Doubling up: Increasing Charge Storage in Organic Donors and Acceptors for Non-Aqueous Redox Flow Batteries

Tuesday, 30 May 2017: 08:20
Grand Salon B - Section 12 (Hilton New Orleans Riverside)
S. A. Odom, A. P. Kaur, M. D. Casselman (University of Kentucky), J. D. Milshtein, J. A. Kowalski (Joint Center for Energy Storage Research), C. F. Elliott, S. R. Parkin, C. Risko, J. Anthony (University of Kentucky), and F. R. Brushett (Joint Center for Energy Storage Research)
Redox flow batteries (RFBs) are promising candidates for grid storage, with a few large-scale systems currently in operation. However, current systems have not met the stringent cost and/or safety requirements needed for widespread implementation. Replacing vanadium with organic compounds may lower materials cost, and utilizing non-aqueous (aprotic) electrolyte solvents, in place of water, could enable a 2- to 3-fold increase in operating voltage. Both features make non-aqueous RFBs candidates for large-scale stationary storage. Currently a limited number of organic compounds have been reported as stable electron donors and acceptors, with even fewer materials being studied as small molecule two-electron donors and/or two-electron acceptors. Yet if the amount of charged stored within an individual molecule were raised without significantly increasing the molecular weight, then electrolyte capacity could be increased proportionally, assuming solubility of neutral and charged species is retained. Our recent efforts have focused on the development of highly soluble electron donors and acceptors with stable oxidized and reduced states. This presentation will focus on design strategies utilized to increase molecular stability in all relevant states of charge as well as solubility. In particular, we highlight the design, synthesis, and electrochemical analysis of phenothiazine and napthoquinone derivatives designed to serve as two-electron donors and two-electron acceptors, respectively. We show that tactical placement of substituents leads to improved stability of doubly oxidized and doubly reduced species, whilst retaining atom economy and that high solubility.