Multi-redox Organic Species for High-Energy-Density Aqueous Redox Flow Batteries: Mechanism, Characteristics, and Applications

The pursuit of carbon neutrality demands scalable, safe energy storage, driving interest in aqueous organic redox flow batteries (AORFBs) for their sustainability and molecular tunability. Developing redox-active organic materials capable of multi-electron transfer offers a highly promising route to overcome the limitations of energy density in AORFBs. This review comprehensively summarizes recent advances in multi-redox organic species for AORFBs, highlighting their critical role in boosting energy density, and critically analyze key material classes—including viologens, quinones, azines, and naphthalene diimides—alongside emerging molecules like azobenzenes, phenylamines, and fluorenones. The discussion focuses on molecular design principles, redox mechanisms, and structure-property relationships underpinning multi-electron transfer. Finally, the challenge and perspective on the development of multi-redox organic species for high-performance AORFBs are also provided.