Battery turns sea water into fresh water, no magic necessary

As the world's population continues to grow, fresh water is becoming one of the most valuable (and contested) resources on the planet. Whether it's for drinking, agriculture, or keeping our armpits clean, we need more of it, and we now may be able to make that happen with little more than a fancy battery.

Trying to get fresh water out of the ocean is not a new idea, and we've been pulling it off successfully for a long using techniques like evaporation and reverse osmosis. It's hard work, though, which means a lot of energy is required, which also means a lot of money is required, to the point where California has been considering the importation of fresh water in bulk from Canada using converted oil tankers.

Until the oil tankers thing gets going, it might be worth checking out a new technique that only requires a battery. Last year, some researchers at Stanford University discovered that you could generate an electrical current by pumping salty water followed by less salty water through an electrochemical cell. That's neat, but if you run the same experiment backwards, it turns out that adding electricity to an electrochemical cell with salt water running through it will make that water less salty.

Here's how the system works: you put together an electrochemical cell with two electrodes, add seawater to it, and then turn on an electric current. The current sucks chlorine ions onto an electrode made of silver and sodium ions onto a an electrode made from manganese oxide nanorods. Once the ions have been removed, the fresh(er) water is taken out of the battery, and more salt water is put in. Then, those trapped ions are released into that water, you get rid of it as a waste product, and start over again. Since no heat or pressure is involved, it's very efficient, and it's also much cheaper and easier to construct.

There's still plenty of work to be done before a system like this will be able to produce water that's suitable for drinking. At the moment, one pass through the battery removes 50% of the salt from seawater, but to call something "fresh," it needs to be 98% salt-free. Sulfates still need to be taken care of, and there are questions about how reliable the system will be, but this is all stuff that's to be expected in a brand-new technology that's just barely out of the lab.

C&EN, via Slashdot

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