Swiss scientists have developed a device that generates electricity simply by…walking on it! appointment “Triboelectric nanogenerator“, abbreviated TENG, their system uses the mechanical energy provided by footsteps on the ground to generate electricity. With this concept, the team, consisting of researchers from the Swiss Federal Institute of Technology (ETH) at the University of Zurich and the Swiss Federal Laboratories for Materials Testing and Research (Empa) in Dübendorf, succeeded in making s light up on these panels in just a few simple steps.
In a study from Janah September 2021 in the magazine matterexplain the scientists around the researcher Guido Panzarasa “the energy efficiency of buildings could be significantly improved if building materials could convert the mechanical energy of their users directly into usable electricity.” They therefore propose a prototype of an improved wooden floor that makes it possible to generate electricity as soon as you step on it.
The functional principle seems simple: two modified wooden boards with electrodes attached to the ends touch when you walk on them. While in contact with each other, the wooden planks exchange electrical charges (electrons). Once the foot is off, the contact between the two boards is broken. The electrical charges accumulated in each board then create an electrical potential difference, thus creating a generator.
Video credits: Sun et al./Matter
thengenerator triboelectrican undetectable power generator
The concept of triboelectric nanogenerators is new, the very first dating back to 2012. The term ‘nano’ refers to the size of the generators: they are nanometric, ie about one billionth of a meter in size. Before that, microgenerators – still tiny but a thousand times larger – were born with the same idea of using the environment to generate electricity.
At the origin of triboelectric nanogenerators, called TENG, triboelectricity. The suffix “tribo” refers to friction, thus triboelectricity refers to the phenomenon of electrification by friction. The triboelectric effect, also known as static electricity, occurs when two surfaces generate electricity by coming into contact or rubbing against each other. Such a phenomenon can of course occur on many surfaces. Rub a plastic ruler in your hair and you’ve created static electricity! At night, the effect becomes even more impressive, creating a sparkle that is clearly visible in the dark.
The explanation for such a phenomenon lies at the atomic level. When two materials tend to donate (tribopositive) or attract (tribonegative) electrons, their contact causes a transfer of electrons to the material that attracts them. This transfer then causes an electron deficit at the level of the donor material, which then becomes positively charged, and an electron excess at the level of the receiver material, which then becomes negatively charged. If the electrons set in motion in this way are collected by electrodes in a closed circuit, the two materials then behave like a power generator.
but “IThe wood is basically neutral”explains Guido Panzarasa, researcher at ETH Zurich. “This means that wood doesn’t really tend to gain or lose electrons. This limits the material’s ability to generate electricity, so the challenge is to enable wood to attract and donate electrons.”explains Panzarasa.
A wooden floor improved
The researchers insisted on using wood for a variety of reasons listed in their study, including its “Abundance on earth, its practical mechanical properties for construction and its ecological properties“. However, being triboneutral, improvements were needed to be compatible as a power generator. Therefore, to optimize the performance of the wood, the team enriched the two layers used to generate electricity differently.
First, they coated a layer of wood with polydimethylsiloxane known as PDMS, a silicone that tends to accept electrons, forming a tribonegative layer. The second layer has been enriched with nanocrystals called Zeolitic Imidazolate Framework-8 (abbreviated ZIF-8). On the contrary, this hybrid network, composed of both metal ions and organic molecules, tends to donate electrons. Thus the second layer of wood was made tribopositive. Once the two sets are in contact, they create a triboelectric generator.
Photo credit: Sun et al./Matter
When the ZIF-8 is brought into contact with the PDMS, for example when a person steps on it, the electrification of the contacts generates static charges of the opposite sign. Electrons are transferred from the ZIF-8 surface to the PDMS surface, resulting in balanced, electrostatically paired charges. At this stage (Stage I) there is no flow of electrons in the external circuit.
Once the two layers are separated, the negative charges on the surface of the PDMS cannot be compensated by those on the surface of the ZIF-8, inducing a potential difference between the top and bottom electrodes. At the same time, opposite charges are induced at the electrodes. To mask this potential difference, the electrons circulate between the two conductive electrodes through the external circuit (step II).
During this process, current and voltage outputs are generated until the potentials of the two electrodes again reach equilibrium (Stage III). The potential difference then begins to decrease, causing the charges to flow back in the opposite direction until the original state is reached (stage IV).
Future use in smart buildings
In addition to a material study on wood processing, scientists also tested different types of wood to determine which would be the best candidates for future large-scale mining. The lucky winner was Spruce, which performed the best and was also available at a low price. “Our goal was to demonstrate the possibility of triboelectrically modifying wood using relatively environmentally friendly processes”explains Panzarasa. “Spruce is cheap, available and has favorable mechanical properties. The functionalization process is quite simple and can be scaled up to an industrial scale. vsIt’s just a matter of technique.”
But they didn’t just focus on the technical aspect: the team wanted to optimize production costs, energy efficiency and aesthetics at the same time. Your concept could eventually be integrated into so-called buildings “clever“that is, built with many advanced technologies to optimize their energy efficiency.
As the researchers point out in a press release, “Although we initially focused on basic research, eventually the research we conducted should lead to real applications. The ultimate goal is to understand the potentials of wood beyond those already known and to enable new properties for future sustainable smart buildings.” .”