One path to greener electronics can involve sweat. Engineers design sweat-powered energy storage systems. One uses salt moisture to charge the supercapacitor. The energy it stores later can be used to illuminate LEDs or run some kind of electronics.
Like a battery, the supercapacitor stores energy. The researchers described their new model on May 11 in Advanced Materials. Such devices with a sweaty engine could pave the way for wearable technologies that are both safer and more sustainable.
Today’s wearable electronics include body-related gadgets such as watches and fitness tractors. But engineers also design electronics that are part of clothing or glued right to the skin. “Many times they are made of materials that are not sustainable or environmentally friendly,” says Ravinder Dahiya. He is an electronics engineer at the University of Glasgow in Scotland.
Batteries power most wearable devices today. These batteries often contain harmful chemicals, such as acids. When it is time to dispose of batteries, their chemicals can harm the environment. For safer technology, “then why not use something that is [a] body fluid?” Pita Dahiya.
Sweat serves as an electrolyte or a new filler. “It’s a new way of using sweat,” Mallika Bariya notes. A materials scientist, she works at the University of California, Berkeley and did not participate in the new research. Electrolytes are “an important component of these supercapacitors or even batteries,” she notes. They need these power supplies.
People often think of sweat as gross or unwanted. But sweat is interesting, she argues. He can show facts about someone’s health. Also, its chemical basis can vary depending on what part of the body it makes up. This new work “really shows that sweat is not a useless, flexible liquid,” she says. “It’s something we should think about more.”
To make their device, a team from Glasgow started with a piece of fabric. It is made of polyester and cellulose, a solid material that forms cell walls in plants. On each side of the fabric, the researchers threw a solution containing an electrically conductive polymer. Polymers are long molecules made up of chemical units that repeat over and over again. Once the solution dried, the polymer layers became electrodes. These electrodes store an electric charge.
Now you need sweat, which the cloth absorbs from the skin. Sweat contains salts. Each salt molecule contains a pair of ions, atoms with an electric charge. One ion is positively charged, the other negatively charged. In supercapacity, these charges are shared in other ways. Positive ions pass to one electrode and negative ions to another. These ions react with the polymer.
If the electrodes are connected to a device (such as an LED light), the electrical current generated by the reactions can flow to power it. This will eventually deplete the capacitor charge. More sweat is needed for refilling.
Some of the researchers tied a capacitor to their T-shirts and ran. The device was able to generate enough energy to illuminate several LEDs. The capacitor was powered by a sensor that measured the salinity of that person’s sweat. The team also tested a device with artificial sweat that included water and salt. The device has now created about five times more power than it had with natural moisture. This may be because there was not enough sweat on the runners ’shirts to get the wet completely wet.
The device has operated thousands of charge and discharge cycles. It maintained its performance even when it was twisted and bent. She did less well after washing. Some of the polymers are washed away, causing a drop in capacitor efficiency.
Sweat is “one of the few available energy resources on the skin,” notes Seokheun Choi. An electrical engineer, he works at Binghamton University in New York. Using sweat, he points out, allows people to expend energy that usually goes to waste.
The power produced by these devices is quite small. But they could get a boost by teaming up with other sweat-secreting systems, Choi says. He is part of a team working on one such device, a type of fuel cell. It relies on sweat-eating microbes to produce energy. Such an approach could make sweat-powered electronics exciting and sustainable.