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

Abstract

We demonstrate that nanopores of activated carbon (AC) function as nanoreactors that oxidize perylene (PER) to a redox-active organic compound, 3,10-perylenedione (PERD), without any metal catalysts or organic solvents. PER is first adsorbed on AC in the gas phase, and the PER-adsorbed AC is subjected to electrochemical oxidation in aqueous H2SO4 as the electrolyte. Because gas-phase adsorption is solvent-free, PER is completely adsorbed on AC as long as the amount of PER does not exceed the saturated adsorption capacity of the AC, which enables accurate control of the amount adsorbed. PER is electrochemically oxidized to PERD in the nanopores of AC at above 0.7 V vs Ag/AgCl. The hybridized PERD undergoes a rapid reversible two-electron redox reaction in the nanopores owing to the large contact interface between the conductive carbon pore surfaces and PERD. The resulting AC/PERD hybrids serve as electrodes for electrochemical capacitors, utilizing the rapid redox reaction of PERD. The hybridization method is advantageous for quantitatively optimizing electrochemical capacitor performance by adjusting the amount of adsorbed PER. Moreover, because PERD hybridization in the AC nanopores does not expand the electrode volume, the volumetric capacitance increases with increasing hybridized PERD content. In three-electrode cell measurements, the volumetric capacitance at 0.05 A g-1 reaches 299 F cm-3, and 61% of this capacitance is retained at 10 A g-1 when 5 mmol of PER is used per gram of AC. Meanwhile, pristine AC delivers 117 F cm-3 at 0.05 A g-1 with a capacitance retention of 46% at 10 A g-1. Two-electrode cell measurements reveal that self-discharge is significantly suppressed by the hybridized PERD when AC/PERD hybrids and AC are used as cathodes and anodes, respectively, compared to that of a symmetrical AC cell. Moreover, PERD does not undergo cross-diffusion in the asymmetrical cells during self-discharge tests for 24 h.