Exploring Contemporary Advancements and Outlook in Viologen-Based Aqueous Organic Redox Flow Batteries: A Mini Review

The emerging energy needs of society encourage the use of renewable energy resources, but the sporadic and erratic nature of renewable energy systems impedes high-efficiency and economically viable energy storage technologies. To create a grid-scale energy storage system for erratic energy sources, Redox Flow Batteries (RFBs) are attractive contenders for the large-scale storage of electricity. In this regard, the Aqueous Organic Redox Flow Battery (AORFB), an innovative system with decoupled capacity and power, holds energy in organic redox-active species and can be easily scaled up, making it a promising low-cost energy storage technology. In AORFB, the viologen is one of the most promising redox species due to its electrochemical reversibility and exceptional radical stability. Herein, various breakthroughs in viologen based AORFBs are carefully studied and reviewed. Moreover, viologen possesses several advantageous features such as operation at a wide range of temperatures, easy to tune redox potential, high reversibility, and simple synthetic routes over other materials which enable a good opportunity to develop viologen based AORFBs for large scale applications in the near future. The viologen obstacles are described, and the authors' opinions on the development of viologen based AORFBs are underlined.