French scientists use boron nitride nanotubes to channel osmotic power

March 01, 2013 // By Paul Buckley
The Institut Lumière Matière in Lyon (CNRS / Université Claude Bernard Lyon), in collaboration with the Institut Néel (CNRS), has discovered how to use boron nitride nanotubes to harness energy from the salinity difference between fresh water and salt water.

The osmotic flow through boron nitride nanotubes generates electric currents that have 1,000 times the efficiency of any previous system.

To achieve the result, the researchers developed an experimental device that enabled them, for the first time, to study osmotic fluid transport through a single nanotube.

When a reservoir of salt water is brought into contact with a reservoir of fresh water through a special kind of semipermeable membrane, the resulting osmotic phenomena make it possible to produce electricity from the salinity gradients. This can be done in two different ways: either the osmotic pressure differential between the two reservoirs can drive a turbine, or a membrane that only passes ions can be used to produce an electric current.

Concentrated at the mouths of rivers, the Earth's osmotic energy potential has a theoretical capacity of at least 1 terawatt - the equivalent of 1,000 nuclear reactors. However, the technologies available for harnessing this energy are relatively inefficient, producing only about 3 watts per square meter of membrane. The team of physicists at the Institut Lumière Matière in Lyon (CNRS / Université Claude Bernard Lyon), in collaboration with the Institut Néel (CNRS), may have found a solution to overcome this obstacle.

The primary goal of the study was to reveal the dynamics of fluids confined in nanometric spaces, such as nanotubes. Drawing inspiration from biology and cell channel research, they achieved a world first in measuring the osmotic flow through a single nanotube. The experimental device consisted of an impermeable and electrically insulating membrane pierced by a single hole through which the researchers, using the tip of a scanning tunneling microscope, inserted a boron nitride nanotube with an external diameter of a few dozen nanometers. Two electrodes immersed in the fluid on either side of the nanotube enabled them to measure the electric current passing through the membrane.

Using the membrane to separate a salt water reservoir and a fresh water