New approach removes major barrier to commercialization of organic flow batteries

June 18, 2022

(News from Nanowerk) Researchers from the University of Cambridge and Harvard University have developed a method to dramatically extend the life of organic aqueous flow batteries, improving the commercial viability of a technology that has the potential to store in safe and cost effective energy from renewable sources such as wind and solar. .

The process works much like a pacemaker, periodically delivering a shock to the system that revives the broken down molecules inside the batteries. Their findings, reported in the journal natural chemistry (“In situ electrochemical recomposition of decomposed redox-active species in aqueous organic flow batteries”), demonstrated a net life 17 times longer than previous research.

“Organic aqueous redox flow batteries promise to significantly reduce the costs of storing electricity from intermittent energy sources, but the instability of organic molecules has impeded their commercialization,” said co-author Michael Aziz. from Harvard. “Now we have a really practical solution to extend the life of these molecules, which is a huge step towards making these batteries competitive.”

Over the past decade, researchers have developed organic aqueous flow batteries that use molecules called anthraquinones – made up of naturally abundant elements such as carbon, hydrogen and oxygen – to store and release energy. .

During their research, the team discovered that these anthraquinones slowly break down over time, regardless of the number of battery uses.

In previous work, researchers found they could extend the life of one of these molecules, named DHAQ but dubbed the “zombie quinone” in the lab, by exposing the molecule to air. The team found that if the molecule is exposed to air at just the right time in its charge-discharge cycle, it picks up oxygen from the air and becomes the original anthraquinone molecule again – as if it came back from the dead.

But regularly exposing a battery’s electrolyte to air isn’t really practical, because it unbalances both sides of the battery – both sides of the battery can no longer be fully charged at the same time.

To find a more practical approach, the researchers developed a better understanding of how molecules break down and invented an electrical method to reverse the process.

Researchers from Professor Clare Gray’s group at Cambridge’s Yusuf Hamied Department of Chemistry performed in situ nuclear magnetic resonance (NMR) measurements – essentially ‘MRI for batteries’ – and discovered the recomposition of active materials by an electrical method, called deep. dump.

The team found that if they performed a deep discharge, in which the positive and negative terminals of the battery drained so that the voltage difference between the two became zero, then reversed the polarity of the battery, forcing the side positive negative and the negative positive side, it created a voltage pulse that could reset decaying molecules to their original shape.

“Usually when running batteries you want to avoid completely draining the battery because it tends to degrade its components,” said Harvard co-first author Yan Jing. “But we found that this extreme discharge where we actually reverse the polarity can recompose these molecules – which was a surprise.”

“Achieving single-digit percent loss per year really allows for large-scale commercialization because it’s not a major financial burden to fill your tanks a few percent every year,” Aziz said.

The research team has also demonstrated that this approach works for a range of organic molecules. Next, they aim to explore to what extent they can extend the life of DHAQ and other inexpensive anthraquinones that have been used in these systems.

“The most surprising and beautiful thing to me is that this organic molecule can transform in such a complex way, with multiple chemical and electrochemical reactions occurring simultaneously or sequentially,” said co-first author Dr. Evan Wenbo Zhao, who carried out the work while there was based in Cambridge and is now based at Radboud University Nijmegen in the Netherlands. “Yet we are able to pick up on many of these reactions and let them happen in a controlled way, which helps a redox flow battery work.”

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