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                 Osmosis - the Next Big Step for Clean Energy?

   by Kevin Enochs

   Solar Power is becoming increasingly inexpensive, and efficient.  The
   same goes for wind power, but a natural limitation of both systems is
   that on some days the sun doesn't shine, and on some days, the wind
   doesn't blow.

   But researchers at the Ecole Polytechnique Fédérale de Lausanne
   (EPFL) say they have found a simple way to produce a lot of energy,
   anywhere a river meets the sea.

   Their work is being published in the journal Nature and it's an
   incredibly simple and straightforward idea that uses osmosis to create
   energy.

   Osmosis occurs when salty water hits fresh water across a permeable
   membrane.  Salt ions (atom with an electrical charge) will pass through
   the membrane until the amount of salt is equal on both sides.  Pretty
   simple.
   WATCH: EPFL video

   '

   Catch a charge

   The researchers wondered if they could figure out how to capture that
   electrical charge as it moved across the membrane separating the fresh
   and salty water.  They did it by creating two tiny membranes, just
   three atoms thick, made of molybdenum disulfide, which is plentiful and
   easy to produce.  Then they made a tiny hole in the membranes and let
   osmosis take over and push the electrically charged salt ions through
   this nanopore.

   What makes this unique is that the nanopore lets positively charged
   ions through, while keeping out most of the negatively charged ions.  A
   generator attached to the membrane collects this energy.  It sounds
   simple, but the researchers say it just seems that way.

   "We had to first fabricate and then investigate the optimal size of the
   nanopore.  If it's too big, negative ions can pass through and the
   resulting voltage would be too low.  If it's too small, not enough ions
   can pass through and the current would be too weak," said Jiandong
   Feng, lead author of the research.  Getting that nanopore just right is
   the big news.

   Pure energy

   The researchers say a one meter square membrane with nanopores across
   about 30 percent of its space could produce one megawatt of energy,
   enough to light 50,000 standard energy efficient light bulbs.

   But it isn't easy to drill a nanopore in a three atom thick membrane,
   and standardizing that process is going to take much more work.

   "We can control with sub-nanometer precision pore size when we work
   with the single nanopore," Aleksandra Radenovic, one of the researchers
   told VOA.  "To scale the process and have millions or trillions of
   pores, that would require a different nanopore fabrication process."

   But according to Radenovic that's exactly what they're working on now.
   If they can standardize the process of creating these nanopore filled
   membranes it just might be possible to create huge amounts of energy
   all the time, wherever salty and fresh water mix.


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   [1]http://www.voanews.com/content/estuary-energy/3416728.html

References

   1. http://www.voanews.com/content/estuary-energy/3416728.html