Spatially Constrained Organic Diquat Anolyte for Stable Aqueous Flow Batteries

Redox-active organic materials (ROMs) are becoming increasingly attractive for use in redox flow batteries as promising alternatives to traditional inorganic counterparts. However, the reported ROMs are often accompanied by challenges, including poor solubility and stability. Herein, we demonstrate that the commonly used diquat herbicides, with solubilities of >2 M in aqueous electrolytes, can be used as stable anolyte materials in organic flow batteries. When coupled with a ferrocene-derived catholyte, the flow cells with the diquat anolyte demonstrate long galvanic cycling with high capacity retention. Notably, the mechanistic underpinnings of this remarkable stability are attributed to the improved pi-conjugation that originated from the near-planar molecular conformations of the spatially constrained 2,2'-bipyridyl rings, suggesting a viable structural engineering strategy for designing stable organic materials.