Inspired by the energy storage capabilities found in our own bodies, researchers at Harvard University have come up with a way to create alkaline flow batteries using modified organic vitamin B2 molecules. As these molecules are non-toxic, non-flammable, and able to be produced at low cost, the researchers believe that their use could help revolutionize large-scale, inexpensive electricity storage from intermittent energy sources such as solar and wind.
Flow batteries are rechargeable energy storage units that use chemicals dissolved in liquids stored in two external tanks that are separated by a membrane. After the battery has been charged up using energy from sources like wind or solar to pull electrons from the positively charged solution into the negatively charged solution, an electric current flow is produced when the battery is switched on the and the electron flow is reversed. The resultant cell voltage is normally in the range of 1.0 to 2.2 volts and, as a general rule, the larger the holding tanks, the greater amount of energy they can store.
The new research carries on from previous work, where the Harvard scientists replaced metal ions used as conventional battery electrolyte materials in acidic electrolytes with organic compounds with charge-carrying capabilities called quinones. This was followed by research where they developed a quinone able to operate in alkaline solutions by replacing the original bromine additive with ferrocyanide, which is a common anti-caking agent added to such things as kitchen salt.
This work ultimately led to the search for an even more environmentally-friendly quinone, and the researchers eventually discovered that, with a little fiddling, vitamin B2 could be put to use as a replacement. Vitamin B2 helps our bodies store energy derived from the breakdown of the foods we ingest, with the main difference between B2 and quinones being the way that the two exchange electrons in the process – B2 uses nitrogen atoms, whereas quinone gives off and picks up oxygen atoms.
"With only a couple of tweaks to the original B2 molecule, this new group of molecules becomes a good candidate for alkaline flow batteries," says professor Michael Aziz, the Gene and Tracy Sykes Professor of Materials and Energy Technologies at Harvard. "They have high stability and solubility and provide high battery voltage and storage capacity. Because vitamins are remarkably easy to make, this molecule could be manufactured on a large scale at a very low cost."
Before the Harvard team arrived at the use of modified B2 vitamins in their research, a vast range of other organic molecules were considered, but vitamin B2 won out with its high-performance and low production costs.
The use of molecules such as vitamin B2 has also opened up a new realm of similar organic molecules for the team to explore and exploit, with the goal of developing a high-performing, long-lasting, organic-based flow battery. And they intend to do this by continuing research into similar energy-storage mechanisms found in nature.
"We designed these molecules to suit the needs of our battery, but really it was nature that hinted at this way to store energy," says professor Roy Gordon, the Thomas D. Cabot Professor of Chemistry at Harvard. "Nature came up with similar molecules that are very important in storing energy in our bodies."
The results of this research were recently published in the journal Nature Energy.
The short video below explains the uses of a flow battery in alternative energy storage.