Sample cube of a wooden sponge nanogenerator generates electricity on pressure

Apr, 2021 - By WMR

In a new study, researchers at ETH Zurich and EMPA have started investigating the piezoelectric potential of a common building material - wood.

Swiss researchers have now shown an environment-friendly way to make a wooden floor with a sponge capable of producing electricity at each step. The device operates using a piezoelectric effect. This principle has been applied to PaveGen pavement tiles and its power plants. The same rate of energy harvesting falls into the triboelectric effect, in which electricity is produced by collision as nanofibers rub together.

The frequency is not flexible enough to produce more electricity, so the team developed a new way for its larger supply. Researchers had exposed the wood to a process called “delignification". Lignin is a natural polymer that acts as a supporting structure for plant cells, especially bark and wood, which keeps them strong and durable. The wood became much spongier when some of the lignins were extracted, allowing it to be quickly stretched and then revert to its original form when the weight is released.

In the first experiment, the researchers decorated the wood by placing it in a tub of acetic acid and hydrogen peroxide to soak it properly. In the second case, researchers tried a mild method - using a fungus called Ganoderma applanatum, which rotates in the lignin wood.

In the field, both types of spongy wood were tested as piezoelectric generators. The first was a material cube measuring around 1.5 cm (0.6 in) on the side made using an acid bath. This was able to produce around 0.63 V, which was enough to power a small sensor and remained steady over 600 cycles. When the group gathered 30 of these blocks together and pressed them with the weight of an adult, it was enough to give power to a LCD. Sponge wood is made of the best quality - the same cube can produced a maximum voltage of 0.87 V. Another advantage of this method, the researchers says, that it is eco-friendly in nature.