Researchers from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) (Cambridge, Massachusetts) developed a noncorrosive flow battery to store energy in organic molecules dissolved in neutral pH water.
Flow batteries store energy in liquid solutions in external tanks, with bigger tanks storing more energy. As such, they are a promising renewable energy solution. However, many of these batteries suffer degraded capacity after charge-discharge cycles, requiring maintenance of the electrolyte.
But by modifying molecules used in positive and negative electrolytes, the team engineered a battery that loses only 1% of its capacity per 1,000 cycles.
“Lithium ion batteries don’t even survive 1,000 complete charge/discharge cycles,” says Michael Aziz, a professor on the team.
“Because we were able to dissolve the electrolytes in neutral water, this is a long-lasting battery that you could put in your basement,” adds contributing professor Roy Gordon. “If it spilled on the floor, it wouldn’t eat the concrete and since the medium is noncorrosive, you can use cheaper materials to build the components, like the tanks and pumps.”
Researchers say the key was figuring out why previous molecules degraded so quickly in neutral solutions. By identifying how the molecule viologen in the negative electrolyte decomposed, they modified its structure for more resilience. They then used ferrocene, known for electrochemical properties, for the positive. By functionalizing both the same way, they turned an insoluble molecule into a soluble one that could be cycled stably.
The neutral pH could lower the cost of the ion-selective membrane that separates the battery’s two sides. Many flow batteries use polymers to withstand aggressive chemistry, but those can account for one-third of the total cost, the team says. But since the electrolyte is noncorrosive, polymers can be replaced by cheaper hydrocarbons.
Source: Harvard, seas.harvard.edu.