Derivative Enhances Aqueous Organic Flow Batteries

Research team from the Dalian Institute of Chemical PhysicsDevelop High-Density, Stable Energy Storage for Grid Applications

A research team from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences (CAS) has developed a pyrene tetraone derivative that improves the performance of aqueous organic flow batteries (AOFBs). The study, published in the Journal of the American Chemical Society, addresses challenges related to energy density and stability in AOFBs.

AOFBs are considered suitable for renewable energy storage due to their safety and the use of organic redox-active molecules (ORAMs). However, low energy density, instability at high concentrations, and high synthesis costs limit commercial application. Increasing electron transfers in ORAMs can enhance energy density and reduce electrolyte costs, but often affects stability and solubility.

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Researchers designed an asymmetrical pyrene-4,5,9,10-tetraone-1-sulfonate (PTO-PTS) monomer through a coupling oxidation-sulfonation reaction. This monomer stores four electrons, reaching a theoretical electron concentration of 4.0 M and forming a stable semiquinone free radical.

In AOFBs, the monomer achieved a volumetric capacity of 90 Ah/L. The batteries retained nearly 100% capacity after 5,200 cycles in air. The extended conjugated structure of pyrene tetraone enabled reversible four-electron transfer through enolization tautomerism. Adding a sulfonic acid group reduced molecular planarity, increasing charge density and hydrogen bonding with water molecules, improving solubility.

The monomer stabilized the semiquinone free radical by delocalizing its conjugated structure and maintaining π-π stacking during redox reactions. This contributed to stability in air and at high temperatures.

AOFBs incorporating this derivative reached an energy density of 60 Wh/L. Both symmetric and full cells showed no significant capacity decay after thousands of cycles at 60 °C, with stability maintained for 1,500 hours. The batteries demonstrated performance across a temperature range of 10 to 60 °C, supporting their potential for large-scale energy storage.