Linked Donor-Acceptor Systems for Symmetric Nonaqueous Redox Flow Batteries

Abstract

A series of molecules containing electron donor and acceptor moieties were synthesized and analyzed for potential future use in redox flow batteries (RFBs). These compounds, including D-A, D-A-D, and A-D-A alkyl-linked systems, can exist in at least three stable oxidation states: an oxidized (catholyte) form, a reduced (anolyte) form, and the neutral species. For this study, donors included various organic heterocycles, while acceptors included several imides and diimides. In all cases, cyclic voltammetry revealed highly reversible electrochemical behavior for both the individual redox active moieties as well as for the fully linked system. This approach provides for the independent optimization of anolyte and catholyte properties, while the covalent linkage results in a symmetric system whereby both RFB half-reactions generate an identical product (the neutral species). In principle, this may allow for elimination of the ubiquitous and expensive ion exchange membrane used in typical RFBs. Because the membrane can account for up to 40% of cell costs, this could represent an important opportunity to improve the economics of employing flow batteries for grid-level energy storage applications. The synthesis, characterization and preliminary electrochemical investigation of these molecules will be described. Figure 1