Two electron utilization of methyl viologen anolyte in nonaqueous organic redox flow battery

Methyl viologen (MV) as a bench-mark anolyte material has been frequently applied in aqueous organic redox flow batteries (AORFBs) towards large-scale renewable energy storage. However, only the first reduction of MV was utilized in aqueous electrolytes because of the insoluble MV0 generated from the second reduction of MV. Herein, we report that methyl viologen with bis(trifluoromethane) sulfonamide counter anion, MVTFSI, can achieve two reversible reductions in a nonaqueous supporting electrolyte. Paired with (Ferrocenylmethyl) trimethylammonium bis(trifluoromethanesulfonyl) imide, FcNTFSI, as catholyte, the MVTFS/FcNTFSI nonaqueous organic redox flow battery (NOARFB) can take advantage of either one electron or two electron storage of the methyl viologen moiety and provide theoretical energy density of 24.9 Wh/L and a cell voltage of up to 1.5 V. Using a highly conductive LiTFSI/CH3CN supporting electrolyte and a porous Daramic separator, the NOARFB displayed excellent cycling performance, including up to a 68.3% energy efficiency at 40 mA/cm(2), and more than 88% total capacity retention after 100 cycles. (C) 2018 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. and Science Press. All rights reserved.