A device for converting sea water to fresh water that could be powered by a battery is reported online in Nature Nanotechnology this week. Established desalination methods require high power consumption or can only operate efficiently on a large scale, and are therefore difficult to use in disaster- or poverty-stricken areas.

Jongyoon Han and colleagues developed a device that uses a phenomenon known as ion-concentration polarization, which occurs when a current of ions travels through an ion-selective nanochannel. The nanochannel is situated between two microchannels containing streams of sea water. When a voltage is applied across the nanochannel, ions are enriched at one end of the nanochannel and depleted at the other. As a result, salt ions in the sea water that are near the nanochannel are repelled. By separating one of the microchannels into two channels near this repulsion zone, the saltier water can be pulled off and the desalted water, which has no charge, can pass through the charged region and into a separate freshwater channel.

The method allows both salts and larger particles ― such as cells, viruses and microorganisms ― to be removed at a power efficiency similar to state-of-the-art large-scale plants.