Researchers from EMPA and ETH Zurich have made wood compressible and made it work as a microgenerator. When it is loaded, an electrical voltage is generated. In this way, the wood can serve as a bio-sensor – or generate usable energy. The results of their research were published last March in the journal Science Advances under the title “Enhanced mechanical energy conversion with selectively decayed wood.”
To generate electricity from wood, a piezoelectric effect is needed. Piezoelectricity means that an electrical voltage is generated by the elastic deformation of solids. To modify wood into a material that is easily deformable, lignin must be at least partially removed. This is done by treating wood with a mixture of hydrogen peroxide and acetic acid. In this acid bath, the lignin is dissolved, leaving a framework of cellulose layers. The resulting white wooden sponge consists of superimposed, thin layers of cellulose that can be easily pressed together and then expanded back into their original shape. Wood has become elastic in this way.
The team subjected the 1.5 cm test cube to approximately 600 load cycles. The material showed amazing stability. With each compression, the researchers measured a voltage of around 0.63V, enough for an application as a sensor. In further experiments, the team tried to scale up their wooden nanogenerators. And with success. For instance, they were able to show that 30 such wooden blocks, when loaded in parallel with an adult’s body weight, could illuminate a simple LCD screen. It would therefore be conceivable to develop a wooden floor that can convert the energy of people who walk on it into electricity.
(Innovative Materials 2021 volume 2)