A new type of membrane enables the generation of so-called 'blue energy'. This energy is generated the moment two liquids of different salinity mix. This occurs naturally at the transition from fresh to salt water, among others.
Researchers at Canada's McGill University demonstrate a technique for producing membranes capable of generating blue energy. Selectively permeable membranes play an important role in generating this form of renewable energy. These membranes allow only one part of a saltwater solution to pass through, which can be water molecules or dissolved salt ions. This process is also known as osmosis.
Osmotic power plant
Experiments with generating blue energy are not new. Several large-scale projects have been set up, including the Statkraft osmotic power plant at Tofte in Hurum, Norway. However, available membranes have limited efficiency so far. However, there are developments with membranes fabricated from nanomaterials. However, manufacturing these into components large and strong enough for practical applications is complex.
A new production technique developed by researchers at McGill University could offer a solution. The researchers recently described the technique in Nano Letters. "In our project, we focus on remedying the inevitable mechanical fragility when deploying the excellent selectivity of thin 2D nanomaterials by fabricating a hybrid membrane consisting of hexagonal boron nitride (hBN) monolayers supported by silicon nitride membranes," says Khadija Yazda, who is involved in the project as a researcher in the Department of Physics at McGill University.
Tip-controlled local breakdown
The researchers employ a technique developed by McGill University called 'tip-controlled local breakdown' (TCLB) to produce selectively permeable membranes. Using these techniques, they drill holes in their membrane on a microscopic scale, also called nanopores.
"Our experiments on pore-pore interaction in nanopore arrays shows that optimal membrane selectivity and overall power density is realisable with a pore space that combines the need for a high density of pores with a large charged surface area (≥ 500nm) around each pore," Yazda said.
Scaling up
During their experiments, the researchers managed to create a 20-by-20 pore array on a 40µm² membrane surface. The researchers report that the TCLB technique is also suitable for producing much larger arrays. "A logical next step for this research is to scale up this approach for not only large-scale power plants, but also nano- or micro-power generators," Yazda explains.
Author: Wouter Hoeffnagel
