New organic flow battery breathes life into breaking down molecules back

After years of making progress on an organic aqueous flow battery, Harvard University scientists kept running into an issue: the organic anthraquinone molecules that powered their ground-breaking battery were gradually breaking down after some time, lessening the long-term usefulness of the battery.

Presently, the scientists — led by Michael Aziz, the Gene and Tracy Sykes Professor of Materials and Energy Technologies at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) and Roy Gordon, the Thomas Dudley Cabot Professor of Chemistry and Professor of Materials Science — have made sense of how the molecules decompose, yet in addition how to relieve and even reverse the decomposition.

The outrageous molecule, named DHAQ in their paper yet named the “zombie quinone” in the lab, is among the least expensive to produce at large scale. The group’s restoration strategy cuts the limit blur rate of the battery at any rate a factor of 40, while empowering the battery to be composed altogether out of low-cost chemicals.

The research was published in the Journal of the American Chemical Society.

“Low mass-production cost is really important if organic flow batteries are going to gain wide market penetration,” said Aziz. “So, if we can use these techniques to extend the DHAQ lifetime to decades, then we have a winning chemistry.”

“This is a major step forward in enabling us to replace fossil fuels with intermittent renewable electricity,” said Gordon.

Since 2014, Aziz, Gordon and their group have been pioneering the advancement of safe and cost-effective organic aqueous flow batteries for storing electricity from irregular renewable sources like wind and solar and delivering it when the wind isn’t blowing and the sun isn’t sparkling. Their batteries use molecules known as anthraquinones, which are composed of naturally abundant elements such as carbon, hydrogen, and oxygen, to store and release energy.

At first, the analysts thought that the lifetime of the molecules relied upon how frequently the battery was charged and discharged, as in solid-electrode batteries, for example, lithium ion. Be that as it may, in accommodating conflicting results, the specialists found that these anthraquinones are decomposing gradually through the course of time, regardless of how often the battery has been utilized. They found that the measure of decomposition depended on the calendar age of the molecules, not how frequently they’ve been charged and discharged.

That discovery led the scientists to study the mechanisms by which the molecules were decomposing.

“We found that these anthraquinone molecules, which have two oxygen atoms built into a carbon ring, have a slight tendency to lose one of their oxygen atoms when they’re charged up, becoming a different molecule,” said Gordon. “Once that happens, it starts of a chain reaction of events that leads to irreversible loss of energy storage material.”

The specialists discovered two techniques to maintain a strategic distance from that chain reaction. The first: expose the molecule to oxygen. The team found that if the molecule is exposed to air at simply the correct part of its charge-discharge cycle, it gets the oxygen from the air and transforms once again into the original anthraquinone molecule — as though coming back from the dead. A solitary trial recouped 70 percent of the lost capacity this way.

Second, the group found that overcharging the battery makes conditions that accelerate decomposition. Abstaining overcharging broadens the lifetime by a factor of 40.

“In future work, we need to determine just how much the combination of these approaches can extend the lifetime of the battery if we engineer them right,” said Aziz.

“The decomposition and rebirth mechanisms are likely to be relevant for all anthraquinones, and anthraquinones have been the best-recognized and most promising organic molecules for flow batteries,” said Gordon.

“This important work represents a significant advance toward low-cost, long-life flow batteries,” said Imre Gyuk, Director of the Department of Energy’s Office of Electricity Storage program. “Such devices are needed to allow the electric grid to absorb increasing amounts of green but variable renewable generation.”

This exploration was co-wrote by Marc-Antoni Goulet, Liuchuan Tong, Daniel A. Pollack, Daniel P. Tabor, and Eugene E. Kwan, all from Harvard; and Susan A. Odom of the University of Kentucky; and Alán Aspuru-Guzik of the University of Toronto.

The research was supported by the Energy Storage program of the U.S. Department of Energy, the Advanced Research Projects Agency – Energy, the Innovation Fund Denmark, the Massachusetts Clean Energy Technology Center, and Harvard SEAS.

With help from Harvard’s Office of Technology Development (OTD), the scientists are looking for commercial partners to scale up the technology for industrial applications. Harvard OTD has filed a portfolio of pending patents on innovations in flow battery technology.

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