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 H 2 SO 4 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.

Utilizing Activated Carbon Nanopores for Electrochemical Oxidation of Perylene to Redox-Active 3,10-Perylenedione: Application in Electrochemical Capacitor Electrodes

“…The densities of the AC/PER samples were measured to compare their theoretical and experimental densities (Table S1). The theoretical density was calculated using the density of AC and the adsorbed amount of PER based on the assumption that PER was adsorbed in the AC nanopores without any change in AC particle volume. ,, If PER was deposited on the AC particle surfaces, the interparticle space would expand, leading to an experimental electrode density lower than the theoretical one. The density results indicated that PER was adsorbed into the AC nanopores.…”

“…The following characterization methods were applied according to methods reported elsewhere: X-ray diffraction, N 2 adsorption/desorption, and density measurements, and scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations. UV–vis spectra were recorded on a UV–vis spectrophotometer (UV-1280, Shimadzu) in dichloromethane.…”

“…For comparison, a symmetrical AC cell was prepared with 8.5 mg of AC in both the anode and cathode. The volumetric capacitance of the two-electrode cell was calculated as follows: , C normalv = C normalg × w AC + w AC / PER V AC + V AC / PER where w AC/PER is the mass of the AC/PER sample in the cathode, and V AC and V AC/PER are the volumes of the anode and cathode, respectively.…”

“…We have reported that the nanopores of AC can serve as reaction environments for polymerization, , coupling, and oxidation reactions through electrochemical oxidation without the need for metal catalysts or organic solvents. In these reactions, aniline, , pyrene, and anthraquinone were adsorbed by the AC nanopores in the gas phase. Upon electrochemical oxidation, aniline was polymerized to polyaniline (PANI), whereas pyrene underwent homocoupling to yield a pyrene dimer, while anthracene was oxidized to anthraquinone.…”

“…Upon electrochemical oxidation, aniline was polymerized to polyaniline (PANI), whereas pyrene underwent homocoupling to yield a pyrene dimer, while anthracene was oxidized to anthraquinone. The resulting PANI, pyrene dimer, and anthraquinone are redox-active materials and were hybridized in the AC nanopores; they have large contact interfaces with conductive carbon surfaces, with interactions strengthened by π–π staking. − Consequently, charge transfer proceeded rapidly at the large contact interface without desorption from the AC nanopores when aqueous H 2 SO 4 was used as the electrolyte. ,,, The hybrids showed higher power densities than EDLCs despite their charge storage mechanisms relying largely on the redox reactions. Therefore, the hybrids served as electrodes for aqueous electrochemical capacitors, not as battery electrodes.…”