Redox active organic molecule-Emodin modified graphene for high-performance supercapacitors

Emodin is a natural anthraquinone derivative and contains abundant hydroxyl and carbonyl groups, which has high redox activity. As guest molecules, Emodin molecules were anchored on graphene sheet (GNS) by simple one-step reflux method. In the three-electrode system, the optimal composite electrode material (E@GNS) obtained the high specific capacitance of 338.9 F g-1 at 5 mV s-1 and excellent rate capability in 1 mol L-1 H2SO4. Finally, an asymmetric supercapacitor (ASC) was fabricated by using E@GNS as negative electrode and Caffeic acid non-covalently modified graphene hydrogel (GH-CFA) as positive electrode, respectively. The device achieved the energy density of 32.8 Wh kg-1 along with power density of 0.8 kW kg-1, and a lightemitting diode (LED) could be light up by two ASCs in series. To compare with the performance of ASC, we also assembled symmetric supercapacitor based on E@GNS, proving that the good matching of positive and negative electrode materials could make the supercapacitor exhibit the best capacitive performance.