If you know Murphy's law you know very well that by a curious twist of fate "the fastest queue is definitely the one next to yours".
Imagine that you are really in a similar situation: you stuck in a crowded queue, and next to you a nice sliding line. What would you like to do? Maybe you would immediately try to move. This is exactly what happens to the particles involved in a process called “osmosis”: they move from an area of high concentration to another area of lower concentration. Today a research team has used this trend to create Janus, a membrane that produces energy directly from simple salt water.
How does it work?
When ionic salts, made up of bundles of positively and negatively charged particles, dissolve in water, the bundles break leaving the positively and negatively charged particles free to participate in osmosis.
By placing thin membranes between salt and fresh water, scientists can create highways for particle flow, producing electricity. Often, however, these membranes are expensive to manufacture and tend to wear out relatively quickly. This leads in a short time the particles to make the reverse path, wasting a large part of the current produced.
Today a research team has developed a new type of "generator", a double-sided membrane with different properties for each side, such as the size of the pores on its surface or the electrical charge.
This encourages a constant flow of charged particles from side to side, preventing them from moving in the wrong direction.
Janus membrane
The peculiar characteristic of these membranes led to the determination of their name: Janus, Janus, from the name of the Roman God of gates and passages.
The Janus membrane can also be made to have different charge and different size of the pores on the surface, so as to work with different types of particles.
The tests with salt water
The researchers tested the Janus membrane with sea water on one side and with fresh water on the other: they were able to convert 35,7% of the chemical energy present in the water into electricity.
It is more efficient than many wind turbines, and higher than several solar cells, as Science Advances magazine reports today.
The next steps
Now the researchers plan to build larger membranes to test their behavior in a real marine and river scenario.
If the results are as comforting as those of the "indoor" tests, in a few years the new membranes could be used to power communities that cannot access other forms of renewable energy.
