Air-Stable Ferrocene-Based Catholytes for Improved Performance in pH-Neutral Aqueous Organic Redox Flow Batteries

Area of Science:

• Electrochemistry
• Materials Science
• Sustainable Energy

Background:

• Aqueous pH-neutral organic redox flow batteries offer sustainable grid-scale energy storage.
• Limited catholyte stability and low capacity hinder their advancement.

Purpose of the Study:

• To design and synthesize novel imidazolium-decorated ferrocene derivatives as catholytes.
• To develop a stable and high-performance catholyte for pH-neutral aqueous organic redox flow batteries.

Main Methods:

• Synthesis of imidazolium-decorated ferrocene derivatives.
• Electrochemical cycling in ambient air and inert atmospheres.
• Theoretical calculations and spectroscopic analyses (e.g., hydrogen-bonding interactions).
• Construction and testing of a pH-neutral stacked flow battery.

Main Results:

• Identified an ionic liquid-like catholyte with over 2000 cycles stability in air.
• Achieved 68-day cycling with no capacity loss at 0.5 M in an inert atmosphere.
• Demonstrated a pH-neutral stacked flow battery with 140 W peak power and 95% capacity retention after 20,000 cycles.
• Methyl imidazolium groups enhance stability via hydrogen bonding, reducing attacks on ferrocenium.

Conclusions:

• A novel, highly stable catholyte for pH-neutral aqueous organic redox flow batteries was developed.
• The new catholyte design facilitates the assembly of high-power-density, air-stable flow batteries.
• This work provides a pathway for advancing sustainable grid-scale energy storage solutions.