Imagine tires that charge a vehicle as it drives, streetlights powered by the rumble of traffic, or skyscrapers that generate electricity as the buildings naturally sway and shudder.

These energy innovations could be possible thanks to researchers at Rensselaer Polytechnic Institute that are developing environmentally friendly materials that produce electricity when compressed or exposed to vibrations.

In a recent study published in the journal Nature Communications, the team developed a polymer film infused with a special chalcogenide perovskite compound that produces electricity when squeezed or stressed, a phenomenon known as the piezoelectric effect.

While other piezoelectric materials currently exist, this is one of the few high-performing ones that does not contain lead, making it an excellent candidate for use in machines, infrastructure as well as bio-medical applications.

"We are excited and encouraged by our findings and their potential to support the transition to green energy," said Nikhil Koratkar, Ph.D., corresponding author of the study and the John A. Clark and Edward T. Crossan Professor in the Department of Mechanical, Aerospace, and Nuclear Engineering.

"Lead is toxic and increasingly being restricted and phased out of materials and devices. Our goal was to create a material that was lead-free and could be made inexpensively using elements commonly found in nature."

The energy harvesting film, which is only 0.3 millimeters thick, could be integrated into a wide variety of devices, machines, and structures, Koratkar explained.

"Essentially, the material converts mechanical energy into electrical energy—the greater the applied pressure load and the greater the surface area over which the pressure is applied, the greater the effect," Koratkar said. "For example, 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."

The piezoelectric effect occurs in materials that lack structural symmetry. Under stress, piezoelectric materials deform in such a way that causes positive and negative ions within the material to separate. This "dipole moment," as it is known scientifically, can be harnessed and turned into an electric current.

In the chalcogenide perovskite material discovered by the RPI team, structural symmetry can be easily broken under stress, leading to a pronounced piezoelectric response.

Once they synthesized their new material, which contains barium, zirconium and sulfur, the researchers tested its ability to produce electricity by subjecting it to various bodily movements, such as walking, running, clapping, and tapping fingers.

The researchers found that the material generated electricity during these experiments, enough to even power banks of LED's that spelled out RPI.

"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. 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," Koratkar said.

Moving forward, Koratkar's lab will explore the entire family of chalcogenide perovskite compounds in the search for those that exhibit an even stronger piezoelectric effect. Artificial intelligence and machine learning could prove useful tools in this pursuit, Koratkar said.

"Sustainable energy production is vital to our future," said Shekhar Garde, Ph.D., dean of the RPI School of Engineering. "Professor Koratkar's work is a great example of how innovating approaches to materials discovery can help address a global problem."