Molecular Engineering of Organic Species for Aqueous Redox Flow Batteries.

Redox flow batteries (RFBs) are promising candidates for large-scale energy storage systems (ESSs) due to their unique architecture that can decouple energy and power. Aqueous organic RFBs (AORFBs) use non-flammable and intrinsically safe electrolyte, in which organic compounds composed of earth-abundant and cost-effective elements perform as redox couples. The application of redox-active organics tremendously expands the development space of RFBs owing to the highly tunable molecule structure. Molecular engineering enables the exceeding merits in solubility, stability, and redox potential of different organic molecules. Herein, this review summarizes the application of molecular engineering in several types of organic compounds, focusing on the fundamental overview of their physicochemical properties and design strategies. We discuss the electrochemical merits and performances with the intrinsic properties of the designed organic components. Finally, we outline the requirements for rational design of innovative organics to motivate more valuable research and present the prospect of molecule engineering used in AORFBs.