In a study newly published in Nature, researchers introduce a new source of clean energy: osmotic power (blue energy), or the power generated when fresh water comes into contact with seawater via a membrane.
The term osmotic refers to the movement of water from an area of low concentration of solute (i.e. atoms, ions, or molecules dissolved in a liquid) to an area of higher concentration of solute.
Osmotic pressure is the minimum pressure needed to prevent the inward flow of water across a semipermeable membrane. Fresh water and seawater have different osmotic pressure.
In the study, researchers from EPFL (École polytechnique fédérale de Lausanne) in Switzerland and University of Illinois at Urbana-Champaign in the USA used the osmotic pressure differences between fresh water and seawater to generate electricity.
Basically, a phenomenon called streaming potential occurs when an electrolyte is driven through narrow pores either by a pressure gradient or by an osmotic potential resulting from a salt concentration gradient.
Membranes made of 2D materials are expected to be the most efficient for this task, because water transport through a membrane scales inversely with membrane thickness.
In the study, researchers used a single-layer nanopores as osmotic power generators. They observed a large, osmotically induced current produced from a salt gradient. The power density was estimated to be up to 106 watts per square meter.
The nanopore generator can be used to harvest energy from the local environment and make a self-powered nanosystem.
Researchers suggest that the potential of the new system is huge: a 1m² membrane with 30% of its surface covered by nanopores will be able to generate electricity for 50,000 standard energy-saving light bulbs.
Pilot use of the system is being conducted in Norway, the Netherlands, Japan, and the USA areas where rivers flow into the sea. Once the system become more mature, osmotic power may be a critical source of renewable energy.
Citation: Feng J, et al. (2016). Single-layer MoS2 nanopores as nanopower generators. Nature, 536: 197-200. doi:10.1038/nature18593.
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