Person:

Goulet, Marc-Antoni

Redox flow batteries based on quinone-bearing aqueous electrolytes have emerged as promising systems for energy storage from intermittent renewable sources. The lifetime of these batteries is limited by quinone stability. Here, we confirm that 2,6-dihydroxyanthrahydroquinone tends to form an anthrone intermediate that is vulnerable to subsequent irreversible dimerization. We demonstrate quantitatively that this decomposition pathway is responsible for the loss of battery capacity. Computational studies indicate that the driving force for anthrone formation is greater for anthraquinones with lower reduction potentials. We show that the decomposition can be substantially mitigated. We demonstrate that conditions minimizing anthrone formation and avoiding anthrone dimerization slow the capacity loss rate by over an order of magnitude. We anticipate that this mitigation strategy readily extends to other anthraquinone-based flow batteries and is thus an important step toward realizing renewable electricity storage through long-lived organic flow batteries.

A highly stable phosphonate‐functionalized anthraquinone is introduced as the redox‐active material in a negative potential electrolyte (negolyte) for aqueous redox flow batteries operating at nearly neutral pH. The design and synthesis of 2,6‐DPPEAQ, (((9,10‐dioxo‐9,10‐dihydroanthracene‐2,6‐diyl)bis(oxy))bis(propane‐3,1‐diyl))bis(phosphonic acid), which has a high solubility at pH 9 and above, is described. Chemical stability studies demonstrate high stability at both pH 9 and 12. By pairing 2,6‐DPPEAQ with a potassium ferri/ferrocyanide positive electrolyte across an inexpensive, nonfluorinated permselective polymer membrane, this near‐neutral quinone flow battery exhibits an open‐circuit voltage of 1.0 V and a capacity fade rate of 0.00036% per cycle and 0.014% per day, which is the lowest ever reported for any flow battery in the absence of rebalancing processes. It is further demonstrated that the negolyte pH drifts upward upon atmospheric oxygen penetration but, when oxygen is excluded, oscillates reversibly between 9 and 12 during cycling. These results enhance the suitability of aqueous‐soluble redox‐active organics for use in large‐scale energy storage, potentially enabling massive penetration of intermittent renewable electricity.

We demonstrate a long-lifetime, aqueous redox-flow battery that can operate at a pH as low as 12 while maintaining an open-circuit voltage of over 1 V. We functionalized 2,6-dihydroxyanthraquinone (2,6-DHAQ) with highly alkali-soluble carboxylate terminal groups. The resulting negative electrolyte material 4,4′-((9,10-anthraquinone-2,6-diyl)dioxy)dibutyrate (2,6-DBEAQ) was six times more soluble than 2,6-DHAQ at pH 12. Symmetric cell cycling with 2,6-DBEAQ on both sides of the cell demonstrates a capacity fade rate of <0.01%/day and <0.001%/cycle. By pairing 2,6-DBEAQ with a potassium ferri-/ferrocyanide positive electrolyte and utilizing a non-fluorinated membrane, this near-neutral flow battery shows a capacity fade rate that is the lowest of any quinone and rivals the lowest ever reported for any flow battery in the absence of rebalancing processes. This result adds the important attribute of long calendar life to quinone-based redox-flow batteries, which may enable massive penetration of intermittent renewable electricity.

We introduce an aqueous flow battery based on low-cost, non-flammable, non-corrosive and Earth-abundant elements. During charging, electrons are stored in a concentrated water solution of 2,5-dihydroxy-1,4-benzoquinone (DHBQ), which rapidly receives electrons with inexpensive carbon electrodes without the assistance of any metal electro-catalyst. Electrons are withdrawn from a second water solution of a food additive, potassium ferrocyanide (K4Fe(CN)6). When these two solutions flow along opposite sides of a cation-conducting membrane, this flow battery delivers a cell potential of 1.21 V, a peak galvanic power density of 300 mW/cm2 and a coulombic efficiency exceeding 99%. Continuous cell cycling at 100 mA/cm2 shows a capacity retention rate of 99.76%/cycle over 150 cycles. Various molecular modifications involving substitution for hydrogens on the aryl ring were implemented to block decomposition by nucleophilic attack of hydroxide ions in solution. These modifications resulted in increased capacity retention rates of up to 99.962%/cycle over 400 consecutive cycles, accompanied by changes in voltage, solubility, kinetics and cell resistance. Quantum chemistry calculations of a large number of organic compounds predicted a number of related structures that should have even higher performance and stability. Flow batteries based on alkaline-soluble dihydroxybenzoquinones and derivatives are promising candidates for large-scale, stationary-storage of electrical energy.

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.

The massive-scale integration of renewable electricity into the power grid is impeded by its intrinsic intermittency. The aqueous organic redox flow battery (AORFB) rises as a potential storage solution; however, the choice of positive electrolytes is limited, and the aqueous-soluble organic positive redox-active species reported to date have short lifetimes. Here we report a stable organic molecule for the positive terminal, 4-[3-(trimethylammonio)propoxy]-2,2,6,6- tetramethylpiperidine-1-oxyl (TMAP-TEMPO) chloride, exhibiting high (4.62 M) aqueous solubility. When operated in a practical AORFB against a negative electrolyte comprising BTMAP-viologen at neutral pH, the flow cell displayed an open-circuit voltage of 1.1 Volts and a coulombic efficiency of >99.73%. The capacity retention rate is among the highest of all-organic AORFBs reported to date, at 99.993% per cycle over 1000 consecutive cycles; the temporal capacity fade rate of 0.026% per hour is independent of concentration.

An aqueous flow battery based on low-cost, nonflammable, noncorrosive, and earth-abundant elements is introduced. During charging, electrons are stored in a concentrated water solution of 2,5-dihydroxy-1,4-benzoquinone, which rapidly receives electrons with inexpensive carbon electrodes without the assistance of any metal electrocatalyst. Electrons are withdrawn from a second water solution of a food additive, potassium ferrocyanide. When these two solutions flow along opposite sides of a cation-conducting membrane, this flow battery delivers a cell potential of 1.21 V, a peak galvanic power den- sity of 300 mW cm−2, and a coulombic efficiency exceeding 99%. Continuous cell cycling at 100 mA cm−2 shows a capacity retention rate of 99.76% cycle−1 over 150 cycles. Various molecular modifications involving substitution for hydrogens on the aryl ring are implemented to block decomposition by nucleophilic attack of hydroxide ions. These modifications result in increased capacity retention rates of up to 99.96% cycle−1 over 400 consecutive cycles, accompanied by changes in voltage, solubility, kinetics, and cell resistance. Quantum chemistry calculations of a large number of organic compounds predict a number of related structures that should have even higher perfor- mance and stability. Flow batteries based on alkaline-soluble dihydroxybenzo- quinones and derivatives are promising candidates for large-scale, stationary storage of electrical energy.

Aqueous organic redox flow batteries (AORFBs) have recently gained significant attention as a potential candidate for grid-scale electrical energy storage. Successful implementation of this technology will require redox-active organic molecules with many desired properties. Here we introduce a naphthoquinone dimer, bislawsone, as the redox-active material in a negative potential electrolyte (negolyte) for an AORFB. This novel dimerization strategy substantially improves the performance of the electrolyte vs. that of the lawsone monomer in terms of solubility, stability, reversible capacity, permeability and cell voltage. An AORFB pairing bislawsone with a ferri/ferrocyanide positive electrolyte delivers an open-circuit voltage of 1.05 V and cycles at a current density of 300 mA/cm2 with a negolyte concentration of 2 M electrons in alkaline solution. We determined the degradation mechanism for the naphthoquinone-based electrolyte using chemical analysis, and predict theoretically electrolytes based on naphthoquinones that will be even more stable.

A water-miscible anthraquinone with polyethylene glycol (PEG)-based solubilizing groups is introduced as the redox-active molecule in a negative electrolyte (negolyte) for aqueous redox flow batteries, exhibiting the highest volumetric capacity among aqueous organic negolytes. We synthesized and screened a series of PEG-substituted anthraquinones (PEGAQs) and carefully studied one of its isomers, namely 1,8-bis(2-(2-(2- hydroxyethoxy)ethoxy)ethoxy)anthracene-9,10-dione (AQ-1,8-3E-OH), which has high electrochemical reversibility and is completely miscible in water of any pH. A negolyte containing 1.5 M AQ-1,8-3E-OH, when paired with a ferrocyanide-based positive electrolyte across an inexpensive, non-fluorinated permselective polymer membrane at pH 7, exhibits an open-circuit potential of 1.0 V, a volumetric capacity of 80.4 Ah/L, and an energy density of 25.2 Wh/L.