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Two 1,4-dihydoxynaphthalene (PhQH 2 )-based derivatives (coded as HBU-551 and HBU-552) are synthesized by reacting with different amines (i.e., tryptamine and phenethylamine, respectively) to use as organic additives of activated carbon supercapacitors. The composite electrodes with HBU-551 and HBU-552 are also prepared by blending with the ratio of 70:25 w/w, and their supercapacitive properties are investigated in terms of redox behaviors and specific capacitance evolutions against scan rate and cycle life. The organic additives and their composites with activated carbon are dominantly characterized by PhQ-PhQH 2 redox transition accompanying a two-electron two-proton process, and weakly affected by reversible redox reaction of nitrogen in the NH group, which involves an additional one-electron one-proton process. Thus, the composite electrodes show higher specific capacitance over 210 F g −1 due to the synergistic effect between activated carbon (pseudocapacitance) and organic additives (redox behavior). Cycle performance and high-rate capability can also be enhanced by the adoption of PhQH 2 -based organic additives for their pore-filling morphology to increase the packing density of composite electrodes. [ABSTRACT FROM AUTHOR]

A quinone-containing conducting additive, 2,5-bis((2-(1H-indol-3-yl)ethyl)amino)cyclohexa 2,5-diene-1,4-dione (HBU) is synthesized and mixed with activated carbon as an active material to yield a composite supercapacitor electrode. Due to the extra redox reaction of hydroquinone/quinone couple, the supercapacitor adopting the composite electrode shows the enhancement of the electrochemical specific capacitance up to about 130 F g −1 in the scan range of 100–1000 mV s −1 and over the repeated redox processes for 1000 cycles at 100 mV s −1 , compared to the case of activated carbon electrode alone (about 100 F g −1 ). The composite with the HBU is also electrochemically stable in the charge/discharge process and thereby can be highly recommended for supercapacitor electrode additive. [ABSTRACT FROM AUTHOR]