ABSTRACT Aqueous organic redox flow batteries offer a safe and potentially inexpensive solution to the problem of storing massive amounts of electricity produced from intermittent

renewables. However, molecular decomposition represents a major barrier to commercialization—and although structural modifications can improve stability, it comes at the expense of synthetic

cost and molecular weight. Now, utilizing 2,6-dihydroxy-anthraquinone (DHAQ) without further structural modification, we demonstrate that the regeneration of the original molecule after

decomposition represents a viable route to achieve low-cost, long-lifetime aqueous organic redox flow batteries. We used in situ (online) NMR and electron paramagnetic resonance, and

molecule. This electrochemical regeneration process also rejuvenates the positive electrolyte—rebalancing the states of charge of both electrolytes without introducing extra ions. Access

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AIR-STABLE NAPHTHALENE DERIVATIVE-BASED ELECTROLYTES FOR SUSTAINABLE AQUEOUS FLOW BATTERIES Article 28 August 2024 AN AMPHOTERIC AND HYDROGEN-BOND-RICH ARTIFICIAL Α-AMINO ACID FOR HIGHLY

DURABLE AQUEOUS REDOX FLOW BATTERIES Article Open access 21 May 2025 AN ACTIVE AND DURABLE MOLECULAR CATALYST FOR AQUEOUS POLYSULFIDE-BASED REDOX FLOW BATTERIES Article 02 October 2023 DATA

AVAILABILITY Data in the main paper and its Supplementary Information are available from https://doi.org/10.6084/m9.figshare.19612128. Source Data are provided with this paper. REFERENCES *

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at Harvard was supported by the US National Science Foundation through grant no. CBET-1914543, by a US DOE award no. DE-AC05-76RL01830 through PNNL subcontract no. 535264, and by a grant

from the Massachusetts Clean Energy Center. Research at University of Cambridge was supported by Centre of Advanced Materials for Integrated Energy Systems (CAM-IES), via EPSRC grant no.

EP/P007767/1 and Shell. E.W.Z acknowledges the STFC Futures Early Career Award, grant no. ST/R006873/1. The funders had no role in study design, data collection and analysis, decision to

publish or preparation of the manuscript. We acknowledge P.A.A. Klusener from Shell for useful discussions. We thank D. A. Pollack, and K. Amini for useful discussions. AUTHOR INFORMATION

Author notes * Evan Wenbo Zhao Present address: Magnetic Resonance Research Center, Institute for Molecules and Materials, Radboud University Nijmegen, Nijmegen, the Netherlands *

Marc-Antoni Goulet Present address: Department of Chemical and Materials Engineering, Concordia University, Montreal, Quebec, Canada * Ali Davoodi Present address: Sichuan

University-Pittsburgh Institute, Sichuan University, Chengdu, China * These authors contributed equally: Yan Jing, Evan Wenbo Zhao, Marc-Antoni Goulet. AUTHORS AND AFFILIATIONS * Department

of Chemistry and Chemical Biology, Harvard University, Cambridge, MA, USA Yan Jing & Roy G. Gordon * Yusuf Hamied Department of Chemistry, University of Cambridge, Cambridge, UK Evan

Wenbo Zhao, Erlendur Jónsson & Clare P. Grey * John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA Marc-Antoni Goulet, Meisam Bahari, Eric

M. Fell, Shijian Jin, Ali Davoodi, Min Wu, Roy G. Gordon & Michael J. Aziz * Materials and Metallurgical Engineering Department, Faculty of Engineering, Ferdowsi University of Mashhad

(FUM), Mashhad, Iran Ali Davoodi Authors * Yan Jing View author publications You can also search for this author inPubMed Google Scholar * Evan Wenbo Zhao View author publications You can

also search for this author inPubMed Google Scholar * Marc-Antoni Goulet View author publications You can also search for this author inPubMed Google Scholar * Meisam Bahari View author

publications You can also search for this author inPubMed Google Scholar * Eric M. Fell View author publications You can also search for this author inPubMed Google Scholar * Shijian Jin

View author publications You can also search for this author inPubMed Google Scholar * Ali Davoodi View author publications You can also search for this author inPubMed Google Scholar *

Erlendur Jónsson View author publications You can also search for this author inPubMed Google Scholar * Min Wu View author publications You can also search for this author inPubMed Google

Scholar * Clare P. Grey View author publications You can also search for this author inPubMed Google Scholar * Roy G. Gordon View author publications You can also search for this author

inPubMed Google Scholar * Michael J. Aziz View author publications You can also search for this author inPubMed Google Scholar CONTRIBUTIONS M.J.A., R.G.G., C.P.G. supervised the project.

Y.J., E.W.Z., M.-A.G., M.J.A., R.G.G. and C.P.G. conceived the idea. Y.J., E.W.Z. and M.-A.G. designed the experiment. E.W.Z. performed the in situ NMR and EPR experiments and analysis. Y.J.

performed the ex situ NMR experiments and analysis. M.-A.G., M.B., E.M.F. and Y.J. performed DHA(L), ADS elctrochemical oxidation, and DHAQ and AQDS cell cycling. M.B. performed

three-electrode cell tests. M.-A.G., S.J. and Y.J. performed postmortem CV, NMR, LC-NMR experiments and a cell cycling. M.B. performed t-cell cycling with periodic aeration. E.J. made

intellectual contributions. M.W. and Y.J. synthesized DHA(L) and ADS, respectively. All authors contributed to the discussion of the project. Y.J., E.W.Z, M.-A.G., M.J.A., C.P.G. wrote the

manuscript with input from all co-authors. CORRESPONDING AUTHORS Correspondence to Clare P. Grey, Roy G. Gordon or Michael J. Aziz. ETHICS DECLARATIONS COMPETING INTERESTS The authors

declare no competing interests. PEER REVIEW PEER REVIEW INFORMATION _Nature Chemistry_ thanks Antoni Forner-Cuenca, Yi-Chun Lu and Edgar Ventosa for their contribution to the peer review of

this work. ADDITIONAL INFORMATION PUBLISHER’S NOTE Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. EXTENDED DATA

EXTENDED DATA FIG. 1 ELECTROCHEMICAL OXIDATION OF DHA(L)2−. A & B, Linear sweep voltammetry (LSV) and the 1st order differential of 10 mM DHA(L)2− in 1 M KOH supporting electrolyte

indicating a peak for dimerization reaction around −260 mV vs. SHE and a second oxidation reaction starting around +300 mV vs. SHE, before being overshadowed by oxygen evolution at around

+650 mV vs. SHE. We consider the potentials (−0.32 V, + 0.57 V) at the 1st order differential peak current as the approximations of oxidation potentials of [DHA(L)2− to (DHA)24−] and

[(DHA)24− to DHAQ2−]. The 1st order differential was from the LSV curve obtained at 20 mV/s. C & D, Cyclic voltammograms of 10 mM pure DHA in 1 M KOH before and after a + 110 mV vs. SHE

10-minute potential hold with a highly porous Zoltek PXFB working electrode. New peaks match those of dimer observed in a previous study[2]; cyclic voltammograms of 10 mM pure DHA in 1 M KOH

before and after +410 mV vs. SHE 10-minute potential hold with a highly porous working electrode. New peaks match those of DHAQ2−. E, Potential hold of 0.1 M DHA(L)2− in 1.2 M KOH negolyte

in full cell containing a 2X excess of 50 mM K4[Fe(CN)6] and 50 mM K3[Fe(CN)6] posolyte. The Y-axis represent the number of coulombs extracted from DHA(L)2− electrolyte over electrochemical

oxidation. F, 1H NMR spectra of DHA(L)2− negolyte before and after 30-min hold at different cell voltages. EXTENDED DATA FIG. 2 DHAQ REGENERATION HYSTERESIS. A, Repeated application of

electrochemical regeneration of negolyte in battery composed of 6 mL 100 mM DHAQ2− in the negolyte and a mixture of 35 mL 100 mM K4[Fe(CN)6] and 50 mM K3[Fe(CN)6] in the posolyte.

Galvanostatic cycling at ±50 mA/cm2 with potential holds at 1.0 and 1.5 V and current cutoff of ±1 mA/cm2 during normal cycles. Every 50 cycles an additional discharge step at −2 mA/cm2

until potential limit and a further hold until current decreases to −0.2 mA/cm2. B, Aggregate data for 3 cell replicates with varying potential limits for regeneration treatment indicating

partial dependence of recovery ratio on recovery from prior treatment. EXTENDED DATA FIG. 3 ENERGETIC COST OF ELECTROCHEMICAL REGENERATION IN FIG. 4A AND C. A, Integrated areas above and

below 0 V of the cell discharge voltage profile with electrochemical regeneration in Fig. 4c. B, Integrated areas above and below 0 V of the cell discharge voltage profiles with 13

regeneration processes in Fig. 4a. The area ratio (%) represents the percentage of discharged electrical energy that is subsequently used for regeneration during a single discharge process,

reflecting the energetic cost. It is, on average, 1.30%. Note that the electrochemical regeneration step is not performed in every cycle, but rather once every 51 cycles. Relative to the

total electricity discharged during 51 cycles, the energetic cost for regeneration is only 0.025%. EXTENDED DATA FIG. 4 DHAQ CONCENTRATION TRACKING. A, Cycling of battery composed of 5 mL

100 mM DHAQ2− in the negolyte and 20 mL of a mixture of 100 mM K4[Fe(CN)6] and 50 mM K3[Fe(CN)6] in the posolyte. Galvanostatic cycling at ±50 mA/cm2 with potential holds at 1.0 V and 1.5 V

and current cutoff of ±1 mA/cm2 during normal cycles. Three electrochemical oxidation treatments before an aliquot was removed from negolyte reservoir on day 10 for concentration

measurement. B, Cyclic voltammograms of 20 mM DHAQ2− in 1 M KOH on glassy carbon working electrode. Pristine DHAQ2− electrolyte measured before and after dilution by 10% to verify resolution

of measurement. Cycled DHAQ2− data refers to an aliquot removed from negolyte in part a, after ~25% capacity had been lost. No change in peak current suggests DHAQ2− concentration has not

changed during cycling after regeneration treatment. C & D, Comparison of DHAQ2− NMR peak integral with respect to DMSO internal standard. Similarity of the peak integral of cycled

electrolyte which had lost ~25% of capacity to that of pristine DHAQ2− does not indicate overall decrease in DHAQ2− concentration. An aliquot of the cycled DHAQ2− was taken for 1H NMR

measurement when ~25% capacity was lost on day 10.5. E, LC−MS result of the cycled DHAQ2−. The peak at 10.8–11.1 min is from DHAQ2−, which is the sole compound detected. Other peaks are from

background, which can be ignored. SUPPLEMENTARY INFORMATION SUPPLEMENTARY INFORMATION Supplementary Figs. 1–15 and Discussion after some captions. SOURCE DATA SOURCE DATA FIG. 1 Unprocessed

excel data for DHAQ regeneration hysteresis. SOURCE DATA FIG. 2 Unprocessed in situ NMR data. SOURCE DATA FIG. 3 Unprocessed in situ NMR data. SOURCE DATA FIG. 4 Unprocessed excel and.csv

data for flow battery tests. RIGHTS AND PERMISSIONS Reprints and permissions ABOUT THIS ARTICLE CITE THIS ARTICLE Jing, Y., Zhao, E.W., Goulet, MA. _et al._ In situ electrochemical

recomposition of decomposed redox-active species in aqueous organic flow batteries. _Nat. Chem._ 14, 1103–1109 (2022). https://doi.org/10.1038/s41557-022-00967-4 Download citation *

Received: 16 December 2021 * Accepted: 04 May 2022 * Published: 16 June 2022 * Issue Date: October 2022 * DOI: https://doi.org/10.1038/s41557-022-00967-4 SHARE THIS ARTICLE Anyone you share

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