Host‐Guest Interactions Enhance the Performance of Viologen Electrolytes for Aqueous Organic Redox Flow Batteries

Abstract Host‐guest interactions are an attractive approach to design redox electrolytes, enabling to precisely tune the key properties for redox flow batteries such as half‐cell redox potential, solubility, and stability. Herein we report a host‐guest complex of highly water soluble (2‐hydroxypropyl)‐β‐cyclodextrin with 1‐decyl‐1′‐ethyl‐4,4′‐bipyridinium dibromide as anolyte in a new aqueous organic redox flow battery (AORFB). The supramolecular anolyte ensured the total RFB voltage increase of ≈9 % up to 0.97 V and provided a stable capacity delivery for more than 500 cycles with a capacity fade rate of 0.037 %/cycle (2.84 %/day) at high Coulombic (>99.5 %) and energy (>62 %) efficiencies. The results highlight host‐guest interactions as promising strategy towards more effective storage of renewable energy within AORFBs.