A High Voltage Aqueous Zinc–Organic Hybrid Flow Battery

Abstract

Water-soluble redox-active organic molecules have attracted extensive attention as electrical energy storage alternatives to redox-active metals that are low in abundance and high in cost. Here an aqueous zinc–organic hybrid redox flow battery (RFB) is reported with a positive electrolyte comprising a functionalized 1,4-hydroquinone bearing four (dimethylamino)methyl groups dissolved in sulfuric acid. By utilizing a three-electrolyte, two-membrane configuration this acidic positive electrolyte is effectively paired with an alkaline negative electrolyte comprising a Zn/[Zn(OH) 4 ] 2− redox couple and a hybrid RFB is operated at a high operating voltage of 2.0 V. It is shown that the electrochemical reversibility and kinetics of the organic redox species can be enhanced by an electrocatalyst, leading to a cyclic voltammetry peak separation as low as 35 mV and enabling an enhanced rate capability.