A Six‐Electron Energy Storage Material for Ultra‐Stable Aqueous Organic Redox Flow Batteries

Aqueous organic redox flow batteries (AORFBs) offer sustainable, large‐scale energy storage using tunable, earth‐abundant organic molecules, avoiding resource limitations. While most aqueous redox flow battery materials utilize single‐ (n = 1) or dual‐electron (n = 2) transfer mechanisms, stable multi‐electron (n > 4) redox systems remain largely unexplored. A six‐electron (n = 6) phenazine‐based negative electrolyte, 2,2′,2′'‐(diquinoxalino[2,3‐a:2′,3′‐c]phenazine‐2,8,14‐triyltris(oxy))tripropionic acid (PPA) is engineered with a π ‐extended fused‐ring core and branched hydrophilic side chains. As supported by molecular dynamics simulation, the C─O linked tri‐substituted propanoic acid groups in PPA disrupt intermolecular π – π stacking, achieving an unprecedented aqueous solubility of 1.2 m with six electron storage (7.2 m electron concentration, 193.0 Ah L −1 theoretical capacity). When paired with a ferrocyanide, the PPA‐based AORFB gives a cell voltage of 1.31 V at 3.0 m electron concentration, along with a Coulombic efficiency exceeding 99.8% and a 85% utilization of its six‐electron capacity. The system demonstrates exceptional cycling stability, sustaining a capacity decay rate of 0.032% per cycle, 0.095% per day over 80 operational days. This work provides a scalable approach for stable multi‐electron energy storage materials applicable in AORFBs.