retention of 91.7% after 10,000 charging/discharging cycles at current density of 4 mA cm⁻². The TrGO-0.5 based button cell with 2 M 1-ethyl-3-methylimidazole tetrafluoroborate (EMIMBF₄) as electrolyte shows the practical application to light up three LEDs.