The invention provides an electrochemical cell based on a new chemistry for a flow battery for large scale, e.g., grid-scale, electrical energy storage. Electrical energy is stored chemically at an electrochemical electrode by the protonation of small organic molecules called quinones to hydroquinones. The proton is provided by a complementary electrochemical reaction at the other electrode. These reactions are reversed to deliver electrical energy. A flow battery based on this concept can operate as a closed system. The flow battery architecture has scaling advantages over solid electrode batteries for large scale energy storage.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
 This invention was made with government support under grant number 0670-4322 from the Advanced Research Projects Agency-Energy-U.S. Department of Energy. The government has certain rights to the invention.