The world’s major energy companies seem to live in constant fear that their business of providing carbon-based or nuclear power will be replaced by free and clean sources of energy such as solar and wind. Should they now be concerned about saltwater becoming the next free non-fossil fuel? New research indicates the answer they fear is getting closer to reality.
Scientists from the Laboratory of Nanoscale Biology at the Ecole Polytechnique Fédérale de Lausanne (EFPL - Federal Institute of Technology in Lausanne) in Switzerland (the French-speaking part) announced in the journal Nature that they have successfully generated osmotic power via the movement of salt ion through an osmosis membrane just three atoms thick.
In (very) simple terms, osmosis is the movement of molecules through a permeable wall separating two liquids so that a balance of molecules on each side is achieved. In this case, the membrane separates solutions of salt and fresh water and osmosis draws the salt ions through a single nanopore in the membrane until the concentrations are equal.
The power comes from the fact that salt ions have an electric charge. The nanopores of the membrane are small enough for positively-charged ions to pass through but not the negatively-charged ones. The end result is opposite charges on either side of the membrane, creating an electrical current.
The innovation created by the researchers at the EFPL is the extremely thin membrane. Current generation is inversely proportionally to membrane width. At just a few atoms in thickness, this one – made from molybdenum disulfide - is essentially a two-dimensional barrier.
Osmosis power is not new but EFPL claims it has attained generation levels never seen before. It estimates that a one-square-meter piece of molybdenum disulfide with just 30% of its surface containing nanopores can generate 1megawatt of electricity or enough to power 50,000 standard energy-saving light bulbs.
There’s more good news. Molybdenum disulfide is found in nature in the mineral molybdenite and can also be easily created by treating molybdenum compounds with hydrogen sulfide.
When will we be charging our cellphones while swimming in the ocean? That depends on the membrane. Current molybdenum disulfide are organic and fragile, so work needs to be done on stronger man-made versions. The tests were done with membranes containing just one nanopore, since poking more tiny holes requires a stronger membrane.
Will simple osmosis replace carbon-based fuels? Possibly, if the energy companies let it. Will climate change and rising ocean levels bring seawater power right to your doorstep? Let’s hope not.