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

Area of Science:

• Electrochemistry
• Materials Science
• Energy Storage

Background:

• Aqueous redox-targeting flow batteries (RTFBs) offer high energy density, long cycle life, and safety.
• Dual-molecule redox-targeting (DMRT) systems simplify redox mediator (RM) and solid material matching.
• The interaction mechanism between RMs and solid materials in DMRT systems requires further clarification.

Purpose of the Study:

• To develop and investigate a novel 4-OH-TEMPO/[Fe(CN)6]3-/4--NiHCF||Zn DMRT flow battery.
• To elucidate the redox-targeting synergy mechanism between dual RMs and the solid electrode.
• To advance the mechanistic understanding of DMRT systems for high-energy-density aqueous flow batteries.

Main Methods:

• Fabrication and electrochemical testing of a 4-OH-TEMPO/[Fe(CN)6]3-/4--NiHCF||Zn DMRT flow battery.
• Experimental and theoretical validations to elucidate the redox-targeting synergy mechanism.
• Time-resolved operando UV-Vis spectroscopy and frequency-resolved operando DRT-EIS for mechanistic insights.

Main Results:

• The DMRT flow battery achieved an energy density of 75.04 Wh L-1, a 9.09-fold increase over blank systems.
• Exceptional performance metrics include 99.9% coulombic efficiency, 82.9% solid material utilization, and 99.7% capacity retention per cycle.
• The study identified specific roles for [Fe(CN)6]3-/4- and 4-OH-TEMPO in facilitating charge transfer and delocalization, and clarified the impact of interfacial coupling on resistance.

Conclusions:

• The developed DMRT system demonstrates significant potential for high-energy-density aqueous flow batteries.
• A detailed mechanistic understanding of the dual-mediator redox-targeting synergy was established.
• This work provides crucial insights into optimizing DMRT systems by clarifying interfacial charge transfer and redox targeting resistance.