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

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 8.36Wh 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. (C) The Author(s) 2021. Published by ECSJ.