Electrochemical Impedance Spectroscopy Investigation of Organic Redox Reactions (p-Benzoquinone/Hydroquinone Couple)─Implications to Organic Redox Flow Batteries

Abstract

Redox reactions of organic redox couples are investigated on Nafion-free and Nafion-containing carbon (Vulcan XC-72)-modified glassy carbon disk (GCD) electrodes. The model system chosen is the p-benzoquinone (BQ)/hydroquinone (BQH2) couple because BQ derivatives are common to most of the organic redox couples. The electrochemical impedance spectroscopy patterns show an unexpected rise in real resistance with time and with rotation speed (rpm). This increase in resistance is remarkable with Nafion-containing GCDs. It seems that the sulfonate group on the polymer chain attacks the redox couple to bind the species to the electrode surface. Moreover, the internal and external mass transfer features are better resolved than their nonbinding inorganic counterparts (V4+/V5+ couple). These findings have enormous implications to the development of organic redox flow batteries, organic synthesis, supercapacitors, sensors, and so on.