Highly Water-Soluble 6-Quinoxalinecarboxylic Acid for High-Voltage Aqueous Organic Redox Flow Batteries

Abstract

Aqueous organic redox flow batteries (AORFBs) are promising for grid-scale energy storage, but the aqueous solubility and stability of redox-active organic molecules are usually low. Herein, we report scalable and convenient synthesis of 6-quinoxalinecarboxylic acid (QCA) anolyte material with high solubility (5.5 M) and ultralow redox potential (−0.79 V vs SHE). When coupling with K4Fe­(CN)6 catholyte, the QCA||K4Fe­(CN)6 AORFBs show a cell voltage of 1.28 V, a power density of 199 mW cm–2, and a capacity retention of 99.9% cycle–1. This work highlights the reasonable construction of redox-active organic species to develop advanced AORFBs toward large-scale energy storage applications.

Recent progress and perspectives of liquid organic hydrogen carrier electrochemistry for energy applications

“…These organic compounds can be strategically paired with other organic or inorganic redox couples to form a ow battery to store electricity. 54 h L −1 when AQ-1,8-3E-OH transitions into a liquid at temperatures exceeding 35 °C. Polarization experiments showed higher OCV across all state-of-charge (SOC) levels compared to a lowconcentration cell (Fig.…”

Substituent Impact on Quinoxaline Performance and Degradation in Redox Flow Batteries

“…Quinoxalines are an underexplored but promising class of negative electrolyte molecules in this respect because many derivatives have lower redox potentials 19−22 and higher solubilities 19,23,24 than typical anthraquinones and phenazines. The equivalent weight of quinoxaline (65 g/mol) is also lower than that of anthraquinone (104 g/mol) and phenazine (90 g/ mol), and many substituted quinoxalines are straightforward to synthesize in one-step reactions using widely available precursors.…”

“…Quinoxalines are an underexplored but promising class of negative electrolyte molecules in this respect because many derivatives have lower redox potentials − and higher solubilities ,, than typical anthraquinones and phenazines. The equivalent weight of quinoxaline (65 g/mol) is also lower than that of anthraquinone (104 g/mol) and phenazine (90 g/mol), and many substituted quinoxalines are straightforward to synthesize in one-step reactions using widely available precursors. − Like anthraquinones and phenazines, quinoxalines undergo a two-electron redox reaction. , Although they are known to be viable charge carriers in nonaqueous flow batteries, − studies which have explored the cycling behavior of aqueous flow cells containing quinoxalines ,, reported rapid capacity fade, equivalent to >20%/day.…”

Enabling Long-Life Aqueous Organic Redox Flow Batteries with a Highly Stable, Low Redox Potential Phenazine Anolyte

“…Aqueous organic redox flow batteries (AORFBs) utilize organics dissolving in aqueous solutions as active species in ARFBs and are being explored as a new direction for energy storage systems . These organics consist of earth-abundant elements such as C, H, O, N, P, and S, making AORFBs more promising in terms of cost reduction compared to vanadium-based ARFBs. , Since the first report of AORFBs based on 9,10-anthraquinone-2,7-disulfonic acid (AQDS) by Aziz, there has been substantial progress in the development of high-performance AORFBs, marked by the exploration of novel organic compounds and advancements in electrode designs. − The success of AQDS-based AORFBs has encouraged more researchers to focus on highly soluble and electro-active organic compounds for AORFBs. − Despite progress in the development of AORFBs, many previous reports on this technology are yet to be translated into practical applications due to challenges such as short cycling time (less than 1 month), ,− ,− serious capacity fade (greater than 0.1% per day), ,,,− and low open-circuit voltage (e.g., less than 1 V in al...…”