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The battery, developed at Linköping University in Sweden, could also be used as a power bank for cars.
Redox flow batteries are stationary batteries in which the energy is stored in the liquid electrolyte, outside of the cell itself. They are a promising technology for storing excess energy from renewable sources, and could potentially be recharged an unlimited number of times.
They often contain vanadium however, a scarce and expensive metal. The electrolyte can be water-based, which makes the battery safe to use but results in a lower energy density.
Principal research engineer Mikhail Vagin and his colleagues have now produced not only a water-based electrolyte but also electrodes of organic material, which reportedly increases the energy density considerably.
The team used conducting polymer Pedot for the electrodes, ‘doped’ to transport positive or negative ions. The water-based electrolyte consists of a solution of quinone molecules, which can be extracted from wood.
“It turns out that they are highly compatible with each other, which is like a gift from the natural world,” said Viktor Gueskine, principal research engineer and one of the authors.
The high compatibility means that the Pedot electrodes help the quinone molecules switch between their oxidised and their reduced states, creating a flow of protons and electrons.
“It is normally difficult to control the ion process, but we have managed it here. We also use a fundamental phenomenon within electrocatalysis in which one special ion in solution, in this case quinone ions, is converted to electricity. The phenomenon is conceptualised by us as ion-selective electrocatalysis, and probably exists in other types of membrane storage devices such as batteries, fuel cells and supercapacitors. This effect has never previously been discussed. We showed it for the first time in redox flow batteries,” said Vagin.
The organic redox flow batteries still have a lower energy density than batteries that contain vanadium, but are reportedly extremely cheap, completely recyclable and safe. The researchers suggested they could also be used for off-grid storage at home.
The research was published in Advanced Functional Materials.
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