Chinese researchers have developed a “two-faced” membrane that can convert 35.7 percent of the energy stored in saltwater into useable electricity. This puts it at par with most wind turbines and solar cells as a clean energy generation technology in terms of efficiency.
Dissolving salts in water breaks apart their positively and negatively charged particles, leaving them free to travel and participate in osmosis — the flow of particles from areas of low concentration to high concentration. The placement of charged membranes between saltwater and freshwater allows scientists to create a highway for the flowing particles that creates electric current. This is known as osmotic power.
Traditionally, these membranes are expensive and lose efficiency over time as the membrane begins to leak and ions start flowing in the wrong direction.
However, the membrane recently developed by Chinese researchers — named the Janus membrane after the Roman god of gates and passages — has different properties on each side. This includes differences in pore size and the charge of the membrane. This feature helps maintain the steady flow of particles from one side to the other while stopping particles from drifting in the opposite direction. Its power output density reached 2.66 watt per square meter (W/m2) and up to 5.10 W/m2 at a 500-fold salinity gradient. To check the stability of the flow of current, researchers powered a calculator with a generator built by connecting series of Janus membranes for a period of 120 hours. They didn’t note any notable fluctuation in current. Furthermore, the Janus membrane was also found to have high temperature thermostability and a low swelling ratio.
Janus membranes can also be manufactured to have pores of any size or hold any amount of charge, allowing them to create power using various kinds of solutions. Researchers are currently working on the development of more prototypes that can work under different conditions. However, the model tested by the researchers in China works best with saltwater, `with a concentration similar to that found at 0.5 meters under sea level.