Graphene covalently functionalized with 2,6-diaminoaquinone (DQ) as high performance electrode material for supercapacitors

2,6-diaminoaquinone (DQ) molecules were covalently modified onto the surface of graphene (GO) via the nucleophilic displacement reaction between the epoxy groups on the surface of GO and the -NH2 groups of DQ molecules in the presence of ammonia to form a composite material (labeled as DQ-RGO). The rapid reversible Faraday reaction of DQ molecules is realized in virtue of the good conductivity of the graphene. Therefore, the DQ-RGO composite material can combine the Faraday pseudocapacitance of the DQ with the double-layer capacitance of graphene, thusdisplaying an outstanding electrochemical performance in acidic electrolyte solution, including high specific capacitance (332 F g-1 at 1 A g-1), excellent rate capability (the capacitance retention rate is 72.9% at 50 A g-1) and good cycling stability (maintain the initial capacitance of 81.8% after 5000 cycles). Meanwhile, thionine-functionalized graphene hydrogel (Th-GH) was also prepared via non-covalently strategy. Finally, the DQ-RGO composite was acted as the negative electrode and Th-GH was acted as the positive electrode to construct an asymmetric supercapacitor (ASC). The ASC exhibited the energy density of 14.2 Wh kg-1 along with power density of 0.763 kW kg-1 and long cycling durability (maintain 80% of the original capacitance after 8000 cycles of 5 A g-1). More importantly, two such devices in series successfully lit 16 red light-emitting diodes (LED), demonstrating its outstanding energy storage performance. This work can provide ideas for the construction of green, all-carbon and excellent electrochemical performance devices.