Wood floors can harvest enough energy to turn on a light, study says

Wood floors can harvest enough energy to turn on an LED light, scientists have shown, in a potential energy-efficient breakthrough for interior design.

A team of researchers from Switzerland has developed a wooden ‘nanogenerator’ that uses the energy from the footsteps to generate electricity.

The nanogenerator consists of two pieces of wood with different coatings, sandwiched between two layers of electrodes.

The pieces of wood are electrically charged by periodic contacts and separations when stepped on – a phenomenon called the triboelectric effect.

This effect causes pieces of laundry fresh out of the dryer to stick together, or causes a balloon to become electrically charged when rubbed against the hair.

While the nanogenerator is just a prototype for now, in the future people will be able to power appliances in their homes just by walking around the room. Researchers have not revealed how much it could cost or when the technology could be widely available.

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A wooden 'nanogenerator' uses the energy of footsteps to generate electricity, according to experts at ETH Zurich in Switzerland

A wooden ‘nanogenerator’ uses the energy of footsteps to generate electricity, according to experts at ETH Zurich in Switzerland

THE TRIBOELECTRIC EFFECT

The triboelectric effect is a form of electrification that occurs in some materials.

The materials have two layers that can be pulled apart and become electrically charged if they are.

It has its basis in static electricity, where materials, when rubbed together, interact and exchange electrons. This creates a small tension.

For example, rubbing a balloon on hair exchanges electrons, causing both sides to become slightly charged. This can then attract hair and cause it to stick to the balloon as the positively and negatively charged ends attract each other.

The more the two layers of the triboelectric effect interact and come into physical contact with each other, the greater the exchange of electrons and the greater the electrical potential created.

The research was conducted by experts from ETH Zurich in Switzerland, Chongqing University in China and Northwestern University in Illinois.

“The energy efficiency of buildings can be greatly improved by enabling building materials to directly convert the mechanical energy of their occupants into usable electricity,” they write in their paper.

‘In this regard, approaches based on triboelectric effects are particularly promising.

‘Wood is an excellent building material that is highly valued for its intrinsic durability, low cost and aesthetic value.

‘Our functionalized wooden triboelectric nanogenerators show potential as energy-harvesting floors in smart buildings.’

The team started by transforming wood into a nanogenerator by placing two pieces of functionalized wood between electrodes.

It is the footstep that causes the triboelectric effect, which causes the pieces of wood to become electrically charged.

During the triboelectric effect, electrons — subatomic particles that carry electricity in solids — can be transferred from one object to another, generating electricity.

However, there is one problem with making a nanogenerator from wood.

‘In principle, wood is tribo-neutral,’ says senior study author Guido Panzarasa of ETH Zurich. “It 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 create wood that can attract and lose electrons.

This graphic summary shows how footprints on functionalized wood floors can be used to power small appliances

This graphic summary shows how footprints on functionalized wood floors can be used to power small appliances

This graphic summary shows how footprints on functionalized wood floors can be used to power small appliances

To enhance the triboelectric properties of wood, the scientists coated a piece of wood with polydimethylsiloxane (PDMS), a silicone that takes up electrons on contact.

The second layer of wood was embedded with nanocrystals called zeolite timidazolate framework-8 (ZIF-8).

ZIF-8, a hybrid network of metal ions and organic molecules, has a greater tendency to lose electrons.

They also tested different woods to determine whether certain woods or the direction in which wood is cut can affect its triboelectric properties by serving as a better scaffold for the coating.

The researchers found that a triboelectric nanogenerator made from radially cut spruce, a common construction wood in Europe, performed the best.

Together, the treatments improved the performance of the triboelectric nanogenerator — it generated 80 times more electricity than natural wood.

The electricity output of the device was also stable under constant forces for up to 1500 cycles.

The researchers found that a wooden floor prototype with an area slightly smaller than a piece of paper could produce enough energy to power household LED lights and small electronic devices such as calculators.

They successfully lit a prototype light bulb when a human adult walked on it and turned footsteps into electricity.

“Our focus was to demonstrate the possibility of modifying wood with relatively environmentally friendly procedures to make it triboelectric,” says Panzarasa.

Schematic from the research paper shows the arrangement of wood (that has been 'functionalized' with PDMS and ZIF-8) and electrodes

Schematic from the research paper shows the arrangement of wood (that has been 'functionalized' with PDMS and ZIF-8) and electrodes

Schematic from the research paper shows the arrangement of wood (that has been ‘functionalized’ with PDMS and ZIF-8) and electrodes

‘Firing is cheap and available and has favorable mechanical properties. The functionalization approach is quite simple and can be scalable on an industrial level. It’s just a matter of technique.’

According to the team, the nanogenerator also retains properties that make the wood useful for interior design, including mechanical robustness and warm colors.

These features could help promote the use of wood nanogenerators as green energy sources in smart buildings.

They also say that wood construction can help mitigate climate change by storing CO2 from the environment over the life of the material.

The next step for Panzarasa and his team is to further optimize the nanogenerator with chemical coatings that are more environmentally friendly and easier to implement.

‘Although we initially focused on basic research, the research we do should eventually lead to real-world applications,’ says Panzarasa.

“The ultimate goal is to understand the possibilities of wood beyond those already known and to enable wood with new properties for future sustainable smart buildings.”

Their nanogenerator is presented in a paper published in the journal Matter.

Scientists create ‘reverse solar panel’ that can generate electricity from SHADOWS

Scientists have created a device that can generate electricity from the shadows thanks to different lighting angles.

Developed in Singapore, the Shadow Effect Energy Generator (SEG) uses the contrast in lighting between illuminated and shaded areas to generate electricity.

The inexpensive flexible device, which powered a watch in experiments, even gives an advantage over commercially available solar cells by operating in dark areas.

A wearable SEG could take advantage of ambient light to potentially enhance the versatility of devices such as smartphones and smartwatches.

The device also has the added bonus of being a self-powered sensor for monitoring moving objects by tracking the movement of shadows.

Read more: A new ‘reverse solar panel’ generates electricity from the shadows

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