Polymers and electricity – no contradiction!

Power generation in future will involve the widespread use of clean, renewable sources of energy. Research scientists have now discovered a new way to produce “clean electricity” in the sea. Wave movement, a special polymer material with a modified surface and the forces of physics are what are needed to exploit this new source.

The sun and the wind are a major source of electricity in the meantime. “Clean” power, i.e. electricity generated without polluting the environment, is obtained from these “renewable” sources. The energy that is obtained from water when it is released by a dam or drives electricity generators in tidal power plants can be described as “clean” too.

US scientists recently found out that there are other ways to produce electricity using water as well. The key to success here is in the separation of electrically charged particles. In this context, the research scientists are presenting the prototype of what is known as a triboelectric nanogenerator for the production of energy in the magazine “Angewandte Chemie”.

Generating electricity with the wave movement of the sea: a prototype developed by American scientists takes advantage of the triboelectric effect for this purpose.

The triboelectric effect can be observed when putting on or taking off a pullover – when the fabric crackles and flashes. This effect is caused by the contact and separation of different materials and the exchange of electrically charged particles that occurs during this process – a basic precondition for the flow of electrical current.

Scientists from the Institute of Technology in Atlanta in the US state of Georgia have already developed a triboelectric nanogenerator using solids, with which it is possible to recharge a mobile telephone battery successfully. It only works reliably, however, when the humidity level is not too high. Interestingly enough, this problem appears to be marginal if the process takes place directly in water.

The triboelectric effect is not limited to solids alone; it also works with liquids when they come into contact with a suitable solid. Provided that the electronic energy level of both substances matches favourably. This is the case, for example, with water and a number of plastics like polydimethylsiloxane (PDMS). What is needed for the triboelectric effect can be found – reduced to nanoscale – on the surface structure of the PDMS, which resembles a pyramid landscape.

What procedure did the research scientists adopt? They built the prototype of their triboelectric generator using an insulated plastic tank, to the top and bottom of which copper foil is attached as electrodes. A PDMS layer was applied to inside of the top.

When the PDMS nanopyramids come into contact with water by lowering the top, groups of atoms in the PDMS are ionised and given a negative charge. A positively charged layer is in turn formed on the surface of the water. If the PDMS layer is lifted out of the water, the electric charges are maintained, which means that voltage is created between the PDMS and the water; the resulting difference in the electric potential is the basic precondition for a flow of current.

So that as little water as possible adheres to the material, which would reduce the voltage, the PDMS chosen is a hydrophobic (i.e. water-repellent) polymer and a decision was taken to opt for the pyramid shape, because water can drip off it effectively. Periodic raising and lowering of the top and connection of the electrodes via a rectifier and a capacitor leads to direct current with enough power for 60 LEDs. Periodic contact with water can also be established via waves. Tests with salt water have demonstrated that the generator then has a lower output but can in principle be operated in seawater. GDeußing