A model of the redox flow battery in the laboratory. (Image: Thor Balkhed)

Redox flow batteries are stationary batteries in which the energy is located in the electrolyte, outside of the cell itself, as in a fuel cell. They are often marketed with the prefix “eco” since they open the possibility of storing excess energy from, for example, the Sun and wind. It appears that they can be recharged an unlimited number of times; however, redox flow batteries often contain vanadium, a scarce and expensive metal. The electrolyte in which energy is stored in a redox flow battery can be water-based, which makes the battery safe to use but results in a lower energy density.

Researchers have produced not only a water-based electrolyte but also electrodes of organic material that increase the energy density considerably. It is possible in this way to manufacture completely organic redox flow batteries for the storage of, for example, energy from the Sun and wind, and to compensate for load variation in the electrical supply grid.

The team used the conducting polymer PEDOT for the electrodes, which they have doped to transport either positive ions (cations) or negative ions (anions). The water-based electrolyte consists of a solution of quinone molecules, which can be extracted from forest-based materials.

The high compatibility of quinones and PEDOT means that the PEDOT electrodes help the quinone molecules switch between their oxidized and their reduced states, creating a flow of protons and electrons. The team also used a fundamental phenomenon within electrocatalysis in which one special ion in solution — in this case, quinone ions — is converted to electricity. The phenomenon is conceptualized as ion-selective electrocatalysis and most likely exists in other types of membrane storage devices such as batteries, fuel cells, and supercapacitors.

The organic redox flow batteries still have a lower energy density than batteries that contain vanadium but they are inexpensive, completely recyclable, safe, and perfect for storing energy and compensating for load variations in the electrical supply grid.

For more information, contact Mikhail Vagin at This email address is being protected from spambots. You need JavaScript enabled to view it..