Multiple hetero-redox centers in a phenazine-ketone scaffold for high-energy-density aqueous flow batteries toward durable energy storage.

Organic redox flow batteries operating in alkaline media have attracted significant attention for their inherent safety and environmental compatibility. However, conventional quinone- and ketone-based anolytes suffer from low electron-transfer numbers (≤2 e- per molecule), irreversible isomerization and concentration-dependent side reactions, ultimately limiting their energy density and long-term cycling stability. Here, we introduce a molecular engineering strategy that leverages the conjugation of heterogeneous redox centers to fuse distinct redox-active motifs, thereby creating a new composite phenazine-ketone molecule capable of a six-electron transfer process. This multi-hetero-redox center fused scaffold not only overcomes the intrinsic limitations of conventional structures but also exhibits robust kinetics and chemical stability in an alkaline electrolyte. The resulting compound delivers a record capacity of 79.3 Ah L-1, and sustains stable operation over 3500 cycles (198.5 days), offering a viable pathway toward next-generation high-energy-density, durable and sustainable energy storage technologies.