The ability to store large amounts of electrical energy is of increasing importance with the growing fraction of electricity generation from intermittent renewable sources such as wind and solar. We have developed high performance flow batteries based on the aqueous redox behavior of small organic and metalorganic molecules, e.g. [1-9]. These redox active materials can be inexpensive and exhibit rapid redox kinetics, high solubilities, and long lifetimes, although short lifetimes are more common [7, 10]. We will discuss the economic tradeoff between upfront capital cost and periodic chemical replacement cost [11]. We discuss the very few chemistries with long enough calendar life for practical application in stationary storage [3-6, 9], and on the prospects for reversing capacity fade by recomposing decomposed molecules [8, 12].

[1] B. Huskinson, M.P. Marshak, C. Suh, S. Er, M.R. Gerhardt, C.J. Galvin, X. Chen, A. Aspuru-Guzik, R.G. Gordon and M.J. Aziz, "A metal-free organic-inorganic aqueous flow battery", Nature 505, 195 (2014), http://dx.doi.org/10.1038/nature12909

[2] K. Lin, Q. Chen, M.R. Gerhardt, L. Tong, S.B. Kim, L. Eisenach, A.W. Valle, D. Hardee, R.G. Gordon, M.J. Aziz and M.P. Marshak, "Alkaline Quinone Flow Battery", Science 349, 1529 (2015), http://dx.doi.org/10.1126/science.aab3033

[3] E.S. Beh, D. De Porcellinis, R.L. Gracia, K.T. Xia, R.G. Gordon and M.J. Aziz, "A Neutral pH Aqueous Organic/Organometallic Redox Flow Battery with Extremely High Capacity Retention", ACS Energy Letters 2, 639 (2017). http://dx.doi.org/10.1021/acsenergylett.7b00019

[4] D.G. Kwabi, K. Lin, Y. Ji, E.F. Kerr, M.-A. Goulet, D. DePorcellinis, D.P. Tabor, D.A. Pollack, A. Aspuru-Guzik, R.G. Gordon, and M.J. Aziz, “Alkaline Quinone Flow Battery with Long Lifetime at pH 12” Joule 2, 1907 (2018). https://doi.org/10.1016/j.joule.2018.07.005

[5] Y. Ji, M.-A. Goulet, D.A. Pollack, D.G. Kwabi, S. Jin, D. DePorcellinis, E.F. Kerr, R.G. Gordon, and M.J. Aziz, “A phosphonate-functionalized quinone redox flow battery at near-neutral pH with record capacity retention rate” Advanced Energy Materials 2019, 1900039; https://doi.org/10.1002/aenm.201900039

[6] M. Wu, Y. Jing, A.A. Wong, E.M. Fell, S. Jin, Z. Tang, R.G. Gordon and M.J. Aziz, “Extremely Stable Anthraquinone Negolytes Synthesized from Common Precursors” Chem 6, 1432 (2020); https://doi.org/10.1016/j.chempr.2020.03.021

[7] M.-A. Goulet & M.J. Aziz, “Flow Battery Molecular Reactant Stability Determined by Symmetric Cell Cycling Methods”, J. Electrochem. Soc. 165, A1466 (2018). http://dx.doi.org/10.1149/2.0891807jes

[8] M.-A. Goulet, L. Tong, D.A. Pollack, D.P. Tabor, S.A. Odom, A. Aspuru-Guzik, E.E. Kwan, R.G. Gordon, and M.J. Aziz, “Extending the lifetime of organic flow batteries via redox state management” J. Am. Chem. Soc. 141, 8014 (2019); https://doi.org/10.1021/jacs.8b13295

[9] M. Wu, M. Bahari, E.M. Fell, R.G. Gordon and M.J. Aziz, “High-performance anthraquinone with potentially low cost for aqueous redox flow batteries” J. Mater. Chem. A 9, 26709-26716 (2021). https://doi.org/10.1039/D1TA08900E

[10] D.G. Kwabi, Y.L. Ji and M.J. Aziz, “Electrolyte Lifetime in Aqueous Organic Redox Flow Batteries: A Critical Review” Chem. Rev. 120, in press (2020); https://doi.org/10.1021/acs.chemrev.9b00599

[11] F.R. Brushett, M.J. Aziz and K.E. Rodby, “On lifetime and cost of redox-active organics for aqueous flow batteries” Invited Viewpoint article for ACS Energy Letters. 5, 879 (2020); https://doi.org/10.1021/acsenergylett.0c00140

[12] Y. Jing, E.W. Zhao, M.-A. Goulet, M. Bahari, E. Fell, S. Jin, A. Davoodi, Erlendur Jónsson, M. Wu, C.P. Grey, R.G. Gordon and M.J. Aziz, “Closing the Molecular Decomposition-Recomposition Loop in Aqueous Organic Flow Batteries” Nature Chemistry, in press (2022). Preprint: http://dx.doi.org/10.33774/chemrxiv-2021-x05x1