Solubility and Stability of Redox-Active Organic Molecules in Redox Flow Batteries

The rise of renewable energy sources has spurred the development of energy storage systems, including redox flow batteries (RFBs), which provide a viable solution for scalable and safe energy storage. This spotlight focuses on the design of redox-active organic molecules (ROMs) as active materials in organic RFBs. Various innovative strategies have enhanced the solubility of as-prepared ROMs through chemical functionalization and noncovalent interactions. ROMs should also maintain high solubility and stability during the charging and discharging processes. It requires a comprehensive understanding of ROM behavior during the redox processes, achieved by integrating experimental analyses and computational simulations. While isolated ROMs can often undergo undesirable reactions during the redox process, ROM clustering has proven to be effective in boosting chemical stability and mitigating radical characteristics. The balance between attractive and repulsive forces is essential to maintain small-size clustering while preventing excessive ROM aggregation that leads to precipitation. Additionally, protective additives and electrolyte optimization have been developed in the case of disproportionation, necessitating isolating ROMs.