Electrochemical Oxidation of Anthracene to Anthraquinone inside the Nanopores of Activated Carbon: Implications for Electrochemical Capacitors

Abstract

Anthracene (ANT) is oxidized to anthraquinone (AQ) inside the nanopores of activated carbon (AC) without any metal catalysts. The resulting hybrid of AC and AQ shows high performance as an anode for aqueous electrochemical capacitors due to the reversible redox reaction of AQ inside the nanopores of AC. ANT is first adsorbed inside the nanopores of AC in the gas phase and finely dispersed at the nanolevel. Consequently, the adsorbed ANT has a large contact area with the conductive carbon pore surface. The adsorbed ANT is then electrochemically oxidized to AQ in aqueous H2SO4 electrolyte. The oxidation of ANT requires conductive surfaces for charge transfer, and ANT is efficiently oxidized at the large contact interface between the conductive carbon pore surface and ANT by using AC. The hybrid is capable of fast charging and discharging through rapid charge transfer at the large contact interface. In addition, since the hybridization of AQ inside the AC pores does not expand the volume of AC particles, the volumetric capacitance is enhanced by the hybridization. Furthermore, the nanopores of AC prevent AQ from desorbing into the electrolyte during charging and discharging. Consequently, the hybridization endows the hybrid with a high volumetric capacitance, a high rate capability, and a long cycle lifetime. We demonstrate that nanopores can provide the reaction environment not only for efficient oxidation of ANT as nanoreactors but also for a fast redox reaction of AQ.