The prototype battery assembly used for energy storage efficiency measurements (in French). It is a symmetrical battery used to evaluate the stability of the developed molecule. Reservoirs A and B contain solutions of the organic molecule AzoBiPy, in its oxidized form in A and in its reduced form in B. The solutions are pumped by pumps (C) to the electrochemical cell where electron exchange takes place (D). Image Credit: Helene Lebel et Dominic Rochefort

A Universite de Montreal-led research team has produced an organic molecule that stores renewable energy with unprecedented stability, leading to more sustainable flow batteries. Their findings were published in the Journal of the American Chemical Society.

What if the energy generated by wind turbines on a beautiful day of summer could be kept until January and used to heat houses in the depths of winter? It may be conceivable, due to the discovery of a novel organic molecule capable of holding a charge for months with almost no loss of energy.

The molecule, known as AzoBiPy, was created by a research team from Universite de Montreal's Department of Chemistry in collaboration with experts from Concordia University.

AzoBiPy was tested in a redox flow battery in the lab for 70 days. The molecule demonstrated remarkable stability, losing only 0.02 percent of its capacity every day. It also stores twice as much energy as most similar molecules and is extremely soluble in water, both of which are key qualities for increasing the efficiency of large-scale storage systems.

The study team, led by UdeM researchers Helene Lebel and Dominic Rochefort, as well as Concordia professor Marc-Antoni Goulet, seeks answers to the intermittent nature of solar and wind generation, which is a fundamental impediment to their complete integration into electricity grids.

Redox Flow Versus Regular Batteries

Redox flow batteries work on a different concept than conventional batteries.

Traditional batteries, such as alkaline cells in household devices and lithium-ion batteries in electric vehicles, store charge in electrodes located within the battery. The active materials in these technologies include metals, and scaling them up is difficult.

The difference with a redox flow battery is that we use an active material made of potentially renewable organic molecules dissolved in an aqueous solution and stored outside the battery. —— Dominic Rochefort, Researcher, Universite de Montreal

The system consists of two separate tanks holding an electrolyte solution (water, acid, and organic molecules) connected by tubes to a central cell. The larger the tanks, the greater their storage capacity. Inside the cell is a membrane through which the liquids from the two tanks circulate without ever mixing.

The molecules do not pass through the membrane into the other tank; they only exchange electrons through the external circuit by transferring them via their own electrodes. —— Dominic Rochefort, Researcher, Universite de Montreal

At this point of contact, oxidation-reduction, or redox, happens. This is how the battery charges and discharges. Since the energy stored in the tanks is distinct from the power generated in the cell, these two characteristics can be adjusted separately as needed.

Replacing Vanadium with Organic Molecules

Commercial redox flow batteries are already available on the market. They often employ vanadium on both sides of the system. Vanadium is a metal with desirable electrochemical characteristics, but it is not renewable, prompting the hunt for organic molecules to replace at least one side of the battery.

The organic molecule we have developed contains carbon, hydrogen, nitrogen and oxygen: it blends into water and acid and is oxidized to drive the energy storage reaction. —— Helene Lebel, Researcher, Universite de Montreal

She and her colleagues investigated several molecular groups to determine which were the most effective for energy storage. This effort resulted in the development of AzoBiPy, a member of the pyridinium family of molecules with positively charged heteroaromatic rings that allow for electron exchange.

“For now, we are buying some basic molecules from specialized companies but we are also exploring bio-based molecules derived from wood or food residues,” Lebel added.

This method, she noted, might make it feasible to extract the necessary organic molecules from renewable sources.

The Challenge of Stability

The primary benefit of AzoBiPy is its ability to exchange two electrons rather than just one. This means that each molecule can hold twice as much energy as a single-electron molecule, thus doubling the system's capacity.

But the biggest challenge with these organic molecules is stability. It must be possible for the charge-discharge cycle to run for a long time without the molecule breaking down. —— Helene Lebel, Researcher, Universite de Montreal

This is where AzoBiPy excels. The researchers ran a flow battery based on this molecule for 70 days straight, accomplishing 192 complete charge-discharge cycles. At the end of the experiment, the molecule kept approximately 99 percent of its initial capacity, which the researchers consider unusual for an organic molecule.

From Laboratory to Application

In a festive display at the Department of Chemistry's holiday party in December 2024, the prototype flow battery lit a set of Christmas tree lights for eight hours using only two tablespoons of aqueous solution in each tank.

The demonstration also showed another significant feature of the system: it is water-based and hence non-flammable, unlike lithium-ion batteries, which pose a fire risk.

“This feature is especially important for large-scale, stationary energy storage facilities,” stated Rochefort.

Flow batteries fueled by molecules such as AzoBiPy could be used to store energy from solar or wind farms. Long-term storage of sporadically produced electricity allows for its subsequent use to satisfy peak demand.

There could also be residential applications.

“It may be possible to develop smaller-scale systems with greener, safer batteries for home use,” Lebel suggested.

The research team is currently drafting a patent application and is already working on the following steps.

Lebel concluded, “We are preparing a scientific article that describes a family of molecules with properties similar to AzoBiPy. An entire class of compounds with potential for renewable energy storage is opening up to exploration. We expect this technology to be in wider use within 10 to 15 years.”

Journal Reference:

Lebel, H., et.al. (2026) 4,4′-Hydrazobis(1-methylpyridinium) as a Two-Electron Posolyte Molecule for Aqueous Organic Redox Flow Batteries. Journal of the American Chemical Society. DOI: 10.1021/jacs.5c03524. https://pubs.acs.org/doi/10.1021/jacs.5c03524.

Reviewed by Laura Thomson