Salt water turned into a source of electricity by nanotubes
The smaller it is, the bigger the effect! This paradox has just been observed by a team from the University of Lyon and the Néel Institute (CNRS) in Grenoble. In the journal Nature on February 28, these researchers show that drilling a hole of a few tens of nanometers through an impermeable membrane can have unexpected and significant effects on the transport of chemical species within this mini-channel.
In particular, immersing this device in a salt water tank containing potassium chloride makes it possible to very effectively separate the positive charges (linked to potassium) and negative charges (linked to chlorine) on either side of the wall. An electric current can then be recovered.
"If we extrapolate this result to a membrane pierced with billions of such tubes per square centimeter, we obtain electrical powers 100 to 1 times greater than with current devices of osmotic energy", estimates Lydéric Bocquet, professor at the CNRS and at the Institut Lumière Matière in Lyon. Enough to recover energy from seawater or salt marshes.
In fact, these researchers do not directly pierce their waterproof silicon nitride membrane. They use a nanotube, which they insert inside a larger hole before "sealing" the void with a carbon seal.
"It's very difficult to do! And the result is very beautiful", estimates Loïc Auvray, director of the Matter and complex systems laboratory at the University of Paris-VII. This delicate technique was originally aimed at building a device allowing the phenomena at play in a single small channel to be studied.
PATENT FILING
"Previous experiments had shown surprising effects with several carbon nanotubes, such as rapid gas transport. But, to fully understand what is happening, we had to work on a single tube, says Lydéric Bocquet. One of our hopes is that the fluid mechanics equations we know are different from these nanoscale scales. "
The first tests with carbon tubes fail. The researchers then use boron nitride, for which the process works. And that's the surprise. "We were perplexed and it took time to verify our measurements," recalls Lydéric Bocquet, who thinks he has now understood why electric charges circulate so well.
In the presence of water, the walls of boron nitride are covered with negative electrical charges, promoting the drainage by water of positively charged potassium. The small thickness of the assembly, one micrometer, means that the concentration gradient between the two reservoirs is greater, therefore the effect more spectacular.
The team, which has filed for a patent, now plans to manufacture a wall traversed by several nanometric channels; which requires a new process. Perhaps she will then be able to light a light bulb only from a saltwater bath. For Lydéric Bocquet, "we have to find alternative avenues in terms of energy. And it is all the more stimulating to work on unexplored avenues".
David Larousserie
Source: http://www.lemonde.fr/sciences/article/ ... 50684.html ou https://www.econologie.info/share/partag ... nmB0ja.pdf