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Past ideas for drawing energy out of ocean tides have relied on huge turbines sunk into river deltas or along shorelines. Now engineers at Rutgers University have reduced the mechanism to something as thin as a sheet of paper.
The group has devised a cost-efficient way to make a membrane that generates electricity by exchanging electrical charges between fresh water and saltwater.
The salts in water hold ions – positive and negative electric charges. In a container, it’s easy to draw ions with one kind of charge through a membrane and separate the positively and negatively charged particles. When a battery terminal is dipped into fluid on each side of the membrane, a current will flow.
In 2013, French researchers created such a membrane embedded with a boron nitride nanotube. Boron nitride has a strong negative charge, so the researchers figured the tube would repel negative charges – keeping them on one side of the membrane – while attracting positive ions and pulling them to the other side.
It worked – so well, in fact, that the researchers calculated that a square meter of the membrane impregnated with millions of the nanotubes could power 400 homes for a year.
But there was no cost-effective way to manufacture the membranes so the nanotubes would automatically line up perpendicular to the membrane, so their openings would face the right way.
The Rutgers team simply added iron oxide particles to the tubes and then used a magnet to line them up the right way. The resulting membrane, with about 30 million nanotubes per square inch, yielded 8,000 times more power per area than the earlier French version.
TRENDPOST: Each year, rivers pour about 23,000 cubic miles of fresh water into the oceans. Using these membranes to capture the energy created when that fresh water meets the sea could provide almost limitless power to coastal areas around the world. The technology could be engineered to commercial scale by 2027.

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