At the estuary, fresh water flows into the ocean, and with the help of newly developed membranes, the estuary is expected to become a giant power plant. Image source: LWM
There is a chemical difference between fresh water and salt water. At the estuary, these two liquids with different properties come together. Today, scientists have designed a thin film that can use the difference between the two to generate electricity. If large-scale production can be achieved, the estuary junction in the coastal area is expected to build a power station to provide carbon-free clean electricity to millions of people.
Recently, the research team of Rutgers University announced that they have made a breakthrough in this field. The researchers invented a membrane that can separate positive and negative charges in brine. Water flows through it, and each square meter of membrane can generate about 30 megawatt-hours of electricity per year, enough to power three houses.
"This is impressive. Over the years, our research field has been looking forward to a successful day of research." Park Guangyu, a mechanical engineer at Pohang University of Science and Technology, South Korea, commented.
According to the "Science" report, the fact that water, the "blue energy", can be used by humans is based on facts. Every year, about 37,000 cubic kilometers of fresh water flows from the estuary into the ocean. The intersection of river water and seawater can provide huge power generation potential. It is estimated that the generated electricity can reach 2.6 terawatt hours, which is roughly equivalent to the power generation of 2,000 nuclear power plants.
Salts are a class of compounds that combine metal ions or ammonium ions with acid ions, where different chemicals carry a positive or negative charge. In solids, positive and negative charges attract each other, thereby binding ions (for example, sodium chloride is formed by combining positively charged sodium ions and negatively charged chloride ions). In water, these ions can "slip away" or move freely.
This is the principle of using fresh water and salt water to generate electricity. Previously, there were power plants that used similar principles to obtain energy, but the methods used were costly and difficult to promote smoothly.
The newly developed membrane is a semi-permeable membrane, which can pump positive ions of sodium or potassium to the other side of the membrane. The researchers divided the water flow into two pools: one with a positive charge and one with a negative charge. The electrode is immersed in the cell and connected with a wire, and electrons will flow from the negative charge side to the positive charge, thereby realizing power generation.
Researchers in France originally made this film in 2013. This silicon nitride ceramic film is commonly used in the electronics industry, tool cutting, etc. Boron nitride nanotubes have a lot of negative charges. Ideally, when the film is placed between fresh water and salt water, positive ions will compress from the salt water to the fresh water, but the negatively charged ions are blocked by the film, causing both sides The charge is unbalanced, thereby generating electricity.
But the previous difficulty is that the boron nitride nanotubes in this film cannot be arranged perpendicular to the film as the researchers will. At the recent annual meeting of the American Society of Materials, members of the laboratory of Jerry Wei-Jen Shan, a mechanical engineering scientist at Rutgers University, reported that they solved the problem.
The researchers added the commercially available nanotubes to the precursor polymer to form a 6.5-micron thick film. Then apply a layer of positively charged paint to the negatively charged tube. The paint molecule has a large volume and cannot pass through the boron nitride nanotubes, so the channel of the film is still in a smooth state.
After that, the researchers added negatively charged magnetic iron oxide particles to the mixture, and the particles were fixed on the positively charged coating. At this time, the researchers can manipulate the nanotubes by applying a magnetic field to align them one by one. Next, ultraviolet light is used to stabilize the polymer in place. Some materials on the top and bottom surfaces of the film are etched by the plasma beam to ensure the smoothness of the nanotubes.
In the end, this processed film has about 10 million boron nitride nanotubes per cubic centimeter. The researchers put it in a small-scale container, and the power generated per unit area is four times that of the original film.
The research team said that this increase in efficiency is likely related to the width of the boron nitride nanotubes. Narrower nanotubes can better exclude negatively charged chloride ions. However, this process still needs improvement because only 2% of the boron nitride nanotubes are open on both sides of the plasma-treated film.
Now, researchers are still trying to increase the number of openings in it, to provide the possibility of practical application of "blue energy". (Yuan Liu Fu Rong)
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