Researchers at the Indian Institute of Technology (IIT Madras) have said that all-organic redox flow batteries (NORFBs) could achieve enhanced energy density, stability, and solubility by introducing pyrylium salt into the mix.

This development could pave the way for cleaner and more efficient grid energy storage systems.

The team’s research focuses on non-aqueous all-organic redox flow batteries (NORFBs), which have gained significant interest due to their environmental friendliness and higher energy density than aqueous batteries.

The prototype NORFB developed by the researchers exhibited promising results, operating at a high current density of 40 mA cm-2.

It also demonstrated stability with 60 stable galvanostatic charge-discharge (GCD) cycles and an average coulombic efficiency of 97%.

The key component of a redox flow battery is the redox-active organic molecule (ROM), which stores and releases energy.

However, conventional ROMs often have limitations such as low solubility and poor mass and charge transfer kinetics, leading to low current and energy densities.

To address these challenges, the researchers introduced the use of pyrylium salt in NORFBs for the first time.

Pyrylium salts are widely employed in synthetic organic chemistry as photocatalysts and precursors for various applications. By utilizing two different chemical components – 2,4,6-triphenylpyrylium tetrafluoroborate (TPT), as the anolyte and N-decyl phenothiazine (DPTZ) as the catholyte, the researchers constructed the NORFB.

The study demonstrated that TPT offers high solubility, reversibility, and improved stability, which are crucial factors for achieving high energy density and cyclability in redox flow batteries.

The researchers also noted that the 2nd, 4th, and 6th positions of pyrylium salt provide a versatile platform for tailoring the electrochemical activity and stability of the ROMs.

Ragupathy, an associate professor and principal scientist at the Redox Flow Battery Research Group, CSIR-Central Electrochemical Research Institute, emphasized that the use of non-aqueous solvents with a wider electrochemical potential window, along with low-cost and abundant redox-active organic materials, makes NORFBs an attractive option for grid energy storage applications.

The successful implementation of TPT as the anolyte also highlights its solubility, reversibility, and improved stability, which are crucial for achieving high energy density and cyclability in redox flow batteries.

Furthermore, the study showed that by modifying substituents at different positions of pyrylium salts, it is possible to fine-tune the redox behavior and stability of ROMs, providing a versatile platform for further exploration in this field.

Last year, researchers at the Chinese Academy of Sciences (CAS) claimed to have built a stable kilowatt-scale aqueous redox flow battery with high-performance organic redox-active molecules for renewable storage.

In the same month, researchers at the University of Sydney claimed to have developed a new, low-cost sodium-sulfur battery with four times the energy capacity of lithium-ion batteries.