Advancements of non-viologen-based anolytes for pH-neutral aqueous organic redox flow batteries

Aqueous organic redox flow battery (AORFB) is regarded as the most promising next-generation technology for energy storage that stores electricity in redox-active organics lysed in mild salt-electrolytes. Composed of abundant elements such as C, H, O, and N, the adapted organics have a high degree of structural diversity and tunability, endowing it possible to modulate the physicochemical properties of water solubility, redox potential, and stability, and resulting in potential cost-effectiveness, ecological and environmental safety. Therefore, the designable organics consumedly expand the distance for exceeding battery behaviors in comparison with the inorganic counterparts. Herein, this study presents an overview of pH-neutral AORFBs that employ nonflammable water-soluble molecules with cheap inorganic salts as supporting electrolytes. Particular emphasis is given to the progress of molecular engineering design and synthesis of non-viologen-based organic anolytes and their respective AORFB performance. Additionally, some comments on present opportunities and perspectives of this ascendant domain are also demonstrated.