At a time when renewable energy is slowly but surely overtaking conventional fossil fuels, scientists at EPFL’s Laboratory of Nanoscale Biology have successfully demonstrated the electricity-producing capabilities of yet another sustainable power source: osmosis. Unusual though it is, the natural phenomenon has been found to generate usable power when fresh water comes in contact with seawater, separated by means of a special membrane.
As part of the current project, researchers from EPFL have developed an innovative osmotic power generation technology that boasts incredible efficiency. Recently published in the Nature journal, the breakthrough relies on the use of a three-atom-thick semipermeable membrane to separate liquids with varying salt concentrations. Via the process of osmosis, the salt ions travel from one fluid to another, until a state of equilibrium is reached.
In case of fresh water and seawater, the salt ions will move from the latter through the thin membrane to the other liquid. This continues until the salt concentrations of both come to an equilibrium. Because ions are nothing but atoms with positive or negative charge, their movement results in the production of electricity. The membrane, which is made from molybdenum disulfide, possesses a nanopore (basically, a minuscule hole) that allows the passage of salt ions from seawater into fresh water.
When the ions travel through the nanopore, their electric charge (i.e. electrons) are conveyed to an electrode, which then generates usable electricity. According to the team, the membrane’s unique properties makes it impervious to negatively-charged ions, thus allowing only positive ions to pass through. This results in a voltage that in turn causes the current to flow. Speaking about the research, Jiandong Feng, the study’s chief author, said:
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.
As the researchers explain, in this type of a setup, the amount of current produced is usually inversely proportional to the membrane’s thickness. The current research marks the first time that scientists have managed to create a membrane that is only three atoms thick. Furthermore, it is fashioned using molybdenum disulfide, a chemical substance that is known to increase the generation of osmotic power. Aleksandra Radenovic, a member of the team, stated:
This is the first time a two-dimensional material has been used for this type of application.
Laboratory testing indicates that a single square-meter of a membrane, with approximately 30-percent of its surface possessing nanopores, could produce as much as 1 MW of electricity, which would be enough to power nearly 50,000 energy-efficient light bulbs. Additionally, the easy availability of molybdenum disulfide could make large-scale energy generation an economically feasibly affair. At present, the researchers are trying to figure out the best possible way to create uniform pores in the membrane. Jiandong Feng added:
From an engineering perspective, single nanopore system is ideal to further our fundamental understanding of 8=-based processes and provide useful information for industry-level commercialization.
For the project, the team successfully utilized the osmotic power-generated electricity to run a nanotransistor, thus creating a self-sufficient nanosystem. Once fully developed,the technology could help make the ongoing clean energy trend even more pervasive.