Fabrication of an Organic Redox Capacitor with a Neutral Aqueous Electrolyte Solution

Abstract

Organic redox capacitors using neutral aqueous electrolyte solutions are environmentally friendly and safe. In this study, we report on the fabrication of an all-organic redox capacitor using NaCl solution. We used a 2,2,6,6-tetramethylpiperidinyl-N-oxyl (TEMPO) benzene derivative (4-hydroxy TEMPO benzoate, HTB) and 9,10-anthraquinone (AQ) as active materials for the positive electrode and negative electrode, respectively. The former has a positive redox potential, and the latter reacts with two electrons, which enhances the energy density. The capacitor fabricated with HTB and AQ has an energy density of 8.36 W h kg⁻¹ at a rate of 10 C, which is nearly two times higher than that of the electric double-layer capacitor consisting of Ketjen black. The cycle test indicates that important factors affecting its performance are the ion diffusion and the dispersion of the active materials.