Anthraquinone Flow Battery Reactants with Nonhydrolyzable Water-Solubilizing Chains Introduced via a Generic Cross-Coupling Method

Abstract

Water-soluble anthraquinones (AQs) hold great promise serving as redox-active species in aqueous organic flow batteries. Systematic investigations into how the properties of redox molecules depend on the water-solubilizing groups (WSGs) and the way in which they are bound to the redox core are, however, still lacking. We introduce WSGs linked to anthraquinone by CC bonds via a cross-coupling reaction and convert CC to C−C bonds through hydrogenation. The anthraquinone and the WSGs are connected via (un)branched chains with (un)saturated bonds. We investigate the influence of chains and ionic ending groups on the redox potentials of the molecules and identify three important trends: (1) The electron-withdrawing ending groups can affect the redox potentials of AQs with two unsaturated hydrocarbons on the chains through π-conjugation. (2) For chains with two (un)saturated straight hydrocarbons, WSGs increase the redox potentials of the AQs in the order PO 3 2− < CO 2 − < SO 3 − . (3) AQs with (un)saturated chains at high pH possess desirably low redox potentials, high solubilities, and high stability. Disproportionation leads to the formation of anthrone, which can be regenerated to anthraquinone. Tautomerization results in the saturation of alkene chains, stabilizing the structure. We utilize these observations to identify a potentially low-cost and long-lifetime negative electrolyte that demonstrates a temporal fade rate as low as 0.0128%/day when paired with a potassium ferrocyanide positive electrolyte.

Long‐Life Aqueous Organic Redox Flow Batteries Enabled by Amidoxime‐Functionalized Ion‐Selective Polymer Membranes

“…Further development of the aqueous organic RFBs will also depend on the improvement of the redox molecules with high chemical stability, low decomposition rate, and high solubility in electrolytes. [25] Despite the significantly enhanced cycling stability, the ion-exchanged AO-PIM membranes show relatively high resistance in near neutral pH electrolytes, which is mainly attributed to the relatively weak dissociation of the amidoxime groups. In principle, membrane resistance can be reduced in thin film composite (TFC) membranes.…”

Strategies for Improving Solubility of Redox‐Active Organic Species in Aqueous Redox Flow Batteries: A Review

“…Phosphate units can remain in their ionic state over a wide pH range, making phosphate an ideal pH‐insensitive, water‐solubilizing unit. In addition, the molecular polarity of phosphate is high, rendering phosphate one of the few bifunctional substituents [48a,50] . Aziz et al.…”

Electron transfer of functionalized quinones in acetonitrile

“…However, reports discussing reaction kinetics of functionalized quinones, that is related a) Electronic mail: mathieu.salanne@sorbonne-universite.fr b) Electronic mail: guillaume.jeanmairet@sorbonne-universite.fr to the amount of power a device can deliver, remain very scarce. 4,5,[24][25][26][27] . In particular, the impact of solvent effect on kinetics is often disregarded.…”