Battery Desalinates Seawater | Chemical & Engineering News
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Web Date: February 10, 2012

Battery Desalinates Seawater

Materials Science: Electrochemical cell removes sodium and chloride ions from water
Department: Science & Technology
News Channels: Materials SCENE, Nano SCENE
Keywords: desalination, water purification, drinking water, salt removal, electrochemistry, manganese oxide nanorods
Hold The Salt
In a desalination battery (top, left), seawater’s sodium and chloride ions (orange and blue circles) move into a pair of electrodes (green and gray bars). The electrochemical cell then discharges desalinated water (Step 2) before ejecting a waste stream of concentrated brine (Step 4).
Credit: Nano Lett.
Diagram of desalination battery’s process of removing salt ions
Hold The Salt
In a desalination battery (top, left), seawater’s sodium and chloride ions (orange and blue circles) move into a pair of electrodes (green and gray bars). The electrochemical cell then discharges desalinated water (Step 2) before ejecting a waste stream of concentrated brine (Step 4).
Credit: Nano Lett.

For the first time, researchers have designed an electrochemical cell that can desalinate seawater (Nano Lett., DOI: 10.1021/nl203889e). They think that its cost and efficiency eventually could improve on standard techniques of purifying seawater.

Worldwide demand for freshwater is skyrocketing as the population increases. Many of today’s desalination plants use reverse osmosis or evaporation, both of which require enormous amounts of energy to supply heaters or high-pressure pumps. To find cheaper, room-temperature, energy-efficient solutions, many researchers are looking to nanomaterials and electrochemistry.

The new system uses both. It first draws ions from seawater into a pair of electrodes. As the researchers pass current through the electrodes, electrochemical reactions drive chloride ions into a silver electrode and sodium ions to an electrode made from manganese oxide nanorods. Next, the researchers remove the desalinated water and release the trapped ions into a separate stream of waste seawater by reversing the direction of the electrical current. Although the pilot experiments were not automated, the researchers say that a pump could automate the process.

The desalination system is a spinoff from a Stanford University project to create new sources of clean energy. Last year, Fabio La Mantia, now of Ruhr University Bochum, in Germany, Yi Cui, of Stanford University, and colleagues showed that they could generate electrical energy by flowing streams of water with varying salinity through an electrochemical cell (Nano Lett., DOI: 10.1021/nl200500s). “The desalination battery is essentially the same device, but reversed,” explains La Mantia, who worked again with Cui and other researchers, on the new study.

The desalinated water that comes from the battery still contains too much salt for drinking, La Mantia says: “We removed up to 50% of the original salt, but we need to arrive at 98%.”

Doing several cycles of ion removal with the battery would further desalinate the water, but those extra cycles cost energy, so La Mantia hopes to improve the efficiency enough so that the battery can remove the salt in a single pass.

John H. Lienhard, of the Massachusetts Institute of Technology, applauds the work but cautions, “There’s still some way to go before this technique could be deployed for large-scale seawater processes.” He says the researchers need to find ways to remove sulfates from seawater, lower the cost of the electrodes, and protect the system from deposits of biofilm and scale that could cripple the device.

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Elizabeth Freeman (February 11, 2012 1:10 PM)
I'm not sure if centrifuging would remove the salt. But if the battery could run a centrifuge that the salty waste water drained into maybe it could be spun off. Possibly some other additive would have to be added. ... not sure if i understand where the current is going now!
Aaron Rowe (February 13, 2012 12:49 PM)
A centrifuge would be a nice way to get rid of suspended particles in seawater, but I don't think that it would be able to remove sodium, chlorine, or sulfate ions. If the centrifuge was powered by a sustainable energy source, it might be able to increase the lifespan of the water purification materials by protecting them from sediment.
Lonner (February 11, 2012 2:40 PM)
How does this differ from dialysis?
William (February 12, 2012 12:18 PM)
Just be sure to take the battery out of your glass before you drink - ZAP!
G Venkatesha (February 12, 2012 10:57 PM)
It is a timely research work, which is very much required to solve the drinking water problem appears in near future.It can avoid the Third World War, may happen for Water resources.
Fred Stein (February 13, 2012 1:13 AM)
Some questions:
Can we substitute Silver, which could be prohibitive for scaling?
Is there an estimated 'battery life', again a key factor for scaling?
Also related to scaling. What are the use cases or applications? Is this for urban de-sal or agriculture or for small high-value applications such as boats at sea or remote resorts?
Kaz (February 13, 2012 1:18 AM)
Calling this a battery is misleading since it requires input current.

Aaron Rowe (February 13, 2012 12:56 PM)
There's a lot of discussion about this on Slashdot. Stripping ions out of water into the electrodes of this electrochemical cell is pretty similar to charging a rechargeable battery.
Chris King (February 13, 2012 9:26 AM)
It is good to hear of new approaches to an old problem. It is difficult to tell from this short summary, but it sounds as if this method has some of the problems that the old electro-dialysis method had. A long way to go but I feel it is worth pursuing.
Johnny L.Bennett (February 13, 2012 10:31 AM)
This the new Gold, desalinated water From the sea.
AP (February 13, 2012 11:15 PM)
Maybe this will be good for something like aquaponics? Growing salt water fish but still producing vegetables (which require fresh water of course!) - take the saltwater out on the way up to the veg, put it back in on the way back down...

Alternately I wonder if you could use plants to remove that last X% of salt to produce fresh water.

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