Supercapacitive properties of composite electrodes consisting of activated carbon and 1,4-dihydroxynaphthalene derivatives

• Two 1,4-dihydoxynaphthalene-based derivatives are newly synthesized.
• Their composite electrodes with activated carbon achieved specific capacitance of 210 F g−1.
• Synergistic effect between pseudocapacitance and the redox behavior of organic additives was shown.

Two 1,4-dihydoxynaphthalene (PhQH2)-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-PhQH2 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 PhQH2-based organic additives for their pore-filling morphology to increase the packing density of composite electrodes.