Pomelo, a large citrus fruit commonly grown in Southeast and East Asia, often results in significant food waste due to its thick peel being discarded. A new study from the University of Illinois Urbana-Champaign explores an innovative way to repurpose this biomass, creating tools that can power small electronic devices and monitor biomechanical movements.
“There are two main parts of the pomelo peel – a thin outer layer and a thick, white inner layer. The white part is soft and sponge-like,” explained Yi-Cheng Wang, assistant professor in the Department of Food Science and Human Nutrition at Illinois. “While pomelo peels have been used to extract essential oils or pectin, we aimed to utilize their natural porous structure. By upcycling the peel into high-value products, we can reduce waste and generate new opportunities from food and agricultural byproducts.”
A typical pomelo weighs between 1 and 2 kilograms (2 to 4.5 pounds), with the peel accounting for 30% to 50% of its weight. In their study, researchers separated the peel, removed the outer layer, cut the inner peel into small pieces, and freeze-dried them to preserve their three-dimensional porous architecture. The samples were then subjected to different humidity conditions for further testing.
By analyzing the chemical composition and mechanical properties of the peel, the team successfully engineered devices capable of converting mechanical energy into electricity. These devices also functioned as self-powered motion sensors.
“These devices operate on the principle of contact electrification, also known as triboelectrification,” said Wang. “It’s the same basic phenomenon that causes static shocks when you touch a doorknob in winter. When two materials rub against each other, charges transfer between them, creating static electricity. We wanted to see if we could capture and use that energy.”
The team created triboelectric devices using pomelo-peel biomass paired with a polyimide plastic film. Copper-foil electrodes were attached to each layer, allowing the device to generate electricity when an external force brought the layers into contact.
Tapping the device with a finger was enough to power about 20 LEDs. Integrated with a power-management system and an energy-storage unit, the pomelo-based device could also power a calculator or sports watch — all without external electricity.
