Molecular engineering of dihydroxyanthraquinone-based electrolytes for high-capacity aqueous organic redox flow batteries

Abstract

Aqueous organic redox flow batteries (AORFBs) are a promising technology for large-scale electricity energy storage to realize efficient utilization of intermittent renewable energy. In particular, organic molecules are a class of metal-free compounds that consist of earth-abundant elements with good synthetic tunability, electrochemical reversibility and reaction rates. However, the short cycle lifetime and low capacity of AORFBs act as stumbling blocks for their practical deployment. To circumvent these issues, here, we report molecular engineered dihydroxyanthraquinone (DHAQ)-based alkaline electrolytes. Via computational studies and operando measurements, we initially demonstrate the presence of a hydrogen bond-mediated degradation mechanism of DHAQ molecules during electrochemical reactions. Afterwards, we apply a molecular engineering strategy based on redox-active polymers to develop capacity-boosting composite electrolytes. Indeed, by coupling a 1,5-DHAQ/poly(anthraquinonyl sulfide)/carbon black anolyte and a [Fe(CN)6]3−/4− alkaline catholyte, we report an AORFB capable of delivering a stable cell discharge capacity of about 573 mAh at 20 mA/cm2 after 1100 h of cycling and an average cell discharge voltage of about 0.89 V at the same current density.

Solvation regulation to mitigate the decomposition of 2,6-dihydroxyanthraquinone in aqueous organic redox flow batteries

“…[35][36][37] Note that the hydrogen bonding network between DHAHQ 4À and H 2 O will promote the intermolecular electron transfer and disproportionation reaction, according to the decomposition mechanism of DHAHQ 4À verified by computational studies and in-operando ATR-FTIR measurements. 18 The addition of TMA + changes the bindings between DHAQ anions and water. Our calculations confirmed that the binding energies of DHAQ 2À -H 2 O, DHAQ 3À -H 2 O, and DHAHQ 4À -H 2 O were all smaller with TMACl than those without TMACl (Fig.…”

“…14,15 But, molecular decompositions of AQs, causing battery capacity loss and short cycling lifetime, have been observed. 14,15 Aziz et al 16,17 discovered that the decomposition of a typical AQ, namely 2,6dihydroxyanthraquinone (DHAQ), was initiated by anthrahydroquinone (DHAHQ 4À , the reduced form of DHAQ 2À ) disproportionation, and Wang et al 18 revealed the hydrogen bond-mediated degradation mechanism. In addition, Grey et al 19,20 confirmed the electrochemical reduction of DHAHQ 4À with H 2 O through in situ NMR and coupled EPR/NMR metrology.…”

“…The hydrogen bonding between NH 4 + cations and the AQDS 2À anions renders AQDS(NH 4 ) 2 highly soluble under pH-neutral conditions and suppresses side reactions in highly acidic or basic solutions. Additionally, 2,3-dihydroxylated anthraquinone (2,3-DHAQ) 26 and 1,5-dihydroxylated anthraquinone (1,5-DHAQ) 18 exhibited temporal fade rates much slower than that of 2,6-DHAQ, demonstrating that the position of the functional groups on the aromatic ring has a great impact on the chemical stability. These facts prove that engineering the molecular structure of AQs is an effective strategy to circumvent the molecular decompositions and thereby battery capacity loss, as depicted in Fig.…”

Charge-dependent crossover in aqueous organic redox flow batteries revealed using on-line NMR spectroscopy

“…Tackling the climate crisis requires huge increases in renewable power generation from wind and solar 1 . Established technologies are too expensive to regulate their intermittent energy output on a large scale 2,3 , hence research into aqueous organic redox-flow batteries (AORFBs) has recently intensified [4][5][6][7] . An AORFB consists of two aqueous electrolytes (anolyte and catholyte) that are separated by an ion-selective membrane (Fig.…”

Advances in functional organic material-based interfacial engineering on metal anodes for rechargeable secondary batteries

“…25e), owing to the combination of redox-active polymer- Reproduced with permission. 226 Copyright 2022, Nature Publishing Group.…”