Mimosa seed bio-piezoelectric device functions as self-charging supercapacitor with high efficiency

Most energy generators currently employed within the electronics industry are based on inorganic piezoelectric materials that are not bio-compatible and contribute to the pollution of the environment on Earth. In recent years, some electronics researchers and chemical engineers have thus been trying to develop alternative devices that can generate electricity for medical implants, wearable electronics, robots and other electronics harnessing organic materials that are safe, bio-compatible and non-toxic.

Researchers at the Indian Institute of Technology recently introduced a new device based on seeds from the mimosa pudica plant, which can serve both as a bio-piezoelectric nanogenerator and a self-chargeable supercapacitor. Their proposed device, outlined in a paper published in the Chemical Engineering Journal, was found to achieve remarkable efficiencies, while also having a lesser adverse impact on the environment.

“This study was motivated by the need for biocompatible, self-sustaining energy systems to power implantable medical devices (e.g., pacemakers, neurostimulators) and wearable electronics,” Dr. Bhanu Bhusan Khatua, senior author of the paper, told Tech Xplore.

“Existing inorganic piezoelectric materials like lead-based compounds [e.g., (Pb, Zr)TiO₃, PbTiO₃] posed risks of toxicity, ecological harm, and surgical complications due to non-biodegradability, which inspired us to explore Mimosa pudica linn (MPL) seeds—a natural, edible, and abundant resource—as a green alternative.”

The recent study by Dr. B. B. Khatua and his colleagues had three primary objectives. Firstly, the researchers set out to develop a new bio-piezoelectric nanogenerator, which utilizes a hydrogel derived from MPL seeds to harvest mechanical energy, such as that associated with finger pressure.

Using the same hydrogel, the researchers also wished to design a self-chargeable supercapacitor with electrodes based on RGO/NiZTO, which could efficiently store energy harvested by the nanogenerator. Their final goal was to integrate these two capabilities (i.e., energy harvesting and storage) into a single biocompatible device that could autonomously operate inside various electronics, including medical implants and wearable technologies.

“The cooperative effect of the electroactivity and intricate transformations within the molecular framework of MPL seed powder particles when subjected to mechanical stress can be used to characterize the nano energy generation mechanism of the MSPEG device,” explained Dr. Khatua.

“The MPL seed powder is composed of tubulin, glycosylflavones, phenolic ketone, buffadienolide, glucuronoxylan polysaccharides (i.e., hemicellulose in angiosperms composed of xylose chain substituted with glucuronic acid (often 4−O−methylated) and acetyl groups), and other N–containing bioligands. These components frequently contain −OH groups, which are connected by the inter/intramolecular H−bonding and transfer mechanical stress into electrical energy as these functional groups deform.”

The primary advantage of the new device developed by Dr. Khatua and his colleagues is that it is based on edible MPL seeds, thus it is not as toxic for the environment as currently employed energy harvesting solutions based on inorganic materials. Despite its biocompatibility, the device was found to achieve a high energy efficiency and energy conversion efficiency.

“As a piezoelectric nano energy harvester (MSPEG), our device achieved a piezoelectric output of ~13.5 V and ~2.98 μA, surpassing many bio-based competitors,” said Dr. Khatua. “Moreover, the MPL seed bio-hydrogel exhibits 24 pC/N of piezoelectric coefficient and 40.2% energy conversion efficiency.”

When working as a supercapacitor, the device developed by Dr. Khatua and his colleagues was found to exhibit good cycling stability, retaining 87.5% of its capacitance after 6,000 operation cycles. It was also found to have an energy density of 125.4 Wh/kg at 1200 W/kg of power density and is capable of autonomously generating and storing voltage, even under mechanical stress.

“Our device can enable safer, longer-lasting power for implants (e.g., pacemakers) without risky battery replacements,” said Dr. Khatua. “It can also support the development of flexible electronics for health monitoring or IoT sensors, helping to reduce reliance on toxic materials and promoting circular energy systems.”

In the future, the new nanogenerator and supercapacitor developed by this research group could be improved further and tested in various electronic devices. As the MPL seed-derived hydrogel it is based on is susceptible to biodegradation, Dr. Khatua and his colleagues also plan to try to enhance its piezoelectric response by modifying its structure.

“In our next studies, we will concentrate on the scalability of cost-effective synthesis methods for RGO/NiZTO electroactive materials, as well as the developed MSPEG and SCS devices and their integration and testing in practical medical and wearable prototypes,” added Dr. Khatua. “We will also explore the multifunctionality of hybrid systems combining piezoelectric, triboelectric, and solar energy harvesting.”

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