Redox‐Targeting Synergy With Dual Mediators for Prussian Blue Analogue Flow Batteries

Abstract

ABSTRACT Aqueous redox‐targeting flow batteries (RTFBs) are highly promising electrochemical energy storage systems due to their high energy density, long cycle life, and high safety. Dual‐molecule redox‐targeting (DMRT) system simplifies the matching between redox mediators (RMs) and solid materials. However, the interaction between RMs and solid material is not well clarified in reported works. Here, a 4‐OH‐TEMPO/[Fe(CN) 6 ] 3−/4− ‐NiHCF||Zn DMRT flow battery is developed in this work, delivering an outstanding energy density of 75.04 Wh L −1 (9.09 times higher than that of blank flow battery), excellent coulombic efficiency (99.9%), solid material utilization (82.9%), and capacity retention (99.7% per cycle) at 10 mA cm −2 . Importantly, a redox‐targeting synergy mechanism of two RMs is elucidated through various experimental and theoretical validations, wherein [Fe(CN) 6 ] 3−/4− facilitates Fe‐Fe electronic delocalization and Na + extraction, while 4‐OH‐TEMPO accelerates Fe‐N interfacial charge exchange. The dual‐mediator design exhibits distinct SOC‐dependent contributions, quantitatively revealed by time‐resolved operando ultraviolet‐visible (UV‐Vis) spectroscopy. Meanwhile, frequency‐resolved operando distribution of relaxation times‐electrochemical impedance spectroscopy (DRT‐EIS) clarifies that direct NiHCF‐mediator interfacial coupling governs the redox‐targeting resistance. This work deepens the mechanistic understanding of redox‐targeting chemistry in DMRT systems, advancing high‐energy‐density aqueous flow batteries.