Voltammetry study of quinoxaline in aqueous electrolytes

Organic compounds have recently received considerable attention as active materials in redox flow batteries (RFBs) due to their good electrochemical reversibility, high theoretical energy densities, and promise for low cost production. Until now, organic active material candidates for aqueous RFBs have been limited to the quinone family, a set of aromatic-derived organic molecules, distinguished by an even number of ketone (R-C(=O)-R') groups. This work aims to elucidate and optimize the electrochemical behavior of quinoxaline, an organic molecule consisting of fused benzene and pyrazine rings, in aqueous electrolytes. More than 30 electrolytes are screened by cyclic voltammetry, and the five most promising electrolytes are investigated further using rotating disk voltammetry. Electrochemical behavior of quinoxaline shows pH dependent thermodynamics and reaction mechanisms, while chloride-containing supporting electrolytes greatly enhance solubility. This study sheds light on the promising characteristics of quinoxaline as a low potential compound for aqueous RFBs; quinoxaline has a redox potential of E degrees approximate to -0.02 V vs. RHE, is soluble up to similar to 4.5 M in water, exhibits a two-electron transfer capability, and possesses a low molecular weight (130.15 g mol(-1)), resulting in a theoretical capacity of 410 mAh g(-1). (C) 2015 Published by Elsevier Ltd.