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