Developing New Chemistry for Redox Flow Batteries

Abstract

Aqueous organic redox flow batteries (AORFBs) have emerged as an attractive alternative RFB technology because redox active organic molecule materials are synthetically tunable, sustainable, and potentially low cost. The presentation will cover our recent research efforts in developing two electron storage viologen molecules as anolyte materials for AORFBs. These viologen anolytes in neutral NaCl solutions have a theoretical capacity up to 96.5 Ah/L in H2O and exhibit a low reduction potential down to -0.78 V vs NHE. The neutral aqueous flow battery demonstration of two two-electron storage viologen molecules with (ferrocenylmethyl)trimethylammonium chloride (FcNCl) delivered up to 1.38 V cell voltage, and outstanding battery performance including a power density up to 130 mW/cm2, capacity retention up to 99.99% per cycle, and energy efficiency up to 65% at 60 mA/cm2. When paired with a TEMPO catholyte, a 1.72 V total organic RFB was also demonstrated. In addition, a fundamental study of the redox couple of [Fe(CN)6]4+/3+ in different supporting electrolytes with pH from 7 to 14 will be presented. We found that the redox couple functions best at neutral or near neutral conditions in RFBs. The entire presentation emphasizes that fundamental understandings of redox active electrolytes at molecular level are crucial to develop new generations of redox flow batteries for large scale and dispatchable renewable energy storage.