A Fused Quinone-Pyrazine-Based Aqueous Flow Battery Negolyte with Record Volumetric Capacity and Long Lifetime

Area of Science:

• Electrochemistry and Energy Storage
• Materials Science for Renewable Energy

Background:

• Aqueous organic flow batteries are crucial for storing energy from intermittent renewable sources.
• Existing redox materials require optimization for redox potentials, solubility, and stability.

Purpose of the Study:

• To create a novel redox core by fusing quinone and pyrazine motifs for enhanced flow battery performance.
• To synthesize and characterize 2,2'-((6,11-dioxo-6,11-dihydrobenzo[b]phenazine-2,3-diyl)bis(oxy))dipropionic acid (DCNQBP) for high-capacity energy storage.

Main Methods:

• Synthesis of DCNQBP by fusing quinone-pyrazine redox motifs and decorating with solubilizing groups.
• Electrochemical characterization using cyclic voltammetry.
• In situ monitoring (pH, IR), NMR spectroscopy, and Density Functional Theory (DFT) calculations.

Main Results:

• DCNQBP achieved a record volumetric capacity of 121 Ah L⁻¹ and a low temporal fade rate of 0.018% day⁻¹.
• A unique four-electron transfer mechanism was observed, involving alternate electron uptake by quinone and pyrazine groups.
• Decomposition was primarily due to hydrolysis-induced chain cleavage; deep discharge avoidance improved longevity.

Conclusions:

• Fusing redox motifs is an effective strategy to create new redox platforms with doubled electron-storage capacity.
• DCNQBP demonstrates significantly improved structural stability and high performance for aqueous organic flow batteries.
• Optimized operating conditions, such as avoiding deep discharge, are key to maximizing battery lifespan.