Loofah sponges are popular bath products used to exfoliate skin in the shower. But give them a special chemical treatment and they could generate enough electricity to light up LEDs when squeezed, researchers report in the journal Proceedings of the National Academy of Sciences.
The development could lead to sustainable, low-cost, and biodegradable power supplies for small sensors and devices, says Li-Hua Shao, a professor of aeronautics science and engineering at Beihang University in Beijing.
The phenomenon behind the advance is piezoelectricity, the ability of certain materials to generate electric power when they flex or move. Quartz, the most commonly known piezoelectric crystal, finds use in watches and microphones. Most piezoelectric materials typically generate a tiny amount of charge. Wood, for example, can generate a very small piezoelectric power output, but researchers recently found a way to boost that output by chemically modifying wood to become more spongy.
Hua and her colleagues decided to see if natural sponges could do better. Made by drying out the ripe fruit of a gourd plant, loofah sponges are abundant natural materials that are light-weight and economical.
The researchers first chemically treated the dried sponge to remove two of the molecules that make up its structure: lignin and hemicellulose. This left behind a cellulose crystal form of the loofah. Others in the past have done similar chemical magic to make wood squishy, colorless and Styrofoam-like, or foldable.
By squeezing a 6 mm-thick piece of the sponge repeatedly by hand, the researchers could generate 8 nanoamperes of electricity. That’s small, but by connecting multiple sponges together, they were able to power LED lights briefly. “The output of the electricity per unit mass exceeds the commonly used traditional piezoelectric materials,” Hua says. It’s up to 50 times more than one common commercially used piezoelectric.
While the power output is small, the work suggests a path to designing artificial porous materials that could be more efficient. That could lead to materials that can harvest motion from the natural world to create electricity.
“We believe that by mimicking and optimizing the natural materials to design materials for higher output we will be able to power other larger portable equipment,” she says, “and effectively harvest other energies from the environment such as waves, vibrations and winds.”
Source: Yudi Jiang et al. The giant flexoelectric effect in a luffa plant-based sponge for green devices and energy harvesters. Proc. Natl. Acad. Sci. 2023.