Researchers at the University at Buffalo in the US have found that a dye called methylene blue dissolved in water is good at storing and releasing energy.
"Methylene blue is a widely used dye. It can be harmful to health, so it's not something you want to dump into the environment without treating it," said Timothy Cook, assistant professor of chemistry in the UB College of Arts and Sciences. "There's been a lot of work done on ways to sequester methylene blue out of water, but the problem with a lot of these methods is that they're expensive and generate other kinds of waste products."
"But what if instead of just cleaning the water up, we could find a new way to use it? That's what really motivated this project," said researcher Anjula Kosswattaarachchi.
The study looked at how methylene blue from industrial wastewater can be used in batteries.
"For this to be practical, we would need to avoid the costly process of extracting the dye from the water," said Cook. "One of the things we're interested in is whether there might be a way to literally repurpose the wastewater itself. In textile-making, there are salts in the wastewater. Usually, to make a redox flow battery work, you have to add salt as a supporting electrolyte, so the salt in wastewater might be a built-in solution. This is all speculative right now: We don't know if it will work because we haven't tested it yet."
In experiments, the team built two simple batteries that used the dye dissolved in salt water to capture, store and release electrons. The first battery the researchers made operated with near-perfect efficiency when it was charged and drained 50 times, but the capacity fell after that as molecules of methylene blue became trapped on the separating membrane in the battery.
A new membrane material, Nafion NE1035, for the second battery showed no decay in performance.