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Flow battery design possible boost for solar, wind energy

Posted: 20 Aug 2013 ?? ?Print Version ?Bookmark and Share

Keywords:flow battery? storage? membranes?

Braff built a prototype of a flow battery with a small channel between two electrodes. Through the channel, the group pumped liquid bromine over a graphite cathode and hydrobromic acid under a porous anode. At the same time, the researchers flowed hydrogen gas across the anode. The resulting reactions between hydrogen and bromine produced energy in the form of free electrons that can be discharged or released.

The researchers were also able to reverse the chemical reaction within the channel to capture electrons and store energya first for any membraneless design.

In experiments, Braff and his colleagues operated the flow battery at room temperature over a range of flow rates and reactant concentrations. They found that the battery produced a maximum power density of 0.795 watts of stored energy per square centimetre.

More storage, less cost

In addition to conducting experiments, the researchers drew up a mathematical model to describe the chemical reactions in a hydrogen-bromine system. Their predictions from the model agreed with their experimental resultsan outcome that Bazant sees as promising for the design of future iterations.

"We have a design tool now that gives us confidence that as we try to scale up this system, we can make rational decisions about what the optimal system dimensions should be," Bazant says. "We believe we can break records of power density with more engineering guided by the model."

Yury Gogotsi, a professor of materials science and engineering at Drexel University, says eliminating the membrane is the next step towards scalable, inexpensive energy storage. The group's design, he says, will help engineers better understand the physics of membraneless systems.

"You cannot have an inexpensive energy-storage system by piling up tens of thousands of individual small cells, like cell phone or computer batteries," says Gogotsi, who did not contribute to the research. "As any new technology, the laminar flow battery will need time to prove its viability. It's like a newborn babywe'll only know what the technology is good for after a few years."

According to preliminary projections, Braff and his colleagues estimate that the membraneless flow battery may produce energy costing as little as $100 per kilowatt-houra goal that the U.S. Department of Energy has estimated would be economically attractive to utility companies.

"You can do so much to make the grid more efficient if you can get to a cost point like that," Braff says. "Most systems are easily an order of magnitude higher, and no one's ever built anything at that price."


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