Design of new electroactive fluids for redox flow batteries based on quinones.

Abstract

Redox Flow Batteries (RFBs) store energy in electroactive solutions stowed outside the electrochemical cells and are strong candidates to serve as load-leveling devices contributing to the development of smart grids and to offset the intermittency of renewable energy sources. Current RFBs use aqueous solutions of electroactive species1 (i.e. aqueous vanadium solutions, max conc. 2M) whose limited solubility limits in turn the energy density of the systems. In this work quinones are proposed as electroactive species to be explored as the main components in molten fluxes or in concentrated organic fluids. This approach would increase considerably the concentration of electroactive species eventually leading to a competitive alternative to vanadium solutions by providing increased voltage range, specific capacity and energy density. Quinones are known to have an electrochemical reversible process between quinone and hydroquinone, with good kinetics and a high electrochemical equivalent2 (two electrons per mole of quinone). Our work has centered on the initial and preliminary studies of electroactivity of simple quinones in organic media to determine their solubility, electroactivity, feasible voltage range and redox processes with different electrodes and electrolytes.