Wooden floors can harvest enough energy to turn on an LED lightbulb, scientists have shown, in a potential energy-efficient breakthrough for interior design.
A team of researchers based in Switzerland have developed a wooden ‘nanogenerator’ that uses the energy from footfall to generate electricity.
The nanogenerator consists of two pieces of wood with different coatings, sandwiched in between two layers of electrodes.
The wood pieces become electrically charged through periodic contacts and separations when stepped on – a phenomenon called the triboelectric effect.
This effect is what causes bits of laundry that’s fresh out of the dryer to stick to one another, or a balloon to become electrically charged when rubbed against hair.
While the nanogenerator is just a prototype for now, in the future people could power devices in their home just by walking around the room. Researchers have not revealed how much it might cost or when the technology could be widely available.
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A wooden ‘nanogenerator’ uses the energy from footfall to generate electricity, according to experts at ETH Zurich in Switzerland
THE TRIBOELECTRIC EFFECT
The triboelectric effect is a form of electrification which occurs in some materials.
The materials have two layers which can be pulled apart and become electrically charged when they are.
It has its foundations in static electricity, where to materials when rubbed together interact and electrons are exchanged. This creates a small voltage.
For example, the rubbing of a balloon on hair exchange electrons, making both sides slightly charged. This can then attract hair and cause it to stick to the balloon as the positive and negatively charged ends attract.
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 larger the electrical potential that is created.
The research has been conducted by experts at ETH Zurich in Switzerland, Chongqing University in China and Northwestern University in Illinois.
‘The energy efficiency of buildings could be strongly improved by enabling building materials to convert their occupants’ mechanical energy directly into useful electricity,’ they say in their paper.
‘In this regard, approaches based on triboelectric effects are especially promising.
‘Wood is an excellent building material, highly appreciated for its intrinsic sustainability, low cost, as well as aesthetic value.
‘Our functionalised wood triboelectric nanogenerators show potential as energy-harvesting floors in smart buildings.’
The team began by transforming wood into a nanogenerator by sandwiching two pieces of functionalised wood between electrodes.
It’s footfall that causes the triboelectric effect, making the wood pieces electrically charged.
During the triboelectric effect, electrons – subatomic particles that carry electricity in solids – can transfer from one object to another, generating electricity.
However, there’s one problem with making a nanogenerator out of wood.
‘Wood is basically triboneutral,’ said senior study author Guido Panzarasa at ETH Zürich. ‘It means that wood has no real tendency to acquire or to lose electrons.’
This limits the material’s ability to generate electricity, so the challenge is making wood that is able to attract and lose electrons.
This graphical abstract shows how footsteps on functionalised wood floors can be used to power small devices
To boost wood’s triboelectric properties, the scientists coated one piece of the wood with polydimethylsiloxane (PDMS), a silicone that gains electrons upon contact.
The second layer of wood was embedded with nanocrystals called zeolitic imidazolate framework-8 (ZIF-8).
ZIF-8, a hybrid network of metal ions and organic molecules, has a higher tendency to lose electrons.
They also tested different types of wood to determine whether certain species or the direction in which wood is cut could influence its triboelectric properties by serving as a better scaffold for the coating.
The researchers found that a triboelectric nanogenerator made with radially cut spruce, a common wood for construction in Europe, performed the best.
Together, the treatments boosted the triboelectric nanogenerator’s performance – it generated 80 times more electricity than natural wood.
The device’s electricity output was also stable under steady forces for up to 1,500 cycles.
The researchers found that a wood floor prototype with a surface area slightly smaller than a piece of paper can produce enough energy to drive household LED lamps and small electronic devices such as calculators.
They successfully lit up a lightbulb with the prototype when a human adult walked upon it, turning footsteps into electricity.
‘Our focus was to demonstrate the possibility of modifying wood with relatively environmentally friendly procedures to make it triboelectric,’ said Panzarasa.
Schematic from the research paper shows the arrangement of wood (which has been ‘functionalised’ with PDMS and ZIF-8) and electrodes
‘Spruce is cheap and available and has favourable mechanical properties. The functionalisation approach is quite simple, and it can be scalable on an industrial level. It’s only a matter of engineering.’
According to the team, the nanogenerator also preserves features that make the wood useful for interior design, including mechanical robustness and warm colours.
These features might help promote the use of wood nanogenerators as green energy sources in smart buildings.
They also say that wood construction could help mitigate climate change by sequestering CO2 from the environment throughout the material’s lifespan.
The next step for Panzarasa and his team is to further optimise the nanogenerator with chemical coatings that are more eco-friendly and easier to implement.
‘Even though we initially focused on basic research, eventually, the research that we do should lead to applications in the real world,’ said Panzarasa.
‘The ultimate goal is to understand the potentialities 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 allows electricity to be generated from the shadows thanks to different illumination angles.
The shadow-effect energy generator (SEG), developed in Singapore, makes use of the contrast in illumination between lit and shadowed areas to generate electricity.
The low-cost 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 make use of ambient light to potentially improve the versatility of devices such as smartphones and smartwatches.
The device also has the added bonus as a self-powered sensor for monitoring moving objects by tracking the movement of shadows.