Abundant Natural Dye-Based Organic Molecule As Sole Redox Active Material for Symmetric Aqueous Redox Flow Battery

Abstract

Organic redox flow batteries (ORFBs) are considered potential substitutes to their traditional metal-based counterparts for application as large scale energy storage device[1] . This is in consideration to the merits offered by organic redox active materials i.e. inexpensive, environment friendly, high solubility and existence in diverse molecular structures that facilitates synthetic tunability to design molecules with the desired physicochemical properties[2] . However, capacity fade as result of cross-contamination has been one of the main challenges hindering development of this energy storage technology[3] . Symmetric redox flow batteries that employs a single redox active material in both electrolytes have the potential to address this challenge making them very attractive[4] .In this work, a low-cost organic dye is coupled with a radical organic molecule to form a sole bifunctional redox active material that can be used as both negoyte (-0.71V) and posolyte (0.52V versus Hg/Hg2SO4) in an organic symmetric aqueous redox flow battery. Cyclic voltammetry studies of the combined bifunctional molecule reveal reversible redox reactions of the redox couples leading to a theoretical cell voltage of 1.23V. A symmetric pumped cell testing demonstrated over 100 consecutive charge/discharge cycles with nearly 85% coulombic efficiency at current density of 2.5 mAcm-2. The battery utilizes a pH neutral supporting electrolyte (NaCl in water) which is inexpensive, non-corrosive and non-flammable resulting to a low-cost, durable, safe and environmental-friendly redox flow battery.