(Nanowerk News) Researchers from the University of Cambridge and Harvard University have developed a method to dramatically extend the life of organic water flow batteries, which improves the commercial viability of a technology that has the potential to safely and cheaply store energy from renewable sources such as wind and solar. .
The process works a bit like a pacemaker and periodically gives a shock to the system that revives degraded molecules inside the batteries. Their results, reported in the journal Natural chemistry (“In situ electrochemical recomposition of degraded redox active substances in aqueous organic flux batteries”), showed a net lifespan 17 times longer than previous research.
“Organic aqueous redox flux batteries promise to significantly reduce the cost of storage from intermittent energy sources, but the instability of the organic molecules has hindered their commercialization,” said Harvard co-author Michael Aziz. “Now we have a really practical solution to extend the life of these molecules, which is a huge step in making these batteries competitive.”
Over the past decade, researchers have developed organic water flow batteries using molecules known as anthraquinones – composed of naturally abundant elements such as carbon, hydrogen and oxygen – to store and release energy.
During the course of their research, the team discovered that these anthraquinones decompose slowly over time, no matter how many times the battery has been used.
In previous work, the researchers found that they could extend the life of one of these molecules, called DHAQ but called “zombie quinone” in the lab, by exposing the molecule to air. The team found that if the molecule is exposed to air in just the right part of its charge-discharge cycle, it takes oxygen from the air and turns back into the original anthraquinone molecule – as if it returned from the dead.
However, regularly exposing a battery’s electrolyte to air is not exactly practical, as it drives the two sides of the battery out of balance – 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 the molecules break down and invented an electrical method to reverse the process.
Researchers from Professor Clare Gray’s group at the Yusuf Hamied Department of Chemistry in Cambridge, conducted in situ nuclear magnetic resonance (NMR) – mainly “MRI for batteries” – measurements and discovered the recomposition of active materials by an electrical method, the so-called deep discharge .
The team found that if they performed a deep discharge, where the positive and negative poles of the battery are dropped so that the voltage difference between the two becomes zero, and then reversed the polarity of the battery, which forced the positive side negative and negative side positive, it created a voltage pulse that could restore the decomposing molecules return to their original form.
“Usually, when running batteries, you want to avoid draining the battery completely because it tends to degrade its components,” said Harvard author Yan Jing. “But we have found that this extreme discharge where we actually reverse the polarity can recompose these molecules – which was a surprise.”
“Getting to a single-digit percentage of the loss per year really enables extensive commercialization because it’s not a huge financial burden to replenish your tanks by a few percent each year,” Aziz said.
The research group also showed that this approach works for a number of organic molecules. Next, they aim to explore how much further they can extend the life of DHAQ and other inexpensive anthraquinones that have been used in these systems.
“The most surprising and beautiful thing for me is that this organic molecule can be transformed in such a complex way, with multiple chemical and electrochemical reactions occurring simultaneously or sequentially,” said co-author Dr. Evan Wenbo Zhao, who performed the work while based in Cambridge and is now based at Radboud University Nijmegen in the Netherlands. “Still, we can remove many of these reactions and allow them to occur in a controlled manner that benefits the operation of a redox flux battery.”
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