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

ABSTRACT 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.