Wooden floors laced with silicon generate electricity from footsteps
by Matthew Sparkes  /  1 September 2021

“Wooden floors infused with silicon and metal ions can generate enough electrical power from human footsteps to light LED bulbs. Researchers hope that they could provide a green energy source for homes. Some materials can generate an electrical charge when they come into contact with another such material and are then separated, due to a phenomenon called the triboelectric effect. Electrons are transferred from one object to another and generate a charge. Materials that tend to donate electrons are known as tribopositive and those that tend to receive them are known as tribonegative. Guido Panzarasa at ETH Zürich in Switzerland and his colleagues found that although wood sits in the middle of this spectrum and doesn’t readily pass electrons, it can be altered to generate larger charges. The team infused one panel of wood with silicon, which picks up electrons on contact with an object. A second panel was infused with nanocrystals of zeolitic imidazolate framework-8 (ZIF-8), a compound containing metal ions and organic molecules, and these crystals tend to lose electrons. They called this impregnation process “functionalisation”.

The team found that this treatment made a device that contained both wooden panels 80 times more efficient than standard wood at transferring electrons, meaning it was powerful enough to light LED bulbs when human footsteps compressed the device and brought the two wooden panels into contact. Panzarasa said: “The challenge is making wood that is able to attract and lose electrons. The functionalisation approach is quite simple, and it can be scalable on an industrial level. It’s only a matter of engineering.” The engineered wood was fitted with electrodes from which the charge could be directed, and the team found that a 2-centimetre-by-3.5-centimetre sample that was placed under 50 newtons of compression – an order of magnitude less than the force of a human footstep – was able to generate 24.3 volts. A larger sample that was around the size of an A4 piece of paper was able to produce enough energy to drive household LED lamps and small electronic devices such as calculators. Panzarasa and his team now hope to develop chemical coatings for wood that are more environmentally friendly and easier to manufacture.”

Journal reference: Matter, DOI: https://www.doi.org/10.1016/j.matt.2021.07.022

Wooden floors rotted by fungi generate electricity when walked on
by Adam Vaughan / 10 March 2021

“Fungi have helped scientists make a breakthrough in transforming wood into a useful source of clean electricity, which could one day lead to “energy ballrooms”. The possibility of applying pressure to wood to produce an electric charge, known as the piezoelectric effect, has been discussed since the 1940s and 1950s. However, the vanishingly small amount of electricity the process produces has held back the idea. Now, a team led by Ingo Burgert at ETH Zurich, Switzerland, has discovered how to tweak the internal structure of balsa wood to make the piezoelectric output 55 times higher. The solution was to deliberately rot the wood. Burgert and his colleagues applied a white rot fungus (Ganoderma applanatum) to balsa wood for several weeks. This rapidly decayed the lignin and hemicellulose within the wood, reducing its weight by almost half. They found the sweet spot was six weeks of treatment to create wood that was more compressible – meaning it could generate more electricity from the pressing and releasing action when pressure was applied – without losing its strength.

>“After the rigid wood structure (left) has been dissolved with an acid, flexible cellulose layers remain (middle / right). When pressed together, differently charged areas are displaced against each other. The surface of the material becomes electrically charged.” 

The team then rigged up nine blocks of the decayed wood, covered with a wooden veneer, to create a prototype “energy floor” that was wired up to power an LED. “It’s clear this is only a first step in this direction. But it’s important to show there’s potential,” says Burgert. The amount of electricity generated is still very small, just 0.85 volts from one cube of decayed wood 15 millimetres across. Initially, the electricity could power remote sensors, for example ones that detect whether an older person has fallen over, suggests Burgert. However, in the longer run he envisages energy floors such as a wooden ballroom producing a much greater output, and is talking with companies about commercialising an energy wood product. The development could lead to more buildings being made from wood, which are already being encouraged because wooden structures have a lower carbon footprint than those made from concrete and steel. The UK’s Climate Change Committee has said that the 15 to 28 per cent that wood makes up in construction materials in new homes today should climb to 40 per cent by 2050 to help meet the country’s net-zero target. Team member Javier Ribera at the Swiss Federal Laboratories for Materials Science and Technology says: “We can do much more than just the traditional use of wood. We can tune the properties, we can do many other things with wood, that could be part of future smart cities or new building materials.”

For now, the technique is only possible with balsa, which Burgert says has a particularly low density and thin cell walls. More research will be needed on different fungal treatments for other tree species. Xiping Wang at the United States Department of Agriculture, who wasn’t involved in the study, says the results are promising. “The proposed fungal pre-treatment of native wood does represent a breakthrough at the fundamental level,” he says.”

Journal reference: Science Advances, DOI: 10.1126/sciadv.abd9138



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