Modern organophotocatalysts: a new inspiration source for Symmetrical Organic Redox Flow Batteries

Redox flow batteries (RFBs) have emerged as significant energy storage systems amid the growing adoption of renewable energy. However, the advancement of all-organic RFBs is hindered by material crossover, limited energy density, and the time-consuming selection of suitable electrolyte partners. To address these challenges, bipolar redox-active organic molecules (BRMs) show promise for charge storage in symmetric organic redox flow batteries (SORFBs), although their development can be complex and tedious. In this study, we report an approach aimed at streamlining the identification of suitable compounds through an examination of the organophotocatalyst literature, illustrated through six acridinium compounds exhibiting stable redox states. These compounds were thoroughly characterized in electrochemical cells and subjected to cycling tests in fully symmetric flow batteries. Notably, a trisubstituted electron-rich acridinium compound emerged as a potential candidate, demonstrating over 20 days of cycling stability. Given the extensive library of organic catalysts and the advantages of SORFB designs, this approach will prove to be essential for developing an innovative electrochemical storage system.