Episode 5: Triboelectric nanogenerator powered by wind-driven leaf motion

In this podcast episode, MRS Bulletin’s Laura Leay interviews Fabian Meder from the Italian Institute of Technology in Genova and the Sant’Anna School of Advanced Studies in Piza, Italy about his research group’s device that makes use of wind-driven plant leaf motion to generate electricity which can power a chemical delivery system. Their triboelectric nanogenerator involves an artificial leaf made of a 500 μm silicone elastomer layer and an electrode made from indium tin oxide. This is attached to the leaf of a plant. A gold-coated pin electrode inserted in the stem of the plant harvests charges from the plant tissue. This work was published in a recent issue of Bioinspiration & Biomimetic. 

Transcript

LAURA LEAY: Welcome to MRS Bulletin’s Materials News Podcast, providing breakthrough news & interviews with researchers on hot topics in materials research. My name is Laura Leay. Modern life relies heavily on the natural world. Plants provide us with food as well as raw materials for clothing and support a wealth of other vital natural processes. Although technology can monitor plant health to supply data which humans can act on, one team of researchers is looking at a way to give plants the ability to act on these data and draw chemicals from a reservoir with minimal human intervention and greater precision. In a proof-of-concept experiment, the team has developed a device that makes use of wind-driven plant leaf motion to generate electricity which can power the chemical delivery system. 

FABIAN MEDER: With relatively few electrical components we can use this static electricity forming on the leaves to drive a delivery system. So here we don’t need a battery, we don’t need any control circuits – microcontrollers – it is basically only passive elements so this is something that can be completely driven by nature.

LAURA LEAY: That was assistant professor Fabian Meder from the Italian Institute of Technology in Genova and the Sant’Anna School of Advanced Studies in Piza, Italy. Creation of the device – a triboelectric nanogenerator – involved an artificial leaf made of a 500 μm silicone elastomer layer and an electrode made from indium tin oxide. This was attached to the leaf of the plant. A gold-coated pin electrode inserted in the stem of the plant harvested charges from the plant tissue. As the leaves fluttered in the wind, the artificial leaf made contact with leaf of the plant, producing charges on both surfaces. When the leaves separated, this caused electrostatic induction of the charges of opposite polarity in the artificial leaf electrode and the plant tissue. This alternating current was converted to direct current using an off-the-shelf component. The thin layer of silicone directly charged a purpose-built organic electronic ion pump. 

FABIAN MEDER: It is enough to use a thin layer of silicone to produce electrical charges with leaves. And that we are already studying now since several years but the combination with this ion pump is something not as straightforward; you may think one thing produces electricity and the other thing uses electricity to be powered but such devices have never been powered by this type of energy source. The types of current our energy harvester with the plant surface produces are very small current spikes with high voltage.

LAURA LEAY: The triboelectric effect utilized in the leaf-motion device relies on some interesting properties of a natural wax that is present on the surface of the plant’s leaves. 

FABIAN MEDER: The waxes are nanostructured. It’s a dielectric polymer so it doesn’t conduct electricity and it’s working quite well for producing these static charges. So, this triboelectric effect that we use depends strongly on the materials that are in contact. That’s why, for example, silicone elastomers together with leaves produce high charging. 

LAURA LEAY: The device is a product of collaboration between the research group in Italy who are pioneering the artificial leaf, and another group at Linkoping University in Sweden, who specialize in developing the ion pump. To develop this proof-of-concept, researchers from Italy travelled to Sweden to marry the artificial leaves with the ion pump and test the ability of the device to transport protons.

FABIAN MEDER: The ion pump that has been developed by Linkoping University is very specialized device. In this study we used an ion selective membrane for H+, so hydrogen. And this can be adapted for the use of plant hormones which can then stimulate plant growth for example or make plants more resilient. A very big challenge was for the PhD student to go to the laboratory, bring the technology there. Bring 2000 km far from our laboratory where we are used to work where we have every material available in case something goes wrong and to establish this in another environment. Research and science is often connected to a certain factor of luck and we were lucky that it worked out and the experiments immediately showed that each current spike could drive this ion pump.

LAURA LEAY: To be sure that the leaf motion – which was initiated using a laboratory fan – caused current harvesting, several control experiments were conducted to rule out leakage through the membrane in the ion pump, or electrostatic “noise” in the environment which has previously been shown to affect plants. This proof-of-concept opens up other avenues for research to understand what other technologies could be combined. The device could be used to deliver vital hormones and nutrients which could make plants more resilient to the effects of climate change such as drought. Ultimately it provides more autonomy and responsiveness compared to current agricultural methods. This work shows that technology can work with nature to provide benefits for humankind.

FABIAN MEDER: There is a lot of opportunity for technology when we don’t try to dominate nature which a lot of technology tries to do. But if we try to leverage nature in a way that it can be useful for us and also protect the environment.

LAURA LEAY: This work was published in a recent issue of Bioinspiration & Biomimetics. My name is Laura Leay from the Materials Research Society. For more news, log onto the MRS Bulletin website at mrsbulletin.org and follow us on X, @MRSBulletin. Don’t miss the next episode of MRS Bulletin Materials News – subscribe now. Thank you for listening.