Pomelo, a large citrus fruit native to Southeast and East Asia, is commonly consumed for its juicy flesh, but its thick peel is often discarded as waste. A groundbreaking study by researchers at the University of Illinois Urbana-Champaign has found a way to repurpose this agricultural waste into functional devices that generate electricity and monitor biomechanical movements.
The pomelo fruit, weighing between 1 to 2 kilograms (2 to 4.5 pounds), has a peel that makes up 30% to 50% of its total weight. This thick peel consists of two layers: a thin outer layer and a spongy, white inner layer. Unlike previous studies that have used pomelo peels for extracting essential oils or pectin, the research team saw an opportunity in its unique porous structure.
“If we can upcycle the peel into higher-value products instead of simply throwing it away, we can significantly reduce food waste and create more value from agricultural byproducts,” explained Yi-Cheng Wang, an assistant professor in the Department of Food Science and Human Nutrition at Illinois.
To explore the potential of pomelo peels, researchers removed the outermost layer and cut the remaining spongy peel into smaller pieces. These pieces were then freeze-dried to maintain their three-dimensional, porous structure and stored under different humidity conditions. The team then analyzed the peel’s chemical composition and mechanical properties before integrating it into triboelectric devices.
The principle behind these devices is contact electrification, a phenomenon we experience daily—like the static shock from touching a doorknob. By rubbing or tapping two materials together, electrical charges transfer between them, creating static electricity.
The researchers used pomelo-peel biomass and a plastic (polyimide) film as two triboelectric layers. They attached a copper foil electrode to each layer and tested the device’s ability to generate electricity from mechanical energy.
The study demonstrated that simply tapping these pomelo-peel-based devices with fingers could generate enough electricity to power 20 light-emitting diodes (LEDs). According to interesting engineering, when connected to a power-management system with an energy-storage unit, the device was able to run a calculator and a sports watch—all without requiring an external power source.
“This application has strong potential to convert wasted energy into useful electricity. The naturally porous structure of the pomelo peel makes triboelectric devices highly sensitive to force and frequency, inspiring us to develop sensing devices for biomechanical monitoring,” Wang added.
Beyond generating electricity, the research team found another promising application: biomechanical motion sensors. When attached to different parts of the body, the sensors successfully monitored joint movements and gait patterns. These movements create contact electrification between the triboelectric layers, generating distinct electrical signals corresponding to different motions.
“This capability has great potential for healthcare and physical rehabilitation,” Wang noted. “Wearable sensors made from pomelo peels could help track patient recovery, optimize athletic performance, and improve overall health monitoring.”
By upcycling agricultural waste, this innovation aligns with global efforts toward sustainability and waste reduction. The pomelo-peel-based triboelectric nanogenerator (PP-TENG) developed in this study showed an open-circuit voltage of 58 V and a peak power density of 254.8 mW/m².
The Illinois research team has already filed a provisional patent for their technology and plans to expand testing to evaluate the devices under varying temperature and humidity conditions. Future applications may include energy-harvesting flooring systems and wearable electronic devices, making this a potentially transformative innovation for renewable energy and waste management.
The full study was published in the scientific journal ACS Applied Materials & Interfaces, under the title: “Food waste valorization: use of natural porous materials derived from grapefruit peel biomass to develop triboelectric nanogenerators for energy harvesting and self-powered sensing”.
