High Performance Electrochemical Capacitor Using Redox-Active Organic Molecule Coupled with Irreversible Chemical Process

Abstract

Redox-enhanced electrochemical capacitors (Redox-ECs), in which electrons are stored and released by redox reactions of organic molecules either dissolved in an electrolyte or adsorbed on an electrode surface, represent a promising energy storage system with electrochemical characteristics of both rechargeable batteries and electrical double-layer capacitors. However, the choices for redox-active organic molecules in Redox-ECs are often limited due to an irreversible nature induced by chemical processes, such as hydrolysis, coupled with etransfer reactions. Here, this thesis describes the effects of nano-confinement on enhanced reversibility in the redox reaction of an electro-active organic molecule undergoing irreversible hydrolysis after etransfers in a nanoporous carbon electrode. The redox reaction between hydrated Rhdizonic acid (RDZ·2H2O) and Hexahydroxybenzene (HHB) via Tetrahydroxy-1,4- benzoquinone served as a model in which RDZ is irreversibly hydrolyzed to RDZ·2H2O. Due to the enhanced reversibility of the RDZ·2H2O/HHB redox reaction in a nanoporous carbon electrode, Coulombic efficiency of the cell ix remained near 90% despite the irreversible nature of RDZ via hydrolysis. This thesis provides fundamental insights into new opportunities to use organic molecules in energy storage using redox electrolytes such as Redox ECs and organic redox flow batteries.