The invention provides an electrochemical cell based on a new chemistry for a flow battery for large scale, e.g., gridscale, electrical energy storage. Electrical energy is stored chemically in quinone molecules having multiple oxidation states, e.g., three or more. During charging of the battery, the quinone molecules at one electrode are oxidized by emitting electrons and protons, and the quinone molecules at the other electrode are reduced by accepting electrons and protons. These reactions are reversed to deliver electrical energy. The invention also provides additional high and low potential quinones that are useful in rechargeable batteries.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
 This invention was made with government support under grant number DE-AR0000348 from the Advanced Research Projects Agency--Energy--U.S. Department of Energy. The government has certain rights to the invention.