Unlocking Multielectron Transfer in a Quinone–Pyrazine Conjoined Redox Core for Capacity-Doubled and Ultrastable Aqueous Organic Redox Flow Batteries

Aqueous organic redox flow batteries (AORFBs) face energy density and stability challenges. We introduce DAPQ, an anthraquinone-phenazine fused molecule with a π-conjugated architecture enabling four-electron storage. The rigid fused-ring structure integrates four redox-active sites, enhancing aromaticity to resist degradation while achieving reversible multielectron transfer and superior volumetric capacity. The 0.6 M DAPQ-based AORFB delivers an exceptionally high energy density of 53.59 Wh L^-1 (53.48 Ah L^-1), and the 0.5 M DAPQ-based AORFB delivers a capacity retention of 99.86% over 2,300 cycles (1991 h), showing merely 0.0017% daily decay. Stable operation persists even at 50 °C, confirming conjugated rigidity's critical role in redox core stabilization and longevity. Mechanistic studies reveal that extended π-conjugation and balanced charge distribution synergistically inhibit parasitic reactions. This conjugation-driven multielectron design establishes a paradigm for developing high-capacity, durable organic charge carriers, advancing scalable, safe, and sustainable grid-scale energy storage solutions.