Toward Soluble, Stable Organic Electroactive Materials for Non-Aqueous Redox Flow Batteries

Abstract

Commercial redox flow batteries (RFBs) contain highly acidic and corrosive electrolytes, a cause for concern with widespread use to due concerns about safety and environmental contamination. Replacing these electrolytes with non-aqueous equivalents allows for a safer storage medium. Additionally, utilization of organic electroactive materials may lead to more scalable technologies that do not rely on mined materials such as vanadium and lithium. Furthermore, non-aqueous electrolytes could enable a 2- to 3-fold increase in operating voltage due to the wider operating voltage of non-aqueous systems. Despite the promise for a safer, scalable, higher energy system, the number of organic compounds reported in non-aqueous flow battery systems has been limited to a few classes of compounds, many of which suffer from instability and/or insolubility, especially in charged states. Our recent efforts have focused on the development of organic electron donors and acceptors with stable oxidized and reduced states. This presentation will focus on design strategies utilized to increase molecular stability and solubility in all relevant states of oxidation while keeping syntheses short, high yielding, and scalable. In particular, we highlight the design, synthesis, and electrochemical analysis of new phenothiazine and napthoquinone derivatives designed to serve as one- or two-electron donors. We show that tactical placement of substituents leads to improved stability and increased solubility. Additionally, a new approach to modification of redox potentials using strategic substituent placement will be presented.