Scientists have developed technology that can turn footsteps into electricity.
By tapping into an unexpected energy source, wooden flooring, researchers from Switzerland have developed an energy-harvesting device that uses wood with a combination of a silicone coating and embedded nanocrystals to produce enough energy to power LED lightbulbs and small electronics.
This device, called a nanogenerator, is based on sandwiching two pieces of wood between electrodes.
The wood pieces become electrically charged owing to contact and separation when stepped on via a phenomenon called the triboelectric effect. This effect occurs when electrons can transfer from one object to another, akin to the static electricity produced when you rub a balloon on your hair for a few seconds.
If a material is tribo-positive it tends to lose electrons, and if it is tribo-negative it tends to attract electrons, said the senior study author, Guido Panzarasa, a group leader in the professorship of wood materials science located at Eidgenössische Technische Hochschule Zürich and the Swiss Federal Laboratories for Materials Science and Technology Dübendorf.
“Wood doesn’t have a strong tendency to lose nor attract electrons. As such, wood is a terrible triboelectric material, but wood is an excellent building material,” he said, noting that it is also beneficial given the material is a natural and renewable resource that also stores carbon dioxide.
To boost wood’s triboelectric properties, the researchers coated one piece of it with a common silicone that gains electrons upon contact, while the other piece was embellished with nanocrystals that have a tendency to lose electrons. After testing different types of wood, they found that radially cut spruce – a common wood for construction in Europe – generated 80 times more electricity than natural wood.
Using a wood floor prototype with a surface area slightly smaller than an A4 piece of paper produced enough energy to drive household LED lamps and small electronic devices such as calculators, the researchers found. They successfully lit up a lightbulb with the prototype when a human adult walked upon it, according to the paper published in the journal Matter.
“Imagining making a floor with these kinds of devices, the amount of energy that could be produced by people just walking,” said Panzarasa. “Our focus was to demonstrate the possibility of modifying wood with relatively environmentally friendly procedures to make it triboelectric. Spruce is cheap and available and has favourable mechanical properties.”
Prof Nick Jenkins, the leader of the centre for integrated renewable energy generation and supply research group at Cardiff University, who was not involved in the research, suggested the typical application of such a device could be powering an Internet of Things device. “Of course, if a continuous supply of energy were required, such as for lighting, then this would need continuous motion to provide the input power.”
Panzarasa cautioned that so far, this was proof-of-concept data, and the technology needed more work before it could be scaled up for industrial use.
“We have been focusing our attention on developing the approach to make it even more industrially friendly. And for this we need to maybe sacrifice the overall efficiency in favour of easier methods of a wood modification,” he said.
“So that even though the electrical output of a single device would not be as high as the one we published, the union of many devices across a larger flooring unit will eventually produce a significant amount of energy.”
