By Andrew Wong, a second year graduate student in the Applied Physics program at Harvard University.
      The increase in global energy demand and subsequent carbon dioxide emissions has driven advancements in renewable energy generation technologies such as wind turbines and solar cells. However, these technologies are inherently intermittent, and require robust energy storage devices. Inexpensive, large-scale energy storage systems such as aqueous flow batteries could support wide-spread solar and wind energy generation installments when the wind isn’t blowing and the sun isn’t shining.
     Recently, a new generation of aqueous flow batteries have been developed at Harvard’s Paulson School of Engineering and Applied Science: rather than using metal ion chemistries in traditional batteries, this technology uses quinones, which are small organic molecules similar to many found in plants. In addition to enabling safe, inexpensive batteries, the natural fluorescence of quinones opens a new opportunity to probe the inside a working flow battery. In the Lord of the Rings story, Frodo was unable to navigate through Shelob’s lair until he remembered to use the light of the star Elendil; similarly, quinones help illuminate the shadowed interworking of flow batteries.
     This image was taken by fluorescence microscopy of a porous carbon paper electrode flooded with a solution of redox-active quinones. The black lines in this image are conductive carbon filaments which provide a high surface area for chemical reactions. The blue backlighting is from the fluorescence of these quinone molecules when the battery is charged—the quinones do not fluoresce when the battery is discharged and all external light has been filtered out. These images provide a unique opportunity to directly map chemical reactions inside a working battery. Further analysis will better inform future engineering designs for more efficient batteries. Someday, this technology could support renewable energy generation around the world. Or perhaps Middle Earth.
If you’d like to learn more about organic flow batteries, click here.

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