Redox flow batteries (RFBs) are a viable technology to store renewable energy in the form of electricity that can be supplied to electricity grids. However, widespread implementation of traditional RFBs, such as vanadium and Zn-Br₂ RFBs, is limited due to a number of challenges related to materials, including low abundance and high costs of redox-active metals, expensive separators, and corrosive and hazardous electrolytes. To address these challenges, we demonstrate an aqueous organic redox flow battery (AORFB), named FcNCl/MV AORFB,¹ featuring a high theoretical energy density, 45.5 Wh/L, the highest value known for AORFBs. The battery is built from earth abundant elements (C, H, N, and Fe), specifically consisting of a newly designed organic catholyte based on a highly water soluble ferrocene compound, (ferrocenylmethyl)trimethylammonium chloride(FcNCl), a methyl viologen anolyte which was studied in our previous work,² non-flammableand non-corrosive NaCl supporting electrolyte, and low cost anion exchange membrane. This is the first application of a water-soluble ferrocene compound in aqueous RFBs. The batteries exhibit extraordinary electrochemical performances, 700 cycles with 99.99% capacity retention per cylce and 65% energy efficiency at 60 mA/cm², and delivered power density up to 125 mW/cm². The presented AORFB technology underlines great promise of soluble redox-active organic molecules for green energy storage.

Reference

1. Hu, B.; DeBruler, C.; Rhodes, Z.; Liu, T. L., J. Am. Chem. Soc., 2017, 139, 1207.

2. Liu, T. B.; Wei, X. L.; Nie, Z. M.; Sprenkle, V.; Wang, W., Adv. Energy. Mater., 2016, 6, 1501449.