Tires can charge cars, traffic can light lamps? Thin film turns moves into power

Researchers at the Rensselaer Polytechnic Institute (RPI) have developed a polymer film that produces electric current whenever it is pressed, squeezed, or stressed.

“It could be used beneath highways to generate electricity when cars drive over them. It could also be used in building materials, making electricity when buildings vibrate,” Nikhil Koratkar, one of the researchers and a professor at RPI, said .

Moreover, using the film, one could produce electric current even from body movements such as clapping, walking, dancing, tapping, and running, according to the researchers. All of this is possible because of its ability to harness the piezoelectric effect .

A non-toxic piezoelectric material

The piezoelectric effect is a phenomenon that enables a material to turn mechanical energy into electric current. A common example is the microphone in your headphones that converts sound (a type of mechanical vibration) to electric signals.

“Piezoelectric materials show potential to harvest the ubiquitous, abundant, and renewable energy associated with mechanical vibrations. However, the best-performing piezoelectric materials typically contain lead which is a carcinogen,” the researchers note .

Since the most efficient piezoelectric materials contain lead, they can’t be used in medical devices, body sensors, and various other applications. “Lead is toxic and increasingly being restricted and phased out of materials and devices,” Koratkar

This is where the new film could make a huge difference. It is composed of special chalcogenide perovskite — materials that have a perovskite crystal structure and include chalcogen elements (such as sulfur). These materials are also used in solar cells and other electronic devices due to their excellent light absorption properties, which makes them valuable for energy-related uses.

In addition to sulfur-based perovskite crystals, the 0.3-millimeter-thick film also contains barium and zirconium. However, it doesn’t contain lead, making it a desirable piezoelectric material for a wide range of applications including medical devices and sensors.

“Essentially, the material converts mechanical energy into electrical energy” without using any toxic materials. “The greater the applied pressure load and the greater the surface area over which the pressure is applied, the greater the effect,” Koratkar explained.

This non-toxic film has the potential to reduce our reliance on batteries and fossil fuels, making the transition to green energy easier. For instance, imagine vehicles charging while moving, and traffic lights receiving power from people walking on the road.

Does the film really work?

In simple words, the film is nothing but a bunch of barium zirconium sulfide (BaZrS3) particles mixed and enclosed in a polymer called polycaprolactone (PCL). To check whether it could really generate some current, the researchers performed some interesting experiments.

They applied varying amounts of stress on the film through different hand and body movements and measured the output voltage by connecting the film with a rectifier. While the film converted stress into alternate current (AC) , the rectifier turned this current into DC voltage.

“For regular walking, jogging, and running, the resulting maximum DC voltage was ~21.2, ~40.4, and ~72 V, while it was ~5.3, ~10.4, and ~19.8 V for elbow bending, clapping, and hand tapping, respectively,” the researchers note in their study.

They used this current to power an LED board, successfully demonstrating that their non-toxic film can indeed produce electric current from mechanical stress. “These tests show this technology could be useful, for example, in a device worn by runners or bikers that lights up their shoes or helmets and makes them more visible,” Koratkar said.

However, this is just a proof of concept, as we’d like to eventually see this kind of material implemented at scale, where it can really make a difference in energy production,” he added.

The study is published in the journal Nature Communications .