The staunch environment supporters, who always advocate clean energy, will soon propagate for a new source with their existing array of solar, wind, and hydropower: osmotic power – energy generated by a natural phenomenon occurring when freshwater comes into contact with seawater through a membrane. Researchers at the Ecole Polytechnique Fédérale de Lausanne’s (EPFL) Laboratory of Nanoscale Biology after long research have finally arrived at a method to harness energy with the help of water and a very thin membrane!
The concept in scientific words – when a semi-permeable membrane separates two fluids having different salt concentrations due to ion exchange generates electricity. The thin membrane used in this process was of molybdenum disulfide separating freshwater and seawater. Naturally, the seawater ions start passing through this membrane’s nanopore into the freshwater until the two fluids are of equal salt concentrations. This phenomenon is called osmosis. During osmosis when the salt ions pass through the membrane’s nanopore (the tiny hole), (an ion is nothing but simply an atom with an electrical charge), the movement of these ions is harnessed to generate electricity by transferring their electrons to an electrode.
EPFL’s system consists of two liquid-filled compartments separated by a membrane of molybdenum disulfide, this membrane allows only positively charged ions to pass through, in turn pushing away the negatively charged ions, thus creating the voltage between the two liquids. This voltage causes the current generated by the transfer of ions.
“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. The specialty of the EPFL’s system is its membrane. In such systems, thinner the membrane higher is current. And EPFL’s membrane is just a few atoms thick, made of molybdenum disulfide, most ideal for generating an osmotic current. “This is the first time a two-dimensional material has been used for this type of application,” said Aleksandra Radenovic, head of the laboratory of Nanoscale Biology.
This new system has huge potential. One square meter molybdenum disulfide membrane with 30% of its surface having nanopores will be able to produce 1MW of electricity. Molybdenum disulfide (MoS2) is easily found in nature or can be grown by chemical vapor deposition but the major challenge involved in this process is making uniform nanopores on the surface of the membrane.
Until now, researchers have worked on a membrane with a single nanopore.