# A metal-free organic–inorganic aqueous flow battery

 Title: A metal-free organic–inorganic aqueous flow battery Author: Huskinson, Brian Thomas; Marshak, Michael; Suh, Changwon; Er, Suleyman; Gerhardt, Michael; Galvin, Cooper J.; Chen, Xudong; Aspuru-Guzik, Alan; Gordon, Roy Gerald; Aziz, Michael J. Note: Order does not necessarily reflect citation order of authors. Citation: Huskinson, Brian, Michael P. Marshak, Changwon Suh, S?leyman Er, Michael R. Gerhardt, Cooper J. Galvin, Xudong Chen, Alán Aspuru-Guzik, Roy G. Gordon, and Michael J. Aziz. 2014. A metal-free organic–inorganic aqueous flow battery. Nature 505(7482): 195-198. Full Text & Related Files: Nature paper website version.pdf (542.7Kb; PDF) Abstract: As the fraction of electricity generation from intermittent renewable sources—such as solar or wind—grows, the ability to store large amounts of electrical energy is of increasing importance. Solid-electrode batteries maintain discharge at peak power for far too short a time to fully regulate wind or solar power output$$^{1, 2}$$. In contrast, flow batteries can independently scale the power (electrode area) and energy (arbitrarily large storage volume) components of the system by maintaining all of the electro-active species in fluid form$$^{3, 4, 5}$$. Wide-scale utilization of flow batteries is, however, limited by the abundance and cost of these materials, particularly those using redox-active metals and precious-metal electrocatalysts$$^{6, 7}$$. Here we describe a class of energy storage materials that exploits the favourable chemical and electrochemical properties of a family of molecules known as quinones. The example we demonstrate is a metal-free flow battery based on the redox chemistry of 9,10-anthraquinone-2,7-disulphonic acid (AQDS). AQDS undergoes extremely rapid and reversible two-electron two-proton reduction on a glassy carbon electrode in sulphuric acid. An aqueous flow battery with inexpensive carbon electrodes, combining the quinone/hydroquinone couple with the $$Br_2/Br^-$$ redox couple, yields a peak galvanic power density exceeding 0.6 W cm^{−2} at 1.3 A cm^{−2}. Cycling of this quinone–bromide flow battery showed >99 per cent storage capacity retention per cycle. The organic anthraquinone species can be synthesized from inexpensive commodity chemicals$$^8$$. This organic approach permits tuning of important properties such as the reduction potential and solubility by adding functional groups: for example, we demonstrate that the addition of two hydroxy groups to AQDS increases the open circuit potential of the cell by 11% and we describe a pathway for further increases in cell voltage. The use of π-aromatic redox-active organic molecules instead of redox-active metals represents a new and promising direction for realizing massive electrical energy storage at greatly reduced cost. Published Version: doi:10.1038/nature12909 Terms of Use: This article is made available under the terms and conditions applicable to Open Access Policy Articles, as set forth at http://nrs.harvard.edu/urn-3:HUL.InstRepos:dash.current.terms-of-use#OAP Citable link to this page: http://nrs.harvard.edu/urn-3:HUL.InstRepos:11688785 Downloads of this work: