Electrochemical active small organic molecules are potential electrode materials for supercapacitors due to their sustainable and good redox reversibility. However, the poor electrical conductivity restricts their application in supercapacitors. Herein, a water soluble organic dye of methylene blue (MB) has been supported on graphene (GR) through a facile ultrasonic method to form a methylene blue/graphene (MB/GR) composite. A small amount of MB (13%) in MB/GR composite improves the wettability of GR and supplies pseudocapacitance. The MB/GR composite can be used as a binder-free electrode for supercapacitors, and gives a high specific capacitance of 517 F g-1 at 0.5 A g-1 in 0.5 mol L-1 H2SO4 aqueous electrolyte with a satisfactory capacitive retention of 91% after 2000 consecutive cyclic voltammetry tests at 10 mV s-1. Benefiting from the high specific capacitance of MB/GR composite, the as-assembled symmetrical solid-state supercapacitor (MB/GR//MB/GR) delivers a high energy density of 30.36 Wh kg-1 at 0.7 kW kg-1, and excellent cycle stability (nearly 27% drop after 10,000 consecutive constant current charge-discharge at 5 A g-1). This work offers some enlightenment to design and preparation of high-performance electrode materials for supercapacitors.
Keywords: Energy density; Graphene; Methylene blue; Specific capacitance.
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